Copolymerization Of Aniline And Its Derivatives In Situ Uv - Visible Spectroelectrochemical Studies

Polyaniline (PAN) has been attracting significant interest due to its high conductivity, good redox reversibility and environmental stability. Aniline derivatives also receive greater attention because they can provide more functional groups.In recent years, several studies have been reported on the electropolymerization of aniline and its derivatives. So research on the copolymerization mechanism and electrochemical properties of the electrode developed accordingly. However, the traditional analysis of electrochemistry depends on the electricity signals, and only the total microcosmic information can be acquired, which can not reflect the changes of electrode/solution interface clearly and accurately. So it is difficult for people to interpret the electrochemical reaction mechanism correctly. In situ UV-Vis spectroelectrochemistry technique combine the UV-Vis spectra and electrochemical method together, as a result, two kinds of information can be reported simultaneously. It becomes an effective method to detect the intermediates during the polymerization of aniline and its derivatives.The paper includes the following three sections:1. The electrochemical copolymerization of o-aminophenol (OAP) with aniline (AN) in 0.5 mol/L H2SO4 has been investigated using in situ UV-Vis spectroelectrochemistry. The results reveal that OAP can be firstly oxidized to its cation radical,which shows a peak atλ=460 nm in the UV-Vis spectra. Then a mixed dimer intermediate is formed through the cross-reaction of OAP and AN cation radicals with their monomers in solution. The absorption peak atλ=490 nm in the UV-Vis spectra is assigned to this intermediate. The intermediates then react each other to form the oligomer which shows an absorption peak atλ<460 nm. On the other hand, the spectroelectrochemical results reveal that OAP can inhibit the polymerization of AN with the increase of the amount of OAP in the mixed solutions.2. In situ UV-Vis spectroelectrochemical study of the electrochemical copolymerization of o-phenylenediamine (OPD) with aniline (AN) at a constant potential using the indium tin oxide (ITO)-coated glass electrodes as the working electrode has been carried out. The electrochemical copolymerization is performed in 0.1 mol/L H2SO4 aqueous solution containing 0.1 mol/L Na2SO4. The homopolymerizations of OPD and AN are also done independently in the same medium. The intermediate species for the homopolymerization of OPD and the copolymerization of OPD with AN have been identified by spectroelectrochemical studies. The spectroelectrochemical results reveal the formation of an intermediate in the initial stage of copolymerization through the cross-reaction of OPD cation radicals and AN cation radicals. An absorption peak atλ=480 nm in the UV-Vis spectra is assigned to this intermediate. Electron paramagnetic resonance (EPR) has been used to verify the existence of intermediates such as radicals in the initial stage of copolymerization.3. A composite film of polyaniline (PAN) nano-networks/p-aminobenzene sulfonic acid (ABSA) modified glassy carbon electrode (GCE) has been fabricated via an electrochemical oxidation procedure and applied to the electrocatalytic oxidation of uric acid (UA) and ascorbic acid (AA). The ABSA monolayer at GCE surface has been characterized by X-ray photo-electron spectroscopy (XPS) and electrochemical techniques. Atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS), UV-Visible absorption spectra (UV-Vis) and cyclic voltammetry (CV) have been used to investigate the PAN-ABSA composite film, which demonstrates the formation of the composite film and the maintenance of the electro-activity of PAN in neutral and even in alkaline media. Due to its different catalytic effects towards the electro-oxidation of UA and AA, the modified GCE can resolve the overlapped voltammetric response of UA and AA into two well-defined voltammetric peaks with both CV and differential pulse voltammetry (DPV), which can be used for the simultaneous and selective determination of these species in a mixture. The catalytic peak currents are linearly dependent on the concentrations of UA and AA in the range of 50-250 and 35-175μmol/L with correlation coefficients of 0.997 and 0.998, respectively. The detection limits for UA and AA are 12 and 7.5μmol/L, respectively. The modified electrode exhibits good stability, reproducibility, sensitivity and selectivity.