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

1 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
2 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
1 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.
2 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.
3 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
4 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
5 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.
6 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 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.
7 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
8 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.
9 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 the peaks of the polymer at +0,34 and + and 1.8-DAN 5mM solutions.
10 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: Figure 3.11. The CV line of poly(1.8- It can be observed that the DAN) film in HClO4 0.1M solution. 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. 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
11 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.
12 Figure 3.14. Diagram of polyelectrolyte polymerization poly(1.8-DAN) 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 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, 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) 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
13 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 Figure 3.20. The CV lines synthetic +0.66 V appeared. From the second poly(1.5-DAN) in HClO4 1 M and 1.5-DAN 5 mM 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 Figure 3.21. The CV line of poly(1.5- DAN) 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.
14 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 cm- poly(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 1.5- 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
15 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.
16 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(1.5- Figure 3.28. The CV lines in DAN)/MWCNT film 0.1M acetate buffer of poly(1.5- 3.4.3.1. Raman spectra of poly(1.5- DAN)/ MWCNT/ Pt and MWCNT /Pt DAN)/MWCNT film
17 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 Fingure 3.30. The Raman spectra off MWCNT MWCNT show very (a), poly(1.5-DAN)/ MWCNT with 2 CV cycles clearly the characteristic (b), 10 cycles (c), and 25 cycles (d) and poly(1.5- 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 (1.5- 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
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 Figure 3.31. The FE-SEM images of: a) in Figure 3.31. The results showed MWCNT; b) poly (1,5-DAN); c) poly (1,5-DAN)/MWCNT synthesized with that poly(1.5-DAN) formed and 10 cycles and d) poly (1,5-DAN) / covered MWCNT fibers, giving a MWCNT synthesized with 25 cycles. 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 Figure 3.32. The SWV lines analyzes Poly(1.5-DAN)/MWCNT Cd(II) and Pb(II) at 10-5 M of Pt, microplate coatings were investigated MWCNT/ Pt and poly(1.5-DAN) /MWCNT / Pt electrodes. Potential sensitivity ions Pt(II) and Cd(II) by an gain -1.2 V, enrichment time 420 analytical dissolve the anot by square seconds, acetate buffer 0,1 M pH = 4.5. 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. Figure 3.33. Influence of number scans 3.4.5. Factors affecting Pb(II) and CV to Cd and Pb dissolution intensity of poly (1,5-DAN) / MWCNT. Cd(II) ion sensitivity