Research Collection

Doctoral Thesis

Synthesis of new and modified activated carbon for theadsorption of persistent organic pollutant (chlordecone) fromwater

Author(s): Rana, Vijay K.

Publication Date: 2016

Permanent Link: https://doi.org/10.3929/ethz-a-010705566

Rights / License: In Copyright - Non-Commercial Use Permitted

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ETH Library

Diss. No. ETH 23409

SYNTHESIS OF NEW AND MODIFIED ACTIVATED CARBON FOR THE

ADSORPTION OF PERSISTENT ORGANIC POLLUTANT

(CHLORDECONE) FROM WATER

A thesis submitted to ETH Zurich

for the degree of Doctor of Sciences

(Dr. sc. ETH Zurich)

Presented by

VIJAY KUMAR RANA

M.Sc. Chem., C.C.S. University Meerut, India.

Born on 20.10.1985

Citizen of India

Accepted on the recommendation of,

Prof. Dr. Hansjörg Grützmacher, Examiner

Prof. Dr. Joelle Levalois-Grützmacher, Co-Examiner

Prof. Dr. Maksym Kovalenko, Co-Examiner

2016

I dedicate this thesis to my wife ‘Jyoti’

ACKNOWLEDGMENT

Once, while watching my brother’s so-called after-marriage-DVD, I saw that he has

acknowledged my name by writing brother ‘Dr. Vijay Rana’. Actually, at that time I was

looking for a PhD position somewhere in India, which ended dramatically after getting a

project assistant position at N.C.L. Pune. Personally, I found the Dr. title very impressive

and in that moment I had a hunch that one day, I would have this title with my name!

I can easily recall the day when I was asked to come on Skype to interview for an open

Ph.D. position in the Grützmacher Group, ETH Zurich. It was 22nd December 2011.

Hansjörg, Joelle, Hartmut and later on Christine interviewed me. I guess, everything went

okay and that is why I was asked to join the group and starts pursuing my doctorate from

1st April 2012. Since then, the fifty months of my PhD tenure in the group have been

magnificent and haunting. However, this journey would not have been so amazing without

several wonderful and supporting personalities/folks.

I convey my deep sense of gratitude to Prof. Hansjörg Grützmacher for the great

opportunity he gave me to carry out my doctorate in his group. I consider myself fortunate

for having a chance of working with a person like him, who is a rare blend of many unique

qualities.

I am extremely grateful to my supervisor Prof. Joelle Levalois-Grützmacher for her

guidance and support. Her constant supervision has enabled me to complete my Ph.D.

research work.

I am thankful to Prof. Maksym Kovalenko for kindly accepting to be my co-examiner and

to support my Ph.D. thesis.

I would like to thank Prof. Sarra Gaspard and Prof. Ulises Jáuregui Haza for their

stimulating scientific discussions and suggestions. Whenever I approached them with my

problems they were always ready to help.

With deep regards and profound respect, I thank to Christine Rüegg for her constant

support during my ups and downs and for administrative work.

I would like to acknowledge Dr. Hartmut Schönberg for general assistant and supports,

and Dr. Reinhard Kissner for calculations and electrospray GC/MS assistance.

I am thankful to the ETH Zürich, for providing the world class infrastructure with the

state-of-the art R & D facilities for my research work.

I am deeply and thoroughly indebted to my family in India for their sacrifice, patience,

and kind support throughout my upbringing.

I am at a loss of words while expressing my feeling of gratitude towards my friends from

LAB H136: Rafael, Jia En, Dipshikha, Johanna and Xiuxiu for making an amazing lab

environment.

I owe deeply to ever-trustful friends for always being with me. I sincerely thank Manjesh,

Chander, Roopender, Bhaumik and Lipi for the discussions and suggestions (both

scientific and nonscientific) in shaping my career as professionally and personally.

I would like to give a special compliment to my wife ‘Jyoti’ and son ‘Yuvkrit’ for their

sacrifice, patience, and being so special for every moments of my life. I’ve cherished all

those moments we have spent together.

Last but not least, I would like to thank my colleagues. Without their support, cooperation,

discussions and timely help, my research work would not have matured enough. So I

extend my gratitude to my earlier and present lab-mates for maintaining a warm and

friendly atmosphere.

GENERAL REMARK

Prof. Ulises Jáuregui Haza and his group has performed all the calculations in this thesis.

THESIS ABSTRACT

Chlordecone (CLD) has been categorized among the most persistent organic pollutants present

on Earth. It is very toxic to people and wildlife. CLD has been used over decades to control the

proliferation of various insects such as banana root borer especially in tropical countries.

Although no longer employed, contamination of soils and rivers by this pollutant is persistent

and causes deadly diseases, therefore its removal from water is a sanitary emergency. For the

removal of CLD from water, the adsorption process has been observed to be the most effective

technique. Common activated carbon (AC) filters have a limited efficiency. Consequently,

drinking water has been the major source of CLD exposure to the people and the wildlife.

Chapter 1 represents the brief history about the use and the side effects of CLD.

Thus far, only one report has been published on the adsorption of CLD from water using AC as

an adsorbent. On the other hand, the latest studies have proven that AC in its current form is

insufficient to provide CLD-free water.

Therefore, the focus of the PhD thesis presented herein is 1) to improve the adsorption

efficiency of AC towards CLD by surface modification of AC and 2) to develop new,

economically competitive ACs from waste biomass for effective CLD adsorption.

Three different strategies were employed towards the surface modification of AC. In the first

strategy, physical modification of AC using radio frequency (cold) plasma was performed. In

the second strategy, metal oxide nanoparticles were immobilized on the surface of AC. The

third strategy covered the chemical modification of AC to fix cyclodextrin on its surface.

Chapter 2 describes the application of cold plasma to treat commercially available AC. To this

end, different reactive gases (ie. NH3, O2, CO2, C2H2, N2, Ar) were injected inside the plasma

chamber to produce reactive plasma species. To achieve highest density of reactive species on

the surface of AC, a specially designed and centrically placed hollow electrode, for a drum-like

sample holder, was developed. Numerous plasma recipes were made to optimize the best

parameters for the surface modification of AC. Nevertheless, it has been observed that,

fundamentally, plasma has affected the surface properties of AC but without any significant

improvement towards CLD adsorption. The plasma modified ACs were further characterized

to investigate this behavior.

AC-metal oxide composites are of great interest and possess unique synergistic properties.

Metal oxide nanoparticles, especially iron oxide nanoparticles, have shown many potential

applications in chemistry, biology and medicine. Conveniently, iron oxide nanoparticles are

cheaply available and known for their remarkable adsorption properties. Chapter 3 concerns the

synthesis of AC-iron oxide nanocomposites for the removal of CLD from water. Forced

hydrolysis technique was used to immobilize iron oxide and iron oxyhydroxide nanoparticles

(Nps) on the surface of AC. The challenging target was to try to maximize the use of Fe (III)

salt and consequently minimize the residual waste. Thus, Fe (III) filtrates were reused to

immobilize iron oxide Nps on the surface of fresh AC. Detailed characterization techniques

(TEM, XPS, XRD etc.) have been used to describe the particular form of iron oxide nanoparticle

present onto AC. AC-iron oxide composites have improved the CLD adsorption by ca. 65 %.

Furthermore, the thesis explores a specific and selective adsorbent for CLD. Cyclodextrin are

macrocyclic molecules and known for wonderful host-guest chemistry. Thus, a host-guest

complexation method using Cyclodextrins (CDs) is proposed in chapter 4. α-, β- and γ-CDs

were used for that purpose and found, in the case of β- and γ-CD, to form stable complexes

(CLD@CD) with CLD. Interestingly, these complexes are insoluble in water and in most

organic solvents (apart from DMF and DMSO). This phenomenon makes this approach

promising because insoluble complexes are easily removable from water. Characterization

techniques like elemental analysis, ATR-FTIR, NMR, DSC etc. have confirmed that a single

CLD is included inside the inner rim of a single CD held together by van der Waal interactions.

The insoluble complexes could be filtered off from water with AC filters. Electrospray GC/MS

results have shown that the resulting water is almost CLD free.

Moreover, a conformational study of γ-CD was made in order to build a model for the formation

of the inclusion complex with chlordecone. Multiple Minima Hypersurface methodology has

been used to theoretically characterize the formation of CLD@γ-CD. The observed interactions

in the complex and the possible changes in the conformations of γ-CD also explain the low

solubility of the inclusion complex.

Alternatively, a precipitation process was further developed in order to intensify the CLD

adsorption process after fixing γ-CD on AC. γ-CD was chosen for modification, so that it forms

a bond/link to the surface of AC. To this end, two different approaches were considered in

chapter 5.

In the first approach, bis(mesitoyl) phosphane (BAP) and acrylated CD are reacted in a

phospha-Michael addition and bis(mesitoyl) phosphane oxide linked on gamma cyclodextrin

(BAPO-γ-CD) was obtained after oxidation. Characterization techniques like 31P NMR, 13C

NMR, UV-vis etc. have confirmed the successful synthesis of BAPO-γ-CD. However, the

photochemical reaction between BAPO-γ-CD and AC was not possible because, AC has

absorbed all given amount of light, hence, homolytic cleavage of P-C bond of BAPO-γ-CD

could not take place.

In the second approach, mono-6-azide-deoxy-6-cyclodextrin (γ-CD-N3) and dried AC were

reacted under conventional reaction conditions under an argon blanket. This route has produced

a hybrid material (AC-γ-CD). XPS and textural properties have indicated that nearly 3 wt% γ-

CD was functionalized on AC. Expectedly, AC-γ-CD was found to be a 15 % better adsorbent

for CLD from water when compared to AC alone.

The work in chapter 6 of the PhD thesis has aimed to study the development of new, cheaper

and effective activated carbons. To this end, three major waste biomass (banana peel, sugarcane

bagasse, and coconut husk), were selected. The obtained ACs (waste@ACs) are different in

their physical appearance, textural properties (surface area, pore volume etc.), atomic

composition and remarkably great in their adsorption properties. Waste@ACs are able to adsorb

CLD in a greater amount and found up to ~200% statistically better adsorbent than AC received

from the company which is cleaning the CLD contaminated water on the French West Indies

Islands. The adsorption properties of waste@ACs varied principally on the origin and the

lignocellulosic composition of the raw material and available surface function groups on a

respective AC. Detailed characterization of waste@ACs has been achieved using surface

analytic techniques.

All the experimental details are summarized in last chapter (7) of the thesis. In the end, overall

conclusion and the outlook of the thesis is revealed.

ZUSAMMENFASSUNG

Chlordecon (CLD) gehört zu langlebigsten organischen Schadstoffe auf der Erde und ist sehr

giftig für Menschen und Tier. CLD wurde jahrzehntelang dazu benutzt, die Ausbreitung

verschiedener Insekten wie den Bananenkäfer besonders in tropischen Ländern zu

kontrollieren. Obwohl es nicht länger benutzt wird, ist die Kontaminierung von Boden und

Flüssen mit diesem Umweltgift persistent und verursacht tödliche Krankheiten, weshalb die

Entfernung aus Wasser eine gesundheitliche Notwendigkeit ist.

Es hat sich gezeigt, dass CLD am effektivsten durch Adsorptionsprozesse zu entfernen ist.

Normale Aktivkohlefilter (activated carbon, AC) haben eine limitierte Effizient. Folglich ist

Trinkwasser die Hauptquelle der CLD-Belastung von Mensch und Tier. Kapitel 1 beschreibt

kurz die Geschichte der Verwendung und die Nebenwirkungen von CLD.

Bis jetzt wurde nur eine Arbeit publiziert, welche die Adsorption von CLD aus Wasser mittels

AC als Adsorbens beschreibt. Auf der anderen Seite zeigen neueste Studien, dass AC im

gegenwärtigen Zustand ungeeignet ist, CLD-freies Wasser bereitzustellen.

Daher lag der Fokus der vorliegenden Doktorarbeit darauf, zum einen die Adsorptionseffizienz

von AC gegenüber CLD durch Oberflächenmodifikationen der Aktivkohle zu verbessern und

zum anderen, neue, wirtschaftlich konkurrenzfähige Aktivkohlen zur effektiven CLD-

Adsorption aus Abfallbiomasse zu entwickeln.

Drei verschiedene Strategien wurden zur Oberflächenmodifikation von AC benutzt. In der

ersten Strategie wurden physikalische Modifizierung mittels Radiofrequenz-Plasma (kaltes

Plasma) vorgenommen. In der zweiten Strategie wurden Metalloxid-Nanopartikel auf der

Oberfläche der AC fixiert. Die dritte Strategie umfasst chemische Modifizierungen der AC, um

Cyclodextrin auf ihrer Oberfläche zu fixieren.

Kapitel 2 beschreibt die Anwendung von kaltem Plasma zur Behandlung von kommerziell

erhältlicher AC. Dazu wurden unterschiedliche Reaktivgase (NH3, O2, CO2, C2H2, N2, Ar) in

die Plasmakammer eingebracht, um reaktive Plasma-Spezies zu erzeugen. Um eine möglichst

hohe Dichte reaktiver Spezies an der Oberfläche der AC zu erreichen, wurde eine speziell

designte, zentrisch platzierte Hohlelektrode für einen trommelartigen Probenhalter entwickelt.

Viele Versuche mit unterschiedlichen Parametern zur Erzeugung des Plasmas wurden

durchgeführt, um die besten Parameter für die Oberflächenbehandlung von AC zu finden. Auch

wenn wir nachweisen konnten, dass das Plasma die Eigenschaften der AC-Oberfläche

verändert, hatte dies keinen signifikant verstärkenden Effekt auf die CLD-Adsorption. Die

plasmamodifizierte AC wurde weiteren Untersuchungen unterzogen, um die Ursachen für

dieses Verhalten zu ergründen.

AC- Metalloxid-Komposite sind von grossem Interesse und besitzen einzigartige synergistische

Eigenschaften. Metalloxid-Nanopartikel, vor allem Eisenoxid-Nanopartiel, zeigen viele

potentielle Anwendungen in Chemie, Biologie und Medizin. Eisenoxid-Nanopartikel sind

günstig verfügbar und für ihre bemerkenswerten Adsorptionseigenschaften bekannt. Kapitel 3

beschäftigt sich mit der Synthese von AC-Eisenoxid-Nanokompositen für die Entfernung von

CLD aus Wasser. Forced hydrolysis-Technik wurde benutzt, um Eienoxid- und

Eisenoxyhydroxid-Nanopartikel (Nps) auf der Oberfläche von AC zu immobilisieren.

Verschiedene Charakterisierungsmethoden (TEM, XPS, XRD etc.) wurden zur Beschreibung

der spezifischen Form der Eisenoxid-Nanopartikel auf AC angewandt. Die Komposite von AC

und Eisenoxid-Nanopartikel haben die Adsorption von CLD um ca. 65% verbessert.

Ausserdem untersucht diese Doktorarbeit ein spezifisches und selektives Adsorbens für CLD:

Cyclodextrine sind makrocyclische Moleküle und für wunderbare Wirts-Gast-Chemie bekannt.

Daher wird in Kapitel 4 eine Wirts-Gast-Komplexierungsmethode unter Nutzung von

Cyclodextrinen (CDs) vorgeschlagen. α-, β- und γ-CDs wurden für diesen Zweck angewendet

und wir fanden heraus, dass im Falle von β- und γ-CD stabile Komplexe (CLD@CD) mit CLD

gebildet werden. Interessanterweise sind diese Komplexe in Wasser und in den meisten

organischen Lösungsmitteln abgesehen von DMF und DMSO unlöslich. Dieses Ergebnis ist

vielversprechend, da schwerlösliche Stoffe leicht aus Wasser zu entfernen sind. Mit

verschieden Techniken zur Charakterisierung, wie Elementaranalyse, ATR-FTIR, NMR, DSC

usw., konnte nachgewiesen werden, dass ein einzelnes CLD durch van der Waals-

Wechselwirkungen im Inneren eines CD-Ringes gebunden ist. Die unlöslichen Komplexe

konnten mit AC-Filtern vom Wasser abfiltriert werden. Elektrospray-GC/MS-Messungen

zeigten, dass das resultierende Wasser nahezu CLD frei ist.

Weiterhin wurden konformative Studien von γ-CD durchgeführt um ein Model zur Bildung des

Einschlusskomplexes mit Chlordecon zu erhalten. Multiple Minimums Hyperflächen

Methoden wurden für die theoretische Charakterisierung der Bildung von CLD@γ-CD

verwendet. Die beobachteten Wechselwirkungen im Komplex und die möglichen Änderungen

in der Konformation von γ-CD können auch die geringe Löslichkeit des Inklusions-Komplexes

erklären.

Alternativ wurde ein Präzipitationsprozess zur Verstärkung der CLD-Adsorption nach

Fixierung von γ-CD auf AC entwickelt. Daher wurden in Kapitel 5 zwei Methoden beschrieben,

um γ-CD mit der Oberfläche der AC zu verbinden.

Bei der ersten Methode wurde Bis(mesitoyl)phosphan (BAP) mit acryliertem CD in einer

Phospha-Michael-Addition umgesetzt und anschliessend zu einem Bis(mesitoyl)phosphanoxid

oxidiert, welches an γ-Cyclodextrin gebunden ist (BAPO-γ-CD). Durch verschiedene

Analysenmethoden, wie 31P-NMR, 13C-NMR, UV-Vis Spektroskopie usw. wurde die

erfolgreiche Synthese von BAPO-γ-CD nachgewiesen. Leider fand keine Reaktion von BAPO-

γ-CD mit AC unter photochemischen Bedingungen statt, weil die Aktivkohle die benötigte

Lichtmenge vollständig absorbierte und daher eine homolytische Spaltung des

Bisacylphosphanoxid nicht möglich war.

Bei der zweiten Methode wurde Mono-6-azido-6-deoxy-cyclodextrin (γ-CD-N3) mit

getrockneter AC unter normalen Reaktionsbedingungen unter Argon zur Reaktion gebracht.

Dabei entstand ein Hybridmaterial (AC-γ-CD). XPS und die strukturellen Eigenschaften

zeigten, dass das AC mit nahezu 3 % γ-CD funktionalisiert ist. Erwartungsgemäss ist AC-γ-CD

ein um 15 % besseres Adsorptionsmittel für CLD aus wässriger Lösung als reines AC.

Kapitel 6 der Doktorarbeit beschreibt die Arbeiten zur Suche nach und zur Entwicklung von

neuen, billigeren und effektiveren Aktivkohlen. Sie führte zu drei Hauptabfall-Bioprodukten

(Bananenschalen, Zuckerrohr Bagasse, Kokosnussschalen). Die daraus erhaltenen ACs

(waste@ACs) unterscheiden sich in ihren physikalischen und texturellen Eingeschaften

(Oberfläche, Porenvolumen etc.), atomaren Zusammensetzungen und beträchtlich in ihren

Adsorptionseigenschaften. Waste@ACs vermögen zum Teil statistisch bis zu 200 % mehr an

CLD zu adsorbieren als kommerzielle Aktivkohle, welche zur Wasserreinigung auf den

französischen Antillen eingesetzt wird. Dabei variieren die Adsorptionseigenschaften dieser

wast@ACs abhängig von der Herkunft und der Zusammensetzung der Lignozellulose des

Rohmaterials und der vorhandenen funktionellen Gruppen an der Oberfläche der ACs. Eine

eingehende Charakterisierung der waste@ACs wurde unter Verwendung von

Oberflächenanalysen durchgeführt.

Die experimentellen Arbeiten sind in Kapitel 7 der Doktorarbeit zusammengefasst. Am Ende

wird die gesamte Arbeit zusammengefasst und ein Ausblick gegeben.

TABLE OF CONTENTS

1. General introduction 1

2. LOW PRESSURE PLASMA TREATMENTS TO TAILOR THE ADSORPTION

PROPERTIES OF ACTIVATED CARBON

2.1 Introduction 27

2.2 Low Pressure Plasma Instrument 29

2.3 Developed Electrodes 30

2.4 Testing the Machine for Plasma Confirmation 31

2.5 Plasma Treatments for the Surface Modification of Activated Carbon 33

2.6 Conclusion 47

2.7 References 48

3. ACTIVATED CARBON AND FORCE HYDROLYSIS IMMOBILIZED IRON

OXYHYDROXIDE NANOPARTICLE COMPOSITES: FOR IMPROVED CHLORDECONE

ADSORPTION

3.1 Introduction 49

3.2 Synthesis of Iron Oxyhydroxide/Iron Oxides Nps Immobilized Activated Carbon 50

3.3 Characterization of Modified Activated Carbon 52

3.4 Chlordecone Adsorption Properties 59

3.5 Conclusion 65

3.6 References 66

4. SUPRAMOLECULAR COMPLEXATION BETWEEN CYCLODEXTRIN AND

CHLORDECONE: AN ELEGANT WAY TO REMOVE CHLORDECONE FROM WATER

4.1 Introduction 69

4.2 Inclusion of Chlordecone into Cyclodextrins 71

4.3 Characterization of Complex 71

4.4 Computational Study of Complex Formation between Cyclodextrin and Chlordecone 81

4.5 Adsorption of Chlordecone 88

4.6 Conclusion 90

4.7 References 91

5. SYNTHESIS OF CYCLODEXTRIN GRAFTED/ FUNCTIONALIZED ACTIVATED

CARBON

5.1 Introduction 93

5.2 Synthesis of bis(mesitoyl) Phosphane Oxide Gamma Cyclodextrin (BAPO-γCD) 94

5.3 Characterization of BAPO-γCD 96

5.4 Synthesis of γCD-N3 Functionalized Activated Carbon 101

5.5 Characterization of γCD-N3 Functionalized Activated Carbon 102

5.6 Adsorption Kinetics of Chlordecone 106

5.7 Conclusion 107

5.8 References 108

6. WASTE BIOMASS-BASED SUSTAINABLE ACTIVATED CARBONS: EXCELLENT

CHLORDECONE ADSORPTION PROPERTIES FROM WATER

6.1 Introduction 109

6.2 Synthesis of Activated Carbon (adsorbents) From Waste Biomass 110

6.3 Characterization of New Activated Carbons (waste@ACs) 112

6.4 Chlordecone Adsorption Properties of waste@ACs 127

6.5 Conclusion 130

6.6 References 131

7. EXPERIMENTAL PART

7.1 General Techniques 135

7.2 Chemicals 135

7.3 Detection of Chlordecone 136

7.4 Analytical Methods and Equipment 137

THESIS CONCLUSION AND OUTLOOK 141

1

CHAPTER - 1

GENERAL INTRODUCTION

1.1 Persistent Organic Pollutants (POPs)

One of the greatest concerns for the environment are those chemicals, which are toxic and

persistent and their corresponding effects, after the absorption, on the development of living

beings. Such chemicals are categorized as persistent organic pollutants (POPs). POPs are

mainly synthetic chemicals. While some of them are pesticides, others are industrial products

or unintended by products resulting from industrial process or combustion. They do not readily

decompose in the environment and remain intact for many years. POPs are/were used in

agriculture as pesticides, around homes as termiticides, and in grains as fungicides. They were

designed to attack the nervous system of pests, which eventually leads to overstimulation of the

nerves and results in deaths. Three main types of natural processes are responsible for the

transport of POPs to locations far from their primary emission sources. These processes are

atmospheric transport, transport in ocean currents and rivers, and transport as bioaccumulated

chemicals in migratory animals (biovectors). Other sources of exposure are from dust and soil,

which were contaminated after the use of pesticides and termiticides. It is therefore likely that

landfilled POPs will leach into the environment, contaminating ground or surface water as well

as escaping to atmosphere by volatilization (Figure 1.1).

It may take decennia or centuries to degrade them. POPs are lipophilic in nature and have

tendency to remain in fat- rich tissues. Such properties of POPs help them to bioaccumulate and

bioconcentrate in the body of humans and animals. Eventually, POPs enter into a cycle or food

chain and start to accumulate in the bigger animals (carnivores & humans) as they eat the

smaller ones (prey). Those animals could be in form of meat, poultry, dairy products and fish.

Highest level of POPs were found in marine mammals. It is postulated that the consumption of

seals and fishe, which are POPs contaminated, may lead to vitamin and thyroid deficiencies and

causes increased susceptibility to microbial infections and reproductive disorders. Root

vegetables and leafy from agricultural run-off can contribute as well to the biomagnification

the POPs.

POPs exposure to the humans and the animals can trigger the adverse health effects. The effects

involved after POPs intoxication were not widely recognized until 1962. One of the best

documented and the clearest evidence of their effects have been found in birds and marine

mammals. Indeed, the book called ‘Silent Spring’ of Rachel Carson, in 1970, drew great

2

attention with details on the declining bird populations.1, 2 This work, along with other studies

augmented the public awareness on such issues.

Figure 1.1: Flow chart of POPs/persistent toxic substances and human exposure and the

important role of landfills, stockpiles and contaminated sites, soils and sediments for the POPs

life cycle (Waste Management & Research, 29(1) 107-121, 2011.) 3

Due to public awareness on the danger of POPs, in 1995, the Governing Council of the United

Nations Environment Programme (UNEP) called a meeting for global action on POPs. During

the meeting, POPs were defined as "chemical substances that persist in the environment, bio-

accumulate through the food web, and pose a risk of causing adverse effects to human health

and the environment". Following this, the Intergovernmental Forum on Chemical Safety (IFCS)

and the International Programme on Chemical Safety (IPCS) have prepared first list of 12 POPs,

which were banned to use and called ‘dirty dozen’. Later, the Stockholm Convention was

adopted and put into practice by the United Nations Environment Programme (UNEP) on May

2001.

3

1.2 Role of Stockholm convention on Persistent Organic Pollutants

The United Nations Environmental Programme (UNEP governs the Stockholm Convention on

persistent organic pollutants (POPs). Ninety two (92) nations and the European community

initially signed the Stockholm Convention in May 2001 in Sweden. Later on, in May 2004, over

150 countries have signed under the Stockholm convention. The Global Environmental Facility

(GEF) is the designated interim financial mechanism for the Stockholm Convention.

The Stockholm Convention is perhaps best understood as having five essential aims:

• Eliminate the dangerous POPs

• Support the transition to safer alternatives

• Target additional POPs for action

• Cleanup old stockpiles and equipment containing POPs

• Work together for a POPs-free future

The original ‘dirty dozen’ POPs listed in the convention were all chlorinated molecules. They

include eight POPs pesticides and four unintentionally produced industrial wastes/chemicals

called polychlorinated biphenyls (PCBs), hexachloro benzene (HCB) polychlorinated dibenzo-

p-dioxins (PCDDs) and dibenzofurans (PCDFs). They are listed in table 1.1.

Table 1.1: List of 12 initial POP (Dirty Dozen), which have been recognized as causing adverse

effects on humans and the ecosystem.

1.

Aldrin

Pros:

- Insecticide,

- Kill termites, grasshoppers, corn

rootworm etc.

Cons:

- Can kill birds and fish,

- Possible human carcinogen,

- Toxic to aquatic organisms.

4

2.

Chlordane

Pros:

- Insecticide,

- Termiticide.

Cons:

- Can kill mallard ducks, bobwhite

quail and pink shrimp,

- May affect the human immune

system.

3.

DDT

Pros:

- Used in WWII to protect the soldiers

and civilians from malaria, typhus,

- Insecticide.

Cons:

- Very toxic to egg-shell thinning

among birds,

- Highly persistent,

- Chronic health effects to humans and

infants.

4.

Dieldrin

Pros:

- Termiticide and pesticide,

- To control insect-born disease.

Cons:

- Highly toxic to fish and aquatic

animals,

- Found in water, soil, birds, mammals

- Affect the humans health.

5.

Endrin

Pros:

- Insecticide,

- To control rodents such as mice and

voles.

Cons:

- Highly toxic to fishes and sheepshead

minnows after exposure.

5

6.

Heptachlor

Pros:

- To kill cotton insects, grasshoppers,

crop pests, malaria-carrying

mosquitoes.

Cons:

- Responsible for the decline of

Canadian Geese and American

Kestrels,

- Fatal to mink, rats and rabbits,

- Possible human carcinogen.

7.

Hexachloro benzene

Pros:

- Fungicide,

- Used to control wheat bunt.

Cons:

- After exposure, symptoms like

photosensitive skin lesions, colic and

debilitation, metabolic disorder and

porphyria turcica,

- Persistent, mothers passed to their

infants.

8.

Mirex

Pros:

- Combat fire ants,

- Termiticide,

- Fire retardant for plastics, rubber etc.

Cons:

- Possible human carcinogen,

- Toxic to fishes and crustaceans,

- One of the most persistent and stable

pesticide.

9.

Toxaphene

Pros:

- Insecticide used on cotton, cereal

grains, fruits, nuts and vegetables,

- To control ticks and mites in

livestock.

Cons:

- Possible human carcinogen,

- Toxic to fishes, brook trouts etc.

6

10.

Polychlorinated biphenyls

Pros:

- Used in industry as heat exchange

fluids,

- In electricity transformers and

capacitors,

- Additives in paint etc.

Cons:

- Toxic to fishes,

- Suppression of immune system in

wild animals like seals and minks,

- After exposed in humans, symptoms

like pigmentation of nails and mucous

membranes, swelling of the eyelids,

fatigue, nausea and vomiting

occurred,

- Possible human carcinogen.

11.

Polychlorinated dibenzodioxins

- Produced unintentionally,

- Emitted after incomplete combustion

of hospital waste, municipal waste

and so on.

Cons:

- Adverse effects in humans , including

immune and enzyme disorders and

chloracne,

- Possible human carcinogens.

12.

Polychlorinated dibenzofurans

- Produced unintentionally,

- Emitted after incomplete combustion

of waste incineration and

automobiles.

Cons:

- Possible human carcinogens,

- Detected in breast-fed infants after

exposure in mothers.

After a period and some reasonable debates/discussions, the list of POPs were further extended.

Therefore, nine new POPs were included under Stockholm Conventions, in 2009. This list was

extra stretched after the inclusion of endosulfan and hexabromocyclodecane in 2011 and 2013,

respectively. Table 1.2 comprises the details of new POPs.

7

Table 1.2: The list of new 11 POPs is as follow:

1.

Chlordecone (Kepone)

Target Molecule of the

PhD thesis

2.

alpha hexachlorocyclohexane

Pros: - Insecticide. Cons: - Highly persistent in water in

colder regionsM - Bioaccumulate and

biomagnifes in biota and arctic food webs,

- Potential carcinogens to humans,

- Affected humans and wildlife health.

3.

Beta hexachlorocyclohexane

Pros: - Insecticide. Cons: - Highly persistent in water in

colder regions, - Bioaccumulate and biomagnify

in biota and arctic food webs, - Potentials carcinogens to

humans, - Affected humans and wildlife

health.

4.

Lindane

Pros: - Used as insecticide for seed

and soil treatment, - Foliar applications, tree and

wood treatment, - Used against ectoparasites in

both veterinary and human applications.

Cons: - Persistent and bioaccumulates

easily in food chain and bioconcentrates rapidly,

- Toxic to laboratory animals and aquatic organisms.

8

5.

Pentachlorobenzene

Pros: - Fungicide, - Flame retardant, - Used in dyestuff carriers. Cons: - Persistent and bioaccumulate

easily in food chain and bioconcentrates rapidly,

- Moderately toxic to humans and very toxic to aquatic organisms.

6.

Hexabromodiphenyl ether and

heptabromodiphenyl ether

Pros: - Main components of

commercial octabromodyphenyl ether.

Cons: - High potential for

bioaccumulation and food-web biomagnification.

7.

Hexabromobyphenyl

Pros: - Flame retardant Cons: - Highly persistent &

bioaccumulative in the environment,

- Possible human carcinogens.

8.

Hexabromocyclododecane

Pros: - Flame retardant additive - Used as insulator in expanded

and extruded polystyrene foam etc.

Cons: - Strong potential to

bioaccumulate and biomagnify, - Highly persistent, - Toxic to aquatic animals.

9

9.

Tetrabromodiphenyl ether and

pentabromodiphenyl ether

Pros: - Main components of

commercial pentabromodiphenyl ether

Cons: - High potential for

bioaccumulation and food-web biomagnification

- Toxic to wildlife and mammals

10.

Perfluoroocatne surfonic acid and its salt

Pros: - Used in electric and electronic

parts, firefighting foam, photo imaging,

- As a hydraulic fluids and textiles.

Cons: - Extremely persistent, has

substantial bioaccumulating and biomagnifying properties,

- It binds to proteins in the blood and the liver.

11.

Technical Endosulfan and isomers

Pros: - Insecticide to control crop

pests, tsetse flies and ectoparasites of cattle,

- A wood preservative, - Used to control pests of crops

including coffee, cotton, rice etc.

Cons: - Persistent in the atmosphere,

sediments and water, - It bioaccumulates, - Toxic to humans, aquatic and

terrestrial organisms - Its exposure can cause physical

disorder, mental retardations etc.

10

1.3 Chlordecone (CLD): Names and Structure (3-9)

Chlordecone (CLD) is a chlorinated caged structured organic molecule. It is a combination of

10 carbon (C) atoms, 10 chlorine (Cl) atoms and one oxygen (O) atom. CLD can be identified

with several different names as mentioned in Table 1.3. Chemically, it is closely related to

mirex. The only difference between their structures is that two chlorine atoms in mirex replace

the oxygen of the keto group in CLD. The structure of CLD is depicted in Figure 1.2.

Table 1.3: Different names of Chlordecone

Figure 1.2: Structure of Chlordecone

CAS chemical name 1,1a,3,3a,4,5,5,5a,5b,6-decachloro-octahydro-1,3,4-

metheno-2H-cyclobuta-[cd]-pentalen-2-one

CAS registry number 143-50-0

Trade names (Pure

product)

1. Kepone

2. GC 1189

3. Merex

4. ENT 16391

5. Curlone (from1981 to 1993).

11

1.4 Physical and Chemical Properties of Chlordecone

CLD is an extremely stable compound and it is not expected to react with hydroxyl radicals

present in the atmosphere or to hydrolyze or to photolyze. The physical and chemical properties

of CLD are listed in table 1.4.

Table 1.4: Physical and chemical properties of Chlordecone (3-9)

Property Value

Molecular formula C10Cl10O

Molecular weight (g/mol) 490.6

Appearance Tan-white crystalline solid

Reported

Vapour Pressure (Pa)

3.0x10-5 (25 °C)

< 4.0x10-5 (25 °C)

4.0x10-5 (25 °C)

Water solubility (mg/L) Max. 2.7 (25 °C)

Melting point (°C) 350 (decomposes)

Log KOW 4.50- 5.41

Log Kaw -6.69

Log Koc 3.38-3.415

1.5 Production and the Application of Chlordecone (3-9)

Synthesis of CLD was first reported in 1952. It was produced after reacting

hexachlorocyclopentadiene with sulfur trioxide under heat and pressure in presence of

antimony pentachloride as a catalyst. The reaction product was hydrolyzed with aqueous alkali

and neutralized with acid. CLD was recovered after filtration and drying in hot air.

After the successful synthesis, CLD was first patented in 1952 and introduced commercially by

Allied Chemical of the United States in 1958. Kepone® was told trade name of it. Between 1951

and 1975, approximately 1.6 million kg of CLD was produced in the United States. Production

of CLD, however, was stopped in 1976. On the other hand, production of CLD continued in

France and the French Caribbean from 1981 to 1993. De Laguarique formulated it into Curlone.

Soon after, the French ministry of agriculture also withdrew the authorization of Curlone in

1990 and the use of CLD was stopped in September 1993.

Historically, CLD was used in various parts of the world to control a wide range of pests.

Specific applications of CLD include in the control of banana root borer, application on non-

12

fruit-bearing citrus trees to control rust mites, wireworms in tobacco fields, apple scab and

powdery mildew, to control the Colorado potato beetle, grass mole cricket, slugs, snails, and

fire ants.

1.6 Exposure of Chlordecone (3-9)

The first evidence of environmental exposure with CLD was found at its manufacture site in

Hopewell, Virginia. Poor production management of CLD had led the James River and the area

close to the production plant contaminated, at excessive level. There was an estimation that

nearly 47 000 kg of CLD lie on the bottom of the James River. On the other hand, the soil

residue levels in Hopewell ranged from as high as 10 000 to 20 000 mg/kg near the plant to 2 ‐

6 mg/kg at a distance of 1 km. It was estimated that ~1000 kg of CLD lay within a 1 km radius

of the CLD production plant. Exposure of CLD even reached in the Bailey bay where the CLD

sediment levels were as high as 10 mg/kg. The soil samples, tested in Hopewell, were contained

CLD and the detectable levels of CLD with the concentrations generally decreases with the

increasing distance from the production plant. CLD residues was expected in sediments of

waterways near other production‐formulation facilities, but no data was available on this.

Meanwhile, in the French West Indies islands (Martinique and Guadeloupe) the widespread use

of CLD has contaminated the soils and drinking water. Extensive use of CLD has badly

contaminated their soils, rivers and so the bank of oceans. Even now, more than 9% of cultivated

area in Guadeloupe area is contaminated with CLD. The percentage of CLD present in crops or

vegetable are directly proportional to that of CLD in contaminated soil. It mainly concerns the

root vegetables such as radish, sweet potatoes, taro root. Aerial part of plants were contaminated

as well, such as sugar cane, pineapple and banana. Among them banana fields are highly

contaminated with > 9 mg/kg conc. of CLD. Florence et al have recently confirmed that root

vegetables like yam, dasheen and sweet potatoes, which are among the main sources of CLD

exposure in food in French West Indies, are still CLD contaminated.10. Concentrations in

fisheries products (freshwater and estuarine water) have also been found to exceed in some

occasions the national residues limits up by a factor of 100 (max. 20 mg/kg). This amount is

much higher than the Lethal Concentration 50 (LC 50) for the fishes (~0.065ppm).

People who used to live or are living, in the areas where CLD was used or produced, have very

high level of CLD exposure in their body. Biomagnification of CLD occurs due to its

bioaccumulation in the food chain (log Kow = 4.5 – 6.0) and reaches a dangerous level in the

human body. The monitoring data received from the agricultural soils, crops, freshwater fish,

and littoral fish and shellfish samples indicates that CLD exposure in the human being is

13

continuing even after 2 decades in Martinique and Guadeloupe. CLD is present in the whole

food chain, which include beef and chickens and be with high concentrations in eggs.

Unfortunately, it is even exist in the milk of nursing mothers.

1.7 Toxicity of Chlordecone in the experimental animals (3-9)

The toxicity of CLD is mainly depended on how it will react with the metabolic system of

animals and humans. A best possible metabolic reaction with CLD has been proposed as shown

in Figure 1.3. Although CLD is not metabolized in mammals, Chlordecone alcohol is formed

in humans and some laboratory animal species by the reduction of the hydrated carbonyl group.

A cytosolic aldo-keto reductase enzyme appears to be responsible for the formation of

chlordecone alcohol. Chlordecol (chlordecone alcohol) is excreted in bile primarily as a

glucuronide conjugate. The metabolism of chlordecone to Chlordecol occurs in humans,

gerbils, pigs and less significantly in rats, mice, guinea pigs, or hamsters.6

Figure 1.3: A proposed metabolic scheme for chlordecone

14

In animals, the CLD was absorbed or exposed through the oral, dermal and inhalation routes.

Exposure of CLD (in animals) was tested on experimental animals to know the toxicity level.

For example, if a single oral dose is given to rats at 40 mg/kg body weight, the highest

concentrations were found in the adrenal glands and liver, followed by the fat and lung. CLD

has been reported to be slowly metabolized via reductive biotransformation to CLD alcohol in

the rat (Figure 1.3). Elimination from the body was slow, with a half-life of the order of several

months. CLD eliminates faster from tissues than from the liver. Elimination take place mainly

via the faeces. Total 66% was eliminated over faeces of an eagle and 2% came off through

urination within 84 days after a given CLD dose.

The neurotoxic effects coming after CLD administration have been reported in chicken, quail,

fish, hamster and rats. Acute oral administration of CLD is also associated with reproductive

effects and hepatotoxicity in some studies. Repeated exposure to CLD also causes reproductive,

neurological, musculoskeletal and liver toxicity at doses as low as 10 mg/kg blood wassermann

(bw)/day, although effects in other organs like kidney, thyroid, adrenals, and testes have also

been reported. A Lowest-Observed-Adverse-Effect-Level (LOAEL) of 1.17 mg/kg bw/day

was recorded in a study after 3-month feeding to rats and signs of toxicity included focal

necrosis in liver, enlargement of the adrenal gland, tremor, hyperactivity and exaggerated startle

response. Oral administration of CLD to animals causes decreased fertility or fecundity and

litter size, reduced sperm count and testicular atrophy. A LOAEL of 0.83 mg/kg bw/day was

recorded for sperm effects in a 90 day feeding study in rats, while effects on seminal vesicles

and prostate were apparent at 1.67 mg/kg bw/day.

CLD is very toxic to aquatic organisms as well. The most sensitive groups are the invertebrates,

which is not surprising for a substance with insecticidal properties. Chlordecone is considered

to have a high potential for bioaccumulation and biomagnification with bio-concentration factor

(BCF) values in algae up to 6,000, in invertebrates up to 21,600, in fish up to 60,200, and

documented examples of biomagnification in aquatic organisms.

15

1.8 Toxicity of Chlordecone in humans (3-9)

CLD is very toxic to hominids as well. It shows similar toxicity in humans as animals do. First

CLD toxicity effect was controlled after CLD exposure in the 32 male workers of

manufacturing plant at Hopewell, Virginia. A very high bioconcentration of CLD was detected

in their liver (range 13.3-173 mg/kg), whole blood (range 0.6-32 mg/litre), and subcutaneous

fat (range 2.2-62 mg/kg). Serum CLD concentrations of occupationally exposed workers was

from 120 to 2109 µg/L however it was dropped to 37 - 486 µg/L within 6-7 months. Similarly,

the exposure of CLD in the workers was found due to the combination of inhalation, oral, and

dermal absorption. Out of all, dermal route was suggested to be the predominant one. The

exposure of CLD into workers had toxified their nervous system. The toxicity was manifested

as tremors, visual difficulties, muscle weakness, gait ataxia, in coordination with headache and

increased cerebrospinal fluid pressure. Prolonged exposure have resulted in a high

concentration of CLD into workers, caused oligospermia, and decreased sperm motility among

the male workers, although fertility was not impaired. A correlation between blood levels,

atmospheric levels and sperm effects has, however, been difficult to prove conclusively.

Epidemiological evidence for carcinogenicity in the CLD exposed humans following inhalation

is extremely limited. Liver biopsy samples taken from 12 workers with hepatomegaly resulting

from intermediate- or chronic-duration exposures to high concentrations of CLD showed no

evidence of cancer. However, this study was limited to very small number of samples

(workers). Recently, a study has suggested that there is causal relationship between CLD

exposure and prostate cancer risk. Authors have investigated 623 men with prostate cancer with

total 671 controls. Exposure was analyzed according to case-control status, using either current

plasma concentration or a cumulative exposure index based on years of exposure.11 The half-

life of CLD in these workers was estimated to be 63-148 days. It was followed and found that

the CLD was eliminated, primarily in the faeces, at a mean daily rate of 0.075% of the estimated

total CLD stored in their body. Reductive biotransformation to CLD alcohol has also been

reported in humans (Figure 1.3).

16

1.9 Degradation of Chlordecone

After terrible exposure of CLD in the United States and French West Indies, it was immensely

challenging for the world and especially CLD exposed countries, to find out the best possible

technique for the degradation or the removal of CLD. Therefore, biodegradation of CLD was

the first funded work by the fines lived on Allied Chemicals. To date, few attempts have been

made for the degradation of CLD.

Carnes, who was an environmental scientist, has made the very first attempt to

degrade/decompose CLD.12 He had developed a special high temperature quartz tube apparatus,

which was designed in the University of Dayton Research Institute (UDRI). Using the UDRI

process, the CLD was first vaporized at a low temperature (between 200 °C and 300 °C) then

passed through the high temperature quartz tube at approximately 1000 °C (1832 °F) for one

second. At high temperature, all the CLD was degraded into innocuous products. The main

drawback of this work was applicable on the small-scale work in laboratories.

Schrauzer et al have employed one of the most promising work for dechlorination of CLD by

inducing the opening of the bishomocubane cage in anaerobic condition.13 They have used

vitamin B12s in strongly alkaline condition (pH > 9) for reductive dechlorination and

degradation of Kepone (CLD). Catalytic and stoichiometric reactions between CLD and the

Co(1)-supernucleophile of vitamin B12s were performed. In the catalytic experiments Kepone

were reacted with small amounts of vitamin B12s in the presence of an excess of reductant like

NaBH4, 1-thioglycerol, 2,3-dimercaptopropanol and acetoin. In the stoichiometric reactions,

solutions of vitamin B12s were injected into the solutions of Kepone (CLD). Authors have

observed that the obtained results were extraordinarily complex and have not been fully

resolved. Nevertheless, such reactions can be interesting to prototypes of soil for the

decontamination process.

Photolysis of CLD was also examined. Alley et al have found that CLD hydrates are more

vulnerable than pure CLD under the ultraviolet (UV) irradiation in cyclohexane and that UV

irradiation have resulted two major products.14 However, hydrated CLD was obtained after the

reduction of CLD with lithium aluminium hydride. Therefore, direct use of this method is

limited. Pseudomonas Aeruginosa (P.A.) bacteria was used as well to degrade CLD

biologically. Orndorff et al have used P.A. strain KO3 and a mixed aerobic enrichment culture,

isolated from sewage sludge lagoon water, to degrade Kepone. Tthey obtained an aerobically

transformed Kepone (CLD) into mono and di hydro-Kepone.15 The mixed culture and P. A.

strain KO3 have produced 4 and 16%, mono and dihydro-Kepone derivatives, respectively. But,

this work was limited to the removal of 1 or 2 chlorine atoms from the carbon backbone.

17

Experiments conducted under anaerobic conditions were observed more promising. Jablonski

et al. subsequently showed that a pure culture of acetate-grown Methanosarcina Thermophila

can convert CLD to polar and nonpolar products. These results were as similar as CLD

decomposition products with reduced vitamin B12, and reduced coenzyme F430 isolated from

M. Thermophile.16

Studies say that CLD is resistant to the aerobic degradation but the biodegradation in the

anaerobic condition is possible to some extent. Dolfing et al have given a complementary that

anaerobic bacteria can actually obtain energy for growth from the reductive dechlorination of

CLD.17 Thus far, there are no indications for the existence of CLD respiring organisms. But,

the fact that halorespiring anaerobes exist for a wide variety of aliphatic and aromatic

organohalides, including hydrophobic compounds like chlorinated dioxins and PCBs, makes

such a hypothesis reasonable. Therefore, authors have performed ab initio quantum chemical

calculations to estimate ΔfHm° and ΔfGm° values of CLD and selected dechlorination products

and used these data to calculate their Gibbs free energy and redox potential. After computational

calculations, they have found that the redox potentials in the range of 336−413 mV for CLD

has an Eo′ value similar to that of other organochlorines. Calculation results indicate that there

are no thermodynamic reasons why CLD-respiring or -fermenting organisms should not exist.

Apparently, work done on the degradation of CLD is limited to small scale and performed under

laboratory conditions. Therefore, it is extremely important to work beyond CLD degradation.

Adsorption is one of the techniques, which is gaining more and more attention because of its

easy operations and versatility. It allows kinetic and equilibrium measurements without using

any highly sophisticated instruments.

18

1.10 Adsorption of Chlordecone

After the rain, CLD contaminates the surface and ground water due to run off from the

contaminated soil and accumulates in the water reservoirs. Such water reservoirs are

responsible for drinking water supply. Due to water consumptions, the contamination of CLD

has caused a major upheaval among the poor families who derive part of their livelihood from

market gardening in Guadeloupe and Martinique. For this reason, the decontamination of CLD

from drinking water becomes a highly important issue. Hence, adsorption of CLD has been

considered an anticipated step to avoid its accumulation into the local bodies. To this end,

commercial activated carbon (AC) filters are equipped to remove CLD from drinking water

sources. Nonetheless, according to the recent reports and data, CLD is still present in the blood

of locals, including newborns and pregnant women.18-23 R. Dallaire et al have evaluated the

impact of prenatal and postnatal exposure to CLD on the cognitive, visual and motor

development of 7-month-old infants from Guadeloupe. The have mentioned that infants were

chronically exposed to CLD through consumption of contaminated foodstuff and water. There

findings indicate that prenatal exposure was associated with reduced visual recognition memory

and an increasing risk of non-optimal fine motor development. Keeping this in mind, it is in

high demand to develop new filters, which are more effective and inexpensive for the

elimination of CLD from water.

Only one report has been published so far on the adsorption of CLD from water. Durimel et al

have used sugar cane bagasse to develop new activated carbons as an adsorbent for CLD.24

19

1.11 Modeling of Adsorption

Adsorption is a surface phenomenon, which includes the uptake of atoms, ions, or molecules

from a gas, liquid, or dissolved solid (called adsorbate) to the external and/or internal surface

of porous solid (called adsorbent). Adsorption at surface or interface is largely dependent on

the binding forces between atoms, molecules and ions of adsorbate and adsorbent. There are

conveniently two type of forces involved in the adsorption.

Physical Adsorption (Physisorption) is the adsorption in which the forces involved are

intermolecular forces (van der Waals forces) and do not include a significant change in the

electronic orbital patterns of the species involved. In short, no exchange of electrons is observed

between the adsorbent and the adsorbate. Physisorption is a non-specific and reversible process.

Chemical Adsorption (Chemisorption) is adsorption in which a particular chemical reaction

takes place between the adsorbed species and the adsorbent. A chemical reaction is possible

when the exchange of electrons occurs between adsorbed species and the surface of the

adsorbent. Chemisorption is usually a stronger process than physisorption.

1.12 Adsorption Modeling and Isotherms

An adsorption isotherm is a valuable curve describing the phenomenon governing the retention

(or release) or mobility of a substance from the aqueous porous media or aquatic environments

to a solid-phase at a constant temperature and pH. It is the amount of adsorbate adsorbed on the

adsorbent as a function of its pressure (if gas) or concentration (if liquid) at constant temperature

and pH.25 There have been several adsorption isotherms models explored. Out of all, few of

them were applied in the presented thesis.

Modeling

The correlation of adsorption data using either a theoretical or empirical equation is essential

for practical purposes. Five different models are used to fit single-component isotherms (Table

1.5). They can be classified into: (i) two-parameters isotherm model for homogeneous surfaces

without lateral interactions, Langmuir equation;26 (ii) three-parameters isotherm model for

homogeneous surfaces with lateral interactions, Fowler equation;27 (iii) two- and three-

parameters isotherm models for heterogeneous surfaces without lateral interactions,

Freundlich,28 Redlich–Peterson29 and Khan30 equations.

20

Table 1.5: Adsorption isotherm models. qe is the amount of adsorbate adsorbed at equilibrium

per unit amount of adsorbent, qs is the monolayer capacity, ce is the concentration of adsorbate

in aqueous phase at equilibrium, is the adsorbate-adsorbate interaction parameter, is the

heterogeneity parameter, k and a are other parameters.

Model Equation

Langmuir eese KcKcqq 1/ (1)

Fowler e

qq

ese KceKcqq se /

/

(2)

Freundlich

ee Kcq (3)

Redlich-Peterson

eee KcaKcq 1/ (4)

Khan eee KcaKcq 1/ (5)

Fitting of the adsorption isotherm models to the experimental data is performed using a non-

linear regression algorithm (trust region method). The procedure calculates the values of the

isotherm parameters, which minimize the residual sum of squares (RSS):

2

1

n

i

i,tiexp, qqRSS

(6)

where iqexp, and itq , are the experimental and calculated values for each data point, respectively.

The best fitting model, taking into account that models with different amount of parameters are

evaluated, is chosen according to the second-order corrected Akaike information criterion

(AICC) and average of absolute relative errors (AARE).

n

i i

iti

q

qq

nAARE

1 exp,

,exp,100

(7)

The AICC methodology attempts to find the model that best explains the data with a minimum

of free parameters.31 Assuming that model errors are independently and normally distributed,

the AICC is defined by the following equation:

21

1

122ln

kn

kkk

n

RSSnAICC

(8)

where k is the number of parameters in the model, and n is the number of data points. The

preferred model is the one with the lowest AICC value.

1.13 Adsorption Kinetics

Two-adsorption kinetics models were used to probe the mechanism that controlled the sorption

process of adsorbent. These are pseudo first and second-order kinetics models, which are

expressed in equation 9 and 10, respectively.32

log(𝑞𝑒 − 𝑞𝑡) = 𝑙𝑜𝑔𝑞𝑒 −𝑘1

2.303𝑡 (9)

t

qt=

1

k2qe2 +

1

qe𝑡 (10)

Where qe and qt are the amount of CLD adsorbed at equilibrium and at time t (μg/mg),

respectively. k1 and k2 are the equilibrium rate constant of pseudo first-order and second-order

kinetics, respectively. In pseudo first-order kinetics, the (qe) and rate constants (k1) were

calculated from the slope and intercept of the plot of log (qe-qt) vs. t. However, in pseudo second

order kinetics, by plotting t/qt against t, one can calculate qe and k2 from slope and intercept,

respectively.

22

1.14 Aim of the PhD Thesis Presented Herein

The aim of the PhD thesis presented herein is to improve the adsorption efficiency of ACs and

to discover inexpensive, selective and affordable adsorbents for the removal of CLD from

water. Activated carbons are commercially available porous filters, which are known for their

excellent adsorption properties. It has been mentioned above that adsorption is the best

technique to remove CLD from water, hence, ACs are equipped on islands to provide CLD-

free, clean water to local residents. However, AC filters were found to unable to clean water to

a sufficient level and the problem with CLD remains. Consequently, the modification of ACs

or finding new adsorbents is necessary to solve this problem.

The initial strategy was to directly modify the functionality of the surface of AC by radio

frequency (cold) plasma treatments. Several plasma recipes were impinged on the surface of

AC to modify the surface. In the second strategy, metal oxide nanoparticles were immobilized

on the surface of AC. To this end, forced hydrolysis technique was used to immobilize iron

oxide and iron oxyhydroxide nanoparticles (Nps) on the surface of AC for greater removal of

CLD from water.

Additionally, host-guest complexation technique was used for the selective removal of CLD

from water. Cyclodextrins (CDs) are well known for their unique supramolecular complexation

chemistry with lipophilic molecules. As mentioned above, CLD is a lipophilic pesticide.

Therefore, host-guest complexation between CLD and CDs was investigated. The complexes

were characterized by several techniques including NMR, TGA, IR etc.

The third strategy involves the chemical modification of AC to fix cyclodextrin on its surface.

For this purpose, two different methods were used to modify -CD, and subsequently, the

surface of AC.

This PhD thesis work also aims to find an inexpensive alternative for CLD adsorption. Waste

biomass are freely available and can be used to develop new and effective ACs. To this end,

three different waste biomass (banana peel, sugarcane bagasse and coconut husk) were chosen

to develop new ACs for the removal of CLD from water. The development ACs and their

characterization employing analytical techniques such as BET, SEM, TEM, TGA, and XPS

were executed. In the end, the CLD adsorption properties of these ACs was to be performed.

23

1.15 References

1. Prest I, Jefferies DJ, Moore NW. Polychlorinated biphenyls in wild birds in Britain and

their avian toxicity. Environ. Pollut. 1970; 1: 3-26

2. Jones Kc, de Voogt P. Persistent organic pollutants (POPs): state of the science 1999;

100: 209-221.

3. Weber R, Watson A, Forter M, Oliaei F, Waste Management & Research 2011; 29(1):

107-121.

4. US ATSDR. Toxicological profile for mirex and CLD. U.S. Department of Health and

Human Services. August 1995 (http://www.atsdr.cdc.gov/toxprofiles/tp66-p.pdf).

5. Toxicological review of CLD (Kepone), U.S. Environmental Protection Agency

Washington, DC, September 2009.

6. IPCS (1984): Environmental Health Criteria 43 (EHC 43): CLD. IPCS International

Programme on Chemical Safety. United Nations Environment Programme.

International Labour Organisation. World Health Organization. Geneva 1990.

7. IPCS (1990): CLD. Health and Safety Guide No. 41 (HSG 41). IPCS International

Programme on Chemical Safety. United Nations Environment Programme.

International Labour Organisation. World Health Organization. Geneva 1990.

8. CLD risk profile, Stockholm Convention on Persistent Organic Pollutants, Geneva,

2006 (UNEP/POPS/POPRC.2/17/Add.2).

9. Epstein SS. Kepone-hazard evaluation. The Science of the total Environment 1978;

9(1):1-62.

10. Florence C, Philippe L, Magalie L.-J. Organochlorine (chlordecone) uptake by root

vegetables. Chemosphere 2015; 118: 96–102.

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B, Thome JP, Blanchet P. Chlordecone exposure and risk of prostate cancer. J. Clin.

Oncol. 2010; 1-10.

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kepone with vitamin B12s. Bioinorganic Chemistry 1978; 9: 123-143.

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Agr. Food Chem. 1974; 22: 442-445.

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16. Jablonski PE, Pheasant DJ, Ferry JG. Conversion of Kepone by Methanosarcina

thermophila. FEMS Microbiology Letters. 1996; 139(2–3):169-73.

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chlordecone and potential degradation products: implications for remediation strategies

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146–151.

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visual, and motor development of 7-month-old Guadeloupean infants exposed to

chlordecone. Environ. Res. 2012; 118: 79–85.

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quantification of chlordecone in contaminated soils from the French West Indies by GC-

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Bataille H, Kadhel P, Multigner L, Cordier S. Perinatal exposure to chlordecone and

infant growth. Environ. Res. 2015; 142: 123-134.

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26

27

CHAPTER - 2

LOW PRESSURE PLASMA TREATMENTS TO TAILOR THE ADSORPTION

PROPERTIES OF ACTIVATED CARBON

2.1 Introduction

It is nowadays well established that low pressure plasma techniques, in continuous

development, are excellent tools to modify the surface properties of various substrates from

small electronic devices to large surfaces as fabrics. The extent of the modification is as varied

as the large diversity of existing plasma techniques. Among them, surface functionalization

stands out. Specific surface modifications can be achieved by using various gases as the source

of plasma. For instance, a hydrophobic surface can be rendered hydrophilic using oxygen-

containing gases as the plasma source. Inversely, a hydrophilic surface can become

hydrophobic by using hydrocarbon or fluorinated gases as the source of plasma. This is

achieved with full respect of the bulk properties of the substrate. Compared to the chemical

modification methods (wet process), plasma treatment is a solvent free, non-polluting process

and has advantages of shorter reaction time, and provides a wide range of different functional

groups depending on the reacting gas (species). Materials like polymeric films, textiles etc. have

been modified by means of plasma treatment. 1-6 Out of those materials, the surfaces of carbon-

based constituents were also modified after using several plasma treatments. Park et al.7 have

examined the surface and textural properties of activated carbon fibers (ACFs) with an

atmospheric pressure plasma treatment. They have observed the presence of new oxygen-

containing functional groups on the surface of ACFs after oxygen plasma treatment. Tang et al.

have performed low pressure oxygen plasma treatment on the surface of ACFs. They have

emphasized that plasma-treated ACFs exhibit tiny voids in their structure and an increased

surface roughness, which unusually improved the textural properties.8 In addition, the increased

roughness and voids on the surface may offer space to accommodate the newly generated

oxygen functional groups. Boudou et al.9 have investigated the surface modification of an

isotropic carbon fiber with microwave oxygen plasma. They have also observed the similar

effects after plasma treatment on carbon fibers. Orfanoudaki et al.10 studied the modification of

ACFs using a plasma deposition technique with the aim of forming pore constrictions by

narrowing the surface pore system of the ACFs. They have worked with combination of

propylene/nitrogen and ethylene/nitrogen gases as plasma source and reported that plasma

deposition made an external film on the surface of the ACFs with incorporated nitrogen groups

into the surface. Moreover, Ruelle et al. illustrated the effect of microwave plasma post-

28

discharge, where the authors used a mixture of argon and nitrogen gases to treat the surface of

carbon nanotubes in order to obtain nitrogenous groups (Amines etc.) on the surface.11 Plasma

is the combination of several highly reactive species. Therefore, if it is used for longer than a

certain time limit, it can damage the substrate’s inherent properties (i.e. adsorption, conductivity

etc.). A few reports have already stated that the intense plasma treatments have negative effects

on the surface functionality and the surface properties.9

The surface chemistry of activated carbons (ACs) clearly determines the specific adsorption of

different chemical species. The surface modification of activated carbons therefore deserves

attention, as it can lead to rational improvements in its adsorption properties for metal ions and

lethal pesticides or as a catalyst support.

Therefore, this chapter is focused mainly on the modification of ACs by means of several low

pressure plasma treatments to improve the adsorption property of ACs. Chlorendic acid

(C9H4Cl6O4, CLA) was initially used as a model compound for chlordecone (C10Cl10O) to

examine the adsorption property of plasma treated ACs. If the adsorption of CLA enhances to

any significant extent then Chlordecone (CLD) adsorption will be considered.

29

2.2 Low Pressure Plasma Instrument

All plasma treatments were generated by the ‘Plasonic Radio Frequency Plasma Machine’ as

revealed in Figure 2.1 in our group at the ETH Zurich. This instrument is very convenient and

easy to use. It has 40 KHz plasma generator and three inlets to introduce the plasma sources

(gases) whereas one inlet is to discharge the vacuum. The computerized touch-screen was

mounted to operate the machine. This screen is used to set the desired recipes, which consists

of mainly the generator power, plasma source gases, gas flow rate and the treatment time. Table

2.1 summarizes the properties of the Plasma Machine.

Figure 2.1: Plasma instrument (left) and engineered sketch (right).

Table 2.1: Properties of Plasma Producing Machine (Figure 2.1).

Excitation Frequency - 40KHz

Working Pressure - 25Pa

Gases: - Ar, H2, N2, O2, CO2, NH3, etc. & their mixture (Max. 3).

Power - 150W - 300W

Flow rate of Reacting gases - 10 sccm to 25 sccm

Plasma Treatment time - 1 to 1000s/recipe (Recipe combination possible)

Dimensions of Plasma Chamber - 230 x 230 x 300 mm

Electrodes - Fixed Plate Electrode

- Movable Plate Electrode

- Centered Cooled Hollow Electrode

30

2.3 Developed Electrodes

The electrodes used in this project were designed and developed exclusively in our laboratory.

All of them were used to produce plasma. They are:

A Fixed Plate Electrode (Figure 2.2a),

A Movable Plate Electrode (Figure 2.2b),

A Centered Cooled Hollow Electrode (CCHE), (Figure 2.3).

Plate electrodes are mainly useful for short plasma treatments and for film like samples.

Figure 2.2: Fixed plate electrode (a) and Movable plate electrode

To ensure a long plasma treatment time, CCHE is the most useful and convenient electrode. It

was engineered with inner water circulation. The cross section of the electrode (Figure 2.3)

shows the water inlet and outlet which maintains the electrode at low temperature. The rotatory

hollow drum was further engineered (Figure 2.1) to hold the powder samples (ACs) and to

accommodate the CCHE electrode. This will enable highest density of plasma reactive species

on the surface of AC as well as a better homogeneity of the treatment.

Figure 2.3: Centered cooled hollow electrode (CCHE, above) and cross-section image (below).

31

2.4 Testing the Machine for Plasma Confirmation

2.4.1 Plasma Treatments on Polypropylene Thin Films

Before doing any plasma treatment on ACs, proper functioning of plasma machine was checked

to know whether the plasma is being produced or not. To this end, polypropylene thin films

(PPtF) were used as a substrate because, the surface modifications of this polymer will be easier

to monitor and characterize than using 3-D, black materials like ACs. Ammonia (NH3) and

carbon tetrafluoride (CF4) gases were used discretely as plasma source. Experimental

conditions used to treat PPtF with these gases are tabularized in Table 2.2.

Functional groups present on a polymeric surface are responsible for the surface energy,

which plays an indispensable role in the wetting phenomena. Low-energy surfaces primarily

interact with liquids through dispersion (van der Waals) forces, whereas high-energy surfaces

don’t. Therefore, the surface energy of PPtF was monitored by means of water contact angle

measurements. The obtained results are presented in Table 2.2.

Table 2.2: Plasma recipes used to treat PPtF at constant gas flow rate (50sccm).

Sample Generator Power

(W)

Plasma Source Time

(s)

Contact Angle

PP - - - 90°

PP-1 200 NH3 30 73.5°

PP-2 200 NH3 60 57.0°

PP-3 200 NH3 90 48.5°

PP-4 150 NH3 30 74.9°

PP-5 150 NH3 60 59.6°

PP-6 200 CF4 30 110°

PP-7 200 CF4 60 118°

PP-8 200 CF4 90 120°

PP-9 150 CF4 60 110°

PP-10 150 CF4 90 114°

The obtained contact angle values indicate substantial effects on the surface energy of PPtF

after distinct plasma treatments. Ammonia plasma generates polar nitrogen-containing surface

functional groups which improves the surface energy of PPtE. On the other hand, CF4 plasma

fluorinates the surface of PPtF after replacing –C-H with –C-F, which reduces the surface

energy of PPtF. Energetically higher PPtF surface (PP-1 to PP-5) will have relatively small

32

contact angle with water than that of energetically lower PPtF surface (PP-6 to PP-10).

Moreover, it has observed that plasma treatment time and plasma generator power also affect

the surface properties of PPtF.

There is physical aging, which is also an important issue in surface modification. It depends on

the substrate and the functional groups present on the near-surface layers of a bulk (substrate).

Sometimes functional groups are not permanently fixed. They (can) slowly move and diffuse

from the topmost layer of bulk (PPtF) after exposure to the air. Complete polymer segments

equipped with functional groups diffuse into the bulk. This mobility of functional groups and

macromolecular segments is called surface dynamics or hydrophobic recovery.12 However, it

further depends on the properties of bulk (polymer) to be investigated. Surface dynamics in the

soft (less cross-linked) polymer is a regular motion but the case is not same with the highly

cross-linked polymers. Herein, we have worked with PP thin film, which is not a cross-linked

polymer and has a soft outmost surface.

We have observed that the contact angle (hydrophobicity) of CF4 plasma treated PPtF did not

change after their exposure to air for 3 days. This could be because the newly obtained and

permanently fixed -C-F functional groups on the top-most layer of PPtF are more hydrophobic

than that of -C-H groups. Therefore, the water contact angle of CF4 plasma- treated PPtF was

not affected after the surface dynamics.

Thus, these experiments confirm that the plasma machine is functioning well and generates a

plasma in the chamber.

33

2.5 Plasma Treatments for the Surface Modification of Activated Carbon

As explained above, plasma treatment affects the surface properties of PPtF. Therefore, the

selection of a right plasma source (gases) is critical, as this can significantly influence the

surface functionality of a substrate. AC has an inert and porous surface to work with because it

is a crude form of randomized graphite sheets. Whereas, graphite sheets are the stacked form

of graphene sheets, which are held together by van-der Waal forces. Graphite/graphene is one

of the most thermodynamically stable form of carbon. Therefore, the effects of plasma

treatment on the surface properties of AC will not be similar to PPtF.

The surface modification of AC is aimed ultimately for the adsorption of CLD. There are

numerous factors, which can lead to a greater CLD adsorption onto AC from water. One of

them includes hydrogen bonding, which could play an important role in the adsorption of CLD

onto AC. Therefore, we first considered the possibility to modify the surface functional groups

on AC such that hydrogen bonding can take place between the carbonyl group and chlorine

atoms of CLD. To this end, the plasma generated by the ammonia gas was first used to alter the

surface of ACs. Figure 2.4a describes all possible ammonia (NH3) plasma species, which could

be formed in the plasma chamber between the electrodes. It is a complex composition of

reactive species, which can create a broad variety of nitrogenized functional groups on the

surface of ACs. Out of these functional groups, primary and secondary amino groups could play

a crucial role in the adsorption of CLD by means of hydrogen bonding, as shown in Figure 2.4b.

Furthermore, the ammonia plasma treatment will possibly improve the surface energy as well

as the surface basicity of ACs. This is why ammonia gas was primarily used as a plasma source

to work with.

Figure 2.4: Possible ammonia plasma species (a) and possible adsorption of CLD on the surface

of AC after hydrogen bonding with nitrogenized surface functional groups.

34

2.5.1 Ammonia Plasma Treatments

100 mg of AC was used throughout the experiments. AC was placed into a rotatory hollow

drum, which was placed in such a way that the CCHE electrode is right in the middle of the

drum, inside the plasma chamber. Ammonia gas was used as a plasma-producing source.

Almost 50 different plasma treatment recipes were made by varying the generator power (150-

250w), the plasma treatment time (5-300 s) and the gas flow rate (10-25 sccm). Among them,

first four optimum NH3 plasma treated ACs were selected after keeping the plasma generator

power (150 W) and the gas flow rate (15 sccm) constant and changing the treatment time 5s,

10s, 20 and 30s. The name of these plasma treated ACs are AC-1, AC-2, AC-3 and AC-4,

respectively.

2.5.3 Characterization of Ammonia Plasma Treated Activated Carbons

2.5.3.1 Elemental Analysis

In order to determine the amount of nitrogenized surface functional groups present on untreated

ACs and plasma treated ACs, elemental analysis was performed. Results obtained after the

analysis are summarized in Table 2.3. Surprisingly, the elemental analysis shows that the

nitrogen composition (N%) in the plasma treated ACs did not change at all and found almost

equal to that of untreated ACs. It means nitrogen species are not present or did not increase

after the NH3 plasma treated ACs. On the other hand, carbon and oxygen content in AC-4 was

found to be lower compared to the rest of ammonia plasma treated ACs and untreated ACs. The

difference between AC-4 and the rest of treated and untreated ACs is their plasma treatment

time. It is longer for AC-4 (30s) than ACs, AC-1, AC-2 and AC-3, this hints that the longer

plasma treatment have burnt the surface of AC-4 and decreased the carbon and oxygen content

of it.

35

Table 2.3: Elemental composition of AC and ammonia plasma treated ACs.

Samples Plasma Treatment

time (s)

Elements

C% H% N% O%

AC 0 87.07 0.83 0.72 5.18

AC-1 5 86.58 0.63 0.66 5.45

AC-2 10 86.28 0.65 0.72 4.96

AC-3 20 86.58 0.73 0.75 4.68

AC-4 30 83.97 0.73 0.74 4.10

2.5.3.2 X-Ray Photoelectron Spectroscopy

XPS is a powerful and very sensitive technique to analyze the surface group composition of a

substrate. Figure 2.5 illustrates the XPS survey scan spectra of ACs and plasma treated ACs.

Figure 2.5: XPS survey scan spectra of AC and ammonia plasma treated ACs (AC-3 & AC-4).

It is quite visible from the figure that survey scan spectra of all ACs (AC and AC-3 & 4) look

alike. There are two individual binding energy peaks at 284.6 and 532.6 eV, which corresponds

to C1s and O1s, respectively. Conversely, N1s binding energy peak is neither present in AC

nor in the plasma treated ACs. Such observations from XPS analysis complements the results

obtained after element analysis.

36

Elemental and XPS survey scan analysis have confirmed that no nitrogen species were present

on the plasma treated ACs. Besides, AC-4 has shown lower carbon and oxygen content than

treated and untreated ACs. To know the plasma treatment effects on the surface of AC-4 better,

the topographic analysis was carried out.

2.5.3.3 Scanning Electron Microscopy (SEM)

SEM images of AC and NH3 plasma treated (AC-4) at different magnified range is shown in

Figure 2.6. The surface of AC depicts a clear image of the three-dimensional porous structure

in Figure 2.6a and 2.6b.

Figure 2.6: Scanning Electron Microscopy images of AC (a, b) and AC-4 (c, d).

On the other hand, the surface of AC-4 appears patchy and burnt (Figure 2.6c & 2.6d). Clearly,

the roughness was increased (Figure 2.6d) on the surface of AC-4, which possibly will

deteriorate the porous network of AC-4 and can create the flaws on its surface. The etching

effect of plasma impingement on the surface of a substrate could be the cause for these flaws.

Etching can cause volatilization of ACs by means of oxidation or combustion of carbon and

37

formation of carbon oxides and ash, which causes weight loss in ACs. That is why, AC-4 has

less C % as expressed in the elemental analysis (Table 2.4).

The flaws and the roughness on the surface of ammonia plasma treated ACs will likely decrease

the textural properties of ACs. Therefore, plasma treated ACs were further analyzed to

investigate their textural properties.

2.5.3.4 Textural Properties

Textural properties of an adsorbent play an imperative role in adsorption related applications.

But, plasma etching can substantially affect the porous structure of AC and produces visible

pits, holes and cracks. Similarly, this effect in NH3 plasma treaded ACs (AC-1 to AC-4) has

decreased their surface area and pore volume, as mentioned in Table 2.4.

Table 2.4: Textural properties of AC and ammonia plasma treated ACs.

Sample Surface area

(m2g-1)

Average Pore

Diameter

(nm)

Total

Pore Volume

(cm3 g-1)

AC 653 4.74 0.77

AC-1 647 4.76 0.74

AC-2 651 4.80 0.73

AC-3 650 4.71 0.76

AC-4 641 4.84 0.71

All above techniques have proved that ammonia plasma treatments have changed the inherent

surface properties of ACs. That means, it must have altered the overall surface functionality of

plasma treated ACs. Therefore, a Boehm titration was carried out to investigate the surface

basicity and acidity of NH3 plasma treated ACs.

38

2.5.3.5 Boehm Titration

The basic principle of Boehm titration is to distinguish present basic and acidic functionalities

of a substrate (ACs) after neutralizing them. The amount of various oxygen-containing acidic

groups present on AC were measured assuming that NaOH neutralizes carboxylic, phenolic and

lactone groups; Na2CO3 neutralizes carboxylic and lactone groups; and NaHCO3 neutralizes

carboxylic groups only. On the other hand, surface basicity can be calculated from the amount

of HCl consumed.

Figure 2.7: Typical Boehm titration curves of AC and ammonia plasma treated ACs

The Boehm titrations are not informative when dealing with small amount of samples.

Therefore, 500 mg of each sample were placed in a Schott bottle with 50 ml of HCl (1mM) and

NaOH (1mM) solutions. CO2 was removed after degassing the solution by bubbling through

N2 for 2 hrs. Later on, the potentiometric back-titrations were performed under a nitrogen

blanket. Figure 2.7 depicts the typical Boehm titration curve of ACs and the NH3 plasma treated

ACs. Whereas, Table 2.5 summarizes the calculated acidic and basic groups concentration

present on AC and NH3 plasma treated AC-2 to AC-4.

39

Table 2.5: Presence of total acidic and basic surface functional groups on the AC and treated

ACs.

Samples Acidic groups

(µeq/g)

Basic groups

(µeq/g)

AC 0.720 0.63

AC-2 0.499 1.56

AC-3 0.363 1.87

AC-4 0.139 1.88

The obtained results prove that after the NH3 plasma treatment, the acidic surface functional

groups of AC-2 to AC-3 have decreased and their basic groups have increased.

Arguably, Boehm titration can only determine the half of the total oxygen content available on

ACs. Therefore, the Boehm titration is for the qualitative analysis only not for the quantitative

analysis.

2.5.4 Adsorption Properties of Ammonia Plasma Treated Activated Carbon

CLD is a very toxic and carcinogenic insecticide and there is a danger of dermal exposure while

working with CLD. Therefore, to avoid unnecessary exposure and the waste from using CLD,

Chlorendic acid (CLA, Figure 2.8.) was used instead to check the adsorption properties of

plasma treated ACs. The adsorption behavior of CLA and CLD on the surface of AC is

comparable.

Figure 2.8: Structure of chlorendic acid (CLA).

40

The kinetics of CLA adsorption onto AC in water was monitored by UV-vis spectroscopy. The

absorption peak at 205 nm represents the C=C chromophore with excitation energy π→π*

transition. The absorption peak related to the C=O chromophore is not observed.

Figure 2.9 shows the kinetic behavior of CLA adsorption (μg) onto the untreated AC (per mg)

and NH3 plasma treated ACs (AC-1 to AC-4). It has been observed that if the plasma treatment

time is longer than 30s or shorter than 5s, adsorption of CLA onto the plasma treated ACs was

always poor.

Figure 2.9: Adsorption kinetics of AC and ammonia plasma treated ACs.

The obtained adsorption kinetic results indicate that it takes ~1h for all ACs to reach the

adsorption equilibrium. After 1 hour, untreated AC has adsorbed 70% of total CLA present in

the solution and NH3 plasma treated ACs has adsorbed only 50% of it. This means that NH3

plasma treated ACs show a diminished adsorption capacity when compared to untreated AC.

Thus far, we have observed that ammonia plasma is insufficient to promote the adsorption

properties of AC. Therefore, mixtures of gases were used as plasma source to amend the surface

properties of AC. Combinations of plasma reactive gases produce several hybrid and reactive

41

species and can play an imperative role.. These species could be responsible for diverse

functional groups on the substrate surface at same time. To this end, several recipes were tried

after the combination of different gases.

2.5.5 Ethylene/Ammonia and Acetylene/Ammonia Plasma Treatments

Ethylene and acetylene plasma treatments are able to produce a very thin layer of plasma

polymeric film on the surface of a substrate, as depicted in Figure 2.10. The hydrophobic

polymeric film is easy to modify after the ammonia plasma treatment.10 And, that will enable

outwardly a very thin polymeric layer with aminated groups on the surface of AC.

Figure 2.10: Possible mechanism to obtain polymeric thin film after ethylene and acetylene

plasma on the surface of AC and followed by ammonia plasma to produce aminated groups on

thin films.

Therefore, ethylene/ammonia (C2H4/ NH3) and acetylene/ammonia (C2H2/NH3) plasma

treatments were introduced on the surface of AC (50 mg). Several plasma recipes were made

after varying the generator power (150-250w), plasma treatment time (5-300 s) and the gas flow

rate (10-25 sccm).

42

Figure 2.11: Adsorption kinetic of AC and H2/N2 plasma treated ACs.

After the C2H4/ NH3 and C2H2/NH3 plasma treatment, the unbound hydrophobic polymeric thin

film was formed on the AC. And, it was possible to see when the plasma modified ACs were

immersed in the water. The floating black dust (in water) is the confirmation that a thin film

was formed on the surface of AC. This phenomenon was not observed in the case of NH3 plasma

treated and untreated ACs.

However, ~ 1% nitrogen content was obtained after the elemental analysis on C2H4/ NH3 and

C2H2/NH3 plasma treated AC. Before performing a complete characterization of C2H4/ NH3

and C2H2/NH3 plasma treated AC, the CLA adsorption properties of plasma treated ACs was

investigated. Figure 2.11 shows the adsorption kinetic behavior of C2H2/NH3 (1:1) and C2H4/

NH3 (1:1) plasma treated AC and untreated AC. Again, we could not observe any significant

improvement towards the CLA adsorption onto C2H2/NH3 and C2H4/ NH3 plasma treated AC.

43

2.5.6 Nitrogen/Hydrogen Plasma Treatments

Thus far, single and combinations of ‘bigger’ gaseous molecules (NH3, C2H2 and C2H4) have

been examined as plasma-producing source to alter the surface of ACs to achieve aminated

surface functional groups. Finally, we have studied N2 and H2 (small molecules) and their

combinations (N2/H2) as plasma source. A possible reaction mechanism on the surface of AC

to obtain the aminated surface functional groups, after the N2/H2 plasma treatment, is illustrated

in Figure 2.12.

Figure 2.12: A possible mechanism to obtain aminated surface functional groups on AC after

H2/N2 combined plasma treatment.

Several conditions were prepared to treat the surface functionality of AC. Among them, four

better plasma conditions (N2/H2) were chosen for CLA adsorption (before characterization),

after varying the plasma treatment time from 10, 20, 30 and 60 seconds and keeping the

generator power (150 W) and gas flow rate (15/15 sccm of N2/H2) constant. These samples are

labelled AC-NH-1, AC-NH-2, AC-NH-3 and AC-NH-4, respectively. CLA adsorption kinetic

behavior of AC and N2/H2 plasma treated ACs is depicted in Figure 2.13. Up to 30 min., CLA

adsorption onto N2/H2 plasma treated ACs and untreated AC was equally fast, from water.

However, after 30 min., CLA adsorption onto Plasma treated ACs has started to stabilize,

whereas untreated ACs was adsorbing CLA linearly up to 60 min. Overall, the adsorption

kinetic result indicate that neat AC is still a better adsorbent than N2/H2 plasma treated AC.

44

Figure 2.13: Adsorption kinetic of AC and H2/N2 plasma treated ACs.

- It has been observed that NH3 plasma, C2H4/ NH3 and C2H2/NH3 plasma, and N2/H2

plasma treatments on AC did not help to enhance the CLA adsorption efficiency of AC.

The defects and flaws on the surface of plasma treated ACshas possibly weakened the

adsorption forces of ACs and could be a major reason for lesser CLA adsorption onto

plasma treated AC than untreated AC.

- Durimel et al. published the only paper on the CLD adsorption for treating contaminated

water in 2013.13 They have observed that carboxylic-like surface functional groups of

an acidic AC surface play a major role in the CLD adsorption and proposed that CLD

may bound to the activated carbon surface by the formation of hydrogen bonds between

the carboxyl groups of ACs and the carbonyl groups as well as chlorine atoms of CLD.

It must behave similarly towards the CLA (model compound) adsorption onto ACs. But,

we have found via Boehm titration that after the NH3 plasma treatment, the acidic

surface functional groups were decreased onto ACs. This could be another reason for

the weaker CLA adsorption on plasma treated ACs.

Therefore, this work was further expanded for the modification of AC using an oxygen plasma

treatment

45

2.5.7 Oxygen Plasma Treatments

On exposure to an O2 plasma, a broad variety of O-functional groups should be produced on

the surface of AC. The major dissociation product of an O2 plasma is atomic oxygen, which is

chemically reactive and readily interacts with solid materials. The possible O-functional groups

are C-O-C, C-OH, CHO, >C=O, COOR, COOH, CO3, etc. Figure 2.14 shows, one possible

reaction mechanism to form carboxylic acid group on the surface of AC after exposure to

oxygen plasma.

Figure 2.14: A possible mechanism to obtain acidic surface functional groups on AC after O2

plasma treatment.

Numerous O2 plasma conditions were impinged on the surface of AC after varying plasma

generator power, treatment time and gas flow rate. Yet again, CLA was used as a model

adsorbate molecule to know the adsorption properties of O2 plasma treated ACs.

46

Figure 2.15: Adsorption kinetic of AC and H2/N2 plasma treated ACs.

Before characterizing the O2 plasma treated ACs, adsorption properties of these sample was

tested. Several O2 plasma treated ACs sample were taken in account. But, we have observed

that none of them have shown better adsorption towards CLA than untreated AC. Figure 2.15

shows the kinetic behavior of one (better than the rest) O2 plasma treated AC (AC-O2) and AC.

Sadly, untreated AC is still a better CLA adsorbent that O2 plasma treated AC.

47

2.6 Conclusion

Radio frequency plasma was used throughout the whole experiments to modify the surface of

ACs. Electrodes used in this work were developed according to their requirements and sample

types (film and powder). CCHE electrode was categorized as the best electrode for powder like

samples (ACs). Presence of plasma in the chamber of plasma producing machine was confirmed

after using PPtF as a standard substrate.

Ammonia gas was initially used as plasma source. Several recipes were examined with

ammonia plasma to enhance the adsorption forces of ACs. Elemental and XPS analysis of

ammonia plasma treated ACs have shown no improvement in the N content. SEM analysis has

confirmed that plasma treated ACs have several defects on the surface, which lower their

surface area and pore volume. Moreover, combined-gas and post-gas plasma recipes were made

as well after the combination of hydrogen/nitrogen, ethylene and acetylene gases with and

without ammonia to treat the surface of ACs.

Chlorendic acid (CLA) was used as a model adsorbate (drug) instead of Chlordecone (CLD) to

track the adsorption property of plasma treated ACs. However, we have seen that plasma

treatment has changed the inherent properties of AC. However, such changes could not improve

the adsorption properties of plasma treated AC.

Moreover, to have greater acidic surface functional groups onto AC, oxygen plasma was further

used to alter the surface properties of AC. CLA adsorption kinetics behavior of O2 plasma

treated AC was different than those of ammonia plasma treated ACs but not better than the

untreated AC.

If the adsorption properties of plasma treated ACs was not promising, the analytical

characterization of those ACs was not further pursued.

48

2.7 References

1. Kaczmarek H, Kowalonek J, Szalla A, Sionkowska A. Surface modification of thin

polymeric films by air-plasma or UV-irradiation. Surf. Sci. 2002; 883: 507-510.

2. Chen Q, Dai L, Gao M, Huang S, Mau A. Plasma Activation of Carbon Nanotubes for

Chemical Modification J. Phys.Chem. B 2001; 105: 618-622.

3. Steen ML, Flory WC, Capps NE, Fisher ER, Plasma Modification of Porous Structures

for Formation of Composite Materials. Chem. Mater. 2001; 13: 2749-2752.

4. Ginn BT, Steinbock O. Polymer Surface Modification Using Microwave-Oven-

Generated Plasma. Langmuir 2003; 19: 8117-8118.

5. Shin GH, Lee YH, Lee JS, Kim YS. Preparation of Plastic and Biopolymer Multilayer

Films by Plasma Source Ion Implantation. J. Agric. Food Chem. 2002; 50: 4608-4614.

6. Kuppers J. The hydrogen surface chemistry of carbon as a plasma facing material. Surf.

Sci. Rep. 1995; 22: 249-321.

7. Park SJ, Kim BJ. Influence of oxygen plasma treatment on hydrogen chloride removal

of activated carbon fibers. J. Colloid Inter. Sci. 2004; 275: 590-595.

8. Tang S, Lu N, Wang JK, Ryu S.-K, Choi H.-S. Novel Effects of Surface Modification

on Activated Carbon Fibers Using a Low Pressure Plasma Treatment. J. Phys. Chem. C

2007, 111, 1820-1829.

9. Boudou JP, Paredes JI, Cuesta A, Martinez-Alonso A, Tascon JMD. Oxygen plasma

modification of pitch-based isotropic carbon fibres. Carbon 2003; 41: 41-56.

10. Orfanoudaki T, Skodras G, Dolios I, Sakellaropoulos GP. Production of carbon

molecular sieves by plasma treated activated carbon fibers. Fuel 2003; 82: 2045-2049.

11. Ruelle B, Peeterbroeck S, Godfroid T, Bittencourt C, Hecq M, Snyders R, Dubois P.

Selective Grafting of Primary Amines onto Carbon Nanotubes via Free-Radical

Treatment in Microwave Plasma Post-Discharge. Polymers 2012; 4: 296-315.

12. J. Friedrich, Book ‘The Plasma Chemistry of Polymer Surface’ Chapter 2, 11-12.

13. Durimel A, Altenor S, Miranda-Quintana R, Couespel Du Mesnil P, Jauregui-Haza U

et al. pH dependence of chlordecone adsorption on activated carbons and role of

adsorbent physico-chemical properties. Chemical Engineering Journal 2013; 229: 239-

49.

49

CHAPTER - 3

ACTIVATED CARBON AND FORCE HYDROLYSIS IMMOBILIZED IRON

OXYHYDROXIDE NANOPARTICLE COMPOSITES: FOR IMPROVED

CHLORDECONE (KEPONE) ADSORPTION

3.1 Introduction

Owing to iron oxides natural abundance, their nanoparticles (Nps) play a crucial role in several

applications. For example, haematite (α-Fe2O3) is the most studied material and is being used

in several applications for example as gas sensor,1 catalyst2 and electrode material.3 Magnetic

iron oxide nanomaterials (Fe3O4 and Fe2O3) are studied for various biomedical applications

including magnetic resonance imaging (MRI) contrast agents, magnetic-guided drug-delivery

vehicles and the magnetic separation of biological molecules.4, 5 Among them, alpha iron

oxyhydroxides (α-FeOOH) Nps have shown impressive application to purify ground and

surface water. Mainly they are explored in removing heavy metal ions from water.6 Moreover,

magnetic/iron oxides Nps and AC nanocomposites have also been reported for the removal of

dyes,7-10 heavy metal ions,11, 12 inorganic13, 14 and organic molecules15-18 from water. However,

to the best of our knowledge, there are no reports regarding the adsorption of persistent organic

pollutant (like CLD) onto iron oxides and ACs composites.

There are major challenges for α-FeOOH Nps synthesis, which strongly influence the

performance of α-FeOOH in several applications. This depends mainly on the reactant’s

concentrations, temperature, type of anions, additives, etc. the forced hydrolysis technique is

known to produce α-FeOOH Nps effectively in different shapes and sizes. The presence of extra

ions plays an important role in force hydrolysis.19 Phosphate ions have been reported by several

groups as an attractive capping agent to decrease the particle size of α-FeOOH in forced

hydrolysis. Previous reports have shown that treating AC with very high concentrations of PO43-

/Fe3+ to obtain α-FeOOH Nps on the substrate surface facilitates higher metal adsorption on the

treated AC without significant loss in surface area and pore volume.12, 20

The main objective of this work is to improve the adsorption efficiency of CLD on AC through

the immobilization of iron oxyhydroxide and iron oxide (FeOs) Nps on the surface of activated

carbon by means of force hydrolysis technique. Phosphates were used as a capping agent.

Finally, the adsorption of CLD on the modified AC was studied.

50

3.2 Synthesis of Iron oxyhydroxide/Iron oxides Nps Immobilized Activated

Carbon

Major improvements have been made to a previously reported method.20 In this report, authors

have used highly concentrated phosphate ions as a capping agent for FeOs Nps. Similarly, the

fabrication of FeOs Nps (mainly α-FeOOH) on the surface of AC is illustrated in the Scheme

3.1. There are three synthetic stages where FeOs filtrates were used to their maximum potential.

In step one, 1 g AC, 5 mL 3M FeCl3.6H2O and 5 mL 3M H3PO4 were sealed hermetically in a

Schott bottle and kept at 80 °C.

Scheme 3.1: Procedure to synthesize Fe@mACs.

The reaction was stopped after 48 h. Once the reaction mixture was cooled down, it was filtered

off. The modified AC (Fe@mAC1) was obtained and the dark orange colored filtrate (F.1) was

recovered for further use. F.1 is the mixture of unreacted FeCl3.6H2O, FeOs Nps and the

51

capping agent (H3PO4). To evaluate the amount of Fe(III) left in F.1 filtrate, it was titrated

against EDTA. 1.3±0.3M Fe(III)) was found in F.1. The filtrate (F.1) was further adjusted to 10

mL with water and 1 g of fresh AC, 0.6M mass of FeCl3 and 0.6M mass of H3PO4 were added.

Then, this solution was sealed hermetically in a Schott bottle and kept at 80 °C for 48 h followed

by the same previous work up. From this step Fe@mAC2 and F.2 were obtained. F.2 which

contains 1.0(±0.3) M of Fe(III) was recovered and subjected to the same previous protocol to

produce Fe@mAC3 and F.3 [0.8 (±0.3) M Fe(III)] which exhibit a yellowish color. All FeOs

and AC composites, namely Fe@mAC1, Fe@mAC1 and Fe@mAC3 issued from the three step

work-up procedures were washed thoroughly with distilled water and dried at 80 °C for 48 h

under vacuum. Note that, Fe@mACs will be used to denote the combined Fe@mAC1,

Fe@mAC2 and Fe@mAC3 composites.

52

3.3 Characterization of Modified Activated Carbon

From the known depicted protocols for the synthesis of Fe@mACs composites,20 the

challenging target was to try to maximize the use of Fe (III) salt and consequently minimize the

residual waste. Therefore, Fe (III) filtrates were reused to modify fresh AC and in total 3 g of

Fe@mACs were obtained out of total 4.2M FeCl3.6H2O. It is worth mentioning here that the

amount of modified AC obtained by following this improved procedure is six times higher than

the previously reported one, 20 where only 0.500 g of modified AC out of 3M FeCl3.6H2O was

reached.

3.3.1 Elemental Analysis

Elemental analyses has provided 1.30, 1.70 and 1.50 wt % of iron and 0.80, 1.10 and 1.00 wt

% of phosphorus in Fe@mAC1, Fe@mAC2 and Fe@mAC3, respectively. These results

confirm the presence of immobilized FeOs Nps on the surface of Fe@mACs.

3.3.2 Boehm Titration

The content of acidic and basic groups on the surface of AC and Fe@mACs was determined

by Boehm titration21 and the results are given in table 3.1. At a first glance, it can be seen that

raw AC exhibits a lower content of basic groups than acidic groups. After the first treatment

step which involves H3PO4, the amount of acidic groups on the surface of Fe@mAC1 is

increased at the expense the basic groups. In the subsequent steps they have completely

disappeared on the surface of composites Fe@mAC2 and FemAC@3. Clearly, the production

of FeOs on the surface of AC lowers significantly the pH of the surface.

Table 3.1: Acidic and basic groups content on AC and Fe@mACs and their pHpzc.

Sample Acidic Groups

(μeq/g)

Basic Groups

(μeq/g)

pHpzc

AC 0.216 0.125 6.2

Fe@mAC1 0.227 0.075 2.5

Fe@mAC2 0.280 0 2.7

Fe@mAC3 0.281 0 2.8

53

3.3.3 Textural Properties

The textural characteristics of AC and Fe@mACs are given in the Table 3.2. Clearly, the

specific surface areas of Fe@mACs are in the similar range, but slightly lower (~ 11%) than

the raw AC, although the total pore volume (Vpore) of the different Fe@mAC composites is

almost not affected. Other observations can be made from this table: (i) the average pore

diameter increased for the modified AC, Fe@mAC1 and Fe@mAC2, while it decreases for

Fe@mAC3; (ii) a 20% lower value of the micropore volume for all the Fe@mAC composites.

This indicates that the particles present on the surface do not block the pores and the available

channels on AC. However, small nanoparticles (~2 nm) might be immobilized in the

micropores, which cause their volume lessening in all Fe@mACs. Overall, Fe@mAC2 has

lower specific surface area and pore volume than Fe@mAC1 and Fe@mAC3. A possible

explanation for this could be the higher concentration of FeOs NPs present on Fe@mAC2

surface. Settling FeOs Nps on the surface of AC could also be a reason for the reduction in the

specific surface area.20

Table 3.2: BET surface area and pore volume of AC and and Fe@mACs.

Sample SBET /

m2 g-1

Vpore /

cm3 g-1

Vmicro /

cm3 g-1

Ave. Pore

Size micro Å

AC 603 0.44 0.10 26.9

Fe@mAC1 558 0.44 0.08 31.4

Fe@mAC2 516 0.37 0.08 33.2

Fe@mAC3 551 0.43 0.08 24.9

54

3.3.4 Scanning Electron Microscopy (SEM)

The morphology of Fe@mACs has been investigated and the resulting SEM images are given

in Figure 3.1. The Overall morphology of Fe@mACs composites shown in Figures 3.1b, 3.1c

and 3.1d is similar to the unmodified AC (figure 3.1a). This allows us to conclude that the shape

of the particles is not affected by the experimental conditions.

Figure 3.1: SEM image of untreated AC (a), Fe@mAC1- (b), Fe@mAC2- (c) and Fe@mAC3-

(d) composites.

55

3.3.5 Transmission Electron Microscopy (TEM)

The presence of FeOs Nps on the surface of Fe@mACs composites was detected by TEM and

EDX analyses (Figure 3.2). Images obtained after TEM analysis show white spotted Nps on the

surface of Fe@mACs (TEM images LHS). The elemental composition of these white spotted

Nps was determined by EDX measurement. The presence of Fe_k and Fe_L energy dispersive

peaks at 6.4 KeV and at 0.7 KeV, respectively (EDX=RHS) confirms that all white spotted Nps

consist of FeOs Nps.

Figure 3.2: TEM images (LHS) and their respective EDX (RHS) spectra of Fe@mAC1 (a-d),

Fe@mAC2 (e-h) and Fe@mAC3 (i-l).

Although, round and oval like shapes FeOs Nps are homogeneously distributed throughout the

surface of Fe@mACs, the forced hydrolysis technique leads to significant variations in the size

of FeOs Nps (2-30 nm).

56

Moreover, these Nps are not visible in the TEM image of AC as well as in its EDX spectra,

which only displays the C energy dispersive peak (Figure 3.3).

Figure 3.3: TEM image (LHS) and EDX (RHS) spectra of neat activated carbon.

57

3.3.5 X-ray Photoelectron Spectroscopy (XPS)

The surface chemical compositions and the valence states of FeOs Nps on Fe@mACs are

revealed by XPS analyses. Figure 3.4 shows the survey XPS spectra of AC and Fe@mACs.

The most important observation in the survey spectra of Fe@mACs stands in the existence of

Fe2p binding energy peak at 720 eV, which confirms the occurrence of iron species on the

surface of the composites.

Figure 3.4: Survey scan XPS spectra of AC and Fe@mACs. In the inset, Fe 2p narrow XPS

scan spectra of Fe@mACs.

On the other hand, the survey spectrum of untreated AC does not exhibit such peaks. The

narrow XPS signals of Fe2p of Fe@mACs are shown in the inset of Figure 3.3. These signals

can be deconvoluted into two peaks centered at 712.4 and 725.9 eV, which are in a range where

the binding energy of Fe 2p3/2 and Fe 2p1/2 has been assigned to the Fe(III) surface species in

goethite (α-FeOOH) and/or hematite (α-Fe2O3).22, 23 It confirms that goethite and/or hematite

Nps are present on the surface of ACs. However, it is always difficult to predict which iron

oxide will be preferentially formed under a given set of conditions. The reaction mechanism

and stability of particular iron oxides Nps is still not fully understood.24

58

3.3.5 X-ray Diffraction (XRD)

XRD is known as a comprehensive resource, which can determine distinct nanoparticles present

on matrixes. Figure 3.5 displays XRD patterns of AC and Fe@mAC2. The XRD pattern of AC

shows an amorphous structure containing random sets of crystalline graphene sheets. The

crystallinity of AC mainly depends on the synthetic procedure and its mineral components. The

XRD pattern of Fe@mAC2 exhibits a similar profile.

Figure 3.5: X-ray diffractograms of AC and Fe@mACs.

The background is higher than that of AC due to non-crystalline scattering of Fe@mAC2. The

height of the background reflects the level of crystallinity of a partially crystallized amorphous

solid. Despite that, the XRD diffractogram of Fe@mAC2 displays clearly, at least one new and

visible XRD peak of goethite at ~68° 2θ and one intensified peak associated to hematite at 50°

2θ (inset in Figure 3.5).25 It has been resolved that the rest of XRD peaks derived from goethite

and hematite are overlapping either due to their amorphous nature or their lower density on the

surface of Fe@mAC2. Such observations endorse the presence of both α-FeOOH and α-Fe2O3

Nps, which decreases the crystallite size and crystallinity of Fe@mACs.

59

All above techniques have confirmed the presence of α-FeOOH and other iron oxides Nps on

the surface of AC. According to the previously reported work,15-18 FeOs Nps modified AC

(Fe@mACs) should improve the adsorption of an organic molecule and in our case, of

Chlordecone.

3.4 Chlordecone Adsorption Properties

3.3.1 Adsorption Kinetics

Adsorption kinetics of CLD on the different Fe@mAC composites and untreated AC is depicted

in Figure 3.6. Overall, it is expected that the low concentration of CLD solution would lead to

slow adsorption onto the adsorbent due to the low driving force of adsorbate. However, CLD

adsorption is faster onto Fe@mACs than onto AC.

Figure 3.6: The kinetics of CLD adsorption onto the AC and Fe@mACs. Initial concentration

of CLD was 2.2 mg L-1

60

The adsorption equilibrium for Fe@mACs and AC was reached after ~24 h. GC/MS analyses

of the residual CLD solution revealed that 95% of the CLD present in water is adsorbed onto

Fe@mACs against 62% for untreated AC. Based on these results we can conclude that

Fe@mACs are better adsorbent than untreated AC, indeed.

Two-adsorption kinetics models were used to probe the mechanism that controlled the sorption

process of CLD onto AC and Fe@mACs. These are pseudo first and second-order kinetics

models, which are expressed in equation 9 and 10 of Chapter 1.

In pseudo first-order kinetics, qe and rate constants (k1) were calculated from the slope and

intercept of the plot of log (qe-qt) vs. t (Figure 3.7a). However, in pseudo second order kinetics,

by plotting t/qt against t, one can calculate qe and k2 from slope and intercept, respectively as

shown in Figure 3.7b. The values and the comparative fits of both kinetic models shown in

Table 3.3 indicate that both models are relevant.

Figure 3.7: Linear plots of a) pseudo first-order and b) second-order kinetics for AC and

Fe@mACs.

61

Table 3.3: Determined constants of pseudo first/second-order kinetics.

Samples

Pseudo first-order kinetics

Pseudo second-order kinetics

qe (μg/mg) k1 (μg/mg·min) R2 qe

(μg/mg)

k2 (μg/mg·min) R2

AC 63.09 0.0009 0.84 72.99 0.00039 0.98

Fe@mAC1 67.61 0.0025 0.98 90.91 0.00016 0.99

Fe@mAC2 64.86 0.0021 0.97 91.74 0.00020 0.98

Fe@mAC3 63.10 0.0021 0.95 86.96 0.00018 0.98

Nevertheless, pseudo second-order kinetics seems to fit better due to the correlation coefficient

(R2) which is, in all cases, closer to unity (0.98-0.99). It is known that the rate-limiting step in

pseudo second-order kinetic model is chemisorption. However, we believe that there is more

physisorption between CLD and Fe@mACs than chemisorption. This was confirmed after

isotherm calculations (Table 3.4).

Hydrogen bonding (an intermediate interaction between chemisorption and physisorption),

which will take place between the hydroxide groups of α-FeOOH (Fe@mACs) and the carbonyl

group of CLD, would certainly play an important role as well. Nevertheless, the higher

equilibrium adsorption (qe) capacity values demonstrates that Fe@mACs have better and faster

CLD adsorption than AC.

62

3.4.2 Adsorption Isotherm

The correlation of adsorption data using either a theoretical or an empirical equation is essential

for practical purposes. Five different models are used to fit single-component isotherms. All the

equations are shown in table 1.5 of Chapter 1.

The experimental adsorption data of CLD on AC and Fe@mACs are plotted in Figure 3.8. The

average relative error of the measured concentrations in the liquid phase was less than 5 % in

all cases. These curves correspond to the L-type isotherm, according to Giles classification.26

The pattern of all Fe@mACs isotherms is similar. This result is in agreement with physico-

chemical and textural properties of composites (Table 3.1-2), and confirms that the preparation

method of composite does not influence the Fe@mACs adsorption properties. Moreover, the

adsorption capacity of CLD of the new materials is higher than that of untreated AC.

Figure 3.8: Comparison between experimental adsorption data of chlordecone on Fe@mACs

and AC (symbols) and values calculated using the Langmuir model (lines).

Table 3.4 summarizes the results of the nonlinear regression analysis of the evaluated models.

AICC and AARE values show that the agreement of the models with the experimental data is

good. In almost all cases, the best fit (lower AICC and AARE) was obtained for Langmuir

model with the average standard error estimation in the range of 3.6-9.2 %.

63

Table 3.4: Comparison of model correlations for CLD. qs is the monolayer capacity. is the

adsorbate-adsorbate interaction parameter; is the heterogeneity parameter; k and a are other

parameters.

Model and parameters Fe@mAC1 Fe@mAC2 Fe@mAC3 AC

Langmuir

qs, μg/mgAC 79.5 80.6 79.1 48.6

K, μg/ mgAC 0.0064 0.0061 0.0054 0.022

R2 0.99 0.94 0.98 0.98

AICC 26.6 39.9 26.5 21.0

AARE, % 3.6 9.2 4.3 4.2

Fowler

qs, μg /mgAC 79.5 73.7 73.0 48.5

K, μg/ mgAC 0.0065 0.0022 0.003 0.021

χ 0.0019 2.1 1.4 0.057

R2 0.99 0.96 0.99 0.98

AICC 32.2 40.6 27.4 25.4

AARE, % 3.7 7.1 3.7 4.2

Freundlich

K, μg1-γ Lγ 1

ACmg 10.8 11.3 9.7 13.7

ν 0.27 0.26 0.28 0.18

R2 0.98 0.92 0.97 0.95

AICC 29.3 42.9 32.0 30.3

AARE, % 4.9 9.9 7.0 7.8

Redlich-Peterson

a, μgγ L1-γ 1

ACmg 35.7 39.0 40.0 38.0

K, Lγ μg-γ 0.021 0.018 0.014 0.033

ν 0.89 0.90 0.91 0.96

R2 0.99 0.94 0.98 0.98

AICC 29.9 45.3 31.5 24.5

AARE, % 3.6 9.3 4.2 3.8

Khan

a, μg /mgAC 57.4 66.2 59.8 43.0

K, L/μg 0.013 0.011 0.010 0.029

ν 0.89 0.95 0.9 0.97

R2 0.99 0.94 0.98 0.98

AICC 29.9 44.5 31.6 24.5

AARE, % 3.6 9.8 4.2 3.8

64

The average monolayer capacity of studied Fe@mACs composites (79.8 μg /mg) calculated

from Langmuir model is 64 % higher than for untreated AC. Conversely, it is 14 % lower for

CLD adsorption on sugarcane bagasse AC (when phosphoric acid was used as an activating

agent but without FeOs Nps) obtained by Durimel et al.,21 at the same pH value of CLD

solution. However, the average BET surface area of Fe@mACs is 1.1 and 2.3 times lower than

AC (Table 3.2) and the surface area of the previously mentioned Durimel’s AC (542 m2/g vs.

1269 m2/g), respectively. But, the CLD adsorbed by the unit of adsorbent surface is higher for

Fe@mACs (147 μg /m2) than for AC (80 μg /m2) and Durimel’s AC (72 μg /m2). It means that

the number of adsorption sites is higher in Fe@mACs, confirming the role of FeOs Nps in the

adsorption process of CLD. Figure 3.9, is a graphical illustration of how iron oxy-hydroxide

Nps polymorph can enable the hydrogen bonding with CLD that could induce the CLD

adsorption on Fe@mACs.

Figure 3.9: How iron oxy-hydroxide enables the hydrogen bonding with CLD, which could

induce the CLD adsorption on Fe@mACs.

On the other hand, the positive values of in Fowler equations show the importance of repulsive

adsorbate-adsorbate interactions in the sorption process. Regarding the surface heterogeneity,

it can be observed that the parameter in Freundlich, Redlich-Peterson and Khan models is

different to unity for all supports. When the heterogeneity parameter is equal to unity,

adsorption takes place on homogeneous surface.

Then, as it can be expected, the Fe@mACs studied here have strongly heterogeneous surfaces.

This fact is well known, due to both their pore size distribution and the presence of the different

functional groups on the composite surface. Moreover, the presence of several functional

65

groups in the adsorbate molecule has been reported to diversify the interactions with adsorption

sites and thus to increase energy dispersion.27 Other research groups that studied the adsorption

of organic pollutants or metals on Ac and Fe@mACs composites obtained similar results.7-18

3.5 Conclusion

New FeOs immobilized activated carbon (Fe@mACs) with maximum use of FeOs filtrate have

been achieved successfully. Textural properties of Fe@mACs show that surface area has been

decreased slightly without significant loss in the pore volume. SEM has confirmed that particle

size of modified AC remains unchanged. TEM analysis has shown variances in the FeOs Nps

size which are from 2 nm to 30 nm. Expectedly, XPS and XRD analysis have proved that α-

FeOOH Nps and other iron oxides Nps exist on the surface of activated carbon.

Pseudo first and second-order kinetics models have proved that adsorption of CLD is better and

faster onto Fe@mACs than the untreated AC utilized for this application.

Four different adsorption models were used to find out the best-fit model for the obtained

experimental data. A Langmuir model was found to give the best fit with the average standard

error estimation in the range of 3.6-9.2 %. The average monolayer capacity of Fe@mACs

composites (79.8 μg /mg) calculated from Langmuir model is 64 % higher than for unmodified

AC. It ascertains that immobilization of FeOs Nps into the AC can actually enhance CLD

adsorption from water.

66

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67

12. Arcibar-Orozco JA, Josue DB, Rios-Hurtado JC, Rangel-Mendez JR. Influence of iron

content, surface area and charge distribution in the arsenic removal by activated carbons

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nitrate removal from water using activated carbon and composite of activated carbon

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69

CHAPTER - 4

SUPRAMOLECULAR COMPLEXATION BETWEEN CYCLODEXTRIN AND

CHLORDECONE: AN ELEGANT WAY TO REMOVE CHLORDECONE FROM

WATER

4.1 Introduction

Cyclodextrins (CDs) are a family of naturally occurring macrocyclic oligosaccharides. They

are non-toxic, biodegradable and biocompatible. CDs are torus-like micro-rings built up mainly

of six, seven or eight glucopyranose units for α-, β- and γ-CD respectively. Figure 4.1 depicts

the chemical structure of cyclodextrins and their physical dimensions are included in Table 4.1.

Glucopyranose units are linked together via α-(1,4) bonds which render these macromolecules

chemically stable. These cyclic oligosaccharides exhibit a cavity lined by hydrogen atoms and

glycosidic oxygen bridges where secondary hydroxyl groups are located on the wider edge

(called secondary face). Primary hydroxyl groups are on the narrower edge (called primary

face) of the ring. This results in a hydrophilic outer sphere, which is responsible for its solubility

in water and a highly hydrophobic central cavity, which provides ample space to host

hydrophobic guest molecules of similar sizes.1 These host-guest complexes find applications in

pharmaceutical sciences, physiology,1, 2 catalysis,3, 4 chemical sensing,5 and gas storage.6

Besides, CDs have been used to treat wastewater and to adsorb toxic metals, metal salts and

organics from water. Consequently, CDs were considered as adsorbents for chlordecone. 7, 8

Figure 4.1: Structure of commercially available and most common cyclodextrins

70

Table 4.1: Cyclodextrins and their structural properties.2

Cyclodextrin Mass

Outer

diameter

(nm)

Cavity Diameter (nm)

Inner rim Outer rim

α, (Glucose)6 972 1.52 ± 0.1 0.45 ± 0.1 0.53 ± 0.1

β, (Glucose)7 1134 1.66 ± 0.1 0.60 ± 0.1 0.66 ± 0.1

γ, (Glucose)8 1296.5 1.77 ± 0.1 0.75 ± 0.1 0.83 ± 0.1

This chapter will describe the complexation behaviour of three different sizes of CD (α-, β- and

γ-CD) towards CLD. Their efficiency to bind CLD has been evaluated by means of several

techniques such as ATR-FTIR, NMR, DSC and ITC (Isothermal Titration Calorimetry).

Because of the limited solubility in water of CLD, we studied the complexation of chlorendic

acid (CLA) as better soluble and less toxic model compound as well. Structure and physical

dimensions of CLD and CLA are shown in Figure 4.2.

Figure 4.2: Structure and dimensions of chlordecone (CLD) and chlorendic acid (CLA).

71

4.2 Inclusion of Chlordecone into Cyclodextrins

In separate recipients, 0.01mM of α-, β- and γ-CD were dissolved in 10 mL of water and in

stoichiometric amount, chlordecone or chlorendic acid were dissolved in a minimum amount

of methanol. Once host and guest compounds are totally solubilized in their respective solvents,

solutions were mixed together. Instantaneously, in the case of β- and γ-CD, a white precipitate

appears. Then the supernatant was decanted and the solid was washed four to five times with

50 mL of a mixture of water-methanol (1:1). Finally, the solid obtained was dried under vacuum

in a desiccator over phosphorus pentoxide.

4.3 Characterization of Complex

Figure 4.3 illustrates the results obtained after mixing stoichiometric amounts of host molecules

(α-, β- or γ-CD) and the guest molecule (CLD) previously dissolved separately into water and

methanol, respectively.

Figure 4.3: Optical representation of the solution obtained after mixing cyclodextrins (i) α-CD

(ii) β-CD (iii) γ-CD and chlordecone.

As can be seen, the result is completely different and depends on whether the inner size of the

host molecule is smaller or larger than the dimension of the guest molecule (Figure. 4.2). With

β- and γ-CD, which exhibit cavities with diameters in the same range or larger (Table 4.1) than

the dimension of the guest molecule (CLD), a white precipitate appeared almost instantaneously

(less than 30s). The same experiment performed with α-CD, which exhibits the smallest cavity

size, led to a perfectly clear solution.

Moreover, the yields of aggregates formed either with β-CD or with γ-CD exceed 94% and

remain insoluble in most organic solvents except for DMF or DMSO. Solubility of precipitated

72

aggregates is listed in Table 4.2. We therefore assume that CLD forms inclusion complexes

only with β-CD and γ-CD. Note that chlorendic acid (CLA), which is used as model compound

for CLD, behaves similarly as chlordecone and likewise forms 1:1 complexes with β-CD and

γ-CD under similar conditions. For a detailed analysis, only CLD complexation with γ-CD was

studied.

Table 4.2: Solubility of complexes in different solvents

Solvents CLD : γ-CD CLA : γ-CD

Water x x

Acetone x x

Ethanol x x

Methanol x x

Isopropanol x x

Acetonitrile x x

Chloroform x x

DCM x x

DME x x

Ether x x

THF x x

n-Hexane x x

Benzene x x

Toluene x x

DMF

DMSO

73

4.3.1 Elemental Analysis

In order to determine the ratio γ-CD : CLD, the elemental composition of the washed and dried

precipitate was investigated. Table 4.3 shows the average experimental elemental composition

of the precipitates. These values were compared with a calculated composition for a 1:1 host-

guest interaction. The result of this analysis shows a good match between the calculated and

the experimental values, confirming that CLD and γ-CD interact in a 1:1 ratio.

Table 4.3: Elemental analysis result of complexes CLD: γ-CD precipitate.

Element, %

CLD: γ-CD C H O Cl

Theoretical Value 38.96 4.51 36.70 19.83

Experimental Value 38.48±0.09 4.93±0.05 37.18±0.70 19.41±0.57

74

4.3.2 ATR- Fourier Transmission Infrared Analysis

In general, IR spectroscopy was not found to be especially useful for the interpretation of host-

guest complexes.9 However, in our case, significant changes in IR absorption spectra could be

observed as shown in Figure 4.4. The spectrum of free γ-CD exhibits a broad and slightly

disordered band at 3260 cm-1 attributed to the –OH group of γ-CD. This absorption band

becomes more intense and shifts to 3322 cm-1 in the CLD@ γ-CD complex. This indicates the

occurrence of interactions involving the –OH groups of γ-CD and the guest molecule. Also the

insolubility of the complex in most solvents suggests that the hydroxyl groups are not available

anymore for the interaction with solvent molecules. Only highly polar solvents like DMF or

DMSO, which are known to form strong hydrogen bonds with hydroxyl groups, are able to

dissolve the CLD@ γ-CD complex likely under decomplexation of the guest from the host (see

below).

Figure 4.4: ATR-FTIR spectra of γ-CD, CLD and CLD@ γ-CD.

In the 900 to 1100 cm-1 range, all -C-O stretching bands of γ-CD and –C-C stretching bands of

CLD shift and lead to new absorption wavenumbers band at 1000, 1024, 1056, 1078 and 1108

cm-1 for the CLD@γ-CD complex (see inset of Figure 4.4). Moreover, absorption bands

corresponding to the vibrations of the C-Cl bond are modified. Firstly, the absorption band

corresponding to the C-Cl stretch shifts from 848 cm-1 in the free CLD to 860 cm-1 in the

complex. Secondly, the intensity of the absorption bands at 638 - 670 cm-1 corresponding to C-

Cl bend of the free CLD is strongly decreased in the complex. The combined results from

elemental analysis and IR spectroscopy suggest the formation of a rather strong 1:1 inclusion

complex between CLD and γ-CD.

75

4.3.3 Proton Nuclear Magnetic Resonance (1H NMR) Analysis

Figures 4.5a and 4.5b depict the 1H NMR spectra of γ-CD and its complex with CLD,

respectively, in d6-DMSO as solvent. The Figure and the data listed in Table 4.4 show that the

chemical shifts of the protons in the CLD@ γ-CD complex are slightly more shielded when

compared to pure γ-CD. The following observations can be made: (i) 1H NMR spectra of the

complex show that proton H-3 and H-5, which are located inside the γ-CD, are slightly

downfield shifted. (ii) H-1 has the highest upfield shift compared to the other –C-H protons of

the complex. (iii) -OH (OH-2, OH-3 and OH-6) chemical shifts are affected as well. (iv) 13C

Carbon satellite peaks appear in the 1H NMR spectra of CLD@ γ-CD (labelled by asterisks)

which are typical for an “intermolecular coupling” involving C atoms of the CLD and the

protons (-C-H or –CH-OH) of γ-CD.

Figure 4.5: 1H NMR spectra of γ-CD and CLD@ γ-CD in DMSO-d6.

Even though the extent of these chemicals shifts variations appear meagre (maximum 0.07

ppm), they indicate a host-guest inclusion phenomenon, as was also previously reported for a

similar case.10, 11 The most significant chemical shift deviation concerns H-1 of CD and we

therefore assume that CLD penetrates into the cavity of γ-CD such that its carbonyl group forms

a hydrogen bond to this proton (Figure 4.6). The overall stability of the complex is provided by

the sum of the–OH interactions of γ-CD with chlordecone which are also indicated in the ATR-

FTIR spectra.

76

Table 4.4: Change in 1H NMR chemical shifts [δ (ppm)] of C-H and –OH protons of γ-CD and

CLD@ γ-CD in DMSO-d6.

H-1 H-2 H-3 H-4 H-5 H-6 OH-2 OH-3 OH-6

γ-CD 4.89 3.31 3.63 3.37 3.56 3.63 5.76 5.72 4.51

CLD@γ-CD

4.83

3.29

3.66

3.37

3.59

3.63

5.72

5.66

4.44

Difference

0.06

0.02

-0.03

0.0

-0.03

0.0

0.04

0.06

0.07

After a certain period of time (4 hours) (Figure 4.5c), the 1H NMR resonances of the γ-CD

moiety in the complex are found at chemical shifts of the uncomplexed cyclodextrin indicating

that in DMSO as solvent the host-guest interaction is reversed with time.

Figure 4.6: Pictorial representation of the possible conformation of CLD@ γ-CD complex.

77

4.3.4 Differential Scanning Calorimetry (DSC) Measurements

The DSC is a sensitive tool to monitor the host-guest inclusion reaction by comparing the

physical properties of the formed complex (CLD@γ-CD) with those of its free constituents,

CLD and γ-CD. The obtained DSC curves for CLD, γ-CD and complex are portrayed in Figure

4.7. The DSC curve of CLD illustrates two main endothermic peaks. The first one below 100

°C is due to moisture release and the second at 332 °C can be attributed to the decomposition

of the complex. The DSC thermogram of γ-CD also exhibits water loss as first endothermic

peak at 100 °C and at higher temperatures between 285 and 330 °C decomposition starts. In

contrast, the DSC curve of the CLD@ γ-CD complex has a completely different profile. An

endothermic peak at about 240 °C is observed which corresponds to the melting of the complex.

Once temperature upsurges, a sharp exothermic decomposition peak at 275 °C is recorded.

These observations are in agreement with the formation of a definite host (CLD)-guest (CD)

complex and comparable similar DSC thermograms of host-guest complexes have been

previously reported.9

Figure 4.7: DSC thermograms of CLD, γ-CD and CLD@ γ-CD.

78

4.3.5 Isothermal Titration Calorimetry (ITC)

Further insight in the complex formation is obtained by evaluation of the thermodynamic

interaction parameters between CLD and γ-CD by Isothermal Titration Calorimetry (ITC).

Again, this technique has to be performed in a single solvent.

Figure 4.8: Isothermal Titration Calorimetry (ITC) of 1mM CLD (dissolved in DMSO/DMF)

and 0.05mM γ-CD (dissolved in water) at 25°C.

Unfortunately, as mentioned previously, CLD and γ-CD are not sufficiently soluble in the same

solvent except for DMF and DMSO in which decomplexation occurs (as reported in the 1H

NMR discussion). Nevertheless, ITC measurements between a solution of CLD in different

organic solvents and aqueous solutions of γ-CD were performed. As expected, the results were

not exploitable: the heat evolved from mixing two different solvent overshadowed the

exothermic heat signal resulting from the host-guest reaction as described in Figure 4.8, where

79

heat minima did not reach whatsoever from low to high concentrations. Therefore, we have

moved on to find out similar but water soluble drug for the same experimental analysis.

Because of its much better solubility in water, chlorendic acid (CLA) was used as model

substrate for the complexation with γ-CD. It has similar physical dimensions as CLD does and

mentioned in Figure 4.2 as well. We have observed that CLA also form an insoluble complex

with γ-CD called CLA@γ-CD. Elemental analysis has further confirmed that one γ-CD include

one CLA molecule and forms 1 : 1 complex. Results obtained after elemental analysis is shown

in Table 4.5.

Table 4.5: Elemental analysis result of complexes CLA@γ-CD precipitate.

Element, %

CLD@γ-CD C H O Cl

Theoretical Value 40.61 5.02 41.75 12.62

Experimental Value 40.33±0.04 5.22±0.02 42.17±0.16 12.28±0.10

Figure 4.9 depicts the result from the ITC analysis of the reaction between CLA and γ-CD. The

following thermodynamic parameters given in the inset of the Figure 4.9 were calculated: (i)

the molar enthalpy of complexation, ΔH = -17.5 ± 0.35 kJ/mol, is obtained from the

extrapolated step-height of the curve. (ii) The stoichiometry of the binding process n (n = 0.989)

is taken from the position of the inflection point along the molar ratio axis, and (iii) the affinity

constant Ka = 2.63×105 M-1 is obtained from the slope of the curve at the inflection point.12

From these parameters, the dimensionless c-value was calculated with the help of the equation

(1)

𝑐 = 𝑛 × [𝑀]𝐾𝑎 (1)

where, Ka is the affinity constant, [M] the concentration of the macromolecule and n, the

stoichiometry of the reaction.

With our data we obtain c = 10.5 which is in the range of c = 5 – 500 for strong host-guest

interactions (12). This indicates that inclusion of CLA into γ-CD is exothermic with a high

binding affinity and a 1:1 stoichiometry (n = 0.989) of the formed CLA@ γ-CD complex.

80

Moreover, the complexation between CLA and γ-CD shows a negative ΔH and a near-zero ΔS

(0.05kJ/Mol.K).

Figure 4.9: Isothermal Titration Calorimetry (ITC) of 0.9mM CLA in 0.04mM γ-CD in water

at 25°C.

According to the literature, these thermodynamic parameters describe “non-classical

hydrophobic interactions” involving hydrophilic solutes CLA and CD.13, 14

By cautious extrapolation of the results obtained with chlorendic acid, a model compound, and

under the assumption that classical hydrophobic interaction prevails in the interaction of CLD

with the inner cavity of γ-CD, one expects a higher positive entropy change (ΔS) but a near-

zero enthalpy change (ΔH) for the CLD/ γ-CD interaction.15

81

4.4 Computational Study of Complex formation Between Cyclodextrin and

Chlordecone

4.4.1 System under study

Cyclodextrins (CDs) in aqueous solution exist in uncountable conformational states (16). For

that reason, it is almost impossible to model their behavior using a single structure.

In order to get some insights about the formation of the inclusion complex between the

𝛾-cyclodextrin (𝛾-CD) and the chlordecone (CLD), a model of 𝛾-CD was built. The model

consists of four symmetrical conformers of 𝛾-CD, namely A, B, C, and C´ according to

intramolecular interactions (See Figure 4.10), which main difference is the magnitude of the

dihedral angle C4-C5-C6-O6 (See Figure 4.11) in every glucopyranodide residue. These

symmetrical conformers were built by means of a conformational search varying the previously

mentioned dihedral, and scanning it using the semi-empirical Hamiltonian PM6-D3H4 (17)

with full optimization as implemented in MOPAC 2012 (18, 19). Table 4.6 shows some of their

characteristics.

B A

82

Figure 4.10: Model of 𝛾-CD representing four symmetrical conformers: A, B, C, and C´.

Figure 4.11: Atoms forming a dihedral angle (C4-C5-C6-O6) in the glucose residue

C C´

83

Table 4.6: Initial dihedral angles δi and relative energy for the used conformers. Relative

Energy equal 0.0 accounts for the less stable conformer.

Conformer δi:C4-C5-C6-O6

(Degrees)

Absolute Energy

(kJ/mol)

Relative Energy

(kJ/mol)

A -129.7 -1797731.3 -155.1

B 5.4 -1797581.8 -5.7

C 57.4 -1797625.0 -58.4

C' 164.8 -1797576.2 0.0

All conformers are stable at PM7 level of theory and they are stabilized by means of

intramolecular hydrogen bonds. In all cases the wider rim is stabilized by means of hydrogen

bonds between the secondary OH in a counterclockwise arrangement.

Conformer A presents intramolecular interesidue hydrogen bonds between primary hydroxyls

making it the most stable of four studied conformers. This characteristic makes primary

hydroxyls less likely to form hydrogen bonds with water, lowing its solubility. It also causes a

contraction in the smaller rim and the enlargement of the wider rim what makes it more open

to accept a guess molecule.

Conformer B stabilizes by forming hydrogen bonds between the primary hydroxyl and O5´ in

the neighbor residue. This interaction is less stable than in the case of A.

Conformers C and C´ stabilizes by intraresidue hydrogen interactions of the primary OH with

O1. In the case of C, 𝛿𝑖 = 570 while in the case of C´, 𝛿𝑖 = 164.80, as it is shown in Table 4.6.

C´ is the less stable structure of all four. However, it is stable enough to be taken into

consideration for this study.

84

4.4.2 Methods and procedures

The formation of the complexes CLD@𝛾-CD were studied using Multiple Minima

Hypersurface (MMH) methodology (20-22). MMH is a non-dynamical stochastic approach that

allows estimating the thermodynamic association functions by means of the internal energy

calculations with semiempirical hamiltonians. MMH methodology combines a quantum semi-

empirical methods for the evaluation of the energies with statistical mechanics to obtain

thermodynamic quantities related to the molecular association process. The main procedure of

this approach will be outlined briefly. An appropriate construction of several random molecular

geometries initially generates a set of n (200 in this study) non-redundant cluster configurations,

starting from the independently optimized structures of AC, CLD and water. The random

structures are optimized, normally following an energy gradient pathway, and a set of clusters

of local minima in the configuration space is obtained. The energy, E, of every cluster of the

ensemble is thus obtained.

The relative energy (E- E0) with respect to a reference state E0 is then obtained. Where the

reference state is the sum of the energies of the separated molecules that conform the molecular

association complex.

𝐸0 = 𝐸𝛾−𝐶𝐷 + 𝐸𝐶𝐿𝐷

𝐸 − 𝐸0 = 𝐸𝐶𝐿𝐷@𝛾−𝐶𝐷 − (𝐸𝛾−𝐶𝐷 + 𝐸𝐶𝐿𝐷)

The partition function of molecular association is calculated by choosing the same set of non-

interacting molecules as reference value for the energy scale, which means that the association

process is taken as isothermal. Thermodynamic properties such as mean association energy

(EASSOC), are then calculated by this procedure (21, 22). The term of mean association energy

used, means the thermodynamic association energy calculated through the statistically weighted

sum (i.e. partition function) of the representative “supermolecule” states (21). A Boltzmann

distribution is used to calculate the thermally averaged state of the typical macroscopic system

at room temperature (298.15 K) using the contribution of each state (n/N) to the mean

association energy (EASSOC).

The adsorption is a thermodynamic competitive process where the stronger interactions

dominate over the weaker interactions. However, it does not mean that, in a real system, only

one type of interaction (the strongest) will determine the adsorption. In this sense, the

association energy takes into account the contribution of several configurations of the 𝛾-

CD/CLD interactions and it is appropriated to describe the adsorption process. The association

85

energy, calculated as implemented in MMH procedure, takes into account the weight of each

configuration to the total energy.

In this case, the semiempirical hamiltonian PM6-D3H4X (17, 23) was used to perform the

optimizations.

4.4.3 Results and discussions

In Table 4.7 the relevant information about the association process in terms of formation of the

complexes CLD@𝛾-CD for each conformer is shown. In addition, Figure 4.12 shows the global

minima for the inclusion complexes obtained.

Table 4.7: Final results of the MMH methodology. 𝐸𝐴𝑆𝑆𝑂𝐶: molecular association energy for

the formation of the CLD@𝛾-CD inclusion complex. E-E0: relative energy with respect to the

reference state. n/N contribution to 𝐸𝐴𝑆𝑆𝑂𝐶.

Conformer EASSOC (kJ/mol)

Global Minima

E-E0 (kJ/mol) n/N

A -91.8 -92.5 34%

B -97.3 -99.4 59%

C -83.1 -85.2 62%

C' -247.7 -247.7 100%

As it can be seen, from Table 4.7, the formation of the inclusion complex is energetically

favored, which means that the complexes CLD@𝛾-CD are more stable than the reference state.

In all cases the relative energies with respect to the reference state (𝐸 − 𝐸0) are very close to

the overall association energies (𝐸𝐴𝑆𝑆𝑂𝐶) and their corresponding contributions to the total

energy (n/N) are high, which support the idea of CLD immobilization in a few configurations

into 𝛾-CD. The effect becomes evident for C’ with the highest 𝐸𝐴𝑆𝑆𝑂𝐶.

86

Figure 4.12: Global minima for CLD@𝛾-CD for each conformer.

A B

C C’

87

The complexation occurs by means of two main interactions. First, a relatively strong,

dispersive type interaction between the hydrophobic interior of the 𝛾-CD and the chlorines of

the CLD, and second, the immobilization of the CLD by an hydrogen bond interaction between

a secondary OH of the 𝛾-CD and the carbonylic oxygen of CLD. The last interaction

compromises one secondary OH at least for conformers A, B, and C’ which makes CD less

soluble in protic solvents like water. For the conformer C’, it is obtained a rearrangement of the

conformer that demonstrate, at this level of theory, that C’ is no longer stable after the formation

of the inclusion complex, collapsing into conformer A and compromising the primary

hydroxyls in intramolecular hydrogen bonds. Once again, all these effects, added to the increase

of the mass and hydrophobicity of the system, are a good explanation for the experimental fact

that this inclusion complex is practically non-soluble in water.

88

4.5 Adsorption of chlordecone

The formation of a stable inclusion complex of CLD with γ-CD, which precipitates in water,

can be practically used for the removal of chlordecone from water. After complexation, a simple

filtration even at large scale may easily allows the removal of the complex giving depolluted

clean water. In a more elaborated approach, the synthesis of a hybrid material between activated

carbon as support and cyclodextrins as active sites for selective CLD complexation can be

envisioned which may serve as filter material. As proof of concept, the following experiments

were carried out.

4.5.1 Direct filtration experiment of CLD@ γ-CD complex with AC

First, a saturated solution of CLD (~2.2 mg/L) in 1 L of ultra-pure water was prepared. To this

solution, a small excess (10%) of γ-CD was added. The solution was kept shaking (120 rpm)

for 30 minutes to achieve complete complexation. Afterwards, a bed of 15 mg of activated

carbon was prepared in a column in order to filter off the complex from the aqueous phase.

(Figure 4.13a) A standard gravity filtration was performed. It is expected that the pore size of

the activated carbon (48 Å) does not allow the diffusion of particles of CLD@ γ-CD into its

pore. The purity of the filtrate was then analysed by GC/MS measurements. GC/MS analyses

shows that nearly all CLD (98 %) has been trapped on the activated carbon filter after it was

complexed to γ-CD (Figure 4.13b and Figure 4.13c).

This experiment reveals that once the complex between CLD and γ-CD is formed in water, only

15 mg of activated carbon is sufficient to decontaminate 1 L or more of CLD-polluted-water.

On the other hand, without complexation, 15 mg AC will adsorbed only ~32 % CLD from 1L

of CLD saturated solution (2200 μg/L). PTFE membrane were used as well to filter off the

complex (CLD@γ-CD) from water. GC/MS analyses have confirmed yet again that ~98 %

CLD was trapped on the membrane.

89

Figure 4.13: A column of activated carbon bed to get pure water out of complex containing

water (a), MS spectra of saturated CLD solution before complexation (b), MS spectra of water

after complexed adsorption on the surface of AC (c).

This technique would certainly be suitable for steady water bodies. However, in the case of

heavy water flow, the probability of complex formation is much smaller. In order to facilitate

the “meeting” between the host and the guest, cyclodextrins immobilized on an activated carbon

support can serve as filter material through which the contaminated water runs if necessary in

repeating cycles.

90

4.6 Conclusion

The results from this work demonstrate that γ-CD is a good complexing agent to remove CLD

from water. Elemental analyses have proven that the ratio between γ-CD and complexed CLD

is 1:1. ATR-FTIR and NMR techniques further confirmed the interactions between γ-CD and

CLD, which lead to the insolubility of the complex in most solvents.

Due to its (CLD) lack of water solubility, ITC could not accomplished between CLD and γ-

CD. Therefore, CLA was further included into the work as a model drug to know the

thermodynamic parameter originates after the complexation between CLA and γ-CD in the ITC

measurement. Elemental analysis and ITC have confirmed that CLA and γ-CD also form a 1: 1

insoluble complex called CLA@ γ-CD. With ITC results, we could conclude that where CLA

(soluble in water) make a non-classical hydrophobic interaction with γ-CD, on the other hand,

CLD would possibly make a classical and strong hydrophobic interaction inside the γ-CD cavity

and form an water insoluble complex called CLD@ γ-CD.

A conformational study of 𝛾-cyclodextrin was made in order to build a model for the formation

of the inclusion complex with chlordecone. Multiple Minima Hypersurface methodology was

used to theoretically characterize the formation of CLD@𝛾-CD. All inclusion complexes were

stables and demonstrate, at PM7 level of theory, the immobilization of CLD into the 𝛾-CD. The

observed interactions in the complex and the possible changes in the conformations of 𝛾-CD

explain the low solubility of the inclusion complex

Moreover, we have noticed that the complex (CLD@ γ-CD) is easily removable from water

and a simple filtration over activated carbon is sufficient to obtain clean water. GC/MS analyses

have confirmed that nearly 98 % CLD (after the complexation) was trapped on the activated

carbon filter.

91

4.7 References

1. Martin Del Valle EM. Cyclodextrins and their uses: a review. Process

Biochemistry 2004; 39 (9): 1033-1046.

2. Hapiot F, Tilloy S, Monflier, E. Cyclodextrins as supramolecular hosts for

organometallic complexes. Chemical Reviews 2002; 106 (3): 767-781.

3. Martínez A, Mellet CO, Fernández JM G. Cyclodextrin-based multivalent

glycodisplays: covalent and supramolecular conjugates to assess carbohydrate–

protein interactions. Chem. Soc. Rev. 2013; 42 (11). 4746—4773.

4. Zhang G, Luan Y, Han X, Wang Y, Wen X, Ding C, Gao J. A palladium complex

with functionalized β-cyclodextrin: a promising catalyst featuring recognition

abilities for Suzuki-Miyaura coupling reactions in water. Green Chem. 2013; 15

(8): 2081-2085.

5. Saenger W. Cyclodextrin inclusion compounds in research and industry. Angew.

Chem., Int. Ed. Engl. 1980; 19 (5): 344−362.

6. Holman KT. Molecule-constructed microporous materials: long under our noses,

increasingly on our tongues, and now in our bellies. Angew. Chem., Int. Ed. 2011;

50 (6), 1228−1230.

7. Sawicki R, Mercier L. Evaluation of mesoporous cyclodextrin-silica

nanocomposites for the removal of pesticides from aqueous media. Environ. Sci.

Technol. 2006; 40 (6), 1978-1983.

8. Arkas M, Allabashi R, Tsiourvas D, Mattausch E-M, Perfler R.

Organic/Inorganic hybrid filters based on dendritic and cyclodextrin nanosponges

for the removal of organic pollutants from water. Environ. Sci. Technol. 2006; 40

(8), 2771-2777.

9. Dailey OD, Bland Jr JM, Trask-Morrell BJ. Preparation and characterization of

cyclodextrin complexes of the insecticides aldicarb and sulprofos. J. Agri. Food

Chem. 1993; 41 (10), 1767-1771.

10. Schneider H-J, Hacket F, Rüdiger V, Ikeda H. NMR Studies of cyclodextrins and

cyclodextrin complexes, Chem. Rev. 1998; 98 (5), 1755-1785.

11. Jiang H, Sun H, Zhang, S, Hua R, Xu Y, Jin S, Gong H, Li L. NMR investigations

of inclusion complexes between 𝛽-cyclodextrin and naphthalene/anthraquinone

derivatives. J. Inclusion Phenom. Macrocy. Chem 2007; 58 (1), 133-138.

12. Schmidtchen FP, Isothermal titration calorimetry in supramolecular chemistry,

Analytical Methods in Supramolecular Chemistry. 55-78.

92

13. Jencks WP. Catalysis in Chemistry and Enzymology, McGraw-Hill, New York,

1969.

14. Cserhati T, Forgacs E. Cyclodextrins in chromatography, Cambridge: The Royal

Society of Chemistry, 2003; 1-10.

15. Harrison JC, Eftnik MR. Cyclodextrin-adamantanecarboxylate inclusion

complexes: a model system for the hydrophobic. Biopolymers 1982; 21 (6), 1153-

1166.

16. Lipkowitz KB Applications of Computational Chemistry to the Study of

Cyclodextrins. Chemical Reviews. 1998, 98, 1829-74.

17. Stewart JJP Optimization of parameters for semiempirical methods V:

modification of NDDO approximations and application to 70 elements. Journal

of Molecular Modeling. 2007, 13, 1173-213.

18. Stewart JJP MOPAC2012. Stewart Computational Chemistry, Colorado Springs,

CO, USA, 2014.

19. Maia JDC, Urquiza Carvalho GA, Mangueira CP, Santana SR, Cabral LAF,

Rocha GB. GPU linear algebra libraries and GPGPU programming for

accelerating MOPAC semiempirical quantum chemistry calculations. Journal of

Chemical Theory and Computation. 2012, 8, 3072-81.

20. Multiple Minima Hypersurface methodology.

21. Montero LA, Esteva AM, Molina J, Zapardiel A, Hernández L, Márquez H, et al.

A theoretical approach to analytical properties of 2,4-diamino-5-phenylthiazole

in water solution. Tautomerism and dependence on pH. Journal of American

Chemical Society. 1998, 120, 12023-33.

22. Montero LA, Llano J, Molina J, Fabian J. Multiple minima hypersurfaces of water

clusters for calculations of association energy. International Journal of Quantum

Chemistry. 2000, 79, 8-16.

23. Řezač J, Hobza P. A halogen-bonding correction for the semiempirical PM6

method. Chemical Physics Letters. 2011, 506, 286-9.

93

CHAPTER - 5

SYNTHESIS OF CYCLODEXTRIN GRAFTED/ FUNCTIONALIZED

ACTIVATED CARBON

5.1 Introduction

To have direct complexation between γCD and CLD in heavy water flow or on the surface of

water purifying filters (bulk, AC), γCD must be attached to the surface of AC. Therefore, the

aim of this chapter is to make a filter (AC) with attached γCD. AC is a complex and robust

material to work with. Therefore, first chemical modification of γCD was initiated. Afterwards,

modified γCD would be functionalized on the surface of AC.

In recent years the group of Prof. Grützmacher has endeavored to develop and improve the

synthetic procedure for bis(acyl)phosphane oxides and specifically bis(mesitoyl) phosphane

oxides (BAPOs).1, 2 BAPOs are well established and well known for their photoionization

properties. They are widely used in industry for radical polymerizations, coatings, adhesives,

inks, photoresistors as well as dental applications. The reasons for such widespread applications

of BAPOs are that they are able to generate (four) radicals after irradiating with visible light,

which leads to a high initiation efficiency. It was observed that the cleavage of the mesitoyl

groups can be performed stepwise using blue LED light in step (I, below) and while LED light

in step (III, below).2

Therefore, we focused on the modification of γCD with bis(mesitoyl) phosphane oxide groups

(BAPO-γCD) for the same approach.

94

5.2 Synthesis of bis(mesitoyl) phosphane oxide gamma cyclodextrin (BAPO-

γCD)

BAPO-γCD was obtained in a three step reaction as shown in Scheme 5.1. First acrylated-γCD

was synthesized according to a method reported by Gil et al. In brief, one equivalent (eq.) of

dried γCD was charged in a 100 mL round bottom flask containing dried NMP. Ten eq. of

acryloyl chloride were added dropwise into the flask under argon (Ar) protection and the

reaction was continued according to a reported procedure. The obtained reaction mixture was

slowly dropped into 250 mL of deionized (DI) water to precipitate the product (acrylated-

γCD).The product was obtained after drying in a desiccator over phosphorus pentoxide.3

Acrylated-γCD was stored in the dark.

A 25 mL Schlenk flask was charged with HP(COMes)2 (0.033 g, 0.11mmol, 1.1 eq.), which

was dissolved in THF (3ml). Triethylamine (one drop, 40 μL) was added to the solution.

Acrlylated-γ-CD3 (0.184 g, 0.1mmol, 1 eq.) was added slowly under an argon blanket. After a

reaction time of 12-15 h at r.t., the solvent was removed under reduced pressure, the solid

residue dissolved in toluene (3 mL) in order to remove NEt3.HCl by filtration in a glove box.

Yellowish solid was recovered, ultimately. The solid was further dried under reduced pressure.

To obtain the oxidized form of a solid (BAP-γ-CD), it was again dissolved in THF (3 mL) and

oxidized with oxygen (O2, dried over phosphorus pentaoxide) overnight. The final product

(BAPO-γ-CD) was received after removing the solvent under reduced pressure and

recrystallizing from THF at 0°C (0.196 g, 91.6% M = 2179.98 g/mol).

95

Scheme 5.1: Synthetic scheme (steps) of acrylated-γCD and BAPO-γCD.

31P NMR (101.28 MHz, THF, 298 K) δ [ppm] = 25.88; 13C{1H} NMR (100 MHz, DMSO-d6,

298 K) δ [ppm] = 20.74 (d, 1Jpc = 67, -CH2P peaks were 21.08/20.41), 25.48 (d, 2Jpc = 29, -

CH2COO- peaks were 25.63/25.34), 135.54 (d, 2Jpc = 46, -C-Mes peaks were 135.77/135.31),

171.32 (d, 3Jpc = 8, -COOR peaks were 171.36/171.28), 216.13 (d, 1Jpc = 51, -COMes peaks

were 216.38/215.87), 8.59 (s, POCH2CH2R), 18.60 (s, o-CH3 Mes), 20.70 (s, p-CH3 Mes),

129.11 (s, C3,5 Mes), 135.29 (s, C2,6 Mes), 141.24 (s, C4 Mes). Rest peaks are attributed to

acrylated-γCD; IR v [cm-1] = 3350, 2924, 1722, 1634, 1409, 1297, 1269, 1185, 1153, 1020,

807, 756, and 659; UV/Vis in DMSO λ [nm] = 289, 360, 388. B.P. = 268±5 °C (decomposed).

96

5.3 Characterization of BAPO- γCD

5.3.1 NMR Spectroscopy

Acrylated-γCD has a very complicated 13C NMR spectrum. However, all phosphorus and

carbon peaks assigned to BAPO were still apparent in the 13C NMR and 31P NMR spectra of

BAPO-γCD. The 31P NMR chemical shift for BAPO-γCD is at δ = 25.88 ppm and a

characteristic 13C NMR chemical shift for mesitoyl carbonyl carbon (PCOMes) observed at δ

= 216-217 ppm. As all doublet chemical shifts are in accordance with those of carbon-

substituted BAPOs reported before.2 Selected chemical shifts assigned for BAPO-γCD moieties

and their coupling constant are given at the end of this chapter.

5.3.2 Elemental Analysis

The elemental composition of BAPO-γCD was determined byelemental analysis. Results

obtained after the analysis and the theoretical values are given in table 5.1.

Table 5.1: Elemental composition of BAPO- γCD.

BAPO-γCD Element (%)

Carbon Hydrogen Oxygen Phosphorus

Theoretical Value 53.99 05.69 38.90 01.42

Experimental Value

53.50±0.01 06.11±0.02 37.08±0.16 01.30±0.007

97

5.3.3 The UV/Vis spectra of BAPO-γCD

UV/Vis spectra of BAPO-γCD is depicted in Figure 5.1. The spectrum shows two local

absorbance maxima. The first maximum is at = 289 nm and the second maximum is observed

at 360 nm with an onset at ~430 nm (inset of Figure 5.1). The first intense absorbance peak at

289 nm arises from the electronic transition of (C=O) and second absorbance comes from

n* (C=O) of mesitoyl (BAPO) and acrylates of (BAPO acrylated-γCD). The excitation

coefficient at = 289 nm is = 6870 M-1.cm-1 and = 550 M-1.cm-1 at = 360, 388 nm. These

values are comparable to those of classical BAPOs.

Figure 5.1: UV-vis spectra of BAPO-γCD and inset of magnified range = 320 – 500 nm in

DMSO (c = 5*10-4 M)

98

5.3.4 Infra-red (IR) Spectra

Figure 5.2 shows typical FT-IR spectra of γCD, acrylated-γCD and BAPO-γCD. The IR spectra

of acrylated-γCD and BAPOs-γCD is strong and different from γCD. In the spectrum of BAPO-

γCD and acrylated-γCD, the peaks at 1153 cm-1 (νC−O−C in the glycosidic bridges) and 1020 cm-

1 (overlapped between νC−C and νC−O) of γCD are still observed. The rest IR peaks which relates

to γCD, are merged in the spectrum of acrylated-γCD and BAPO-γCD. The peaks present in

acrylated-γCD and BAPO-γCD at 1634 cm-1 (νC=C), 1409 cm-1 (νH−C=CH2), and 807 cm-1 (νC−H)

are attributed to the vinyl groups of acrylates. The peak at 1722 cm-1 corresponds to the

stretching vibration of the carbonyl (νC=O) groups present in the esters. On the other hand, the

peaks at 1185 cm-1 and 1297 cm-1 were due to the stretching vibration of C-O groups in the

ester with unsaturated α−β carbons. It confirms that all major IR frequencies associated with

acrylated-γCD remained unchanged in BAPO-γCD.

Figure 5.2: IR spectra of γCD, acrylated-γCD and BAPO- γCD.

However, after the addition of BAPO, the new absorption at ν = 1640-1680 cm-1, 1050-1195

cm-1, 1615-1660 cm-1 and 1580-1610 cm-1,which are assigned to the stretching vibration of the

C=O, P=O, C=C and C-C, could not visible in the IR spectrum of BAPO-γCD. This could be

due to the intense IR spectrum of unreacted acrylates units still present in BAPO-γCD.

99

5.3.5 Thermogravimetric analysis (TGA)

Thermogravimetric analysis was performed to evaluate the effect of phosphorus present in

BAPO-γCD on char formation. Phosphorus is known for its excellent flame retardant

properties, which delay the burning process of a particular substance and produces a higher

yield of char. Thermograms obtained after TGA measurements of γCD, acrylated-γCD and

BAPO-γCD are shown in Figure 5.3. Up to 200 °C, weight loss due to the evaporation of

moisture present in γCD and acrylated-γCD was 3.0 and 1.5 wt%, respectively. Unmodified

γCD started to melt and subsequently decomposed at 279 °C. A major weight loss of acrylated-

γCD started at ~ 233 °C (of acrylates) and a second weight loss of core (γCD) occured at 282

°C. Above 300 °C, both (γCD and acrylated-γCD) decompose. Residual 23.7 and 26.2 wt%

char we obtained at 700 °C.

Figure 5.3: Thermogravimetric thermograms of γCD, acrylated-γCD and BAPO- γCD.

On the other hand, weight loss as a function of temperature for BAPO-γCD was different. About

7 % weight was lost between 90 to 200 °C due to the vaporization of water and solvent

molecules trapped in the cyclodextrin cavity. Subsequently, BAPO-γCD is gradually degraded

up to 300 °C and 32.8 wt% of char is obtained after decomposition up to 700 °C. It is important

to note here that char formed after the decomposition of BAPO-γCD is 6.6 % higher than

acrylated-γCD. This confirms that BAPO is playing a role as a char-forming agent in BAPO-

γCD.

100

5.3 Attempts to Functionalize BAPO-γCD on the surface of Activated Carbon

Once BAPO-γCD was synthesized successfully, the next challenge was to make a successful

bonding between BAPO-γCD and AC. As mentioned in chapter 2, ACs are random

arrangements of graphite sheets. Graphite sheets are the stacked form of graphene sheets, which

are held together via van-der Waal forces. Graphene is an allotrope of carbon in the structure

of a plane of sp2 bonded carbon (-C=C) atoms. Therefore, there is a possibility to make a bond

between radicalized C=C of AC and phosphorus radicals of BAPO-γCD after irradiating them

under UV or blue LED lights. As mentioned above under irradiation, BAPOs are able to

generate phosphorus and acyl radicals, as shown in scheme 5.2.

Scheme 5.2: All possible reaction steps and products, which can form after a reaction between

BAPOs and AC under irradiation with UV or Blue L.E.D. light.

All possible reaction steps (in-situ) and expected products, which should form after a reaction

between radicalized BAPO-γCD and AC (-AC=AC-), are shown in scheme 5.2. However, after

several efforts and controlling numerous parameters, we observed that it is impossible to obtain

products (Scheme 5.2) under irradiation with various light sources, likely because UV light is

absorbed completely by AC.

101

5.4 Synthesis of γ-CD-N3 Functionalized Activated Carbon (AC)

First, Mono-6-(p-toluenesulfonyl)-6-deoxy-cyclodextrin (Ts-γ-CD and mono-6-azide-deoxy-

6-cyclodextrin (γ-CD-N3) were prepared according to a literature procedure and as shown in

Scheme 5.3.1, 2

Scheme 5.3: Synthesis of Mono-6-(p-toluenesulfonyl)-6-deoxy-cyclodextrin (Ts-γ-CD and

mono-6-azide-deoxy-6-cyclodextrin (γ-CD-N3)4,5

In order to improve the adsorption efficiency of activated carbon, γ-CD functionalized AC (AC-

γ-CD) was synthesized by reacting the azide (γ-CD-N3), with AC in the presence of NMP (N-

methyl-2-pyrrolidone) as shown in Scheme 5.4. In brief, AC (200 mg) was dispersed in 100

mL of anhydrous N-methyl-2-pyrrolidone (NMP) and kept in an ice sonicator bath for 2 h.

Subsequently, γ-CD-N3 (25 mg) was transferred to the AC suspension and the reaction mixture

was stirred under argon for 75 h at 170 °C. Once the reaction was complete, the solution mixture

was cooled to room temperature and poured into 200 mL diethyl ether to form a black

precipitate. The precipitate was filtered and washed several times with water. Afterwards, the

solid was dispersed in 50 mL of distilled water and subjected to dialysis (MWCO = 12-14 00

& Diameter = 16mm, of Spectra/Por Dialysis) for at least 3 days. Subsequently, the solid was

centrifuged and lyophilized to obtain γ-CD functionalized AC (AC-γ-CD). In a control

experiment, activated carbon (mAC) was treated using the same conditions but in the absence

of γ-CD-N3.

Scheme 5.4: Synthesis of γ-cyclodextrin functionalized activated carbon (AC-γ-CD).

102

5.5 Characterization of γ-cyclodextrin functionalized activated carbon (AC-γ-

CD)

5.5.1 Textural Properties

The surface area, pore volume and average pore diameters were measured for the three samples

and the results are listed in Table 5.2. Interestingly, while the surface area and the pore volume

of the samples, mAC and AC-γ-CD, were found to be significantly less than pure AC, the

average pore diameter increased. This could be due to the diffusion of solvent molecules into

the pores and channels leading to chemical and/or mechanical erosion of the surfaces.

Table 5.2: Structural properties of AC, mAC and AC-γ-CD.

Functionalization with sterically hindered γ-CD molecules on the surface of AC could be

another reason for the lower surface area and smaller pore volume of AC-γ-CD. However, the

modification of the structural properties of the pores suggests that grafting of γ-CD onto AC

occurred.

Sample Surface Area

(m2g-1)

Pore Volm

(cm3g-1)

Ave. Pore Diameter

(nm)

AC 637 0.69 4.33

mAC 445 0.62 5.56

AC-γ-CD 321 0.43 5.40

103

5.5.2 Thermogravimetric Analysis

Figure 5.4 portrays the obtained TGA curves of AC, mAC and AC-γ-CD. The TGA

thermogram of AC proves that it is very thermostable and loses only 5 wt% up to 700 °C.

Whereas, mAC and AC-γ-CD loose 7.7 and 10.8 weight % (higher than AC) which shows that

they are also thermostable up to high temperatures (700 °C) but less so than AC. It is worth

mentioning here that mAC could have retained some diffused solvent molecules in its vicinity,

however, AC-γ-CD has grafted γ-CD on the surface and hence shows a higher weight loss. It is

of interest to point out that weight loss difference between mAC and AC-γ-CD is about 3%. It

could be a sign that 3 % cyclodextrin would have grafted on the surface of AC.

Figure 5.4: Thermogravimetric thermograms of AC, mAC and AC-γCD.

104

5.5.3 X-ray Photoelectron Microscopy Analysis

The XPS wide scan spectra of AC, mAC and AC-γCD is depicted in Figure 5.5. The appearance

of the N1s signal (3.05 %) in the AC-γ-CD indicates that the nitrene radicals generated during

the solvothermal reduction have successfully reacted with the unsaturated double bond of

activated carbon.6 In comparison, no N1s signal in the XPS spectra of AC and mAC was

detectable, meaning that the NMP solvent was completely removed from the surface of AC

after the work-up. This result strongly indicates the grafting of γ-CD on the surface of AC via

an aziridine linker. The amount of γ-CD molecules grafted on the surface of AC was calculated

from the XPS peak-area and was estimated to be in the range of 2.01 - 3.05 wt%.

Figure 5.5: Wide scan XPS spectra of mAC and AC-γ-CD.

Furthermore, the quantitative analysis and the atomic concentration of nitrogen was calculated

from equation 1.

𝑿𝒊𝒋 =(𝐈𝒊𝒋/𝐒𝒊𝒋)

∑(𝐈𝒊𝒋/𝑺𝒊𝒋) 1

where, Iij is the intensity of the peak i of the element j and Sij is the sensitivity factor.

If we assume that γ-CD is grafted uniformly on the surface of AC, then the first-principles

method is defined for the calculation of sensitivity factor (for homogenous samples) of such

materials, as shown in eq. 2. 7

105

𝑺𝑨 = 𝝈𝑨(𝒉𝒗). 𝜦𝑴𝑨. 𝑳𝑨(𝜸). 𝑻(𝑬𝑨) 2

Where, σ is the Scofield photoionization cross-section,8 LA describes the anisotropy of the

photoemission, calculated according to,9 and T is the transmission function. The transmission

function of an analyzer can be calculated as follows:

𝑻(𝑲𝑬) = (𝒂𝟐

𝒂𝟐+𝑹𝑹𝟐)𝒃

3

RR is the retard ratio, i.e. the ratio between the kinetic energy, KE, and the chosen pass energy,

PE (KE/PE), while a and b are derived by fitting the log/log plot of the normalized intensity

divided by the pass energy versus the retard ratio. The peaks considered were Cu2p3/2, Cu3p

and CuLMM collected at different pass energy values. For Sigma II, the calculated a and b

values are 16.73 and 0.52.

The inelastic mean free path, Λ, was calculated using the TPP-2M formula as a function of the

material characteristics.10 After placing all values in equation 1, the quantitative nitrogen

amount present in AC-γ-CD was found 2.34 wt%.

Taking the surface area into account, this amount of γ-CD molecules should enhance the CLD

adsorption efficiency of AC-γ-CD in comparison to untreated AC by about 10 - 15%.

106

5.6 Adsorption kinetics of Chlordecone

Figure 5.6 illustrates the results obtained in water when the adsorption of CLD (2.2 mg.L-1) on

AC or AC-γCD was followed with time at room temperature. In the first hour (inset of Fig. 6.3),

the adsorption of CLD is very efficient as indicated by the steep decrease in the concentration

of free CLD remaining in solution. The adsorption on AC-γ-CD was faster than that of AC

alone. This is possibly due to the fact that cyclodextrin may be bound to the external surface

(or to large pores) of the AC, leading the diffusion limiting step of the CLD molecules inside

the material to their final adsorption sites to be faster in γ-CD bound AC than in micropores.

Figure 5.6: Adsorption kinetics of CLD for mAC and AC-γ-CD.

The adsorption kinetics of CLD for both adsorbents follow similar trends until 36 hrs. The final

adsorption of CLD is 15% higher for AC-γ-CD when compared to AC. This result is consistent

with the estimated value discussed above and demonstrates how γ-cyclodextrin moieties can be

successfully used in order to enhance the adsorption efficiency of AC for CLD on a larger scale.

107

5.7 Conclusion

A new BAPO-γCD molecule has been synthesized by reacting acrylated-γCD with bis(2,4,6-

trimethlybenzoyl) hydrogen phosphane (BAP-H) in presence of catalytic amount of

trimethylamine. It was further reacted by oxidation with oxygen (dried). 31P and 13C NMR have

confirmed the typical phosphorus and carbonyl peak of BAPOs, respectively. The UV/Vis

absorption spectra are also comparable. IR frequencies of BAPO-γCD have confirmed that

acrylated part has overlapped the IR frequencies assigned to BAPOs. Moreover, TGA has

confirmed that the presence of phosphorus enhance the overall char yield of BAPO-γCD

comparable γCD. Consequently, characterization techniques have confirmed that BAPO-γCD

was synthesized successfully. However, a reaction between AC and BAPO-γCD did not occur

after irradiating with light of different wavelengths (UV/Blue L.E.D), because AC has the

ability to utterly absorb thelight.

This chapter has further focused on the modification of AC by means of γ-CD-N3 grafting on

its surface. Subsequently, a new hybrid material (AC-γ-CD) was generated. Characterization

techniques like BET, TGA and XPS have confirmed that nearly 3% γ-CD was grafted onto AC.

It is observed that AC-γ -CD is a better adsorbent for CLD than AC alone. This improvement

is apparently related to the amount of grafted γ-CD.

108

5.8 References

1. Huber A, Kuschel A, Ott T, Santiso-Quinones G, Stein D, Bräuer J, Kissner R,

Krumeich F, Schönberg H, Levalois-Grützmacher J, Grützmacher H. Synthesis of new

bis(acyl)phosphane oxide photoinitiators for the surface functionalization of cellulose

nanocrystals.. Angew. Chem. 2012; 124: 4726 –4730.

2. Müller GS. Phosphorus Based Photoinitiators: Synthesis and Application, Dissertation

No. 21309 ETH Zürich, Zürich, 2013.

3. Gil ES, Wu L, Xu L, Lowe TL. β-Cyclodextrin-poly (β-amino ester) nanoparticles for

sustained drug delivery across the blood–brain barrier. Biomacromolecules 2012; 13:

3533−3541.

4. Tang W, Ng S-C. Facile synthesis of mono-6-amino-6-deoxy-α-, β-, γ-

cyclodextrin hydrochlorides for molecular recognition, chiral separation and drug

delivery. Nature Protocols 2008; 3(4), 691-697.

5. Xu LQ, Yee YK, Neoh K-G, Kang E-T, Fu GD. Cyclodextrin-functionalized

graphene nanosheets, and their host-guest polymer nanohybrids. Polymer 2013;

54, 2264-2271.

6. Strom TA, Dillon E P, Hamilton CE, Barron AR. Nitrene addition to exfoliated

graphene: a one-step route to highly functionalized graphene. Chem. Comm.

2010; 46(23), 4097-4099.

7. Seah M. P. Quantification of AES and XPS, in Practical Surface Analysis, John

Wiley & Sons, 1990.

8. Scofield JH. J. Electron. Spectrosc. Hartree-Slater subshell photoionization cross-

sections at 1254 and 1487 eV. 1976; 8, 129-137.

9. Reilman RF, Msezane A, Manson ST. J. Electron. Spectrosc. Relative intensities in

photoelectron spectroscopy of atoms and molecules. 1976; 8, 389-394.

10. Tanuma S, Powell CJ, Penn DR. Surf. Interface Anal. Calculations of electron inelastic

mean free paths .5. data for 14 organic-compounds over the 50-2000-EV range. 1994;

21, 165-176.

109

CHAPTER - 6

WASTE BIOMASS-BASED SUSTAINABLE ACTIVATED CARBONS:

EXCELLENT CHLORDECONE ADSORPTION PROPERTIES FROM WATER

6.1 Introduction

Authenticity of activated carbon filters depend mainly on the starting materials and the

activation process used. There are two main sources for the production of activated carbon.

First, coal, coke, petroleum residues, wood,1 peat and lignite are being used to produce

commercially available activated carbons (ACs). Such sources are relatively expensive and

non-renewable.2,3 Therefore, in recent years, bio-waste (biomass) which relies on the

agricultural wastes and lignocelluloses materials resources were shown to be competitive. They

are sustainable, inexpensive and abundant across the world. Such lignocelluloses materials

could be hazel nutshell and bagasse, 4, 5 coconut shell,6, 7 kenaf fiber,8 bamboo,9 rice husk,10

ground nutshell,11 paper mill sludge,12 coconut husk,13 sugar cane bagasse14 jack fruit peel,15

and many others.16

The yield of activated carbon is mainly dependent on the carbon content present in the

precursor. Lignocellulosic precursors have relatively lower carbon content, which eventually

led lower yield of AC. However, its lower cost gives significant impact over the lower yield. 16

To extract AC out of bio-waste, there are two established processes, physical and chemical. The

physical process involves two steps ‘carbonization and dry oxidation (activation)’. Activation

takes place between the carbonized (pyrolyzed) samples and an activating gas (steam, CO2,air

or mixture), at very high temperature (above 700 °C). The chemical process consists in one-

step of carbonization where the precursor is mixed with an activating agent (ZnCl2, H3PO4,

NaOH, KOH etc.) prior to carbonization.

This project has focused only on the chemical activation of three bio-waste to obtain activated

carbons for the adsorption of CLD from water. Coconut husk/shell, banana peel and sugar cane

bagasse are the most common bio-waste available on French West Indies. Therefore, such bio-

waste was chosen as primary precursor to synthesize cost-effective ACs for filters that may be

used for CLD adsorption. There are several parameters (mixing ratio with activating agent,

temperature range, time, workup etc.) which can play an explicit role in the activation process.

To avoid intricacy, only one condition was followed across the AC synthesis for each bio-waste.

KOH was used as an activating agent. All precursors were first hydrothermally processed which

has made biomass friable, odorless, and shows higher bulk density and lower equilibrium

moisture.17

110

It is well known that carbon atoms are etched and gases are evolved during the activation and

therefore defects, such as vacancies and pores, are introduced on the AC. Such defects are solely

responsible for excellent textural properties and the latter are accountable for the adsorption

applications.18,16

6.2 Synthesis of Activated Carbon (Adsorbents) from Waste Biomass

First, banana peel (collected in Zurich) and sugar cane bagasse (collected in Guadeloupe) were

dried on air. Subsequently, the dried waste biomass were crumpled into small pieces. Coconut

husk (collected in Guadeloupe) was simply cut into small pieces. The activated carbons are

synthesized in a two-step process. First, a hydrothermal treatment is performed followed by a

high temperature pyrolysis (the second). For this, crushed bio-waste along with 100 mL of 1 M

H2SO4 are transferred to a teflon-lined steel autoclave and kept at 180 °C for 6 h (Scheme 6.1).

After allowing the system to cool down slowly to room temperature, the hydrothermal product

is washed with deionized water and dried overnight at 100 °C. Subsequently, the dried products

(~ 400 mg) are uniformly dispersed in 10 M aqueous KOH (4 mL) under ultra-sonication (35

kHz, sonorex super RK 100/H), and dried again at 100 °C.

Scheme 6.1: Synthesis procedure to obtain the waste@ACs from waste biomass (for example

banana peel ).

111

The dried gray mixture is kept in a boat-type sample holder inside a long quartz tube and

carbonized in a horizontal tube furnace (Heraeus, Figure 6.1) at 800 °C for 4 h at 100 °C/h

heating rate under a continuous argon flow. Mixtures are held under argon for 2 h at 200 °C

before carbonization at 800 °C.

Once the pyrolysis process is over, the furnace is allowed to cool slowly to room temperature.

Figure 6.1: Horizontal tube furnace (a), long quartz tube (b) and a boat-type sample holder (c).

The activated carbon product is obtained after pouring 2 M HCl over the pyrolyzed solid and

removing the inorganic impurities. The obtained black fluffy solid is washed thoroughly with

deionized water and the final product is dried under vacuum at 110 °C. Activated carbons

obtained from banana peel, sugarcane bagasse and coconut husk wastes are denoted bpe@AC,

bag@AC and coh@AC, respectively. Note that, waste@ACs will be used to name them

without distinction. Adsorption properties of waste@ACs will be compared to the

commercially activated carbon used in Guadeloupe for the purification of water in plant filters,

which is called cm@AC, herein.

While, the synthesis conditions used herein to obtain ACs, particularly from these specific bio-

waste, is not reported, a similar procedure was used to synthesize AC from waste papers.19

112

6.3 Characterization of New Activated Carbons (waste@ACs)

Adsorption properties of all AC have direct consequences on the activation process and the

starting material used. Therefore, all activation parameters are kept identical for all bio-wastes

used in this work to obtain AC. Overall yields of activated carbon from banana peel (bpe@AC),

sugarcane bagasse (bag@AC) and coconut husk (coh@AC) bio-waste is 21.64%, 12.77% and

23.68 %, respectively. It is obvious that with increasing the lignocellulosic part in the waste

biomass (Table 6.1), the yields of obtained waste@ACs is decreased.

Table 6.1: Lignocellulosic molecular composition present in the waste biomass used in this

work

# AC synthesized in the present work.

During the carbonization process, a typical gasification reaction between the reduced KOH,

metallic K and carbon, takes place. Reactions that occur between potassium and carbon are the

following:21,22

6𝐾𝑂𝐻 + 2𝐶 → 2𝐾 + 3𝐻2 + 2𝐾2𝐶𝑂3 . (1)

𝐾2𝐶𝑂3 → 𝐾2𝑂 + 2𝐶𝑂2 (2)

2𝐾 + 𝐶𝑂2 → 𝐾2𝑂 + 𝐶𝑂 (3)

Waste Biomass Lignin Cellulose Hemicellulose AC (Yield %)#

Coconut Husk16 3.54 0.52 23.70 23.68

Banana Peel20 19.06 8.30 21.23 21.64

Sugarcane Bagasse14 19.30 42.16 36.0 12.77

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6.3.1 Scanning Electron Microscopy (SEM) analysis

Figure 6.2 exemplifies the morphology and the porous structure of cm@AC and waste@ACs

after SEM analysis. A big difference could be observed in the morphology of cm@AC and

waste@ACs. It can be seen that surface texture of cm@AC particles (Fig. 6.2a) is irregular and

dense. Conversely, bpe@AC (Fig. 6.2b) seems to have small and regular particles, which are

three dimensionally interconnected and have a uniform distribution of macropores.

Figure 6.2: Scanning electron microscopy (SEM) images of cm@AC (a), bpe@AC (b),

bag@AC (c), and coh@AC (d).

The SEM image of bag@AC (Fig. 6.2c) and coh@AC (Fig. 6.2d) reveals that they are similar

showing flake-like uniformly distributed particles. In all images (b – d), it can be seen that

biomass derived ACs contain homogeneously distributed, thin (laterally) and relatively large

particles. Furthermore, they possess conchoidal like cavities that could ensure the fast access

of adsorbate into the inner pore structure of adsorbent.23

114

6.3.2 Transmission Electron Microscopy (TEM) analysis

Figure 6.3 depicts the nanostructure image of cm@AC (Fig. 6.3a), bpe@AC (Fig. 6.3b),

bag@AC (Fig. 6.3c) and coh@AC (Fig. 6.3d) acquired after TEM investigation. All images

show arrays of randomly distributed graphene sheets which are arranged in such a way that

micropores (<2nm) are well developed in the nanostructure of ACs after the activation. Lattice

spacing across the range of all nanostructured ACs are definitely disordered and indicates the

amorphous nature of all ACs.

(a) (b)

(c) (d)

Figure 6.3: Transmission electron microscopy image of cm@AC (a), bpe@AC (b), bag@AC

(c), and coh@AC (d).

115

6.3.3 Textural Properties Analysis

Gasification during the activation process serves to develop the surface area and the porosity in

waste@ACs. SEM and TEM analyses also confirm that waste@ACs are composed of porous

micro and macroscopic particles. Therefore, to know the textural properties of waste@ACs,

argon adsorption/desorption isotherms are recorded at -196 °C and respective micropore size

distributions derived after nonlocal density functional theory (NLDFT) are illustrated in Figure

6.4a and Figure 6.4b, respectively. bpe@AC exhibits a type I isotherm whereas bag@AC and

coh@AC show a type II isotherm (according to IUPAC classification). The type I isotherm is

the Langmuir isotherm. It is commonly observed in the microporous materials where the sharp

increase of adsorbing volume occurs at a very low relative pressure (< 0.1 P/P0). On the other

hand, type II isotherms correspond to those materials in which mesopores are present and

multilayer adsorption might occur in the middle relative pressure range owing to hysteresis (0.1

< P/P0 > 0.6). Therefore, micropores (pores diameter < 2nm) in bpe@AC appear to be present

in higher amount and occupy a greater volume than in bag@AC and coh@AC (table 6.2). In

notable contrast, bag@AC and coh@AC show a higher amount of mesopores (2nm <pore

diameter< 50nm) than of micropores (Fig. 6.4b).

Figure 6.4: Argon Adsorption/desorption isotherm curves (a) and micropore size distribution

(b) of bpe@AC, bag@AC, and coh@AC.

The calculated specific surface area, total and micropore pore volume, and the average

micropore size distribution are listed in Table 6.2.

116

Table 6.2: Textural properties of all samples used in this work

Sample SBET /

m2 g-1

Vpore /

cm3 g-1

Vmicro /

cm3 g-1

Ave. pore sizemicro

(Å)

cm@AC 905 0.43 0.29 9.7

bpe@AC 816 0.40 0.27 8.9

bag@AC 1121 0.52 0.06 19.4

coh@AC 776 0.38 0.02 20.2

It has been described that the surface area and pore volume increase linearly with the burn-off

of the starting material that leads to the dehydration and elimination reactions with the release

of volatile products.25 Burn-off of the starting materials depends predominantly on the degree

of lignocellulosic molecular units present in the respective bio-wastes. It largely accounts for

the textural properties. In adsorption processes the specific surface areas and the micropore

volumes of AC play a specific role. The specific surface area (SBET) of all ACs decreased in the

order of bag@AC > cm@AC > bpe@AC > coh@AC. The micropore volume (Vmicro) of all

ACs decreased in the order of cm@AC > bpe@AC > bag@AC > coh@AC.

117

6.3.4 Raman Spectroscopy and X-ray Diffraction Analysis

The specific structural composition can be further elucidated by the Raman spectroscopy. In

Figure 6.5(a), the prominent peaks present within 1319 - 1327 cm-1 are due to the breathing

mode of k-point phonons with A1g symmetry, corresponding to the D-bands (C-C, disordered

graphitic structures). The peaks at around 1588 - 1599 cm-1 are assigned to the E2g phonon of

sp2 carbon atoms, which are a distinctive feature of the G-bands (graphitic layers). Raman

spectra of cm@AC show slightly lower ID/IG (1.24) than waste@ACs (1.26). This suggests that

waste@ACs have slightly higher amount of defect sites and edges (~2%) than cm@AC.

Figure 6.5: Raman spectra (a) and XRD diffractograms (b) of cm@AC, bpe@AC, bag@AC,

and coh@AC.

Figure 6.5(b) shows the powder X-ray diffractograms of cm@AC and waste@ACs porous

carbon materials. All samples show two broad diffraction peaks. The diffraction peak at 2θ =

24° is attributed to the (002) reflection of the graphitic-type lattice. Owing to the limited degree

of graphitization, another diffraction pattern at 2θ = 43° corresponds to a superposition of the

(100) and (101) reflections of the graphitic-type lattice.24 Due to the random graphitic carbon

arrangements, diffraction pattern of waste@ACs confirms the characteristics of an amorphous

structure. On the contrary, the diffraction pattern of cm@AC indicates that it is a semicrystalline

amorphous solid.

118

6.3.5 Elemental and Boehm Titration Analysis

Table 6.3 includes the atomic mass composition obtained after elemental analyses of all samples

under investigation. The oxygen content in cm@ACs is higher but the hydrogen content is

lower than waste@ACs. This implies that the cm@AC may contain more oxygen-containing

(not oxygen/hydrogen) functional groups. In waste@ACs, bag@AC shows highest hydrogen

and oxygen content whereas, coh@AC exhibits highest carbon content. The differences in the

atomic composition of waste@ACs could be due to the difference in lignocellulosic

composition of the respective precursor. For example, sugarcane baggage contains highest

amount of lignocellulosic part (Table 6.1) therefore, the obtained AC from sugarcane baggage

(bag@AC) shows highest hydrogen and oxygen content..

Table 6.3: Elemental composition of all samples used in this work

A common method to optimize the quantitative amount of acid and basic functional groups

present on the surface of AC is the ‘Boehm titration’. Table 6. 3 includes the amount of acidic

and basic surface functional groups present on cm@AC and waste@ACs. It is evident that

waste@ACs possess a very high amount of acidic surface functional groups compared with

cm@AC. bag@AC has more acidic groups than bpe@AC and coh@AC. However, the number

of basic surface functional groups of waste@ACs is low and smaller than in cm@AC.

cm@AC possesses the highest oxygen content, which specifies that it is a highly oxidized AC

with a low amount of H-labile functional groups but, non-acidic groups like quinones, ethers

and anhydrides. This means that hydrogen is definitely playing a major role in the acidity of

waste@ACs. Other hydrogen containing functional groups, like carboxyl, aldehydes, phenols

and lactones have been attributed to impart the acidic behavior in AC (waste@ACs, refer to

TPD results).

Samples Carbon Hydrogen Oxygen Acidic Groups

(meq/g)

Basic Groups

(meq/g)

cm@AC 73.36±6.1 1.26±0.70 20.01±2.27 0.289 0.211

bpe@AC 69.24±1.95 3.15±0.27 14.41±2.11 3.186 0.037

bag@AC 68.58±0.57 3.79±0.04 14.86±2.08 3.654 0.102

coh@AC 81.80±0.45 3.04±0.05 10.00±2.51 3.201 0.115

119

6.3.6 Thermogravimetric Analysis

Figure 6.6 illustrates the TGA/DTA curves of all ACs used in this project. All samples were

dried at 100 °C for 24 h before measuring the TG analysis. In all samples, two-stage weight

loss is seen. The first weight loss is observed at the temperature range of 200 to 450 °C where

cm@AC loss only 12 wt% , bpe@AC loss 36 wt%, bag@AC loss 34 wt% and coh@AC loss

31 wt%. The decomposition of all samples is investigated by monitoring the m/z values 18, 28,

and 44. It is worth to mention here that m/z value 28 (CO) did not evolve during the TGA

measurements. The first weight loss in TGA curve of all samples corresponds to the liberation

of only H2O and CO2. In cm@AC, the liberation of H2O and CO2 between 200 and 450 °C is

almost negligible which directly relates to the weight loss (12 wt%). The m/z spectras of H2O

(18, in black) and CO2 (44, in red) of all samples are included in the bottom of each figure with

their respective TGA/DTA curves. It is evident from the figure that waste@ACs have lost

greater weight and evolved a higher amount of CO2 and H2O than that of cm@AC. This

confirms that waste@ACs have a very high amount of surface functional groups.

Figure 6.6: Thermogravimetric analysis (TGA/DTA) curves of cm@AC, bpe@AC, bag@AC,

and coh@AC with the MS (appear in the bottom of the each curves) of m/z = 18 (H2O) & 44

(CO2) of evolved gases

120

Water molecules can easily access the acidic surfaces in the form of water clusters around the

functional groups (mainly acidic). 26 Similarly, waste@ACs have high density of acidic surface

functional groups and ultimately loose a greater amount of weight (in form of water and CO2)

in TGA curves than cm@AC. The higher the functional groups on the surface of ACs the greater

would be the water clusters around them, as illustrated in Figure 6.7. The second weight loss

in TGA curve of all samples is observed after 600 °C. This is due to the pyrolysis of ACs and

during the pyrolysis, CO2 is the only evolved gas detected in MS.

Figure 6.7: Formation of water clusters around the functional groups present on the surface of

activated carbon.

121

6.3.7 Electron Paramagnetic Resonance (EPR)

Boehm titration and TG analysis indicate a high density of surface functional groups on

waste@ACs. In addition, EPR spectroscopy is employed in order to investigate the presence of

paramagnetic/radicals/unpaired electrons present on the carbonized (KOH + biomass) mixture

of waste@ACs. Presence of radicals can encourage and develop functional groups on the

surface of waste@ACs. Three stages of treatment of waste@ACs samples are selected for the

EPR analysis. At first, EPR is measured (Figure 6.8a) of samples, which are prepared in the

glovebox and taken right after the carbonization process. These samples are the carbonized

mixture of KOH and biomass carbon before exposing them to air. Interestingly, we could see

high amount of radicals on the surface of all mixtures, which produce a very sharp EPR signal

at g = 2.0034 for bpe@AC, g = 2.0029 for bag@AC and g = 2.0026 for coh@AC. Considering

the intensity of EPR signals, it is apparent from the figure that the presence of radicals on

bag@AC and bpe@AC are two times higher than that of coh@AC. After normalizing the EPR

signals of the mixtures, we have discovered only one type of radical sites, which are roaming

on the surface of carbonized (KOH + biomass) mixture of waste@ACs.

To know the stability of radicals in an open environment, EPR is carried out for all the

carbonized (KOH + biomass) mixtures after exposing them to air for 36 h. As shown in Figure

6.8b, the EPR signals of all samples became broader and less intense. But the radical sites have

a significant lifetime and are remarkably stable for a rather long time even in air. The presence

of sp2 carbons possibly drives the stability of the radicals on the surface of carbonized (KOH +

biomass) mixtures of waste@ACs in air.

Finally, we have obtained a diamagnetic waste@ACs, after activating the carbonized (KOH +

biomass) mixtures in 2M HCl. The radicals are vanished from the surface of waste@ACs as

shown in Figure 6.8c. This emphasizes that the radicals are ideally reactive once the carbonized

(KOH + biomass) mixtures of waste@ACs are immersed into the HCl solution in air. This

perhaps creates a large amount of surface functional groups on waste@ACs with high

complexity.

122

Figure 6.8: Electron paramagnetic resonance spectra of (a) dried carbonized (KOH + biomass)

mixtures, (b) mixtures exposed in air for 36 h and (c) after the activation and work-up of

waste@ACs.

123

6.3.8 X-ray Photoelectron Spectroscopy Analysis

XPS analysis is further carried out in order to get additional information about the surface

functional groups composition of all samples. Figure 6.9 represents the survey spectra with the

binding energies ranging from 0 to 1200 eV. ACs show two characteristic peaks at 284.9 eV

and 532.6 eV, which are attributed to C(1s) and O(1s) binding energy, respectively.

Figure 6.9: Survey scan XPS spectra of all samples used in this work

Furthermore, C(1s) narrow XPS spectra of all samples are deconvoluted and after the

deconvolution, three different binding energy peaks are popped up. Figure 6.10 depicts the

C(1s) XPS narrow scan spectra of cm@AC and waste@ACs. The first peak at 284.4 eV (± 0.1

eV) of all ACs is assigned to the combined sp2(C=C) and sp3 (C-C) carbons. The second, broad

peak at 285.2 eV (± 0.1 eV) is attributed to the broad variety of C-O/C=O surface functional

groups present on cm@AC, bpe@AC and coh@AC. However, the binding energy peak for C-

O/C=O groups in bag@AC is found at 285.8 eV.

124

Figure 6.10: C1s narrow XPS spectra of cm@AC and waste@ACs.

The assignment of a third peak above 287.0 eV is not straightforward. It is centered at 289.0

eV (± 0.1 eV) in bpe@AC and coh@AC and attributed to O-C=O of both (carboxylic and

anhydride type) surface functional groups and the π→π* shake-up. In bag@AC, the peak at

287.9 eV is mainly due to the carboxylic functional groups present on the surface and the π→π*

shake-up. This is in agreement with bag@AC having a higher concentration of acidic surface

functional groups (TGA/Boehm titration). While the peak at 289.4 eV in cm@AC indicates

mostly O-C=O anhydride type groups and the π→π* shake-up. These results further

compliment the above findings that cm@AC and waste@ACs have oxygenated surface

functional groups.

XPS is a typical surface chemical analysis technique. In order to analyses the surface functional

groups present in the bulk (cm@AC and waste@ACs), TPD analyses is performed.

125

6.3.9 Temperature Programmed Desorption (TPD) Analysis

We further investigated the acidic and basic properties (qualitatively) of waste@ACs and

cm@AC using Temperature Programmed Desorption (TPD). Figure 6.11 represents the TPD

profiles of desorbed CO2, CO and H2O. Oxygenated surface functional groups of AC will

produce CO and CO2 whereas entrapped water molecules and clusters will be released at

different temperatures. The desorption is monitored by mass spectroscopy. CO2-TPD of

waste@ACs shows desorption of CO2 between 200 °C and 600 °C with the maxima at 330

°C/450 °C (for bpe@AC and bag@AC), and 380 °C /440 °C (for coh@AC). CO2-desorption at

this temperature range could be assigned to the carboxylic acid groups that desorb at lower

temperature (330 °C and 380 °C) and lactones at higher temperatures (440-450 °C).27 This

indicates clearly that there is a significant amount of acidic groups present on the surface of

waste@ACs. Generally, CO desorption occurs at high temperature (600-1000 °C), but, CO-

TPD desorption profiles of waste@ACs shows a similar desorption behavior as CO2-TPD does.

This indicates that CO does not desorb at high temperature, which could be due to the absence

of functional groups like quinones, anhydrides and ethers, on the surface of waste@ACs. In

contrast, cm@AC shows a very small bump at 210 °C in the CO2-TPD profile and ensure that

lower amounts of carboxylic groups are present on its surface compared to waste@ACs.

However, the CO-TPD profile shows that cm@AC has a greater amount of CO desorbing

functional groups likely quinone or phenol, which desorb CO at very high temperature (840

°C).

Initial water desorption, which generally takes place at low temperature (< 200 °C), could be

attributed to the water entrapped between the micropores of AC and due to the hydrogen

bonding among the water molecules and the oxygenated surface functional groups (carboxylic

acids, phenols etc.). Such water desorption did not appear in the H2O-TPD profiles of all

samples used herein. Interestingly, H2O-TPD profile of waste@ACs portrays the water

desorption between 200 °C and 500 °C. As stated above, water molecules, which are

accumulated as clusters around the acidic surface functional groups on waste@ACs, desorb in

this temperature range.26 H2O-TPD profile of cm@AC expresses that no water molecules are

significantly desorbed across the temperature range. Therefore, the results obtained after the

TPD analysis suggests that waste@ACs have excessive acidic and less basic surface functional

groups. Whereas, surface of cm@AC is least acidic but higher basic than waste@ACs.

126

Figure 6.11: TPD desorption profiles of all cm@AC and waste@ACs

127

6.4 Chlordecone Adsorption Properties of waste@ACs

6.4.1 Adsorption Isotherm study and Modeling

Three adsorption isotherm models Langmuir, Fowler, and Freundlich are used to fit single-

component isotherms. All equations are shown in Table 1.5 of Chapter 1. The experimental

adsorption data of CLD on ACs are plotted in Figure 6.12. The average relative error of the

measured concentrations in the liquid phase is less than 5 % in all cases. The results obviously

show that the CLD adsorption capacity of waste@ACs is higher than that of cm@AC.

Figure 6.12: Comparison between experimental adsorption data of chlordecone on ACs

(symbols) and values calculated (lines) using the Langmuir model (for bag@AC and coh@AC)

and the Fowler model (for bpe@Ac and com@AC).

128

Table 6.4 summarizes the results of the nonlinear regression analysis of the evaluated models.

AICC and AARE values show that the agreement of the models with the experimental data is

good, with the average standard error of estimation in the range of 3.6-15.7 %. In two cases,

bag@AC and coh@AC, the best fit (lower AICC and AARE) is obtained for the Langmuir

model, when for bpe@AC and cm@AC the best fit is obtained for the Fowler model. Figure

6.12 shows the comparison between experimental adsorption data and values calculated using

the best equation for each isotherm. The monolayer capacity of all new waste biomass-based

adsorbents, calculated with the Langmuir model, is higher in all cases than for cm@AC and for

previously reported sugarcane bagasse ACs obtained after using phosphoric acid as an

activating agent.27 The maximum CLD adsorption capacity (qs) of all ACs decreased in the

order of bag@AC > bpe@AC > coh@AC > cm@AC. There are three major factors, which are

influencing the adoption properties of ACs: acidic surface functional groups, specific surface

area and micro pore volume. The higher adsorption of CLD by waste@ACs might be explained

by the amount of acidic groups, which is about ten times higher when compared with cm@AC

(Table 6.3). The role of acidic groups for chlordecone adsorption on ACs is previously

reported27 and recently confirmed by molecular modeling.28 The highest adsorption capacity

(334.96 μg/mgAC) of bag@AC is due to the greater SBET and the amount of acidic groups which

is the largest from all ACs studied here (Tables 6.2 and 6.3). bpe@AC has a greater Vmicro and

SBET than coh@AC. That is why bpe@AC adsorbs higher amounts of CLD than coh@AC.

However, if we consider the yield of waste@ACs then, the yield-to-CLD adsorption property

is the best for bp@AC among waste@ACs.

The positive in Fowler equation indicates that there is a modest adsorbate-adsorbate (CLD-

CLD) interaction during the adsorption process. Durimel et al have also reported the similar

findings for the adsorption of CLD on ACs.27 The surface heterogeneity parameter (), in

Freundlich model, is different for all the supports (waste@ACs and cm@AC) and not equal to

the unity. This confirms the fact that the ACs studied herein have the heterogeneous surface.

This fact is well known since the pore size distribution and the presence of the different surface

functional groups on waste@ACs, are not homogenous. The obtained values for waste@ACs

is in the range (0.25-0.86) of previously reported values for the adsorption of metals and organic

compounds on ACs obtained after the processing of sugarcane bagasse, banana peel, and

coconut husk. 29-38

129

Table 6.4: Comparison of model correlations for CLD. qs is the monolayer capacity. is the

adsorbate-adsorbate interaction parameter; is the heterogeneity parameter; K is the

equilibrium constant; R2 is the correlation coefficient; AICC the second-order corrected Akaike

information criterion and AARE the average of absolute relative errors.

Model and parameters bpe@AC bag@AC coh@AC cm@AC

Langmuir

qs, μg/mgAC 260.5 334.9 228.5 92.2

K, μg/ mgAC 0.012 0.003 0.021 0.016

R2 0.994 0.999 0.996 0.977

AICC 38.1 17.5 30.4 33.8

AARE, % 7.1 1.6 5.2 4.8

Fowler

qs, μg /mgAC 226.1 328.4 217.9 87.9

K, μg/ mgAC 0.011 0.003 0.018 0.006

χ 0.87 0.05 0.53 1.87

R2 0.997 0.999 0.998 0.992

AICC 36.2 21.9 33.1 27.9

AARE, % 5.6 1.6 5.6 3.0

Freundlich

K, μg1-γ Lγ 1

ACmg 13.9 4.1 27.0 26.8

ν 0.49 0.64 0.36 0.17

R2 0.957 0.996 0.967 0.915

AICC 54.1 31.1 50.4 46.9

AARE, % 13.3 3.4 15.7 9.9

130

6.5 Conclusion

Three different waste biomass banana peels, sugarcane bagasse and coconut husk are selected

to obtain ACs. A two-step synthetic process is used to produce ACs from waste biomass

(waste@ACs). In the beginning, a hydrolytic treatment is performed to pulverize the raw

materials and followed the pyrolysis in furnace after mixing with KOH. The activated carbon

product is obtained after pouring HCl over the pyrolyzed solid. The obtained bp@AC (from

banana peels), bag@AC (from sugarcane bagasse) and coh@AC (from coconut husk) are

thoroughly characterized.

SEM analysis has shown that waste@ACs are unilateral macrostructure particles and have

conchoidal like cavities. TEM and XRD analysis have confirmed that waste@ACs are

amorphous in nature. EPR has confirmed that after the pyrolysis, the mixture of carbonized

KOH and biomass have a significant amount of free radicals. However, all the radicals vanished

once the activation of carbonized (KOH and biomass) mixtures took place in 2m HCl in air.

Hence why Boehm titration and TG analysis have established that waste@ACs have vast

amount of acidic surface functional groups. Further confirmation has been made after the XPS

and TPD analysis, have shown that waste@ACs contain distinct acidic surface functional

groups.

Overall, bag@AC possesses the greatest surface area and the highest number of acidic surface

functional groups. bpe@AC has the highest pore volume and a higher surface area than

coh@AC. However, coh@AC is obtained with the best yield.

Three different adsorption isotherm models are used to evaluate the CLD adsorption capacity

of waste@ACs. A Langmuir model fits best for bag@AC and coh@AC whereas, for bpe@AC

and cm@AC the best fit is obtained with the Fowler. Among waste@ACs, bag@AC adsorbs

the highest amount of CLD (335 μg/mg) but the yield-to-CLD adsorption property is the best

for bpe@AC. Remarkably, the average adsorption efficiency of waste@ACs is found up to be

~200% better than the AC used by the company in charge of the water purification in the French

West Indies.

131

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Modelling, 2016. Submitted!

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leachate. Chem. Eng. J. 2013; 223: 604–610.

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hexachlorocyclohexane (β-HCH) adsorption by activated carbons: molecular modelling

and adsorption–desorption studies. RSC Adv. 2015; 5 85153–85164.

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of Malachite Green in Simulated and Real Effluent by Bio-Based Adsorbents.

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different agricultural waste adsorbents for removal of oxamyl pesticide. Desalination

and Water Treatment 2015; 55: 2109–2120.

33. Gupta H, Gupta B. Adsorption of polycyclic aromatic hydrocarbons on banana peel

activated carbon. Desalination and Water Treatment 2015; 1-12. doi:

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thermodynamics of crystal violet dye on coconut husk-based activated carbon.

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based activated carbon. Inter. J. Heat and Mass Transfer 2011; 54: 4931–4938.

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Silva TL, Moraes JCG, Almeida VC. NaOH-activated carbon of high surface area

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135

CHAPTER - 7

EXPERIMENTAL PART

7.1 General Techniques

All air or moisture sensitive compounds were performed using standard Schlenk vacuum line

techniques in oven-dried (at 120 °C) glassware under an argon atmosphere. Argon was

purchased from PANGAS and was further passed through am M Braun 100 HP system for

purification.

Solvents, used particularly for inert atmospheric reactions, were distilled under an argon

atmosphere and dried over, sodium (toluene), sodium/benzophenone (tetrahydrofuran and

diethyl ether) and calcium hydride (n-methylformamide).

Air sensitive and hygroscopic compounds were stored either in glove box (M Braun Lab

Master) or in desiccator over phosphorus pentoxide/silica.

Light sensitive reactions and chemicals were accomplished and stored in a darker atmosphere,

respectively.

7.2 Chemicals

Plasma source gases used in chapter 2 for plasma treatment were received form PANGAS and

MESSER.

All standard chemicals used were purchased from ABCR, ITC, Acros, Aldrich, Fluca and Merk.

Bio-wastes were collected from Guadeloupe and Switzerland itself.

136

7.3 Detection of Chlordecone

The detection of CLD was carried out using a GC/MS Surveyor MSQ spectrometer (Thermo

Scientific, Waltham MA, USA) that uses electrospray ionization and a quadrupole detector. A

syringe pump (KD Scientific, Cambridge MA, USA) fed the spray nozzle. The delivery rate of

the solution was 100 μL/min, where the solution consists of 25 %vol of aqueous sample plus

75 %vol ethanol. The evaporation temperature was set to 300 °C. The ionization voltage was -

3.5 kV (anionic mode) and the skimmer cone was set to 60 V. All the spectra were averaged

for 1 minute. The spectra obtained correspond to CLD monohydrate and show a characteristic

isotopic peak pattern due to the chlorine atoms. In order to obtain a quantitative value, the

pattern was integrated from m/z 500 to 520.

Adsorption kinetics

Kinetic studies were investigated in 200 mL of saturated CLD aqueous use solution (~2200 μg

L-1) with 5 mg of all sample, at room temperature. CLD aliquots were taken out of the solution

after regular intervals. Adsorption kinetics were repeated at least 2 times for every sample.

Adsorption Isotherm

Isotherm experiments were carried out for five to seven days. The CLD concentrations used in

this study were 1100, 990, 880, 770, 660, 550, 440, 330, 220 and 110 μg L-1. The sample amount

(5 mg), room temperature (23.4 ± 1°C), pH (7.00 ± 0.5) and the volume of CLD solution (500

mL) were kept constant for all experiments. Adsorption isotherm were repeated at least 2 times

for every sample.

137

7.4 Analytical Methods and Equipment

Elemental analyses (EA)

EA were carried out by Micro-Laboratory (Institute of Organic Chemistry), ETH Zurich. Before

carrying out the elemental analyses, all samples were dried. Bulk elemental analysis (C, H, N

and O) of the samples was carried out on a LECO CHN-932 microanalyzer. All samples were

analysed in triplicate and the values are reproducible within ± 0.4% (relative standard

deviation).

Attenuated Total Reflectance– Fourier Transform Infrared spectra (ATR-FTIR)

ATR-FTIR (in mid-IR regions) were recorded using a Thermo Scientific Nicolet 6700 FT-IR

spectrometer. Powdered samples were pressed against a diamond ATR crystal to obtain a

spectrum.

UV/Vis Spectroscopy

UV/Vis spectra were recorded on a Lamda 19 spectrometer (range 200 – 1000 nm) in 2 and

10mm quartz cells.

Nuclear Magnetic Resonance (NMR)

NMR spectra were recorded on a Bruker Avance 300, 400 and 500 NMR spectrometer

operating at room temperature. Chemical shifts δ were measured according to IUPAC and given

in parts per million (ppm) relatives to TMS for 1H and 13C. The solvent signals were used as

internal standard: DMSO-d6: δ(1H) = 2.50 ppm, δ (13C) = 39.52 ppm.

Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC)

TGA and DSC analyses of all samples were performed using a NETZSCH DSC 214

DSC21400A. All experiments were run with samples ranging from 2 to 10 mg under dry

nitrogen or argon (250 mL min-1) in the temperature range of 25 to 1000 °C at a heating rate of

5 °C min-1. The flowing nitrogen/argon was used to prevent moisture pick-up or oxidative

degradation. Before running the experiment, all samples were placed in aluminium sample

pans/ceramics and sealed using the crimping tool made for these types of pans.

138

Scanning Electron Microscopy (SEM)

SEM images for all samples were obtained using a Leo Gemini 1550 FEG SEM instrument

(Zeiss, Germany). Double stick carbon tapes were fixed on aluminium plates and used as

sample holder.

Transmission Electron Microscopy (TEM) and EDX

TEM samples were prepared after dispersing the samples in ethanol. The TEM grid (holey C-

foil on Cu grid) was dipped in the suspension, which was dried in the air. TEM was performed

on a Tecnai F30 (FEI, USA; FEG (field emission gun), Super Twin lens, point resolution ca.

0.2 nm microscope operated at 300 kV. Local elemental analysis was done with an energy-

dispersive X-ray spectrometer (EDAX, USA) which is attached to the microscope.

Temperature Programmed Desorption

Temperature programmed desorption (TPD) of activated carbon was performed with a

BELCAT B (BEL Japan, Inc) equipped with a thermal conductivity detector and a time-of-

flight mass spectrometer. 30 mg samples were used to get TPD profiles of each sample.

Desorption of CO (m/z = 28), CO2 (m/z = 44), and H20 (m/z = 18), was monitored by purging

helium (99.999%) with a flow of 30 mL/min up to a temperature of 900°C and the heating rate

was 5 °C/min.

Raman Spectroscopy

Confocal Raman measurements were performed on a combined STM/Raman microscope

(Ntegra Spectra, NT-MDT, Zelenograd, Russia). All the spectra were obtained by averaging

two accumulations with an acquisition time of 60 s each, using a 632.8 nm HeNe laser at an

incident power of 1.7 mW for excitation.

X-ray Photoelectron (XPS)

XPS spectra presented in this work were acquired with a Sigma-II probe of Thermo Fischer

Scientific. Analyses were carried out with a non-monochromatic Al Kα (1486.6 eV) source.

Full-width-at-half-maximum (fwhm) of Ag 3d5/2 was 1.27 eV. Survey spectra were acquired

with a pass energy of 50 eV and a step size of 1 eV. The pass energy and the step size for narrow

scan were 25 and 0.1 eV, respectively. In both cases, the emission angle was 50°. The

spectrometer was calibrated according to ISO 15472:2001 with an accuracy of ±0.2 eV.

139

X-ray Powder Diffraction (XRD)

XRD were done on a Bruker D8 advance powder diffractometer (Cu Kα1 radiation λ = 1.54051

Å, curved Ge- monochromator, Bragg-Brentano configuration) equipped with a PSD-50m

position sensitive detector (M. Braun).

Electron Paramagnetic Resonance (EPR)

Bruker ESP 300E X-band spectrometer equipped with a LeCroy 9400 dual 125 MHz digital

oscilloscope and using a frequency tripled brilliant B Nd-YAG laser (Quantel, France, 20 Hz

repetition rate, 355nm, ca. 10 mJ/pulse, ca. 8 ns) was used to acquire the EPR signals of solid

samples used in chapter 6. The system is controlled using a software developed, kindly provided

and maintained by Dr. J. T. Toerring (Berlin). Long yang-quartz tube has been used as a sample

holder.

Textural Properties Measurements (BET etc.)

N2 adsorption and desorption isotherms recorded at 77 K on a BELSORP-mini BET analyser

(BEL, Inc., Japan) was used to analyse the Brunauer-Emmett-Teller (BET) specific surface area

and the Barret-Joyner-Halenda (BJH) pore size distribution of the samples, which had been pre-

dried under vacuum at 120 °C for 15 h. And

Argon adsorption isotherms were recorded at -196 °C with a Micromeritics 3Flex analyser after

in situ evacuation of the samples at 125 °C for 3 h.The specific surface area was calculated

according to the BET method, and the pore size distribution was determined using NLDFT.

Isothermal titration calorimetry (ITC)

ITC measurements were performed using a Microcal VP-ITC instrument (MicroCal,

Northampton, MA, USA) and the conditions used were as follows: Firstly, 2 µL of an aqueous

solution (0.9mM) of chlorendic acid (CLA) were injected into an aqueous solution (0.04mM)

of CD followed by 10 µL aliquots of an aqueous solution of CLA every 180s. The stirring speed

was set to 270 rpm at 25 °C for each experiment. The data obtained were fitted with a single-

site binding model using origin software provided by MicroCal. As this measurement has to be

performed in a single solvent (water), it could only be carried out with CLA because of the

insolubility of chlordecone (CLD).

140

Dynamic Light Scattering (DLS)

DLS was measured on a Malvern Zetasizer 3000. Disposable cells with four optical windows,

as the measurement was performed at a 90° angle. Data analysis was performed with the

software DTS 5300.

Melting Point (m.p.)

Solids were transferred to glass capillaries and the melting point determined with a Büchi M-

560/510 device.

141

THESIS CONCLUSION and OUTLOOK

Chlordecone (CLD) is an organochlorine POP, formerly used in the banana plantations of the

French West Indies. CLD is extremely persistent in soils, accumulates in the fatty tissue of

living organism and is toxic to human and wildlife. Due to the exposure lethal side effects, there

is an urge to remove CLD from water in order to avoid its further contact to the younger

generations. Conventional AC filters are being used for the removal of CLD from water.

However, AC in their current form have a low efficiency towards CLD extraction from water.

Therefore, the motivation of the PhD work presented herein was to develop new routes in order

to improve the surface properties of AC for better adsorption.

The manuscript reports the synthetic pathway strategies we have investigated to alter the surface

properties of AC. The first strategy depicted in Chapter 2, involved the modification of surface

functional group of AC by means of low-pressure-plasma processes. The target was to modulate

the surface potential of AC by introducing N- or O-containing functional groups by using

several gases (NH3, N2, H2, O2, C2H2 etc.) pure or in combination. Although it was clear that

the surface properties was modified under plasma exposure (higher basicity, textural

properties), the extent of this modification was insufficient towards this specific application,

i.e. improve the CLD adsorption. However, in order to carry these plasma treatments, we had

to develop a new type of electrode (centered cooled hollow electrode) which would be very

useful for further treatments of powders.

The next strategies involved wet chemical treatment of AC as in Chapter 3 which describes the

immobilization of iron oxide NPs onto AC through forced hydrolysis technique using

phosphoric acid as the capping agent. The modified AC (Fe@mACs) were obtained in

optimised amount after repeatedly using the Fe(III) filtrate. The complete characterization of

modified AC has confirmed the presence of two different iron oxide polymorphs on its surface,

goethite (α-FeOOH) and hematite (α-Fe2O3). Although only a maximum of 1-2 wt% iron oxide

Nps could be immobilized onto the surface of AC, this drastically impacts the AC adsorption

property towards CLD which was improved by 65 % (Table 1). Calculations (Multiple Minima

Hypersurface methodology) have suggested that the hydrogen bonding between the iron oxy-

hydroxide (α-FeOOH) Nps polymorph and CLD is one of the key factors that is responsible of

the CLD adsorption on Fe@mACs. Based on this result, immobilization of iron oxides and

other metal oxides Nps at a greater weight percentage should be investigated. This could be

helpful for improving CLD decontamination.

142

On the other hand, Chapter 4 revealed a quantitative 1: 1 complexation between host (γ-CD)

and guest (CLD) in water. After complexation, the complex (CLD@ γ-CD) starts to precipitate.

Interestingly, CLD@ γ-CD is insoluble in most of the solvents (including water), except DMF

and DMSO which facilitates its extraction from water after a simple filtration over activated

carbon. This was sufficient to obtain CLD-free water. Indeed, Electrospray GC/MS analyses

have confirmed that nearly 98 % CLD (after the complexation) was trapped on the activated

carbon filter.

In the next step, chemical grafting of γ-CD onto AC was considered in order to intensify this

CLD adsorption process. To this end, chapter 5 illustrates two different approaches to link AC

and γ-CD. In the first approach, the connection was foreseen through a phosphane oxide bridge.

Therefore we have synthesized a new photoactive bis(acyl)phosphane oxide acrylated gamma-

cyclodextrin (BAPO-γ-CD). Unfortunately, the photochemical reaction between BAPO-γ-CD

and AC did not occur due to the light absorption capacity of AC, which prevents the homolytic

cleavage of P-C bond of BAPO-γ-CD. However, BAPO-γ-CD is a photoactive macrocyclic

molecule which can be used to synthesize series of photo-induced block-copolymers bearing γ-

CD for the adsorption of CLD form water. The dense and cross-linked network of block-

copolymers and the hydrophobic cavity of γ-CD should trap the great amount of CLD from

water.

In the second approach, an aziridine linkage was successfully achieved after reacting γ-CD-N3

and AC in a single step reaction. The new hybrid material (AC-γ-CD) was found to be a 15 %

better adsorbent for CLD from water when compared to AC alone (Table 1). A maximum of 3

wt% γ-CD could be grafted onto the surface of AC and only when harsh conditions were used.

However, these conditions have adversely affected the textural properties of AC. Therefore, a

new methodology should be developed to introduce cyclodextrin in a greater percentage (≤ 5-

10 %) onto the surface of AC without further losses in the textural properties of AC.

Lastly, in order to develop new, effective and economically competitive activated carbon filters,

three different waste biomass: banana peels, sugarcane bagasse and coconut husk were

investigated and described in Chapter 6. A two-step synthesis process was used to obtain ACs

from waste biomass (waste@ACs). In the beginning, hydrolytic treatment was done to

pulverize the raw materials and followed etching activation by KOH. The obtained bp@AC

(from banana peels), bag@AC (from sugarcane bagasse) and coh@AC (from coconut husk) are

absolutely different in their overall yield, surface functionality and the textural properties.

bag@AC possess the greatest surface area and the most acidic surface functional groups,

whereas bp@AC has the highest pore volume and higher surface area than that of coh@AC.

143

However, coh@Ac was obtained in the best yield. Overall, the yield-to-CLD adsorption

properties were the best for bp@AC among the three new ACs. Remarkably, the average

adsorption efficiency (Table 1) of waste@ACs are found up to ~200% statistically better than

AC received from the company in charge of the water purification in the French West Indies.

The adsorption properties of waste@ACs variation is principally due to the lignocellulosic

composition of the raw material and available surface functional groups on the respective AC.

Table 1 shows the current progress towards the adsorption of CLD from water onto the AC. A

comparison of the CLD adsorption efficiency, between the AC synthesized by Durimel et al.1

,two different commercially available AC, and the new/modified AC developed in the PhD

thesis.

Table 1: Progress made until now towards the adsorption of CLD from water onto the AC.

Name Description Source,

Activating Agent

CLD adsorption

Capacity (at pH 7)

Reference

BagP1.5 Activated carbon Sugarcane Bagasse,

H3PO4

91.1 μg/mg Durimel et al.

BagH2O Activated carbon Sugarcane Bagasse,

Steam

51.2 μg/mg Durimel et al.

AC# Activated carbon Commercially

Available

48.6 μg/mg Chapter 3,

this thesis

Fe@mAC Activated carbon-Iron

Oxide composite

AC#,

Fe(III) salt

~ 80 μg/mg Chapter 3,

this thesis

Gamma-

Cyclodextrin

Macrocyclic Molecules Commercially

Available ~100 %, 1:1 complexation

Chapter 4,

this thesis

AC-γ-CD AC and γ-CD Commercially,

3% γ-CD grafted.

~15 % Improvement Chapter 5,

this thesis

cm@AC AC, Being used to

clean water at French

West Indies

Commercially

Available

92.2 μg/mg Chapter 6,

this thesis

bpe@AC Activated Carbon Banana Peel,

HT$ & KOH

260.5 μg/mg Chapter 6,

this thesis

bag@AC Activated Carbon Sugarcane Bagasse,

HT$ & KOH

334.9 μg/mg Chapter 6,

this thesis

coh@AC Activated Carbon Coconut Husk,

HT$ & KOH

224.8 μg/mg Chapter 6,

this thesis

1 Chem. Eng. J. 2013, 229, 239-49. $ Hydrolytic treatment. # starting Material

144

These results show that our goal has been reached, as we were able to drastically improve the

adsorption efficiency of common AC. However, the handling and working with AC and their

characterization has always been a challenge. Developing new and cheaper adsorbents using

biopolymers could be explored to avoid such complications. Biopolymers like cellulose, chitin,

dextran etc. are among the most abundant polymers on Earth. Therefore, using these

biopolymers and their composites with inorganic fillers to develop ecologically advanced

adsorbent for the selective adsorption of CLD from water, could be an economically desirable

approach.