synthesis, structure, adsorption space and magnetic ... · figure 3.09. layers formed by oxalate...

Universidad del Turabo

Synthesis, Structure, Adsorption Space and Magnetic Properties of

Ni-Oxalate Metal Organic Frameworks

By

Christymarie Rivera Maldonado BS, Chemistry, Pontifical Catholic University of Puerto Rico

Thesis

Submitted to the School of Science and Technology

in partial fulfillment of the requirements for the degree of

Master of Environmental Science

Specialization in Environmental Analysis (Chemistry Option)

Gurabo, Puerto Rico

May, 2012

Universidad del Turabo

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Environmental Science

March 23, 2012 Date of defense

Synthesis, Structure, Adsorption Space and Magnetic Properties of

Ni-Oxalate Metal Organic Frameworks

Christymarie Rivera Maldonado

Approved: ____________________________ Rolando Roque, PhD Research Advisor ____________________________ __________________________

Agustin Rios, PhD Margarita Rodriguez Lopez, PhD Member Member ____________________________ Arnaldo Carrasquillo, PhD Member

____________________________ __________________________ Fred C Schaffner, PhD Teresa Lipsett Ruiz, PhD Associate Dean, Graduate Studies Dean and Research

ii

iii

Dedications

I want to dedicate this research to God who gave me the ability, time and strength

to achieve this goal. To my parents, Wilfredo Rivera and Dimarie Maldonado, and my

sisters, Charlotte Rivera, Chatterllys Rivera, Chamylette Rivera and Challiette Rivera. To

my grandmother, Cristina Rivera and my aunt, Milagros Maldonado. I am honored to

belong to this family and thanks for your support, understanding and trusting in me. To my

husband, Eric Maldonado, for motivating me to continue and never give up, thanks for

your love and comprehension.

To all who collaborate with this research and are filled with joy with the culmination

of this work.

iv

Acknowledgements

This research is also product of dedication, effort and collaboration of my thesis

committee and research collaborators.

First, I wish to thank all the committee members. Agustin Rios, for all the hours we

spent together in the laboratory and for all the support. Margarita Rodriguez Lopez, for

your suggestions, time and genuine interest in this research. Arnaldo Carrasquillo, for your

time and recommendations. But I want to express all my gratitude to my dissertation

committee chairman and advisor Rolando Roque-Malherbe who believed in me and gave

me the opportunity to enter in the IPCAR team.

I also want to thank Pedro Fierro, allowing me the use of the Raman scattering and

the Vibrating sample magnetometer facilities. Luis Fuentes-Cobas for your comments and

suggestions on the manuscript. Fred Schaffner, Associate Dean, Graduate Studies and

Research, for always having the right words and help me in every step to make real this

goal. And I want to recognize the provided help direct or indirect from all other collaborators.

Acknowledge the financial support provided by the US Department of Energy

through the Massie Chair project at the University of Turabo and recognize the support of

the National Science Foundation under the project CHE-0959334.

v

Table of Contents

page

Abstract ix

Resumen xi

Chapter One. Introduction 1

Chapter Two. Experimental Data

2.1 Materials and Synthetic Procedure 6

2.2. Characterization Methods 12

Chapter Three. Results and Discussion

3.1 Synthesis 17

3.2. Structural analysis of the Ni-Ox-PMM

3.2.1. DRIFTS and RS study 22

3.2.2. TGA test 27

3.2.3. XRD structural analysis 29

3.2.4. Proposed layer structure 32

3.3. Adsorption study

3.3.1. Ni-Ox-MOF adsorption space morphology characterization 35

3.3.2. Isosteric heat of carbon dioxide adsorption on Ni-Ox-MOF 36

3.3.3. DRIFTS study of the surface chemistry of the Ni-Ox-MOF

applying carbon dioxide as test molecule

38

3.4. Magnetic study 39

Chapter Four. Conclusion 44

Literature Cited 46

Appendix One. Instrumentation 58

vi

List of Tables

page

Table 2.01. Table of Dicarboxylic Acids used on this research; the

formula, carbon quantity and common name.

10

Table 2.02. Table of the Metal Salts used on this research; the

common name and formula.

11

Table 3.01 Table of the metal organic materials synthesized and

the observations of each reaction.

20

Table 3.02. Parameters of the Raman Resolved Peaks. 27

Table 3.03. Parameters calculated with the TG profile. 28

Table 3.04. Cell parameters and space group. 32

Table 3.05. Resolved Peaks Positions of the DRIFTS Spectra of

Carbon Dioxide Adsorbed on the Tested Ni-Ox-MOF.

39

vii

List of Figures

page

Figure 2.01. A MOF’s Synthesis Flowsheet. 7

Figure 2.02. The Modified Solvothermal Process: Method One. 8

Figure 2.03. MOF synthesis under refluxing conditions. 9

Figure 2.04. The synthesis to prepare Ni-Ox-MOF. 13

Figure 3.01. The example of crystalline and amorphous materials founded

in the XRD data.

18

Figure 3.02. The example of different issues founded in the TGA Data. 19

Figure 3.03. DRIFTS spectra of the Ni-Ox-MOF. 23

Figure 3.04. Molecular structures of the Ni-DMF complex and the bis-

bidentate, bridging-bis-bidentate oxalate ligands.

25

Figure 3.05. Raman spectrum of the as-synthesized Ni-Ox-MOF. 26

Figure 3.06. Ni-Ox-PMM TG profile (a) and its derivative (b). 30

Figure 3.07. XRD profile of the as-synthesized Ni-Ox-MOF (a) and Pawley

refinement of this profile (b).

31

Figure 3.08. XRD degassed profiles of the Ni-Ox-MOF. 33

Figure 3.09. Layers formed by oxalate bridging-bis-bidentate ligands and

Ni-DMF Complex.

34

Figure 3.10. Dubinin-Radushkevitch (DR) plot of the adsorption isotherm

of CO2 on Ni-Ox-MOF at 273K.

37

Figure 3.11. DRIFTS spectrum CO2 adsorbed on Ni-Ox-MOF. 40

Figure 3.12. Magnetization Curves of Ni-Ox-MOF. 43

viii

List of Appendix

page

A-1.01. X-Ray Diffraction (XRD). 58

A-1.02. Thermogravimetric Analysis (TGA) 59

A-1.03. Infrared Spectrometer (DRIFTS) 60

A-1.04. Raman Spectrometer (RS) 61

A-1.05. The quantachrome Autosorb-1 (AS 1) 62

A-1.06. Vibrating sample magnetometer (VSM) 63

ix

Abstract

CHRISTYMARIE RIVERA MALDONADO (BS, Chemistry)

Synthesis, Structure, Adsorption Space and Magnetic Properties of Ni-Oxalate Metal

Organic Frameworks. (May/2012)

Abstract of a master’s thesis at Universidad del Turabo.

Dissertation supervised by Rolando Roque Malherbe, PhD

No. of pages in text _63_

A technological alternative to adsorb carbon dioxide (CO2) and minimize the

greenhouse effect is the use of Metal Organic Frameworks (MOF’s) (Ji et al. 2010). MOF’s

represent a new class of porous crystalline materials for which it is possible to design

organic linkers and inorganic joints (Tranchemontagne et al. 2008). During this research

there were synthesized 35 metal organic compounds using two modifications of the

solvothermal process: The first procedure is at room temperature (27 oC) or heated at 70

oC, and the second was carried out under reflux conditions. The characterizations of the

samples were accomplished with infrared Fourier Transform Spectrometry (DRIFTS),

Raman Spectrometry (RS), Thermogravimetric Analysis (TGA), X-Ray Diffraction (XRD),

adsorption and with a Vibrating Sample Magnometer (VSM). As the study consist in

adsorption, the priority was given to the one that shows the higher weight loss obtained

from the TGA and shows crystalline properties in XRD. From all the samples synthesized,

the Ni-Ox-MOF displayed the highest weight lost and crystalline properties. The TGA data

for Ni-OX-MOF display a 10% of weight loss and indicated that it has a pore volume. The

adsorption analysis showed that the pore volume is 0.10 ± 0.01cm3/g. The XRD profile

indicated that it is a layered compound. The DRIFTS, Raman and XRD data revealed that

x

each layer is formed by nickel cations linked by bisbidentate and bridging-bis-bidentate

oxalate ligands and the DMF molecules are perpendicularly linked to the nickel cations to

produce stacking. The Pawley fitting of the XRD profiles pointed out that the hydrated

sample crystallizes in the P2 / m space group. The cell parameters calculated are

consistent with the proposed structure. The VSM study demonstrates that it is a

paramagnetic material. And then was obtained a new Ni-Oxalic Metal Organic Framework

compound (Ni-Ox-MOF). It was confirmed by using different databases that the Ni-Ox-

MOF is unique and none studied in other research. The significance of this MOF is related

to its porosity, that is, during degassing it releases water turning into a porous stable

structure, showing notable magnetic properties. It’s very difficult achieve both

characteristics in the same material, in the literature was found a small amount of MOF like

it. In this case its porous properties, means that the electronic structure of nickel cations

can be externally manipulated with adsorbed molecules. The material could be sensitive to

small molecules; thereafter Ni-Ox-MOF possibly will be used as magnetic senor to trap

CO2 from the environment.

xi

Resumen

CHRISTYMARIE RIVERA MALDONADO (BS, Chemistry)

Estudio de la Síntesis, Estructura, Adsorción y Propiedades Magnéticas del Enrejado

Organometálico de Oxalato de Níquel. (mayo/2012)

Resumen de la Tesis de maestría en la Universidad del Turabo.

Tesis supervisada por el Dr. Rolando Roque-Malherbe

No. de páginas en el texto _63_

Una alternativa novedosa para absorber dióxido de carbono (CO2) y reducir el

efecto invernadero en el ambiente, es el uso de enrejados organometálicos, conocido por

sus siglas en inglés como MOF (Ji et al. 2010). Los MOF son materiales poroso

cristalinos, en los cuales es posible enlazar materiales orgánicos e inorgánicos

(Tranchemontagne et al. 2008). Durante esta investigación se sintetizaron 35 compuestos

organometálicos realizando dos modificaciones a la síntesis solvotermal (Duan et al.

2006; Tranchemontagne et al. 2008) que se encontró en la literatura. El primer

procedimiento se lleva a cabo a temperatura ambiente (27 oC), si no reacciona, se

calienta a 70 °C en un horno por 24 horas. La segunda se realizo bajo condiciones de

reflujo. La caracterización de las muestras se hizo utilizando la espectrometría infrarroja

(DRIFT), espectrometría Raman (RS), análisis termogravimétrico (TGA), difracción de

rayos X (DRX), adsorción con un Autosorb-1 y con un magnetómetro de muestra vibrante

(VSM). Como el estudio consiste en adsorción, se buscó la muestra con más pérdida de

peso reflejada en el TGA y que mostrara propiedades cristalinas en el DRX. De todas las

muestras sintetizadas, el Oxalato de Níquel mostro la mayor pérdida de peso y las

propiedades cristalinas necesarias para realizar la investigación. A este material se le

xii

llamo Ni-OX-MOF. Los datos del TGA para él Ni-OX-MOF revelaron que es un material

poroso y que tuvo una pérdida de peso de 10%. El análisis de adsorción mostró que el

volumen de poro es de 0.10 ± 0.01 cm3/g. El difractograma del DRX indicó que es un

compuesto en capas. Se observo en los datos de Raman e infrarrojo, que cada capa está

formada por cationes níquel unidos por enlaces bisbidentados y puentes-bis-bidentados

de oxalato; y que las moléculas de DMF están perpendicularmente enlazadas a los

cationes de níquel para unir las capas de los enlaces bisbidentados para formar una

molécula bidimensional. El refinamiento con el método de Pawley señaló que la muestra

hidratada cristaliza en el grupo espacial monoclínico P2 / m. Los parámetros de la celda

calculados son consistentes con la estructura propuesta. El estudio de VSM muestra que

Ni-OX-MOF es un material paramagnético. Todos los resultados obtenidos demostraron

que en esta investigación, se obtuvo un material nuevo. La importancia de este MOF, está

relacionada con su porosidad y sus notables propiedades magnéticas. Es muy difícil

sintetizar un MOF y lograr tener propiedades magnéticas y adsorbentes en un mismo

material. Fueron muy pocos los materiales que se encontraron en la literatura con

propiedades similares al Ni-Ox-MOF. Este material podría ser sensible a moléculas

pequeñas, ya que su estructura puede ser manipulada externamente con moléculas

adsorbidas. Lo cual indica que podría ser utilizado como un sensor magnético para

atrapar y almacenar el CO2 contaminante del medio ambiente.

1

Chapter One

Introduction

This research is intended to develop a feasible method to trap carbon dioxide

(CO2). The use of a cost effective carbon dioxide adsorption and storage methodologies,

using non expensive chemical materials through the synthesis of Metal Organic

Framework (MOF) may be attractive to industries and pharmaceuticals with high CO2

emissions. The synthesis of MOF with adsorption characteristic will serve as a mechanism

to decrease the degree of CO2 contamination on the atmosphere and prevent human

suffering. Carbon dioxide is the most powerful cerebral vasodilator known; inhaling large

concentrations causes rapid circulatory insufficiency leading to coma and death. Low

concentrations of carbon dioxide have been shown to cause increase in respiration and

headache (Hoskin et al. 1990).

Is important get serious about reducing greenhouse gas emissions from energy

production, deforestation, transport and industrial processes. The Earth is warming.

Disasters occur as a result of people’s exposure to particular hazards and their degree of

vulnerability. People in extreme poverty are in no position to withstand the additional

burden of climate change. The literature shows a direct relation between the greenhouse

effect and the higher emission of some gases like CO2.

Carbon dioxide is a colorless, odorless, faintly acidic-tasting, and non-flammable

gas at room temperature, with a molecular formula CO2. The linear molecule consists of a

carbon atom that is doubly bonded to two oxygen atoms, O=C=O. Carbon dioxide is the

fourth most-abundant gas in the Earth's atmosphere. Animals exhale carbon dioxide and a

plant uses it in photosynthesis to convert it to sugars and other forms of energy.

There are various sources of CO2 emissions, which are dominated by combustion

of liquid, solid, and gaseous fuels. The amount of CO2 consumption for organic chemicals

1

2

is relatively small compared to CO2 emitted from fossil fuel combustion. However, CO2

conversion and utilization should be an integral part of carbon management. Proper use of

CO2 for chemical processing can add value to the CO2 disposal by making industrially

useful carbon-based products. Studies on CO2 conversion into carbon-based chemicals

and materials are important for sustainable development. CO2 conversion and utilization

could also be positioned as a step for CO2 recycling and resource conservation (Abrahams

et al. 1991). Carbon dioxide thus can be chemically transformed from a detrimental

greenhouse gas causing global warming into a valuable, renewable and inexhaustible

carbon source of the future allowing environmentally neutral use of carbon fuels and

derived hydrocarbon products (Rosi et al. 2005).

Metal organic materials (MOM’s) are compounds consisting of metal nodes and

organic linkers. Specifically, MOMs presenting permanent porosity, that is, the so-called

metal-organic frameworks (MOF), as well named porous coordination polymers (PCP ’s) or

microporous metal-organic frameworks (MMOF’s), or in the case where are magnetic,

porous molecular magnets (PMM) (Stepanow et al. 2004; Rosi et al. 2005; O’Keeffe et al.

2008; Farha et al. 2010; Corma et al. 2010). These are a fascinating group of hybrid

materials, appearing as crystalline lattices composed of inorganic nodes and multi-dentate

organic linkers (Kinoshita et al. 1959; Hoskins et al. 1989; Desiraju 1989; Hoskins et al.

1990; Fujita et al. 1990; Abrahams et al. 1991; Abrahams et al. 1991; Fujita et al. 1994;

Stepanow et al. 2004; Rowsell et al. 2004; Rosi et al. 2005; O’Keeffe et al. 2008; Farha et

al. 2010; Corma et al. 2010) forming crystalline porous compounds, entailing strong metal-

ligand interactions (Rowsell et al. 2004; Siberio-Perez et al. 2007).

The Metal organic Frameworks (MOF) first arose through the study of zeolites.

Those appear due to a modification of the synthesis of zeolites. The MOF first reported

was in the Cambridge Structural Database (CSD) in 1978, this is software for database

access for structure visualization and data analysis, and structural knowledge bases. The

3

center and connection method for the synthesis of extensive framework materials was

developed in the first years of the last decade of the 20 th century fundamentally by

Robson and Hoskins (Hoskins et al. 1989; Hoskins et al. 1990; Abrahams et al. 1991;

Abrahams et al. 1991), Fujita (Fujita et al. 1990; Fujita et al. 1994), Desiraju (Desiraju

1989) and others (Stepanow et al. 2004; Rosi et al. 2005; O’Keeffe et al. 2008; Farha et al.

2010; Corma et al. 2010). Descriptions of this kind of materials were presented by

Kinoshita and collaborators more than fifty years ago (Kinoshita et al. 1959). The selection

of a concrete metal node, regularly determine the structure of the resulting framework and

the diverse coordination numbers with the favored geometries of the metal (Stepanow et

al. 2004; Rosi et al. 2005; O’Keeffe et al. 2008; Farha et al. 2010). Between these

materials those with shows permanent porosity are the most interesting ones. This

characteristic is the one that normally lead to great pore volumes, specific surface areas

and low densities (Farha et al. 2010; Corma et al. 2010). Some of these materials have

shown potential applications in gas storage (Dinca et al. 2005; Murray et al. 2009; Li et al.

2009; Furukawa et al. 2009), molecular separation (Farha et al. 2010), ion exchange (Min

et al. 2000), catalysis (Ma et al. 2009; Corma et al. 2010), together with luminescence

(Allendorf et al. 2009) and magnetism (Kurmoo 2009).

The perfect gas-storage MOF should have high adsorption capacity and fast kinetics at

workable temperatures, and the gas should interact strongly enough with the material that

it is not lost from the solid on storage but not so strongly that it cannot be released from

the material for use at the required time. They show promising potential for hydrogen,

methane, nitrogen and CO2 storage. MOF’s adsorbed, and store without significant loss,

large quantities of materials. MOF’s are the major candidates that might meet the U.S.

Department of Energy requirements for vehicular gas storage (Millward et al. 2005). The

literature shows that MOF could store as much CO2 as would be stored in nine tanks that

do not contain MOF. By comparison, a tank filled with porous carbon one of the current

4

state of the art materials for capturing CO2 in power plant flues would hold only four tanks

worth of CO2. MOF can be made in large quantities from low cost ingredients.

(Tranchemontagne et al. 2008) Be effectives, low-cost way of reducing CO2 emissions,

according to Yaghi. Tens of thousands of MOF have been synthesized and structurally

characterized; however, only a few of them have been tested for their adsorption

properties. Selective adsorption has been observed in less than about seventy MOF,

mostly based in on gas adsorption isotherms (Li et al. 2008).

Based in the porosity of the frameworks, several groups have successfully studied

the magnetic properties of the materials. The majority of magnetic frameworks are those

containing paramagnetic metal centers and in particular, the first row transition metals (V,

Cr, Mn, Fe, Co, Ni and Cu) (Kurmoo 2008). To construct porous magnets, is required

distance within interaction range. A key point is to fulfill effective magnetic exchange

pathways in the porous MOF.

PMM and molecule-based magnets, (M-BM’s) (Castillo et al. 2001; Nowicka et al.

2007; Coronado et al. 2008) are primarily characterized by the chemical nature of its

organic and metallic constituents and their spatial configuration. In this sense, the bis-

chelating coordination capacity of the oxalate ion and its facility to generate magnetic

interaction between metallic centers has made it a valuable and flexible option in the

design of diverse molecule-based magnetic compounds (Coronado et al. 2008). The

magnetic properties of oxalato-bridged complexes are outstanding owing to the capacity of

the oxalate ligand to assume different bridging modes, together with its ability to take part

in strong magnetic exchange by mediating electronic effects between paramagnetic metal

ions (Castillo et al. 2001). That is, the oxalate anions which have four potential donor sites,

is very attractive as a linker due to its ability to form framework structures and participate in

strong magnetic exchange).

5

One aim of the scientists is to develop bifunctional novel materials. The importance

of this material is the dual function obtained even though the combination of porosity and

magnetism is a complicated to undertaking; because porosity is associated to long

bridging, whereas magnetic exchange needs short distances (Nowicka et al. 2007). In this

case its porous properties, means that the electronic structure of nickel cations can be

externally manipulated with adsorbed molecules. The material could be sensitive to small

molecules; thereafter, used as a magnetic sensor to trap CO2 from the environment.

In the present research it is described the synthesis, structural characterization,

study of the porous structure, surface chemistry and magnetic properties of a new Ni-

oxalate metal organic frameworks (Ni-Ox-MOF). To accomplish the proposed objectives,

the material was designed by: applying a concrete synthesis methodology and the

synthesized materials were carefully studied by diffuse reflectance infrared Fourier

Transform Spectrometry (DRIFTS), Raman Spectrometry (RS), Thermogravimetric

Analysis (TGA), structure analysis by X-Ray Diffraction (XRD), adsorption of carbon

dioxide at 273K and magnetochemistry with a Vibrating Sample Magnetometer (VSM).

Searches in different databases as: Journal of American Chemical Society, Cambridge

Structural Database, Database for Australian National University for MOF, among others;

showed that the material studied in this investigation is unique and none observed in other

investigation.

6

Chapter Two

Experimental Data

2.1 Materials and Synthetic Procedure.

The literature shows four different conditions to synthesize the MOF's:

1. Hydrothermal - All chemicals are prepared using water as a solvent, and heated

at a temperature that fluctuates between 70 °C to 220 °C, from 6 hours up to 6

days (Fang et al. 2008).

2. Solvothermal - All chemicals use a solvent other than water, and prepare it from

4 °C to 250 °C, from 6 hours to 28 days (Tranchemontagne et al. 2008; Duan et

al. 2006).

3. Biphasic solvothermal - Inorganic salts are dissolved in water and organic

compounds are dissolved in an organic solvent and carefully layered above the

aqueous solution. This is then sealed and heated at 70 °C to 150 °C, from 6

hours to 28 days (Kondo et al. 2010).

4. Sol-gel synthesis- Inorganic salts and template are dissolved into a sodium

silicate solution. The organic linker is dissolved in water and carefully layered

above the gel layer. This is allowed to sit at room temperature, from 6 to 20 days

(Hermes et al. 2007).

The four methods were developed by scientist to obtain porous metal organic

materials (MOF), with highly crystalline structures and a large variety of extended porous

frameworks with a considerable range of pore sizes and functionalities. All of them are

based in a basic procedure; where by dissolve a metal salt and a ligand are possible

obtain a MOF. The difference between each method lies in the physical conditions or

materials used to prepare it. Refer to figure 2.01 to observe a general MOF syntheses

flowsheet.

6

7

F

igu

re 2

.01

. A

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F’s

Synth

esis

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ich

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tain

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.

8

In the present project the solvothermal method (Rosi et al. 2005) was slightly

modified to get a new material. This procedure was made by two different ways. The first

method used was a modified solvothermal process at room temperature (27 oC) or heated

at 70 oC, using dimetilformamide (DMF) as solvent. To make it different to the original

process, was added triethylamine (Et3N) 70.3M in dimethylformamide (DMF) and

Hydrogen Peroxide (Figure 2.02).

Figure 2.02. The Modified Solvothermal Process: Method One. This picture present the

scheme used in process one to synthesize MOF.

The second procedure is by refluxing the reaction mixture, showed in figure 2.03,

without H2O2, using heat to accelerate the precipitation. The solid formed precipitates from

the solution in hours. The solutions that slowly react at the first modified solvothermal

process, now precipitates in a couple of hours, less than 6 hours. For this process several

approaches were used, trying to obtain a MOF with adsorbent properties.

All the chemicals used were analytical grade without additional purification. The

water used in the synthesis process was bi-distilled. The Ligands are: Maleic acid, Fumaric

acid, Succinic acid, L-Tartaric acid, 1,2-trans-ciclohexanebicarboxylic acid, 1,4-trans-

ciclohexanebicarboxylic acid, 4,4-bipyridine, Mandelic acid, Glutaric acid, Adipic acid,

Malonic Acid and Oxalic acid. In the table 2.01 is presented the formula, the common

name, IUPAC name and the carbon chain of dicarboxylics acids used for this research.

9

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ure

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10

Table 2.01. Table of the Dicarboxylic Acids used on this research; the formula, carbon

quantity and common name.

The metal salts used were (Table 2.02): zinc nitrate (Zn(NO3)2), cobalt nitrate (Co(NO3)

2),

lead nitrate (Pb(NO3)2), iron nitrate (Fe(SO4)

2), mercury nitrate (Hg(NO3)2), cadmium nitrate

Cd(NO3)2, copper nitrate (Cu(NO3)

2), and nickel nitrate Ni(NO3)2.

The synthetic procedure applied for Ni-Ox-MOF was, the modified solvothermal process

at room temperature (27 oC), it was showed in Figure 2.04. The concrete synthesis procedure

was as follows:

Common name IUPAC name Carbon

Quantity

Formula

Oxalic acid ethanedioic acid 2 C2H2O4

Malonic acid propanedioic acid 3 C3H4O4

Succinic acid Butanedioic acid 4 C4H6O4

Tartaric acid 2,3-dihydroxybutanedioic acid 4 C4H6O6

Maleic acid (Z)-Butenedioic acid 4 C4H4O4

Fumaric acid (E)-Butenedioic acid 4 C4H4O4

Glutaric acid pentanedioic acid 5 C5H8O4

Adipic acid hexanedioic acid 6 C6H10O4

Mandelic acid 2-Hydroxy-2-phenylacetic acid 8 C8H8O3

1,4-Cyclohexane dicarboxylic acid Cyclohexane-1,4-dicarboxylic acid 8 C8H12O4

Bipyridine 4,4-Bipyridine 10 (C5H4N)2

11

Table 2.02. Table of the Metal Salts used on this research; the common name and

formula.

Common name Formula

Zinc nitrate Zn(NO3)2

Cobalt nitrate Co(NO3)2

Lead nitrate Pb(NO3)2

Iron nitrate Fe(SO4)2

Mercury nitrate Hg(NO3)2

Cadmium nitrate Cd(NO3)2

Cooper nitrate Cu(NO3)2

Nickel nitrate Ni(NO3)2

-A 70.3 mM solution of Et3N in DMF was prepared.

-A 0.01 mol of Ni(NO3)2 is dissolved in 50.0 ml of DMF and 0.01 mol of C2H2O4

(oxalic acid) is added and dissolved.

-To the above solution is added 29.0 ml of H2O2 (50%) was added slowly while

stirring manually.

-The reaction mixture is cooled between 5-10 oC and 24.1 ml of Et3N 70.3 mM was

added slowly in a period of 5 to 10 minutes.

-After the addition of the Et3N the flask is sealed and placed in the hood for one

week at room temperature (27 oC).-The solid formed was vacuum filter in a

12

Büchner's funnel washed with two portions of methanol and 5.0 ml of bi-distilled

water.

-It was placed in the oven at 70 oC for 24 hours.

-The solid obtained was pulverized and characterized using XRD, IR and RAMAN

spectroscopy, TGA analysis and others.

To characterize the synthesized materials in different equipments a few gases were

used such as: pure Potassium Bromide (KBr), provided by Nicolet; for adsorption

isotherms of carbon dioxide (CO2 Praxair, 99.99%) and helium (He2 Praxair, 99.99%); to

hydrated and dehydrated samples in spectra, was used a nitrogen flow (N2 Praxair,

99.99%).

2.2. Characterization Methods.

For this research is required found a sample with crystalline properties and highest

porosity, because both are characteristics of a MOF with adsorbent properties. Once was

obtained the material with these characteristics, will proceed to make specific studies to

characterize the sample with the instrumentation will be described below.

As the focal point for this research is got a sampler with crystalline properties, the first

analysis was done to all samples was the X-ray diffraction (XRD), showed in Apendix A-1.01.

Tests were carried out using a Bruker D8 Advance system in a Bragg- Brentano vertical

goniometer configuration. The angular measurements were made with a (Theta / 2Theta) of:

0.0001 degree reproducibility, applying steps of 0.01 degree from 5 to 60 degree to get 5500,

intensity versus angle XRD profiles that could be accurately resolved by least square methods.

The X-ray radiation source was a ceramic X-ray diffraction Cu anode tube type KFL C 2K

of 2.2 kW, with long fine focus. A LynxEye™ one-dimensional detector was employed. This

detector is based on Bruker AXS compound silicon strip technology and increases measured

13

Fig

ure

2.0

4.

Th

e s

yn

thesis

to

pre

pa

re N

i-O

x-M

OF

: (A

) S

am

ple

dis

so

lve

d (

B)

Sa

mp

le r

ea

ctin

g u

nd

er

the

ho

od

at

roo

m

tem

pe

ratu

re

(27

oC

).

(C)

Sa

mp

le

wa

s

filte

red

(D

) P

ulv

erize

(E

) D

ry

it

on

a

de

sic

ca

tor

(F)

Iden

tified

an

d

pu

t on

a

co

rre

spo

nd

ing

con

tain

er.

14

intensities, without sacrificing resolution and peak shape in approximately 200 times compared

with a point detector with identical data quality. This fact together with the small step, bring

excellent XRD profiles to be mathematically treated To carry out high temperature

measurements in vacuum the Anton Paar high temperature stage HTK-1200N was applied.

This high-vacuum chamber is designed to be used in the range from room temperature up to

1200 °C. The sample is mounted on an alumina sample holder and just below the sample the

temperature sensor is located (Roque-Malherbe et al. 2011).

The second main point for this investigation is found a sampler with the highest

porosity, because it was made the Thermogravimetric Analysis (TGA) showed in Apendix

A-1.02. Testing process was carried out with a TA, Q-500 instrument. Samples were

placed onto a ceramic sample holder suspended from an analytical balance. The sample

and holder were heated according to a predetermined thermal cycle, that is: the

temperature was linearly scanned, from 25 to 350 oC, at a heating rate of 5 oC/min, in a

flow of 100 ml/min of pure nitrogen. The data collection, temperature control, programmed

heating rate, and gas flow, were automatically controlled by the software of the instrument.

The TGA data was collected as a Weight (%) versus Temperature (oC) profile. The focal

point for this research is found a sampler with the highest weight loss in the TGA.

Once the sample was selected, DRIFTS was performed in the Infrared Spectrum

(showed in Appendix A-1.03). Diffuse reflectance infrared Fourier transform spectra

(DRIFTS) were gathered using a Thermo Scientific Nicolet iS10 FTIR spectrometer. The

data were collected at a resolution of 4 cm-1 employing 100 scans per sample. A

background, with pure KBr, applying the same conditions used to get the samples spectra

was always made previous to sample collection. The hydrated samples spectra were

obtained at room temperature under N2 flow at a rate of 50 cc/min. To get the spectra of

the dehydrated samples, it was heated, to 100 oC, under a flow of N2 at a rate of 50 cc/min

15

for 2 hours. The spectra of the dehydrated materials were then obtained at room

temperature, under N2.

As a complementary technique, was used a Raman Spectrum (RS) (Refere to

Appendix A-1.04 to observe the Raman instrumentation used). The Raman analysis were

taken with a Renishaw Raman microspectrometer RM2000 system, showed in Apendix A-

1.04, is equipped with a Leica microscope using 20x objective and with a charge-coupled

device (CCD) detector. A spectrum was obtained with laser lines at 532 and 785 nm. The

785 nm laser excitation line was provided by a model PI-ECL-785-300-FS, Process

Instruments, Inc., Salt Lake City, UT. The 532 nm excitation source was a Spectra Physics

EXCELSIOR solid state diode laser. Raman spectra were collected in the range of 100-

3500 Raman Shift (cm-1), with an integration time of 10s per scan. The Raman spectra

were the result of the average of 3 scans.

The fitting process of the Raman and DRIFTS spectra were performed with the

peak separation and analysis software PeakFit (Seasolve Software Inc., Framingham,

Massachusetts) based on the least square procedure, in order to calculate the best fitting

parameters, peak positions, and amplitudes, and peak half width.

Carbon dioxide adsorption at 273 K and pressure up to 1 atm was carried out in an

upgraded Quantachrome Autosorb-1 automatic volumetric physisorption analyzer, is

showed in Apendix A-1.05. The adsorption isotherms of CO2 at 273 K and 298 K were

obtained for samples degassed at 573 K for three hours in high vacuum (10-6 Torr). The

backfilling process was carried out using helium in both cases.

DRIFTS spectra of carbon dioxide adsorbed in the sample selected were obtained

using as background the dehydrated sample at room temperature. That is, a background,

of the dehydrated sample applying the same conditions used to get the adsorbed samples

spectra were always made previous to sample collection. After that, CO2 flow at a rate of

50 cc/min for three minutes was passed through the dehydrated samples; afterward, the

16

sample was purged under N2 flow at a rate of 50 cc/min for one minute. Spectra of the

carbon dioxide molecule adsorbed on the MOF were then obtained at room temperature

under N2 flow.

The magnetic measurements were obtained in the vibrating sample magnetometer

(VSM), Lakeshore 7400 Series, showed in Apendix A-1.06. The magnetization curve,

magnetization (M) versus field strength (H) was carried out at room temperature (300 K).

The powder sample was weighted, located in the sample holder and then applied the ramp

from -2.2 to 2.2 T (T=Tesla) and thereafter in backward direction.

17

Chapter Three

Results and Discussion

3.1 Synthesis

With the center and connection methodology, in the present work it was

synthesized 35 different metal organic materials. The Table 3.01 shows detailed each

reaction and the observations after the characterization in the TGA and XRD. The figure

3.01 showed the XRD data of the nickel oxalic material and other three materials also

synthesized with nickel, in this is seen as a sample was determined amorphous or

crystalline material. The samples were crystalline if it had a defined pattern of peaks and

was amorphous when the sample had no peaks arranged, by the XRD data the nickel

oxalic material showed crystalline properties. The TGA obtained data showed that the

sample with the highest weight loss is the nickel oxalic material. Refer to figure 3.02 to see

the comparison of nickel oxalic material with other three samples also synthesized with

nickel. The 35 samples were compared to each other, but in this research only were

presented three additional samples synthesized with nickel as an example; because the

amount of documentation was massive and the idea was to facilitate the way was token

the conclusion that the nickel oxalic sample was right one. In accordance with the above

information, nickel oxalic product is crystalline and porous.

The Ni-Ox-MOF was Porous Molecular Magnet (PMM); the synthesis process was

repeated, changing slightly the steps described in section 2.1, in order to test the

reproducibility of the synthesis process. The synthesis procedure showed itself extremely

delicate, that is, minimal changes produced a non-porous material.

17

18

.

Fig

ure

3.0

1.

Th

e e

xa

mp

le o

f cry

sta

lline

an

d a

mo

rpho

us m

ate

ria

ls f

ou

nd

ed

in

the

XR

D d

ata

. T

he

fig

ure

sh

ow

ed

th

e X

RD

da

ta o

f th

e n

icke

l o

xa

lic m

ate

ria

l and

oth

er

thre

e m

ate

ria

ls a

lso

syn

the

siz

ed

with

nic

ke

l, in

th

is is s

ee

n a

s a

sa

mp

le h

ow

wa

s d

ete

rmin

ed

am

orp

ho

us o

r cry

sta

lline

ea

ch m

ate

ria

l.

19

Fig

ure

3.0

2 T

he

exa

mp

le o

f d

iffe

ren

t is

su

es f

ou

nde

d in

th

e T

GA

Data

: T

he

sa

mp

le o

f N

i(N

O3)2

+ S

uccin

ic a

cid

, re

pre

sen

ted

by th

e p

urp

le c

olo

r, s

ho

ws n

o w

eig

ht

loss a

nd

a d

eco

mpo

sitio

n a

t 1

50

oC

; T

he

sa

mp

le o

f N

i(N

O3)2

+ M

ale

ic a

cid

, re

pre

se

nte

d

by t

he g

reen

co

lor,

sh

ow

s a

8

% o

f w

eig

ht

loss a

nd

a d

eco

mpo

sitio

n a

t 21

0 o

C;

The

sa

mp

le o

f N

i(N

O3)2

+ O

xa

lic a

cid

,

rep

rese

nte

d

by

the

re

d

co

lor,

sh

ow

s

a

11

%

o

f w

eig

ht

loss

and

a

de

co

mpo

sitio

n

at

20

0

oC

; N

i(N

O3)2

+

cic

loh

exa

ne

dic

arb

oxylic

acid

, re

pre

se

nte

d b

y th

e r

ed

co

lor,

sho

ws a

5 %

of

we

ight

loss a

nd

a d

eco

mp

ositio

n a

t 1

20

oC

.

20

Table 3.01: Table of the metal organic materials synthesized and the observations of each

reaction.

Synthesis Observations

1. Cd(NO3)2 + Fumaric acid + H2O2 (50 %) + DMF + Et3N

(70.3 mM in DMF); at room temperature (27 oC)

No present significant weight loss in TGA

2. Cd(NO3)2 + Succinic acid + H2O2 (50 %) + DMF + Et3N


Poor crystalline properties

3. Cd(NO3)2 + Maleic acid + H2O2 (50%) + DMF + Et3N


Amorphous Material

4. Co (NO3)2.6H2O + Fumaric acid + H2O2 (30 %) + DMF+ Et3N


No Reaction was obtained

5. Cu(NO3)2 + Maleic acid + (30%)+DMF+Et3N (70.3 mM in

DMF); at room temperature (27 oC)

Amorphous Material

6. Fe(SO4) + Fumaric acid + H2O2 (50 %) + DMF + Et3N (70.3 mM in DMF); at room temperature (27 oC)

Amorphous material

7. Fe(SO4) + Maleic acid+ H2O2 (30 %) + DMF + Et3 N (70.3 mM in DMF); at room temperature (27 oC)

Amorphous material

8. Fe(SO4) + Succinic acid + H2O2 (30 %) + DMF + Et3N (70.3 mM in DMF); at room temperature (27 oC)

Amorphous material

9. Fe(SO4) + L-Tartaric acid + H2O2 (30%)+DMF+ Et3N (70.3mM in DMF); at room temperature (27oC)


10. Hg(NO3)2 + L-Tartaric acid + H2O2 (50%) + DMF + Et3N

(70.3mM in DMF); at room temperature (27oC)


11. Hg(NO3)2 + Maleic acid+ H2O2 (30 %)+DMF+ Et3N


Amorphous material

12. Ni(NO3)2 .6H2O + Oxalic acid + H2O2 (50 %)+DMF+ Et3N


Present Crystalline characteristics and weight loss in TGA

13. Ni(NO3)2 .6H2O + Fumaric acid + H2O2 (30 %) + DMF + Et3N



14. Ni(NO3)2 .6H2O + Succinic acid + H2O2 (30 %)+DMF+ Et3N



21

15. Ni(NO3)2.6H2O + Maleic acid + H2O2 (30 %)+DMF+ Et3N


Amorphous material

16. Pb(NO3)2 + Maleic acid + H2O2 (50 %) + DMF + Et3N


Amorphous material

17. Pb(NO3)2 + Succinic acid + H2O2 (50 %) + DMF + Et3N



18. Pb(NO3)2 + Oxalic acid + H2O2 (50 %) + DMF + Et3N



19. Pb(NO3)2 + 1,4-cliclohexanedicarboxilic acid+ H2O2 (30 %) +

DMF + Et3N (70.3 mM in DMF); at room temperature (27 oC)


20. Zn(NO3)2 .6H2O + Oxalic acid + H2O2 (30 %) + DMF + Et3N



21. Co (NO3)2.6H2O + Fumaric acid + (30 %)+ DMF+Et3N

(70.3 mM in DMF) (Heated 70 oC)


22. Cu(NO3)2 + Fumaric acid + H2O2 (30 %)+ DMF+Et3N

(70.3 mM in DMF) (Heated at 70 oC)


23. Cu(NO3)2 + Maleic acid + (30 %)+ DMF+Et3N



24. Cu(NO3)2 + Succinic acid + (30 %)+ DMF+Et3N



25. Cu(NO3)2 + Fumaric acid + H2O2 (30 %)+ DMF+Et3N



26. Ni(NO3)2 + 1,2-cis-ciclohexanebicarboxilicacid + H2O2

(50 %) DMF+Et3N (70.3 mM in DMF) (Heated at 70 oC)


27. Ni(NO3)2 + 1,4-cis-ciclohexanebicarboxilicacid + H2O2 (50

%)+DMF+Et3N (70.3 mM in DMF) (Heated at 70 oC)


28. Pb(NO3)2 + Succinic acid + H2O2 (50 %)+DMF+Et3N



29. Pb(NO3)2 + Maleic acid + H2O2 (50 %) + DMF + Et3N



30. Zn(NO3)2.6H2O + Fumaric acid + H2O2 (30 %) + DMF +

Et3N (70.3 mM in DMF) (Heated at 70 oC)

Amorphous Material

31. Ni(NO3)2 + 1,4-trans-ciclohexanebicarboxilicacid +

Adipic acid + DMF (Reflux at 160 oC)


22

32. Ni(NO3)2 + Mandelic acid + DMF; Reflux at 160 oC

Amorphous Material

33. Ni(NO3)2 + Oxalic acid + DMF; Reflux at 160 oC

Amorphous Material

34. Ni(NO3)2 + 1,4-trans-ciclohexanebicarboxilicacid + DMF;

Reflux at 160 oC Amorphous Material

35. Ni(NO3)2 + 1,2-trans-ciclohexanebicarboxilicacid + DMF;

Reflux at 160 oC Amorphous Material

The idea behind the synthesis procedure was to use oxalate anion in order to

create a 2D layer. To produce the layered structure, Et3N was introduced to neutralize the

oxalic acid. The H2O2 was used to accelerate the reaction, introduce water in the

framework and oxidize a fraction of the Ni2+ to Ni3+. DMF was not only the solvate, also

acted as a shaping molecule.

The layered framework makes possible the combination of paramagnetic nodes at

short distances within the layer associated with long bridging distances in the direction of

the layer stacking. Explicitly, it is possible the combination of magnetism and porosity,

since we have magnetic exchange because of the short distances in the layer and porosity

due to long bridging in the stacking direction.

3.2. Structural analysis of the Ni-Ox-MOF

3.2.1. DRIFTS and RS study

The DRIFTS spectra of the Ni-Ox-MOF sample as-synthesized and degassed at 75

oC in the range between: 500-4000 cm-1 are shown in Figure 3.03. The main IR active

vibrations observed in the range between: 500-2000 cm-1 are the )(CO asymmetric

stretching vibration, at 820 cm-1; the )(CO symmetric stretching vibrations, located at

1321 and 1361 cm-1 and between 1500-1700 cm-1 the )(OCO broad band. These are the

23

Fig

ure

3.0

3.

DR

IFT

S S

pe

ctr

a o

f N

i-O

x-M

OF

. T

he

pic

ture

sho

wed

th

e D

RIF

TS

of

the a

s-s

yn

the

siz

ed a

nd

deg

assed

at

75

0C

N

i-O

x-M

OF

. A

) S

ho

we

d th

e vib

ration

s obse

rve

d in

th

e N

i-O

x-M

OF

as synth

esiz

ed

. B

) S

ho

ws th

e vib

ratio

ns

ob

tain

ed

afte

r th

e N

i-O

x-M

OF

as s

yn

the

siz

ed

was d

eg

asse

d a

t 7

5 o

C.

C)

Sh

ow

s t

he

vib

ratio

n p

rodu

ced

by a

dso

rbe

d

wa

ter

fro

m th

e a

s s

yn

the

siz

ed m

ate

ria

l aft

er

deg

assin

g.

24

distinctive IR bands of the bis-bidentate oxalate-bridging (Figure 3.04) ligand (Tuero et al.

1991). These bands are, with minor shifts, maintained after dehydration at 75 oC. The

band at 1469 cm-1, also very well noticed in the Raman spectrum (Fig. 3.05), correspond

to the )( OCs of the DMF (Fig. 3.04). Additionally, the band 1020 cm-1 corresponds to

the )(CN stretching vibration of DMF (Olejnik et al. 1971).

In the range between 2750-3800 cm-1 are observed the vibrations related to the

water and the DMF included in the Ni-Ox-MOF. In this range are evidenced three broad

bands. The band in the range: 3200-3700 cm-1 correspond to the stretching, )(OH

vibration produced by adsorbed water. This band disappears after degassing at 75 oC

(see in Fig 3.03 the difference spectrum). The other two bands in the range 2750-3200

cm-1 do not disappear after degassing at 75 oC. Since, these two, relatively broad bands,

also found in the Raman spectrum, are produced by )(CH and )( 3NCHs vibrations

corresponding to DMF (Olejnik et al. 1971).

Two very important features of the Raman spectrum are the bands located at 528

cm-1 and 588 cm-1. The band located at 528 cm-1 is normally accepted that corresponds to

the stretching vibration mode of the NiO6 octahedral (Kalyani et al. 2005). The band placed

at 588 cm-1 can be contemplated as the stretching vibration mode distorted octahedral

coordination (NiO6) or pentacoordinated (NiO5) (Park et al. 2006). Both bands are resolved

in two peaks by fitting each band (Table 3.02). To explain these peaks is important

remember that during the synthesis process, H2O2 was added. Consequently, is very

probable that some of the Ni2+ was oxidized to Ni3+, thereafter, in some of the octahedral

and distorted octahedral sites Ni3+ is placed. To justify the band at 588 cm-1 was applied

the Sanderson principle of equalization of the electronegativity (Sanderson 1976). This

rule states that in a molecule composed of atoms with different electronegativity the

electrons are restructured in such a way that they will be equally attracted to the nuclei in

25

Fig

ure

3

.04.

Mo

lecu

lar

str

uctu

res

o

f th

e

Ni-D

MF

co

mp

lex

and

th

e

bis

-bid

enta

te,

bridg

ing

-bis

-bid

en

tate

oxa

late

lig

an

ds.

A)

Brid

gin

g-B

is-b

iden

tate

lig

and

s,

the

nic

ke

l no

de

s h

ave

on

ly five

bon

ds lin

ke

d t

o th

e o

xa

late

io

n,

one

o

f th

e bo

nd

s a

re

un

sa

tura

ted

. B

) N

i-D

MF

co

mp

lex,

the

DM

F m

ole

cu

les p

erp

en

dic

ula

rly c

oo

rdin

ate

d t

o t

he

nic

ke

l. C

) B

is-b

iden

tate

lig

and

s,

had

six

nod

es lin

ked

to

oxa

late

ion

.

26

Fig

ure

3.0

5.

Ra

man

spe

ctr

um

of

the

as-s

yn

the

siz

ed

Ni-O

x-M

OF

. A

) S

pe

ctr

um

ob

tain

ed

fro

m t

he

as s

yn

the

siz

ed

Ni-

Ox-M

OF

in t

he R

S.

B)

Sho

ws t

he b

and

pla

ce

d a

t 5

88

cm

-1 t

ha

t ca

n b

e c

on

tem

pla

ted a

s t

he s

tre

tch

ing

vib

ration

mo

de

of

NiO

5 i

n

dis

tort

ed o

cta

he

dra

l coo

rdin

atio

n (

NiO

6)

or

pe

nta

co

ord

ina

ted

(N

iO5).

27

Table. 3.02. Parameters of the Raman Resolved Peaks.

the bond. Consequently, the molecule average electronegativity is postulated to be the

geometric mean of the compound atoms of the molecule under consideration.

In the analyzed material, the decrease in the number of oxygen atoms from NiO6 to

NiO5 induced a transfer of electronic density from the less electronegative atom, nickel, to

the more electronegative, oxygen; subsequently, an increase in the bond strength

accompanied by an increase in the wave number of the band was produced.

3.2.2. TGA test

To determine the guest molecules lost during heating and study other structural

features, the TGA method was applied. The thermal gravimetric (TG) profile of the Ni-Ox-

MOF is shown in Figure 3.06 a. It is evident that at relatively low temperatures, that is

below 100 oC took place the release of H2O, in two steps. This fact is confirmed in Figure

3.06 b where shown the derivative of the TG profiles of the material resolved in peaks.

These peaks can be related, to the liberation of adsorbed (45 oC) and coordinated water

(80 oC). Finally, also in two steps, 170 oC and 215 oC, DMF was released (Table 3.03).

Finally, the material was decomposed at 300 oC.

Sample λ1 [cm-1] [%]1A λ2[cm-1] [%]2A

Band at 535 cm-1 522 0.32 534 0.31

Band at 585 cm-1 583 0.18 592 0.19

28

Table 3.03. Parameters calculated with the TG profile

TGA was also applied as a method for the measurement of the pore volume in

microporous materials, since the TG profile from 30 oC to 150 oC behaved merely as a

water thermo desorption process (Roque-Malherbe et al. 2005). In this regard it was

possible the calculation of the TGA micropore volume, with the TG data and the Gurvich

rule (Roque-Malherbe, 2010).

Gurvich rule is expressed as follows:

a

L

i nVV (1)

Where, Vi = volume of the adsorption space; an = the amount adsorbed; and V L= the

molar volume of the liquid phase which conforms the adsorbed phase. The amount

adsorbed (in mol/g,) is defined as follows (Roque-Malherbe, 2010):

s

a

am

nn (2)

Where: nna , and, n is the surface excess amount. The mass of degassed adsorbent

(ms), measured in g. Thereafter,

PMMs WtLm 1 (3)

OHPMM

a MWtLn2

(4)

Where in the present case, PMMWtL , was the weight lost at 100oC in g/g; OHM2

= 18 g/mol,

is the molecular weight of water. Since, 182

L

OHV cm3/mol. The micropore volume, OH

TGAW 2 ,

Sample OH

TGAW 2 ][ 3 gcm OH

T 2

1 ][0C OH

T 2

2 ][0C DMFT1 ][0C

DMFT2 ][0C

Ni-Ox-MOF 0.100 45 80 170 215

29

the following relation was applied:

PMM

PMMsOHPMM

L

OHa

L

OH

OH

TGAWtL

WtLmMWtLVnVW

1)(

222

2 (5)

To calculate with our data the micropore volume the following relation was applied:

PMM

PMMOH

TGAWtL

WtLW

12 (cm3/g) (6)

Where, in the present case, PMMWtL , in g/g, was the weight lost at 1000C. The

value for 09.0PMMWtL g/g, consequently 100.02OH

TGAW cm3/g, for the tested Ni-Ox-MOF.

3.2.3. XRD structural analysis

The Figure 3.07 a showed the XRD profile of the as-synthesized Ni-Ox-MOF

sample in the range between: 5-55 o (2θ). After a deep analysis of the pattern displayed in

Figure 3.07 a, was realized its resemblance with the profiles of layered compounds as the

phyllosilicates (Plancon 2002; Ufer et al. 2004). Consequently, it was supposed that the

Ni-Ox-MOF is formed by stacked layers. To justify the previous hypothesis, the powder

pattern reported was resolved into separate Bragg components applying the whole-

powder pattern decomposition (WPPD) the method proposed by Pawley (Pawley 1981),

as shown in Figure 3.07 a. This method can refine the unit cell parameters and

decompose the whole powder pattern into individual reflections. The concrete computer

program applied to carry out the calculations was the Bruker DIFFRACplus TOPAS™

software. This is a graphics based, non-linear least squares profile analysis program that

integrates between other features the WPPD Pawley method without reference to a crystal

structure model. The XRD profile of the hydrated sample was fairly fitted (Figure 3.07 b)

with the help of the Pawley decomposition method supposing that it crystallizes in the

monoclinic P2 / m space group (Table 3.04).

30

Fig

ure

3.0

6.

Ni-O

x-P

MM

TG

pro

file

(a

) a

nd

it’s d

eriva

tive

(b

). T

he

the

rma

l g

ravim

etr

ic (

TG

A)

pro

file

of

the

Ni-O

x-M

OF

is

sh

ow

ed

in

fig

ure

a,

wh

ere

too

k p

lace

the

re

lea

se

of

H2O

an

d D

MF

. T

he

fig

ure

b s

ho

w t

he

de

riva

tive

of

the

TG

A p

rofile

s o

f

the m

ate

ria

l.

31

Fig

ure

3.0

7.

XR

D p

rofile

of

the a

s-s

yn

the

siz

ed N

i-O

x-M

OF

(a

) a

nd

Pa

wle

y r

efine

me

nt

of

this

pro

file

(b

). a

) T

he

pa

tte

rn

dis

pla

ye

d a

s s

ynth

esiz

ed

Ni-

Ox-M

OF

b)

Re

fin

em

en

t o

f th

e X

RD

pro

file

s t

o a

dju

st

it t

o a

sim

ilar

pre

-stu

die

d c

rysta

lline

pro

file

.

32

Table. 3.04. Cell parameters and space group.

To learn about the Ni-Ox-MOF stability, the material was degassed in vacuum at 75

oC and 200 oC in the Anton Paar XRD high temperature stage, and later were collected

both profiles in vacuum at room temperature. The XRD profiles corresponding to both heat

treatments are shown in Figure 3.08. By simple inspection it is evident that in the Ni-Ox-

MOF after heating at 75 oC was preserved the layer structure; however, when heating at

200 oC, the structure collapsed.

3.2.4. Proposed layer structure

The oxalate group main linkages are monodentate, bidentate, bis-bidentate and

bridging bis-bidentate (Cotton et al. 1999). The layers could be formed by a two

dimensional (Figure 3.09) oxalate bis-bidentate and oxalate bridging bis-bidentate nickel

coordination polymer (Wang et al. 2006). In these layers the nickel nodes have only five

bonds linked to the oxalate ion (Figure 3.09); one of the bonds are unsaturated. On the

other way, a layer shaped with bis-bidentate and bidentate ligands, had the six nodes

linked to the oxalate ion, with no possibility to grow to a third dimension and form a porous

material (Keene et al. 2009).

The DMF molecules could act as pillars, linking the remaining bond through the

oxygen. In this research was proposed that the Ni-Ox-MOF could be shaped by the

Sample a [Å] b [Å] c [Å] β SG

Ni-Ox-MOF 6.67 8.85 12.41 84.29 P2/m

33

Fig

ure

3.0

8. La

ye

rs fo

rmed

by o

xa

late

bridg

ing

-bis

-bid

en

tate

lig

an

ds a

nd

Ni-

DM

F C

om

ple

x.

The

la

yers

co

uld

be

fo

rmed

b

y a

tw

o d

imen

sio

na

l o

xa

late

bis

-bid

enta

te a

nd N

i-D

MF

co

mp

lex, a

s s

ho

wed

in

th

is f

igu

re.

34

Fig

ure

3.0

9.

La

ye

rs f

orm

ed

by o

xa

late

brid

gin

g-b

is-b

ide

nta

te l

iga

nd

s a

nd

Ni-

DM

F C

om

ple

x.

Th

e l

aye

rs c

ou

ld b

e

form

ed b

y a

tw

o d

ime

nsio

na

l oxa

late

bis

-bid

enta

te a

nd

Ni-D

MF

co

mp

lex, a

s s

ho

we

d in

th

is f

igu

re.

35

oxalate bis-bidentate and oxalate bridging bis-bidentate layers (Figure 3.09) connected by

DMF molecules perpendicularly coordinated to the nickel included in the layers. This is

consistent with the Raman data.

3.3. Adsorption study

3.3.1. Ni-Ox-MOF adsorption space morphology characterization

A very good probe to test the adsorption space of microporous materials is the

carbon dioxide molecule (Dunne et al. 1996; Cazorla-Amoros et al. 1998; Bacsik et al.

2010). As previously showed, the Ni-Ox-MOF is a material stable under heating up to

about 100 oC. Also was proposed that this framework should be composed of micropores

that pervade the crystal lattice as was suggested by the TGA data. Carbon dioxide

adsorption could be applied to test the morphology of the adsorption space of the Ni-Ox-

MOF.

The study of carbon dioxide adsorption was obtained in an upgraded

Quantachrome Autosorb-1 automatic physisorption analyzer. The adsorption isotherms of

CO2 was at 273K, in samples degassed at 750C (348K), during three hours in high vacuum

(10-6 Torr). Was gathered the adsorption data in the relative pressure range,

03.000003.0 0PP ; where, the micropore filling takes normally place (Roque-

Malherbe 2010), since the carbon dioxide vapor pressure, 0P , at 0 oC (273 K), is very high,

that is: 141,260P Torr.

To calculate the micropore volume and the parameters characterizing the energy of

adsorption, was applied the Dubinin-Radushkevitch (DR) adsorption isotherm equation;

since, a vast amount of data indicates that the adsorption process in the micropore range

is described by it (Roque-Malherbe et al. 2010; Roque-Malherbe 2010).

This adsorption isotherm equation can be represented as follows (Bering et al. 1972;

Dubinin 1975; Roque-Malherbe 2000):

36

2

0

2lnlnln PPERTNn aa (7)

Where, an , is the amount adsorbed; PP0 , is the inverse of the relative pressure,

141,260P Torr; E, is a parameter named the characteristic energy of adsorption; and, Na, is

the maximum amount adsorbed in the micropore volume.

Thereafter, the CO2 adsorption data was linearly fitted to equation “7” (Figure 3.10)

and the calculation of Na and E as the best fitting parameters. Then, the micropore volume

was calculated applying the Gurvich rule, equation “6”. To better understanding, refer to the

following description:

CO2 adsorption data was linearly DR adsorption isotherm equation:

2

0

2lnlnln PPERTNn aa

y = B + mx

The micropore volume was calculated applying Gurvich rule for CO2 adsorption:

WMP= NaVL (8)

Where VL = 41.3 cm3/g, is the molar volume of CO2 at 273K. Solved the linear

equation for B, gives the Ni-Ox-MOF pore volume:

WMP=0.08 cm3/g

3.3.2. Isosteric heat of carbon dioxide adsorption on Ni-Ox-MOF

The parameters calculated with the DR adsorption isotherm equation are not only

to evaluate the micropore volume of the sample, also describe the adsorption interaction

between the adsorbate and the adsorbent. To evaluate this interaction was used the

characteristic energy of adsorption (E) , calculated by fitting equation “7” , to the data. The

quantitative evaluation of the interaction of carbon dioxide was carried out with help of the

isosteric heat of adsorption ( isoq ), (Roque-Malherbe 2010). To calculate, isoq is as follows

37

Fig

ure

3.1

0.

Du

bin

in-R

ad

ush

kevitch

(D

R)

plo

t o

f th

e a

dso

rption

iso

the

rm o

f C

O2 o

n N

i-O

x-M

OF

at

27

3K

. T

he

fig

ure

sho

ws th

e C

O2 isoth

erm

adso

rptio

n,

with th

is d

ata

is p

ossib

le d

ete

rmin

e the

mic

ropo

rou

s v

olu

me

.

38

(Bering et al. 1972; Roque-Malherbe et al. 2011):

),()()( TEFGqiso (9)

Where: aa Nn ; E, is the adsorption energy; na, is the amount adsorbed; and Na, is the

maximum amount adsorbed. Thereafter, was obtained that the qiso(0.37)=1.16E.

The formerly described adsorption data indicated that the interaction of the carbon

dioxide molecule with the Ni-Ox-MOF is not strong, but is accepted for the adsorption of

carbon dioxide (Dunne et al. 1996; Roque-Malherbe et al. 2010; Roque-Malherbe, 2010;

Bacsik et al. 2010; Roque-Malherbe et al. 2011). It is in general acknowledged that this

physical adsorption process attach the carbon dioxide molecule inside the micropores, by

the influence of the dispersive forces and the attraction of the quadrupole interaction (Dunne

et al. 1996; Roque-Malherbe 2010).

3.3.3. DRIFTS study of the surface chemistry of the Ni-Ox-MOF applying carbon

dioxide as test molecule

Another significant application of carbon dioxide adsorption as a means for the

characterization of the surface chemistry of adsorbents is the study of the infrared spectra

of adsorbed carbon dioxide; since, it is a small weakly interacting probe molecule very

useful for the study of the acids and basics properties of solid surfaces (Lavalley et al.

1996; Zecchina et al. 1996; Knozinger et al. 1998; Bonelli et al. 2000).

The free carbon dioxide molecule show four fundamental vibration modes, that is:

the symmetric stretching, 1 (1338 cm1); the doubly degenerate bending vibration, a2 and

b2 (667 cm-1); and the asymmetric stretching vibration 3 (2349 cm-1) (Lavalley et al.

1996; Zecchina et al. 1996; Knozinger, et al. 1998; Bonelli et al. 2000). The 2 and

3 modes are infrared active, whereas 1 is only Raman active, in the free molecule

(Bonelli et al. 2000).

39

However, when a carbon dioxide molecule interacts with a surface it is not more a

free molecule, and its symmetry is lowered, as a result the 1 mode becomes infrared

active, and a small band is observed (Knozinger et al. 1998), whereas the other modes

undergo moderate changes in wave number (Bonelli et al. 2000).

The asymmetric stretching vibration, 3 , of the adsorbed carbon dioxide molecule

is observed at 2338 cm-1 (Figure 3.11). This peak corresponds to carbon dioxide physically

adsorbed inside the Ni-Ox-MOF (Roque-Malherbe et al. 2010). That is, the absorption

band observed at around 2338 cm-1 (Table 3.05) is the result of the attachment of the

carbon dioxide molecule by dispersive and electrostatic forces to the adsorption space

defined by the Ni-Ox-MOF micropores. The band at about 2324 cm-1 (Table 3.05) is

normally assigned to a combination band (Bonelli et al. 2000).

Table. 3.05. Resolved Peaks Positions of the DRIFTS Spectra of Carbon Dioxide

Adsorbed on the Tested Ni-Ox-MOF.

.

3.4. Magnetic study

With the term magnetochemistry (Carlin 1986; Kahn 1993; Bertotti 1998; Miessler

1998; Orchard 2003) is designed the study of the magnetic properties of materials. One

parameter that allows an assessment of the magnetic properties of materials is the

effective magnetic moment, eff)( . This parameter measured in Bohr magnetrons (μB)

Sample λ1 [cm-1] [%]1A λ2 [cm-1] [%]2A λ3[cm-1] [%]3A

Ni-Ox-MOF 2338 cm-1 24 2324 26 2362 50

40

Fig

ure

3.1

1.

DR

IFT

S s

pectr

um

CO

2 a

dso

rbed

on

Ni-O

x-M

OF

. A

) T

he

ba

nd

is n

orm

ally

assig

ned

to a

co

mb

ination

ban

d.

B)

The

ba

nd

ch

ara

cte

rizes th

e in

tera

ction

o

f th

e ca

rbon

d

ioxid

e m

ole

cu

le w

ith

th

e N

i2+ lo

ca

ted

in

th

e

fra

me

wo

rk o

f th

e N

i-O

x-M

OF

.

41

considering only the spin of the unpaired electrons of the magnetic centers present in the

material under study, is given by (Carlin 1986):

beff SS )1(0023.2 (10)

Where eff)( , is the effective magnetic moment; (μB) Bohr magnetrons; and 21S , for

one unpaired electron, 1S , for two unpaired electrons and so on. If was taking in count

the spin and orbital angular momentum in the Russell-Saunders coupling approximation;

then the effective magnetic moment )( , measured in Bohr magnetrons (μB) is calculated

with the following equation (Orchard 2003):

bLLSS )1()1(4 (11)

Where, S , has the meaning previously stated and L is the total orbital angular momentum.

The magnetization curves of the Ni-Ox-MOF measured with the help of the VSM is

reported in Figure 3.12. The calculation of the effective magnetic moment of the Ni-Ox-

MOF is, μeff = 4.9 μB.

The most significant structural characteristic in shaping the paramagnetic behavior

of a material is the number of unpaired electrons in the compound. In the synthesized

MOF, was found by Raman spectroscopy that nickel cations are coordinated in octahedral

(NiO6) (Kalyani et al. 2005) and distorted octahedral or pentacoordinated (NiO5) (Park et

al. 2006) in two valence states, specifically, Ni2+ and Ni3+. In practice Ni2+ in octahedral

coordination, in complexes, showed the following effective magnetic moment range, 2.9 <

μeff < 3.4 (Chaudhary et al. 2010). That is a low value in comparison to data obtained in this

research. If was considered the Russell-Saunders coupling (Lide 2002), with, 1S , and

3L , in this case the calculated effective magnetic moment yielded, μeff = 4.47, a value

approximate to those measured. However, this electronic configuration is highly

improbable, since in solids, L , is normally zero. Recently (Chaudhary et al. 2010), was

42

reported for a pentacoordinated Ni(II) complex a eff

value of b36.4 . That is, an amount

closer to those measured in this investigation. Finally, for Ni3+, the electronic configuration

is, [Ar] 3d7; then, 5.1S , then the spin only equation yields

bb 87.3)15.1(5.10023.2 . Thereafter, the magnetic study is consistent with the

Raman results.

43

Fig

ure

3.1

2.

Ma

gne

tiza

tio

n C

urv

es o

f N

i-O

x-M

OF

. T

he

fig

ure

sho

ws t

he

pa

ram

ag

ne

tic m

agn

etiza

tion

cu

rve

s o

f th

e N

i-O

x-

MO

F.

Th

e m

agn

etiza

tion

cu

rve

, m

ag

ne

tizatio

n (

M)

ve

rsu

s fie

ld s

tren

gth

(H

) w

as c

arr

ied

ou

t a

t ro

om

te

mpe

ratu

re (

30

0 K

).

44

Chapter Four

Conclusions

In the present work were synthesized 35 materials applying the center and

connection method. One of these materials the metal node was nickel and the organic

linker oxalic acid. This material was very sensible to the preparation conditions. However,

was obtained a consistently porous material. This material was thoroughly studied with

DRIFTS, Raman, TGA, precise XRD measurements, CO2 adsorption at 273 K and with a

VSM.

The most important inferences made through the examination of the DRIFTS and

RS spectra were: the bis-bidentate oxalate ligand was found in the frameworks of the

hydrated and dehydrated Ni-Ox-MOF; water was included in the pores of the as-

synthesized Ni-Ox-MOF; and it was released during dehydration at 75 oC; DMF was

present in the as-synthesized and dehydrated Ni-Ox-MOF and the nickel cations were

located in two coordination Ni2+ and Ni3+. The main issues that can be inferred from the

analysis of the TG profile were: the synthesized Ni-Ox-MOF was porous; in the as-

synthesized state the pores were filled by water and after water release DMF was

liberated, and subsequent to DMF release the material was decomposed. The conclusions

made with the help of the XRD data were: the Pawley decomposition of the XRD profile

indicated that, with high probability, the Ni-Ox-MOF crystallized in the monoclinic P2 / m

space group, with a framework made of layers and the Ni-Ox-MOF dehydrated at 75 oC

preserved its structure.

The most important matters deduced with the help of the adsorption data were: it

was confirmed that the synthesized Ni-Ox-MOF was porous after degassing; the estimated

pore volume was, 08.0MPW gcm3; the Ni-Ox-MOF after heating at 75 oC exhibited a

44

45

stable microscopic volume. That is, the tested material had a permanent porosity and the

adsorption field corresponded to a physical adsorption process.

The study by DRIFTS of CO2 adsorption demonstrated that: the Ni-Ox-MOF after

heating at 75 oC had space to accommodate carbon dioxide molecules. The measurement

of the sample effective magnetic moment confirmed that the Ni cations composing the

layer of the Ni-Ox-MOF were located in octahedral and pentacoordinated sites. Finally a

search in different databases confirms that the Ni-Ox-MOF is unique and none used in

other investigations.

After the study, was submitted an article of this research in collaboration with Dr.

Rolando Roque-Malherbe, Dr. Agustin Rios, Dr. Cesar Lozano, Dr. Luis Fuentes, Pedro

Fierro and Geydi Garcia. Actually Pedro Fierro is using the Ni-Ox-MOF, to create sensors

at University of Puerto Rico Mayaguez Campus, with a high chance of achieving patent

the sensor.

This research develops a platform for further development of MOF materials with

academic and industrial interests. The use of a cost effective carbon dioxide adsorption

methodology, by using non expensive chemical materials in the synthesis of MOF’s may

be attractive to industries and pharmaceuticals with high CO2 emissions, especially if this

porosity and magnetic framework could be used for industries as Sensor with electrostatic

interaction on CO2 molecules and the framework atoms.

46

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Appendix One

Instrumentation

A-1.01. X-Ray Diffraction (XRD). The equipment D8 Advance, Bruker AXS

showed in this picture, report important information for characterize the

sample.

58

59

A-1.02. Thermogravimetric Analysis (TGA). The TA Instrument, model TA, Q-500 is

used for characterize the material, because it allows knowing of the weight loss of the

sample, decomposition temperature and porosity of the material under studied.

60

A-1.03. Infrared Spectrometer (DRIFTS). The Diffuse reflectance infrared Fourier is a

Thermo Scientific Nicolet iS10 FTIR Spectrometer used for. It was used to

characterize the material.

61

A-1.04. RAMAN Spectometer (RS). The Renishaw Raman microspectrometer

RM2000 system, is used for characterization.

62

A-1.05. The quantachrome Autosorb-1 (AS 1). The equipment showed in this picture

was used to monitory the carbon dioxide adsorption and determine the pore volume.

63

A-1.06. Vibrating sample magnetometer (VSM). The equipment Lakeshore 7400 series,

showed in this picture was used to determine magnetic properties of the sample.

synthesis, structure, adsorption space and magnetic ... · figure 3.09. layers formed by oxalate...

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