1

MINISTRY OF EDUCATION

AND TRAINING

VIETNAM ACADEMY OF

SCIENCE AND TECHNOLOGY

GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY

……..….***…………

VU HOANG DUY

SYNTHESIS, STUDYING THE PROPERTIES

OF PHENYL RADICAL POLYMER FILM ORIONTED TO

USE AS METAL ION SENSOR

Major: Organic Chemistry

Code: 9.44.01.14

SUMMARY OF DOCTORAL THESIS

IN CHEMISTRY

HANOI - 2019

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The thesis has been completed at: Institute for Tropical

Technology - Graduate university science and technology -

Vietnam Academy of Science and Technology.

Science supervisor: 1. Assoc. Prof. Dr. Nguyen Tuan Dung

2. Prof. Dr. Tran Đai Lam

Reviewer 1: …………..

Reviewer 2: ………….

Reviewer 3: ……………

The thesis was defended at National level Council of Thesis

Assessment held at Graduate University of Science and Technology -

Vietnam Academy of Science and Technology at … on …

Thesis can be further referred at:

- The Library of Graduate University of Science and Technology

- National Library of Vietnam

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INTRODUCTION

1. The urgency of the thesis

Vietnam is in the process of industrialization, modernization,

many industrial parks and trade villages have sprung up, this has

released a large amount of inorganic and organic pollutants. Heavy

metals are considered to be very dangerous pollutants due to their high

toxicity and high bio-accumulation. Heavy metals like Cadmium,

Lead, Mercury, Silver are highly toxic, when accumulated in the

human body will cause diseases such as blood pressure, nervous

system, brain damage, liver, kidney, circulatory system, severe cases

can lead to death. Despite the state regulations on environmental

protection, there is no guarantee that heavy metals will be collected

and treated thoroughly and safely for the environment. Because of this,

environmental monitoring requires measuring instruments, probes

capable of detecting heavy metals at the trace level, thereby preventing

and treating environmental pollution. To contribute to the protection

of green, clean and beautiful living environment.

Conducting polymers are considered to be the next generation of

sensing materials being studied and used, and the trend is gradually

replacing older sensor materials by conductivity, selectivity and

responsiveness. Conducting polymers have been used to manufacture

converters to detect a wide range of gases such as NOx, CO, CO2,

NH3, solvents, alcohols, organic compounds and heavy metal ions.

The phenyl radical conducting polymers (polyaniline, poly(1.8-

diaminonaphthalene), poly(1.5-diaminonaphthalene)) containing rich

electron groups as -NH, -NH2 easily interact with heavy metal cations.

Thus, in order to use phenyl radical conducting polymers derivatives

as sensors, it is necessary to study the interaction between the

electrochemical activity, the structure of the polymer and the metal

cations. On this basis there are further studies such as improving the

sensitivity and selectivity of polymer films with heavy metal cations.

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From that point of view, the thesis aims to: "Synthesis, studying

properties of phenyl radical polymer film oriented to use as metal ion

sensor" as a research topic.

2. The objectives of the thesis

Fabrication of diaphragm sensing material based on phenyl

conductive polymer has stability and high sensitivity with heavy metal

cations, which is used to identify and analyze heavy metal traces in

water.

3. The main contents of the thesis

- Electrochemical polymerization of conductive polymer films

such as polyaniline, poly(1.8-diaminonaphthalene), poly(1.5-

diaminonaphthalene).

- Study characteristics of these polymer films: morphology,

chemical structure, electrochemical activity of conductive polymer

films.

- Study the sensitivity of these polymer films to heavy metal ions

such as Cd(II), Pb(II), Hg(II), Ag(I).

- Research on manufacturing sensing materials based on poly(1.5-

diaminonaphthalene) and carbon nanotubes: synthesis,

characterization and application in simultaneous analysis of Cd(II) and

Pb(II) ions.

CHAPTER 1. OVERVIEW

1.1. Conducting polymer

Conducting polymers are organic polymeric compounds capable

of conducting electricity through the π-conjugate structure. Example

polyaniline (PANi), polypyrrole (PPy), polythiophene (PTh), etc.

Conducting polymers are classified into three main categories:

electron-conducting polymers, oxidation-reducing polymers, and ion-

exchange polymers.

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There are two methods of polymer synthesis: chemical methods

and electrochemical methods.

The conducting polymer satisfies the conditions of a chemical and

biological sensing material so it is being studied and applied in this

field, particularly the field of ionic sensors.

1.2. Conducting phenyl radical polymer

Conducting phenyl radical polymer are conducting polymers in

the main chain containing phenyl rings. The famous of that is PANi,

the derivatives of polydiaminonaphthalen have also recently begun to

be studied for their special properties due to their -NH2 free-radical

function in the molecule.

1.3. Methods for producing conductive polymer films

At present, there are a number of methods for making polymer

films, such as dip-coating, centrifugation, Langmuir-Blodgett method,

vapor phase condensation, drip method and electrochemical

deposition. Only the electrochemical deposition method, the drip

method, is more suitable for making polymer films. Therefore, in the

thesis, drip coating and electrochemical deposition will be applied to

investigate the formation of conductive polymer films as well as the

conductive polymer composite films - nanotubes as ion sensors.

1.4. Heavy metals, methods for analysis and application of

conductive polymer films for heavy metal analysis

1.4.1. Heavy metals

Heavy metals are natural elements with a density greater than 5

g/cm3. Many heavy metals are used in industry, agriculture, health and

science, resulting in emissions to the environment, increasing the risk

of their potential impact on human health and ecosystems. People with

heavy metals have decreased memory, reduced the ability to

synthesize hemoglobin leading to anemia, lung, stomach and

neurologic causes. Causing harms to fertility, causing miscarriage,

degeneration of the breed.

1.4.2. Methods for analysis of heavy metals

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For the determination of heavy metal ions, there are currently

several methods that can be identified in trace form. Examples include

atomic emission spectroscopy (AES), atomic absorption spectrometry

(AAS), Inductively Coupled Plasma emission Mass Spectrometry

(ICP-MS), and electrochemical methods.

1.4.3. Conducting polymers for heavy metal ion analysis

Polyaniline, poly(1.8-diaminonaphthalene) (poly(1.8-DAN)) and

poly(1.5-diaminonaphthalene)(poly(1.5-DAN)) are electrochemically

synthesized on glassy carbon electrode (GCE) or platinum electrode.

The above polymer films can be used to analyze the trace of heavy

metal ions such as Cd(II), Pb(II), Hg(II), Ag(I).

In order to improve the sensitivity of the conductive polymer film

to the determination of heavy metal ions, many studies have developed

composite materials between the conductive polymer with carbon

nanotubes (CNTs), graphene (Gr), graphene oxide (GO),

ferromagnetic nano, etc.

1.5. Composite materials conducting polymer - carbon nanotubes

Composite of conducting polymer - carbon nanotubes (CNTs)

materials include conductive polymers and carbon nanotubes. CNTs

has a large surface area, good conductivity, promising ability will

increase the sensitivity of the sensor, especially the ion sensor.

CHAPTER 2. EXPERIMENTAL AND METHOD STUDY

2.1. Raw materials, chemicals

Monomers: 1.5-diaminonaphthalene (1.5-DAN), 1.8-diamino-

naphthalene (1.8-DAN) and aniline (ANi) are used to synthesize

polymer films. Other chemicals used in the experiment are pure

chemicals of Merck (Germany). Multi-walled carbon nanotubes

(MWCNT), Nafion® 5% for study of conducting polymer composites

- MWCNT. Glass coal electrodes, integrated platinum electrode are

used for research experiments. The Institute of Tropical Technology's

Autolab/ PGSTAT30 multifunctional electrochemical is used for thin

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film deposition, study on electrochemical characterization,

determination of metal cations Cd(II), Pb(II), Hg(II), Ag(I).

2.2. Experimental method

2.2.1. Electrosynthersis polymer thin fims and specialty research

Electrosynthersis three polymer fims: PANi, poly(1.5-DAN),

poly(1.8-DAN) by cyclic voltammetry (CV) scanning.

Research on thin-film properties of synthesized films: Study on

electrochemical deposition of polymer films by CV scanning in

electrolyte solution.

Study of polymer structure by infrared spectra. Surface

morphology studies using field emission scanning electron

microscopy (FE-SEM).

2.2.2. Study on cationic sensitivity

Synthetic polymer films were scanned for CV, scanning square

wave voltammetry (ASW) before being stripping in solutions

containing cations (Cd(II), Pb(II), Hg(II), Ag(I)) have a concentration

of 10-2 M to 10-3 M for 30 minutes, at room temperature.

Use ASW technique to dissolve absorbent metal on polymer film

coated on electrode to detect metal ions.

2.2.3. Research on making composed poly(1.5-DAN)/ MWCNT / Pt

sensor film to detected both Cd(II) and Pb(II)

Fabrication of MWCNT film on platinum electrode followed by

poly(1.5-DAN) polymerization on top.

Survey of influencing factors: Study thickness films through the

number of CV synthetic; Study the enrichment potential from -1.4 to

- 0.9 V; Study electrochemical enrichment time from 250 to 600

seconds; Study the effects of other ions.

Analysis determines Cd(II) and Pb(II) at concentrations of 4 to 150

μgL-1, thus making the basis for the determination of sensitivity;

Determination of detection limits;

Application of poly(1.5-DAN)/MWCNT/Pt film determines

Cd(II), Pb(II) in Nhue River.

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2.3. Research methods

The thesis uses the following basic research methods:

Studies on the polymerization of PANi, poly(1.5-DAN), poly(1.8-

DAN) by electrochemical characterization of polymer films by CV,

SWV.

Studies on cation sensitivity, electrochemical enrichment, metal

dissolution on cathode by SWV method.

Studies on the structure of monomers, polymers by Fourier

transform infrared spectroscopy (FT-IR).

Studies the structure of polymers, MWCNT and composite film

by Raman scattering.

Research on morphology of polymeric structures and thin film

surfaces, composite film by scanning electron microscope.

CHAPTER 3. RESULTS AND DISCUSSION

3.1. Synthetic and characterization of polyanilines

3.1.1. Synthetic polyaniline films

Polyaniline is synthesized on a GC electrode in 0.5 M H2SO4 and

0.1 M aniline, by cyclic voltometry (CV). The results are shown in

figure 3.1. Right from the first round, PANi's CV synthesis lines have

two pairs of redox peaks at +0.18V/+0.02V; +0.48V/+0.42V and

+0.78V/+0.68V as shown in figure 3.1-A.

Figure 3.1. The CV of PANi synthesis in 0.5 M H2SO4 and

0.1 M ANi with (A) two first scans, and (B) 15 scans.

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As the number of sweeps increases, the redox strength increases

with the sweep cycles (figure 3.1-B), indicating that the development

of the PANi films is conductive on the electrode surface.

3.1.2. Characterization of polyaniline films

3.1.2.1. Characteristics of CV: The CV

spectral characteristics of PANi when

scanning the films in 0.1M H2SO4 obtained

as shown in figure 3.3 is very clearly the

typical redox pulses at +0.24V and -0.05 V.

The intensity of the reverse decay

oxidation is relatively high and stable,

indicating that the films has a good

electrochemical activity.

3.1.2.2. Infrared spectrum FT-IR.

The infrared spectrum of PANi and aniline is shown in figure 3.4.

In the range of 4000 to 2000 cm-1, the aniline has absorption peaks

at 3426 cm-1 and 3354 cm-1, which characterizes the covalent bonding

of the C-NH2 group. At the same time, PANi spectra exhibit a wide

spectrum at 3257 cm-1 corresponding to the valence range of the N-H

bond, indicating the presence of a second-order amine group. Thus,

the process of the PANi polymerization takes place, via the reaction

of the NH2 group of the aniline with the para position of the benzene

ring.

Figure 3.3. The CV recorded

of PANi film in aqueous

solution of H2SO4 0.1M

Figure 3.4. FT-IR spectrum of (A) Aniline; (B) PANi film

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The valence range of the C-H bond of the infrared benzene ring

at the ~3000 cm-1, on the infrared spectrum of the aniline, shows the

adsorption peaks at 3214, 3071, 3036 cm-1, and of PANi as peaks weak

at 3036 and 2925 cm-1.

In the range of number wave 2000 to 500 cm-1, the infrared spectra

of the anilines appear infrared absorption peaks at 1620, 1601, 1499,

and 1467 cm-1 waves that characterize the frame oscillations of the

nucleus of benzene core (vibrational covalent bonding C-C). The peak

1276 cm-1, 1207 cm-1 features the oscillation of the C-N bond between

the benzene ring and the nitrogen atom of the amino group. In the case

of PANi, the characteristic absorption peaks at 1594 and 1509 cm-1,

corresponding to the quinoic (Q) and benzoic (B) ring oscillations,

show that the PANi is synthesized at oxidation state (conductance

state). It has also been observed that the peak at 1374 cm-1 is

characterized by Q=N-B boundary oscillation, at 1302 cm-1

corresponding to the perturbation of the C-N-C bond.

The C-H bond in the aniline absorbs infrared at 995, 881, 752 and

692 cm-1 waves, characteristic for off-plane oscillations, while the

peak at 1174, 1153, and 1311 cm-1 for oscillation on the same plane.

PANi variant of the flat surface oscillator exhibits absorption peaks at

825 and 643 cm-1, on the plane at 1161 cm-1. Compared to previously

published literature, PANi's infrared peaks are perfectly matched,

indicating that the PANi films has been successfully synthesized.

3.1.2.3. Characteristic and morphology of PANi film

PANi film was scanned

electronically by Field Emission

- Scanning Electron Microscope

(FE-SEM) and presented in

figure 3.5. The results showed

that PANi synthesized in the

form of fibers, not aligned

closely together.

Figure 3.5. FE-SEM of PANi film with

magnification: a) 10,000 times, b) 100,000

times

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3.1.3. Study sensitivity heavy metal ions of PANi

Figure 3.6 is a result of square wave voltammetry (SWV) before

and after stripping PANi film electrodes with 5 cycles of CV synthesis

in solution containing Cd(II), Pb(II) Hg(II) and Ag(I) at 10-2, 10-3 M

for 30 minutes, at room temperature. In figure 3.6-a no silver oxidation

peaks appears, indicating no

silver ion absorption on the

PANi film.

In the case of Hg(II) (fig.

3.6-b), the weak peak appears at

a voltage value of 0.18 V, which

is the oxidation peak of the

mercury adsorbed on the PANi

film. Unlike silver and mercury,

Cd(II) and Pb(II) obtain very

sharp and strong oxidation

signals at the voltage values of

0.67 V and -0.51V respectively

(fig. 3.6-c, d). Thus PANi film

have different affinities with the cationic study.

3.2. Synthesis and characterization of poly (1.8-DAN)

3.2.1. Synthetic poly (1.8-DAN)

Poly(1.8-DAN) film were

synthesized on GC electrodes by CV

method as shown in Figure 3.9.

In the first CV cycle, the line starts

to rise from the +0.45V, with two

monomer oxidation peaks at +0.53V and

+0.68 V. From the 3rd CV onwards, the

monomer peak no longer exists but only

the peaks of the polymer at +0,34 and +

Figure 3.6. The SWV lines were recorded on

GC/PANi electrodes before and after 30

minutes in aqueous solutions containing (a)

Ag (I) 10-2 M; (b) Hg (II) 10-2 M; (c) Cd (II)

10-2 M, 10-3 M and (d) Pb (II) 10-2 M, 10-3 M.

Figure 3.9. Spectrophotometer

of poly(1.8-DAN) in HClO4 1M

and 1.8-DAN 5mM solutions.

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0,19V, indicating that the poly (1,8-

DAN) has been formed on the electrode

surface.

3.2.2. Study characteristic of poly (1.8-

DAN)

3.2.2.1. Electrolytic activity of poly(1.8-

DAN) film:

It can be observed that the

characteristic redox peaks of poly (1.8-

DAN) films synthesized 8 potential scans at +0.41 V/+ 0.19 V (Figure

3.11), however, it is not clear, indicating that the membrane has a very

limited electrochemical activity.

3.2.2.2. Infrared spectrum FT-IR

The infrared spectrum of poly(1.8-DAN) and 1.8-DAN are shown

in figure 3.12.

In the range of 4000 to 2000 cm-1, the infrared spectra of 1.8-DAN

monomers have absorption peaks at 3413, 3320 and 3223 cm-1, which

characterize the chemo-oscillation of the -NH2 group. The infrared

spectrum of poly(1.8-DAN) appeared a wide absorption peak at 3420

cm-1 which characterized the valence range of the N-H bond,

demonstrating the polymerization of the polymer. Unlike the PANi

case, the absorption peak at 3239 cm-1 was observed on the infrared

spectrum of poly(1.8-DAN), which is related to the valence range of

the -NH2 group. Oscillation deformation of the functional group -NH2

Figure 3.11. The CV line of poly(1.8-

DAN) film in HClO4 0.1M solution.

Figure 3.12. Infrared absorption of 1.8-DAN (A) and of poly (1.8-DAN) (B)

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is shown with the absorption peak at the 1616 cm-1 wave on the

monomer spectrum and at 1626 cm-1 on the polymer spectrum. This

proves that in the 1.8-DAN molecule there is one -NH2 group involved

in the polymerization, one group in the free state. In addition, it is

observed that the adsorption peaks at 3033 cm-1 of the spectrum of the

monomer, and at the 2977 cm-1 wavelength of the polymer spectrum

are the covalent vibrations of the C-H bond.

In the range of 2000 to 500 cm-1, the peaks are absorbed at wave

number 1585, 1519, 1425 cm-1 on the infrared spectrum of 1.8-DAN,

and the absorption peaks at wave number 1584, 1416 cm-1 on the

infrared spectrum of poly(1.8-DAN) are characterizes the oscillation

of the C=C bond within the aromatic naphthalene. Out-of-plane

chemotaxis of the C-H bond is characterized by absorption peaks at

wave number 925, 868, 768 cm-1 on the spectrum of the monomer, and

at 927, 816, 756 cm-1 on the spectrum of the polymer. In this area, 1.8

-DAN polymerization can be observed through the appearance of

infrared absorption peaks at 1277 cm-1, which characterizes the

valence range of the bond. The oscillate of covalent of the chemistry

of the C-N bond in the first-order amine group is shown in the infrared

spectrum of the monomer at 1361, 1298 cm-1, on the polymer spectrum

at 1391 cm-1. Thus, in the macromolecular circuit (1.8-DAN), there is

still a free -NH2 functional group. Another sign that the polymerization

has been successful is the appearance of a wide absorption peak at

1081 cm-1, which is characterized by the presence of a ClO4- is anion-

doped in the membrane.

Compared to previously published documents, the peaks

adsorption of poly(1.8-DAN) are perfectly matched. This proves

successful synthesis of poly(1.8-DAN). Thus poly(1.8-DAN)

polymerization may occur according to the steps shown in figure 3.14.

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3.2.2.3. Morphological analysis of structure:

Figure 3.15 presents the FE-

SEM image of the face poly(1.8-

DAN) film after 1 and 8 CV cycles.

The results showed that the

poly(1.8-DAN) formed had a

particle size of 50-100 nm in the

first 1 cycles, then poly(1.8-DAN)

covered the electrode surface, non-

flat film surface, not fiber as PANi.

3.2.3.Study the sensities metal ionic

poly(1.8-DAN)

In Figures 3.16-a and 3.16-b the

cadmium and lead oxidation peaks

very weakly on the poly(1.8-DAN)

film at -0.713V and -0.33V.

Meanwhile Ag(I) and Hg(II)

obtained a peak very strong and

strong oxidation signal at + 0.153 V

and + 0.38 V respectively. Thus

poly(1.8-DAN) films have different

Figure 3.16. The SWV lines recorded of

poly(1.8-DAN) on GC electrode before

and after keepping for 30 minutes in

aqueous solutions containing: (a) Cd (II)

10-2 M, (b) Pb ) 10-2 M, (c) Hg (II) 10-2 M

and (d) Ag (I) 10-2 M.

Figure 3.15. FE-SEM image of surface of

poly(1.8-DAN) synthesized after 1cycles

(a), and 8 cycles (b).

Figure 3.14. Diagram of polyelectrolyte polymerization poly(1.8-DAN)

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affinities with cationic studies. The selective adsorption of poly(1.8-

DAN) may be related to molecular structure, geometry of poly(1.8-

DAN) and physical and chemical characteristics of investigated ions.

3.3. Synthesis and characterization

of poly (1.5-DAN)

3.3.1. Synthetic poly (1.5-DAN)

Figure 3.20 is a poly(1.5-DAN)

electrochemical polymerization on a

GC electrode using CV scanning. In

the first scan, one oxidation peak at

+0.66 V appeared. From the second

scan, two pairs redox of poly(1.5-

DAN) appeared at values of + 0.34V/+ 0.28 V and +0.48V/+ 0.42 V.

In terms of the poly(1.5-DAN) intensity is higher than poly(1.8-DAN).

A lot of this shows that poly(1,5-DAN) films have far better

conductivity than poly(1.8-DAN) films.

3.3.2. Study characteristic of poly(1,5-DAN)

3.3.2.1. Electrolytic activity of

poly(1.5-DAN)

Figure 3.21 is the result obtained

when CV scanning poly(1.5-DAN)

films in HCLO4 0.1M. The films have

good electrochemical activity, the pair

of oxidation peaks reduce clarity and

high intensity. This may be related to

the structure of poly(1.5-DAN), the

monomers may be arranged in a more rigid poly(1.8-DAN) order.

3.3.2.2. Infrared spectrum FT-IR

Results of the infrared spectrum analysis of poly(1.5-DAN) and

1.5-DAN are shown in Figure 3.22.

Figure 3.20. The CV lines synthetic

poly(1.5-DAN) in HClO4 1 M and

1.5-DAN 5 mM

Figure 3.21. The CV line of poly(1.5-

DAN) in 0.1M HClO4 solution.

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The 1.5-DAN infrared spectra

have absorptive peaks in the range

of 3420 to 3300 cm-1 that

characterize the fluctuations of the

N-H bond in the -NH2 group. This

bond in the poly(1.5-DAN)

molecule shows the absorption peak

at 3422 cm-1, in addition on the

infrared spectra of the polymer, the

fluctuating the N-H of the second

amine, demonstrating that the

polymerization took place in an

amine group, the other group being

in the free state.

In the range of 2000 to 500 cm-

1, the absorption peaks at 1581,

1458, 1403 cm-1 on the spectrum of the monomer and at 1626, 1582,

1521, 1457 cm-1 are on the polymer spectrum, characterizing the

covalent vibration of the C = C bond within naphthalene.

The covalent valence of the C-N (1st amine) linkage in the 1.5-

DAN molecule exhibits absorption peaks at 1356 and 1300 cm-1, in

the poly(1.5-DAN) molecule as the peaks at 1340 and 1271 cm-1. In

Figure 3.22. Infrared spectrum of (A) 1.5-DAN and (B) poly (1.5-DAN).

Figure 3.24. Diagram of

electrosynthesise polymerization

poly(1.5-DAN)

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addition, the adsorption peaks at 1196 and 1183 cm-1 show the

covalent bond of the C-N bond to the second-order amine group.

Successful completion of the absorption peak at 1108 cm-1,

characterized by the oscillation of the ClO4-.

The characteristic peaks shown illustrate the formation of new

conjugates of 1.5-DAN to poly(1.5-DAN). These peaks are perfectly

suited to published studies. On this basis, poly(1.5-DAN)

electrochemical polymerization can take place according to the

reactions shown in Figure 3.24.

3.3.2.3. Structural morphology:

FE-SEM of the poly(1.5-DAN)

film (figure 3.25) shows that in the

first cycle synthetic surface of

electrode is covered with a small

round particle (figure 3.25-a).

To the 10th synthetic cycles

(figure 3.25-b), the polymeric film develops to from woven yarns that

form a series of hollows distributed fairly evenly across the surface of

the electrode.

3.3.3. Study the sensities heavy metal ion of poly(1.5-DAN)

Figure 3.26 is the result of the

soluble of heavy metal cation

adsorbed on poly(1.5-DAN)

films. In contrast to the results

obtained in poly(1.8-DAN),

poly(1.5-DAN) adsorbed

strongly Pb(II) and Cd(II), while

with Ag(I) and Hg(II) does not

obtain soluble signal. This may be

due to the molecular structure of

two different polymers, resulting

Figure 3.26. The SWV lines were recorded

on GC/poly(1.5-DAN) electrode before and

after 30 minutes in aqueous solutions

containing: (a) Pb(II) 10-3 M, (b) Cd(II) 10-3

M, (c) Ag(I) 10-2 M and (d) Hg(II) 10-2 M.

Figure 3.25. The FE-SEM image of

poly(1.5-DAN) film after 1 cycle (a) and

10 sweep cycles (b).

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in complex interactions with different metal cations.

3.4. Study on development of poly(1.5-DAN)/MWCNT

interpenetrated film for simultaneous ions Pb(II) and Cd(II)

analysis

3.4.1. Synthesis interpenetrated poly(1.5-DAN)/MWCNT sensing

film

The platin integrate electrode working is coated MWCNT by

drop solution containing MWCNT dispersion in ethanol nafion 1.25%.

Following electrosynthesised poly(1.5-DAN) by multi-cycle CV on

the surface. CV scane range from -0.15V to + 0.95 V (according to

calomen electrodes), scanning speed 50 mVs-1, results are shown in

Figure 3.27. Poly(1.5-DAN) was also synthesized on uncoated

platinum electrode under the same conditions for comparison.

3.4.2. The electrochemical properties of the

poly(1.5-DAN)/MWCNT film

Poly(1.5-DAN)/MWCNT film was CV

scaned in 0.1M acetate buffer solution, the

result shows the two typical redox pairs of

poly(1.5-DAN) (Figure 3.28).

3.4.3. Structural properties of poly(1.5-

DAN)/MWCNT film

3.4.3.1. Raman spectra of poly(1.5-

DAN)/MWCNT film

Figure 3.27. (A) The CV lines of poly(1.5-DAN) on the Pt / MWCNT

electrode (A); (B) The fifth CV lines of poly(1.5-DAN) on Pt electrode (b),

and Pt/MWCNT electrode (b).

Figure 3.28. The CV lines in

0.1M acetate buffer of poly(1.5-

DAN)/ MWCNT/ Pt and

MWCNT /Pt

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Poly(1.5-DAN)/

MWCNT films were

electrosynthesized in 2,

10, 25 CV cycles and

MWCNT, poly(1.5-

DAN) were analyzed by

Raman spectroscopy,

resulting in Figure 3.30.

The Raman spectra of

MWCNT show very

clearly the characteristic

oscillations of carbon

nanotubes: the D-band peak at 1357 cm-1, the G-band at 1586 cm-1,

and the secondary D-band at 2713 cm-1. Raman spectra of poly (1.5-

DAN) represented the peak characteristic of the naphthalene ring

oscillation at the 1586 cm-1 wave; 1518 cm-1 and 1453 cm-1, also

observed at the 1341 cm-1 wave form that characterizes the C-N

bonding of the polaron (Figure 3.30-e).

Strong intensity peaks at 1586 and 1341 cm-1 are closely related to

the D-band and G-band peak of carbon nanotubes (Figure 3.30-a).

In case of poly(1.5-DAN) thin films, synthesized with two

scanning cycles, the Raman spectrum (Fig. 3.30-b) can be observed at

2713 cm-1 of MWCNT. There are also 2 peaks at 1518 and 1351 cm-1,

showing the structure of both MWCNT and poly(1.5-DAN). Although

the peak peaks at 1518 and 1453 cm-1 were not observed, due to their

low strength and very thin polymer film, it is possible to confirm that

the polymers formed here are based on The intensity of the peak at

1586 cm-1 compared to the peak at 2713 cm-1 is much stronger than

that of the pure MWCNT. As the polymer film thickens (with

increasing number of sweep cycles), the secondary D-band of

MWCNT gradually decreases, and the weakest of poly (1.5-DAN) at

1518 and 1453 cm -1 increases markedly (Figure 3.30-c, d). Thus, the

Fingure 3.30. The Raman spectra off MWCNT

(a), poly(1.5-DAN)/ MWCNT with 2 CV cycles

(b), 10 cycles (c), and 25 cycles (d) and poly(1.5-

DAN) (e).

18

polymerization (1,5-DAN) took place

on the MWCNT film and increasingly

thickened over the sweep cycle.

3.4.3.2. Study morphological

structure: The MWCNT, poly(1.5-

DAN) and poly(1.5-DAN)/MWCNT

on electrodes were analyzed for field

emission scanning electron

microscopy (FE-SEM) and presented

in Figure 3.31. The results showed

that poly(1.5-DAN) formed and

covered MWCNT fibers, giving a

high degree of porosity to the

electrode surface. As the number of

sweep cycles increases, poly(1.5-

DAN) thicker than the spongy will

decrease.

3.4.4. Sensitivity analysis of Pb(II)

and Cd(II) ions

Poly(1.5-DAN)/MWCNT

microplate coatings were investigated

sensitivity ions Pt(II) and Cd(II) by an

analytical dissolve the anot by square

wave technique voltammetry

(SWASV) method (Figure 3.32).

The results showed that peak

dissolved Cadmium and lead of the

poly(1.5-DAN)/MWCNT electrode

was higher than the MWCNT coated

electrode and bare electrode.

3.4.5. Factors affecting Pb(II) and

Cd(II) ion sensitivity

Figure 3.31. The FE-SEM images of: a)

MWCNT; b) poly (1,5-DAN); c) poly

(1,5-DAN)/MWCNT synthesized with

10 cycles and d) poly (1,5-DAN) /

MWCNT synthesized with 25 cycles.

Figure 3.32. The SWV lines analyzes

Cd(II) and Pb(II) at 10-5 M of Pt,

MWCNT/ Pt and poly(1.5-DAN)

/MWCNT / Pt electrodes. Potential

gain -1.2 V, enrichment time 420

seconds, acetate buffer 0,1 M pH = 4.5.

Figure 3.33. Influence of number scans

CV to Cd and Pb dissolution intensity of

poly (1,5-DAN) / MWCNT.

19

3.4.5.1. Results of the round-trip

investigations:

Poly(1.5-DAN)/ MWCNT films

with different CV scanning cycles

showed that the composed film

with 5 cycles CV for the highest

metal dissolved peak (Figure 3.33).

3.4.5.2. Effect of enrichment time:

Figure 3.34 is the results of the

enrichment time of poly(1.5-

DAN)/MWCNT at different time.

Results show that in the range of

400 - 450 seconds (select 420

seconds) is the optimal time. If the

enrichment time is over 450

seconds, the line enrichment time is

almost horizontal, slowly

increasing.

3.4.5.3. Effect of enrichment

potential:

Poly(1.5-DAN)/MWCNT/Pt

synthesized with 5 cycles CV, was

investigated with different

enrichment potential from -1.4 to -

0.9 V, with a time of 420 seconds,

Pb and Cd peak dissolved peak

results show that the most suitable

enrichment for detecting Cd(II)

and Pb(II) is -1.2 V (Figure 3.35).

3.4.6. Calibration of Pb(II) and

Cd(II) analysis.

0

5

10

15

20

25

30

35

-1.4 -1.2 -1 -0.8

I(µ

A)

E(V)

Figure 3.35. Results of effect of potential

enrichment Cd(II) and Pb(II) of poly(1.5-

DAN) / MWCNT / Pt

Pb(II)

Cd(II)

Figure 3.34. Effect of enrichment time

on detection of Pb(II) and Cd II) ion of

poly (1.5-DAN)/ MWCNT / Pt

Figure 3.36. The SWASV lines of

poly(1.5-DAN)/MWCNT when analyzing

determine Cd(II) and Pb(II) ions at

different concentrations

20

Figure 3.36 shows the determination of Cd(II) and Pb(II) of

poly(1.5-DAN)/ MWCNT/ Pt films. Input samples have a

concentration from 4 to 150μgL-1.

3.4.6.1. Determining the Sensitivity Cd(II) of the Sensor: From the

results shown in Figure 3.36, determine the top solubility peak (Ip) at

the input sample concentrations (C) as the basis for the calculation.

The sensitivity of poly(1.5-DAN)/ MWCNT with Cd(II) was 0.496

nALμg-1.

3.4.6.2. Determine the Pb (II) sensitivity of the sensor

Similarly, the sensitivity of poly(1.5-DAN)/ MWCNT to Pb(II)

films was 0.519 nALμg-1.

3.4.6.3. Calculates the detection limit of the Cd(II) ion of the sensor

From the relationship between the sample concentration (C) and

the peak intensity (Ip) obtained in Figure 3.36, we construct the

calibration curve of Cd(II) analysis standard

(Figure 3.37). Poly(1.5-DAN)/ MWCNT-

Cd(II) form Y = 0.516*C - 0.746 with the

squared correlation R2 = 0.989. From the

linear equation the detection of limit (LOD)

Poly (1.5-DAN)/ MWCNT - Cd(II) = 3.2

(μgL-1).

3.4.6.4. Calculates the detection limit of the

Pb(II) ion of the sensor

Similarly, we have calibration curve of

Pb(II) of Poly(1.5-DAN)/ MWCNT-Pb(II)

equation for Y = 0.555*C + 0.954 with the

squared coefficient R2 = 0.989 (Figure

3.38). Calculate the LOD of poly(1.5-

DAN)/ MWCNT- Pb(II) = 2.1 (μgL-1).

The durability of the poly(1.5-

DAN)/MWCNT/Pt sensor was tested after

8 weeks of storage at room temperature in

Figure 3.37. The calibration

of Cd(II) ion

Figure 3.38. The calibration of

Pb(II) ion

21

dry air, room temperature, and the results showed that the sensor

remained good response to Cd(II) and Pb(II) with a decrease of 5.8%

with Cd(II) and 4.1% with Pb(II).

3.4.6.5. Effects of other ions:

When determining ions Cd(II) and Pb(II) with poly(1.5-DAN)/

MWCNT composed film, there are other ions such as Na+, Ca2+, Fe2+,

Bi3+, Al3+, Cu2+, Cl-, Br-, SO42-, …, Hg2+. The results showed that the

deviation of the analytical signal Pb and Cd compared to the absence

of ions did not have a significant effect on the analytical signal Pb and

Cd. Particularly, Bi3+ ion exerts a strong influence on the signal, with

a concentration of up to 5 times, which increases the peak intensity to

20%.

3.4.7. Application of poly(1,5-DAN)/ MWCNT analysis of Cd(II) and

Pb(II) in wastewater

The poly(1.5-DAN)/ MWCNT/ Pt sensor is manufactured using a

combination of a five CV cycles, a sensor for Cd(II) and Pb(II)

analysis in the Nhue River - Hanoi. Results of SWASV water samples

were compared with the AAS method. Due to the low concentration

of Cd(II) and Pb(II), we have used standard method to analyze. The

standard solutions Cd(II) and Pb(II) were added for the two samples

of 40 and 70 μgL-1. The analysis showed that with Cd(II) the sensor

yielded 42.5 and 68.0 μgL-1 while the AAS method yielded 40.5 and

69.4 μgL-1. For Pb(II) the results of the sensor analysis gave 38.8 and

73.7 μgL-1 results, while the AAS method yielded 41 and 70.6 μgL-1

results. The analysis results show that the poly(1.5-DAN)/

MWCNT/Pt sensor is less affected by the components present in the

sample, and the results are consistent with the results of the AAS

analysis. Relative standard deviation (RSD) shows a precision of ≤

2.5% with Cd(II) and with Pb(II) of ≤ 3.2%.

22

CONCLUDE

From the research results of the dissertation, the thesis draws some

main conclusions as follows:

1. Electrochemical synthesis of phenyl as PANi, poly(1.8-DAN)

and poly(1.5-DAN), by multi-cycle scanning, and investigating

sensitivity to certain heavy metal ions, the results are as follows:

- PANi synthesized in water environment containing 0.1M and

0.5M H2SO4 electrolyte, the results of the analysis showed that the

PANi film formation was quite porous on the electrode surface. PANi

films exhibit complexity with Cd(II) and Pb(II) ions, with less

complex Hg (II) ions, and do not form complexes with Ag(I) ions.

- Poly(1.8-DAN) synthesized in water containing 1.8-DAN 5mM

and 1M hydrochloric HClO4, the results of infrared analysis showed

that the polymerization was successful, however The results of

electrochemical measurements show that poly(1.8-DAN) films have a

much lower electrochemical activity than PANi films. Poly(1.8-DAN)

films form complexes with Hg(II) and Ag(I) but form complexes with

Cd(II) and Pb(II) ions.

-Similar to poly(1.8-DAN), poly(1.5-DAN) films are polymerized

in water using HClO4 as the electrolyte. CV results show that the

poly(1.5-DAN) polymerization process is much easier than poly(1.8-

DAN), highly electrochemical and stable. Poly(1.5-DAN) films form

very well with Cd(II) and Pb(II) ions, but do not form complexes with

Ag(I) and Hg(II) ions.

2. The composite membrane of poly(1.5-DAN) with multi-walled

carbon nanotubes (MWCNT) on platinum integrated microwaves was

studied. The pre-coated MWCNT layer on Pt and poly(1.5-DAN)

substrates was Electrochemical Coating to MWCNT. The results of

Raman scattering and scanning electron microscopy showed that the

23

synthesis was successful, CV investigations showed that MWCNT

significantly increased the electrochemical activity of poly(1.5-DAN).

3. The simultaneous analysis of Pb(II) and Cd(II) of poly(1.5-DAN)/

MWCNT/Pt in aqueous solutions by Square Wave Anodic Stripping

Voltammetry. The results show that the optimum film synthesis

conditions are 5 cycles of scanning, the best conditions of -1,2V

enrichment and 420 seconds of enrichment. Benchmarking the

simultaneous analysis of Pb (II) and Cd(II) ions is linear in the range

of 4 μgL-1 to 150 μL-1, with a regression coefficient of 0.989 for Cd(II)

and Pb(II). The poly(1,5-DAN)/MWCNT/Pt films have a sensitivity

to Pb(II) of 0.519 nALμg-1, for Cd(II) 0.496 nALμg-1. The detection

limits for Pb(II) and Cd(II) were 2.1 and 3.2 μgL-1 respectively. The

presence of Na+, Ca2+, Zn2+, Fe2+, Bi3+, Al3+, Cu2+, Cl-, Br-, SO4

2- almost

did not affect the Cd(II) and Pb(II) analysis signals. Only for Bi3+ ion

with a concentration of 5 times was to made increased the signal to

20%.

4. The poly(1.5-DAN)/MWCNT/Pt electrodes were tested

simultaneously with Cd(II) and Pb(II) in the water sample (Nhue river

water) by standard addition and control AAS. The results showed that

the standard deviation of the measurement for Cd(II) ≤ 2.5% and for

Pb(II) had a standard deviation ≤ 3.2%.

THE NEW CONTRIBUTION OF THE THESIS

1. The conducting phenyl polymer as polyaniline, poly(1.8-

diaminonaphthalene) and poly(1.5-diaminonaphtalene), all have

affinity for heavy metal cations through "give-receive" interaction

with atoms nitrogen is rich in electrons, but the degree of interaction

varies greatly depending on the nature of the cations and the structure

of each polymer. Specifically PANi did not absorb Ag(I), weakly

absorbed with Hg(II) and strongly absorbed Cd(II), Pb(II). Poly(1.8-

DAN) adsorbed Hg(II) and Ag(I), but weakly absorbed Cd(II) and

24

Pb(II). Poly(1.5-DAN) adsorbed Ag(I) and Hg(II), but strongly

adsorbed Cd(II) and Pb(II). This makes the polymer selective for use

in the manufacture of metal ion sensors.

2. Microelectrode integrated MWCNT/ poly(1.5-DAN) integrated

microwave electrodes have the potential to develop into a Cd(II) and

Pb(II) concurrent sensor in water. With a detection limit of 2.1 μgL-1

for Pb (II) and 3.2 μgL-1 for Cd(II), the sensitivity for Pb(II) was 0,519

nALμg-1 and with Cd(II) is 0,496 nALμg-1, and less influenced by

other ions.

LIST OF PUBLIC WORKS

1. Vu, H.D.; Nguyen, L.H.; Nguyen, T.D.; Nguyen, H.B.;

Nguyen, T.L.; Tran, D.L. Anodic stripping voltammetric

determination of Cd2+ and Pb2+ using interpenetrated MWCNT/P1,5-

DAN as an enhanced sensing interface. Ionics 2015, 21, p. 571-578.

2. Nguyen Le Huy, Duong Thi Hanh, Vu Hoang Duy, Nguyen

Tuan Dung. Electrosynthesis of poly(1,8-diaminonaphthalene) thin

film for silver(I) ion determination. Journal of Science and

Technology (Technical University), 2012, 87, p. 23-26.

3. Nguyễn Tuấn Dung, Vũ Hoàng Duy, Đăng Thị Thu Huyền,

Nguyễn Văn Tú, Nguyễn Văn Chúc, Nguyễn Hải Bình, Trần Đại Lâm,

Nguyễn Xuân Phúc, Thái Hoàng. Chê tao va nghiên cưu tinh chât

mang tô hơp dang đa lơp graphe/poly(1,5-DAN). Tạp chí Khoa học và

Công nghệ, 2014, 52 (1), trang 115-122.

4. Nguyen Tuan Dung, Vu Hoang Duy, Nguyen Thanh My,

Hoang Van Chinh, Nguyen Le Huy, Tran Dai Lam. Preparation of

poly(1,5-diaminonaphthalene) modified electrode for cadmium

determination. Vietnam Journal of Chemistry, 2012, 50(6B), p.234-

238.