电聚合苯胺过程的在线紫外-可见光谱

STUDY ON ELECTROPOLYMERIZATION OF ANILINE WITH in situ UV-Vis SPECTROELECTROCHEMISTRY

用在线紫外-可见光谱电化学的方法对0.5mol/L硫酸水溶液中苯胺在ITO导电玻璃电极上的电化学聚的过程进行了研究.结果表明在循环伏安条件下苯胺发生了电聚合,聚合速率与苯胺浓度成正关系;而且在线紫外-可见电化学光谱表明,在0.01mol/L苯胺溶液的电聚合过程的诱导期较长.恒电位条件下的在线紫外-可见电化学光谱显示苯胺浓度为0.05mol/L,电位为0.8V时,在ITO电极上苯胺低聚合物中间体可能产生于聚苯胺形成之前;而0.01mol/L苯胺在0.8V电位下不发生聚合,但在线紫外-可见光谱又显示此时在电极上可能存在小的苯胺低聚物的中间体;在线紫外-可见光谱表明这种中间体是可能产生并存在电极表面上的.

The mechanism of the electro-polymerization of aniline in 0.5 mol/L sulfuric acid was studied in detailby in situ UV-Vis spectrometry. Spectroelectrochemical experiments were done in a three electrode cell built with a quartz cuvette of l cm path length. The work electrode was an ITO （indium-tin oxide） conductive glass perpendicular to light path, and the counter electrode was a platinum wire. An Ag/AgCl electrode with saturated KCl served as reference electrode. All potential values in the article were against to the reference. The acquired in situ UV-Visspectra showed that polyanilines could be electropolymerized at aniline concentrations 0.01,0.05 and 0.2 mol/L in sulfuric acid by cyclic voltammetry. Based on in situ UV-Vis spectra corresponding to cylic potential sweep at three different concentration of aniline above, the plots of the relationship between absorbance at 350 nm and 750 nm and elctrolysis time was made, which showed that the obvious inductive period in electropolymerization of aniline bycyclic voltammetry was seen for 0.01 mol/L aniline in 0.5 mol/L sulfuric acid water solution. In order to study how the concerntration of aniline in 0.05 mol/L sulfuric acid and the potential applied on ITO conductive glass electrodes effected the polymerization of aniline, in situ UV-Vis spectra was recorded during electrolysis of solution bypotentiostatic method at different concentrations of aniline in 0.5 mol/L sulfuric acid. These in situ UV-Vis spectra indicated that the polymerization of aniline occurred by electrolysis of aniline at potentials 0.8,1.0 and 1.3 V when the concentration of aniline was greater than 0.05 mol/L, however at potential 0.8 V, the polymerization of anilinedid not happen in 0.01 mol/L solution of aniline, in situ UV-Vis spectra at the earlier phase of aniline electropolymerization by potentiostatic way showed that the 350 nm absorbance band appeared before the 750 nm absorbance band. This fact proposed that lower molecular weight oligomer intermediates during electrochemicalpolymerization of aniline might exist and that the intermediate was brought out prior to the production of polyaniline on ITO electrode. When the ITO conductive glass electrode was placed parallel to the light path, no absorbance bands were observed during electrolyzing 0.05 mol/L of aniline at potential 0.8 V, which showed that the intermediate andpolymer mainly were produced on the ITO conductive glass electrode. These phenomena was not reported up to now. When the aniline concentration was 0.01 mol/L, and the potential applied on the ITO glass conductive electrode was 0.8 V ,there were only an absorbance band at 350 nm in corresponding in situ UV-Vis spectra, which showed that the intermediates such as low molecular oligomers could be produced and exist on the ITO electrode, but did not leadto the formation of polyaniliane because of the low concentration of intermediates. After aniline of 0.05 mol/L in 0.5 mol/L sulfuric acid was electropolymerized by potentiostatic electrolysis at a potential 0.8 V for 70 min, the electrolysis was stopped, but in situ UV-Vis spectra were recorded continually. The red shift of absorbance band in spectra was seen, which indicated that polyaniline produced on the ITO electrode was of oxidized state and could react with aniline monomer in solution to form polyaniline at the reduced state.