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

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. Mời các bạn tham khảo!

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

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

Thesis can be further referred at:

- The Library of Graduate University of Science and Technology

- National Library of Vietnam

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

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 diaminonaphthalene) and carbon nanotubes: synthesis, characterization and application in simultaneous analysis of Cd(II) and Pb(II) ions

poly(1.5-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

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

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

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

2.3 Research methods

The thesis uses the following basic research methods:

Studies on the polymerization of PANi, poly(1.5-DAN), DAN) by electrochemical characterization of polymer films by CV, SWV

poly(1.8-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 H2 SO 4 and

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

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 H 2 SO 4 0.1M

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

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-1corresponding 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

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 HClO 4 1M and 1.8-DAN 5mM solutions

0,19V, indicating that the poly

(1,8-DAN) has been formed on the electrode

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 DAN) film in HClO 4 0.1M solution

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

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 doped in the membrane

anion-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