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Electrochemical synthesis and sensor properties of polyaniline (PANI) films of different oxidative state
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Zhuk Vitalii Petrovich, National Technical University of Ukraine ".Kiev Polytechnic Institute", Chemical Technology Faculty, student Byk Mykhaylo Volodumurovich, Chemical Technology Faculty, Associative Professor E-mail: bmv2000@ukr.net Motronyk Tetiana Ivanivna, Chemical Technology Faculty, Associative Professor
Electrochemical synthesis and sensor properties of polyaniline (PANI) films of different oxidative state
Abstract: Thin polyaniline (PANI) films are known as good optical gas sensors. To improve these properties we have developed new robust transparent PANI films obtained at different electrochemical condition. We demonstrate that PANI films have an increased surface area; give strong, fast and reversible optical sensor responses to ammonia. In case of ammonia-air gas mixtures we demonstrate that the PANI films give linear optical responses to ammonia gas in concentration ranges of 10-114 ppm.
Keywords: polyaniline (PANI), electrochemical oxidation, ammonia sensor, oxidation state.
oxide (chinoide, imine) fragment (В) [1-4].
In the most common case PANI can exist in all intermediate states from completely reduce form to oxide [1-4]. Ratio for abovementioned amine and imine’s fragments in PANI can be change by chemical or electrochemical oxidation/reduction [5].
Modern interest for PANI arises after discovering its semi-conductive properties. The fist works of such direction was [6-8].
It is well known that a polyaniline term describes a class of compounds that has formula:
Thus chemical structure of PANI contains repeating chains as:
reduced (benzoid, amine) fragment (А);
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Section 8. Chemistry
The common procedure of chemical PANI synthesis includes oxidative aniline polymerization in water solution of inorganic acid [9, 10]. In such conditions insoluble in the most organic solvents powder formed [10, 11], which limits of obtained material application.
Electrochemical synthesis of PANI is the most widely used method of its obtaining without traces of oxidizer. Obtained PANI films have good optical characteristics and conductivity in range of 10-10 - 10 3 S/cm. At such synthesis method one can vary different synthesis parameters (potential, charge, time, pH, ionic strange and electrolyte nature), and complex investigation ofpolym-erization mechanisms and PANI characteristics.
Practical value of such work is in applying of obtained PANI films in electro chromic, electroluminescent and photovoltaic device or as conductive coatings.
Experimental: Electrochemical synthesis of PANI was conducted in three-electrode cell. Reference electrode was Ag/AgCl/Cl-. 0.5 М aniline solution in 12 % wt. HCl was used as electrolyte, graphite as counter electrode, working electrode — substrate from Cr with sputtered Au on top. Acid solution was chosen from the reason that in basic form PANI formed non-conducting film.
Results and discussions: Electrochemical PANI synthesis was made in potentiostatic mode at 800, 900 and 1100 mV. Time of film formation was 90, 180 and 300s. Obtained curves of PANI synthesis at 800 mV. showed on Fig. 1.
Fig. 1. Chronoammograms for PANI synthesis process at 800 mV.: 1 - 90 s., 2 - 180 s., 3 - 300 s.
First current peak with maximum describe double layer formation, then decay — monomer adsorption and oligomers formation. The next current rise (as it is obviously for specimen obtained during 300 s.) is the evidence of induction period finishing. After that stage the nucleation of PANI semispherical nucleus on electrode surface starts.
For the specimens synthesized at 950 mV time of synthesis was 30, 90 and 180 s. Obtained plot I vs. time showed on Fig. 2.
Fig. 2. Chronoammograms for PANI synthesis process at 950 mV.:1 - 30 s., 2 - 90 s., 3 - 180 s.
As one can see PANI formation at 950 mV. has the same consistent pattern. But has some distinction — double layer formation is faster then for 800 mV., and gradually increasing ofcurrent faster also. That is the evidence of faster PANI layer formation on electrode surface.
The time of PANI synthesis at 1100 mV. was chosen the same as for 950 mV. synthesis process. For each time two electrodes was obtained. Result plot for 1100 mV. synthesis shown on Fig. 3.
Fig. 3. Chronoammograms for PANI synthesis process at 1100 mV.: 1 - 30 s., 2 - 90 s., 3 - 180 s.
Characterization of obtained materials by cyclic voltammetry (CVA).
From each batch obtained at 800, 950 and 1100 mV. as chosen by one sample and cyclic voltammetry curves obtained (Fig. 4).
Peaks height corresponds to anode and cathode current respectively. All experiments were performed in the same initial solution then activity of acid cations can be neglected. So we can consider that peak height corresponds of electrode resistance decreasing, thus more well-ordered PANI layer formation on contact electrode surfaces.
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Electrochemical synthesis and sensor properties of polyaniline (PANI) films of different oxidative state
Fig. 4. CVA curves for PANI samples obtained at: 1 - 800, 2 - 950 and 3 - 1100 mV.
Sensor responses for obtained electrode materials.
Sensor responses for obtained PANI samples were obtained at ammonium concentration 10, 19, 38, 76 and 114 ppm. Procedure includes 10 s. without gas, probe injection and response measuring during 10 min. From obtained initial data the calibrating plots for each sample was made (Fig. 5-7) (B=AR/Ro).
Fig. 5. Calibrating plot for PANI sample obtained at 800 mV.: 1 - 90 s., 2 - 180 s., 3 - 300 s.
Fig. 6. Calibrating plot for PANI sample obtained at 950 mV.: 1 - 30 s., 2 - 90 s., 3 - 180 s.
Fig. 7. Calibrating plot for PANI sample obtained at 1100 mV.: 1- 30 s., 2 - 90 s., 3 - 180 s.
From obtained data is obviously that sensor response for PANI samples obtained at 950 and 1100 mV. is better then for obtained at 800 mV. This can be explaining by greater quantity of active substance and higher degree of oxidation state of sensor material. Tendency of sensor response improving with synthesis time was also shown.
Fig. 8. Spectral properties for PANI samples obtained at: 1 - 800 mV., 2 - 950 mV., 3 - 1100 mV.
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Section 8. Chemistry
Spectral properties of obtained PANI samples
For spectral properties characterization three samples at 800, 950 and 1100 mV. were deposited 30 min., it was a minimal time for films thickness that sufficient for
obtaining the spectral data. Spectral data for obtained materials with peak position characterization shown on Fig. 8.
The quantities of electricity for PANI electrode formation were calculated for all obtained materials (Table 1).
Table 1. - Calculation the electricity quantity for PANI synthesis
Sample at 800 mV. Sample at 950 mV. Sample at 1100 mV.
t, s. Q, mC. t, s. Q, mC. t, s. Q, mC.
90 4.9 30 34.43 30 19.3
180 5.85 90 148.2 90 36.12
300 30.89 180 113.22 180 34.47
Conclusions: From sensor response for PANI electrodes obtained at different conditions (potential and deposition time) it is visible that best results has electrode formed at 950 mV. during 180 s. So the
optimal electricity quantity for such electrode formation is 113.22 mC. From the working electrode surface we obtain the optimum current density for PANI electrode formation is 4.25 mA/cm 2.
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Urinov Ulugbek Komiljonovich, The senior researcher Maksumova Oytura Sitdikovna, The Doctor of Chemistry, the professor E-mail: Omaksumovas@mail.ru
Studying of the complex compounds, formed by molecules of morpholine betaine and urea
Abstract: Monocrystal compound[OC4H8N+HCH2COO]ra . [(NH2-CO-NH2)2]^ is obtained at slow crystallisation from ethanol solution. The structure of a crystal complex is defined by the method ofX-ray diffraction analysis.
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