Studies On Electrochemical Synthesis Of Polyaniline And Its Derivative And Their Applications

Organic conductive polymers, on account of their excellent physical and chemical properties, are promising in many fields such as electrochemical catalysis, chemical/biosensor, electrochemical capacitor and so on. Among conductive polymers, polyaniline (PANI) has attracted considerable interesting due to its availability, simple synthesis, high conductivity and stability. In recent years, with the rapid development of nanotechnology and composite materials, nano-sized PANI and PANI composite film with better functional properties have been synthesized. In this paper, nano-fibrous PANI films have been templatelessly and nonstrictedly synthesized for the first time by pulse galvanostatic method (PGM). The applications of the nano-fibrous PANI film in electrochemical biosensor, electrochemical catalysis and electrochemical capacitor were investigated. The main progresses are presented as follows:1. Nano-fibrous PANI, for the first time, was templatelessly and nonstrictedly synthesized on stainless steel (SS) electrode by PGM in proton acids with small molecular size, such as H2SO4or HNO3 solution. Influences of electrolytic parameters (the ratio of ton to toff, frequency, mean current density and temperature of electrolyte) on synthesis of nano-fibrous PANI were studied in detail. The process conditions were optimized. The morphology and electrochemical property of PANI films prepared by PGM were investigated by scanning electron microscopy (SEM), transmitting electron microscopy and cyclic voltammetric method (CVM). The results show that the morphology of PANI is nano-fiber with diameter of 70~100nm and many microgaps and pores exist among the PANI fibers. The nano-fibrous PANI films have larger specific surface area, better ionic and electronic conductivity, and higher electrochemical activity than those of granular PANI films prepared by conventional chemical or electrochemical methods. Therefore, the nano-fibrous PANI film is a more excellent functional film or functional carrier than conventional PANI film.2. The novel composite electrode [Pt/(nano-fibrous PANI)] was prepared by using nano-fibrous PANI film as the carrier of Pt catalyst and the electrocatalytic performance of this composite electrode for methanol oxidation was investigated. SEM and energy dispersive spectroscopy results show that the composite electrode is characterized by about 50~80nm Pt microparticles dispersing uniformly on nano-fibrous PANI film. The cyclic voltammetry and electrochemical impedancespectroscopy results show that the composite electrode has excellent catalytic activity for methanol oxidation and there is a synergism for methanol oxidation on Pt/(nano-fibrous PANI) electrode. The composite electrode exhibits higher electrocatalytic activity for methanol oxidation than the granular PANI electrode modified by Pt microparticles and the bare Pt electrode when Pt loading is above 200 ug/cm2. Moreover, the research results present that the catalytic activity of the composite electrode was greatly affected by the deposition methods of Pt (PGM> CVM).3. Poly(m-phenylenediamine) (PMPD) film, PANI-graphite composite film (PGCF) and Pt/(nano-fibrous PANI) film were synthesized on the surface of Pt or SS electrode by PGM or CVM. Three kinds of novel glucose biosensors were prepared by electrochemical doping method based on PMPD, PGCF and Pt/(nano-fibrous PANI), respectively. The morphologies of polymer films and the electrochemical response performances of the enzyme electrodes were investigated by SEM and electrochemical method. The results present that the electrochemical response performances of the enzyme electrodes are related to the morphologies of polymer films. PMPD film and PGCF are porous and netty structure, which possess large specific surface area and are beneficial for the glucose oxidase (GOD) immobilization and the ion transfer. Pt/(nano-fibrous PANI) film is characterized by 50~80nm Pt microparticles dispersing uniformly on 70~100nm PANI nano-fibers, which has very large specific surface area and good electrocatalytic activity for the oxidation of H2O2. Furthermore, the influences of measuring temperature, measuring potential and pH value of glucose solution on the electrochemical response performances of the enzyme electrodes were studied in detail. The results indicate that the enzyme electrodes prepared above all have good electrochemical response performance, reproducibility and stability. The PGCF-GOD electrode, the PMPD-GOD electrode and the PMPD-GOD/Pt/(nano-fibrous PANI) electrode gave a linear response to glucose in the range of l*10-4~8xl0-3 mol/L, 5><10'4~lxl0"2 mol/L and 2xl0-6~12*10-3 mol/L, respectively. Both the PMPD-GOD/Pt/(nano-fibrous PANI) electrode and the PMPD-GOD electrode have good anti-interference to uric acid and ascorbic acid. Moreover, the PMPD-GOD/Pt/(nano-fibrous PANI) electrode was applied to determine glucose concentration in serum, the analytical results determined by using the enzyme electrode and those provided by the hospital agree closely. Therefore, this kind of enzyme electrode has good application prospect. Based on the calculating of the kinetic parameters, the maximum response current density of the PMPD-GOD,...