Summary of doctoral thesis in chemistry: Synthesis, studying the properties of phenyl radical polymer film orionted to use as metal ion sensor

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MINISTRY OF EDUCATION

VIETNAM ACADEMY OF

AND TRAINING

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(1.8diaminonaphthalene), 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(1.5diaminonaphthalene).
- 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(1.5diaminonaphthalene)
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 ionexchange 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-diaminonaphthalene (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(1.8DAN) 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

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.

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.


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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
Figure 3.3. The CV recorded
oxidation is relatively high and stable, of PANi film in aqueous
indicating that the films has a good solution of H2SO4 0.1M
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 3.4. 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
Figure 3.5. FE-SEM of PANi film with
that PANi synthesized in the magnification: a) 10,000 times, b) 100,000
form of fibers, not aligned times
closely together.


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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 Figure 3.6. The SWV lines were recorded on
sharp and strong oxidation GC/PANi electrodes before and after 30
minutes in aqueous solutions containing (a)
signals at the voltage values of Ag (I) 10-2 M; (b) Hg (II) 10-2 M; (c) Cd (II)
0.67 V and -0.51V respectively 10-2 M, 10-3 M and (d) Pb (II) 10-2 M, 10-3 M.
(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
Figure 3.9. Spectrophotometer
monomer peak no longer exists but only of poly(1.8-DAN) in HClO4 1M
and 1.8-DAN 5mM solutions.
the peaks of the polymer at +0,34 and +


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0,19V, indicating that the poly (1,8DAN) has been formed on the electrode
surface.

3.2.2. Study characteristic of poly (1.8DAN)
3.2.2.1. Electrolytic activity of poly(1.8DAN) film:
Figure 3.11. The CV line of poly(1.8It can be observed that the DAN) film in HClO4 0.1M solution.
characteristic redox peaks of poly (1.8DAN) 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.

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

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


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

3.2.2.3. Morphological analysis of structure:

Figure 3.15 presents the FESEM image of the face poly(1.8DAN) film after 1 and 8 CV cycles.
The results showed that the
poly(1.8-DAN) formed had a Figure 3.15. FE-SEM image of surface of
particle size of 50-100 nm in the poly(1.8-DAN) synthesized after 1cycles
first 1 cycles, then poly(1.8-DAN) (a), and 8 cycles (b).
covered the electrode surface, nonflat 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) Figure 3.16. The SWV lines recorded of
poly(1.8-DAN) on GC electrode before
obtained a peak very strong and and after keepping for 30 minutes in
strong oxidation signal at + 0.153 V aqueous solutions containing: (a) Cd (II)
10-2 M, (b) Pb ) 10-2 M, (c) Hg (II) 10-2 M
and + 0.38 V respectively. Thus and (d) Ag (I) 10-2 M.
poly(1.8-DAN) films have different


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affinities with cationic studies. The selective adsorption of poly(1.8DAN) may be related to molecular structure, geometry of poly(1.8DAN) 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
Figure 3.20. The CV lines synthetic
poly(1.5-DAN) in HClO4 1 M and
+0.66 V appeared. From the second
1.5-DAN 5 mM
scan, two pairs redox of poly(1.5DAN) 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 Figure 3.21. The CV line of poly(1.5DAN) in 0.1M HClO4 solution.
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.


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

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
Figure 3.24. Diagram of
in the free state.
electrosynthesise polymerization
In the range of 2000 to 500 cmpoly(1.5-DAN)
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 1.5DAN 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


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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 Figure 3.25. The FE-SEM image of
poly(1.5-DAN) film after 1 cycle (a) and
round particle (figure 3.25-a).
10 sweep cycles (b).
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 Figure 3.26. The SWV lines were recorded
on GC/poly(1.5-DAN) electrode before and

due to the molecular structure of after 30 minutes in aqueous solutions
two different polymers, resulting 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.


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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

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).

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(1.5Figure 3.28. The CV lines in
DAN)/MWCNT film
0.1M acetate buffer of poly(1.53.4.3.1. Raman spectra of poly(1.5- DAN)/ MWCNT/ Pt and
MWCNT /Pt
DAN)/MWCNT film


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Poly(1.5-DAN)/
MWCNT films were
electrosynthesized in 2,
10, 25 CV cycles and
MWCNT,
poly(1.5DAN) were analyzed by
Raman
spectroscopy,
resulting in Figure 3.30.
The Raman spectra of
Fingure 3.30. The Raman spectra off MWCNT
(a), poly(1.5-DAN)/ MWCNT with 2 CV cycles
MWCNT show very
(b), 10 cycles (c), and 25 cycles (d) and poly(1.5clearly the characteristic
DAN) (e).
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 (1.5DAN) 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


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(1.5DAN) 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(1.5DAN) 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

Figure 3.34. Effect of enrichment time
on detection of Pb(II) and Cd II) ion of
poly (1.5-DAN)/ MWCNT / Pt
35

Pb(II) 30
I(µA)

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(1.5DAN)/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.

-1.4

Cd(II)

-1.2

-1

25
20
15
10
5
0
-0.8

E(V)

Figure 3.35. Results of effect of potential
enrichment Cd(II) and Pb(II) of poly(1.5DAN) / 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)/ MWCNTCd(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).
Figure 3.37. The calibration
3.4.6.4. Calculates the detection limit of the of Cd(II) ion
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(1.5DAN)/ MWCNT- Pb(II) = 2.1 (μgL-1).
The durability of the poly(1.5DAN)/MWCNT/Pt sensor was tested after Figure 3.38. The calibration of
Pb(II) ion
8 weeks of storage at room temperature in

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(1.8DAN), 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-, SO42- 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(1.8diaminonaphthalene) 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(1.8DAN) adsorbed Hg(II) and Ag(I), but weakly absorbed Cd(II) and