In Situ Ultraviolet - Visible Spectroscopy Of Aniline And Its Derivatives

Polyaniline(PAN) has been attracting significant interest and is a most promising material due to its relatively easy preparation, high conductivity, good redox reversibility and environmental stability. Aniline derivatives also receive greater attention because they can provide more functional groups.In recent yeas, several studies have been reported on the electropolymerization of aniline and its derivatives. So research on the copolymerization mechanism developed accordingly. The in situ UV–Vis spectroscopy appears to be an effective and useful tool for studying the initial stages of electrochemical polymerization and copolymerization of aniline and its derivatives, because the sensitive UV-Vis spectrum can effectively recognize and detect the short-lived intermediates formed during electrooxidation of aniline and its derivatives.The paper includes three sections as followed:1. Cyclic voltammetry(CV) and in situ UV-vis spectroelectrochemical techniques were used to investigate the homo-/co-copolymerization of o-methoxyaniline(OMA) and diphenylamine(DPA). The different electrochemical behaviors for the homopolymerization of OMA and DPA and the copolymerization of OMA and DPA in 4 mol/L H2SO4 at platinum electrode indicated the occurrence of copolymerization. In situ UV-vis spectroelectrochemical study for the copolymerization of OMA and DPA with different concentration ratios was carried out in 4 mol/L H2SO4 using indium tin oxide(ITO) coated glass electrode as working electrode at 0.9 V. The results indicated that, during the copolymerization of OMA and DPA, OMA and DPA were firstly oxidized to generate their cation radicals, then a mixed dimer intermediate was formed through the cross-reaction between the cation radicals of OMA and DPA and the monomers of OMA and DPA. The new absorption peak at 419 nm in the UV-vis spectra was assigned to this intermediate,which can also be con?rmed by the results derivative cyclic voltabsorptogram(DCVA). Under sweeping potential, we can see the transformation between oxidation and reduction in the UV–Vis spectra. Further studies showed that the copolymerization of OMA and DPA was controlled by the concentration ratios of OMA and DPA in solution: The OMA concentration in solution dominant in the process of copolymerization of OMA and DPA. The formation of a copolymer in the copolymerization of OMA and DPA was also proved by FT-IR spectroscopy. A plausible copolymerization mechanism was proposed.2. The in situ ultraviolet-visible(UV-Vis) spectroelectrochemical study on the copolymerization of o-Aminophenol(OAP) and o-phenylenediamine(OPD) has been performed at a constant potential of 0.8 V using indium tin oxide(ITO)-coated glass electrodes as working electrode. And also, as a comparison, the electrochemical homopolymerizations of OAP and OPD have been investigated by using the in situ spectroelectrochemical technique. The intermediate species generated during the electrochemical homopolymerization of OAP and OPD, and the copolymerization of OAP with OPD have been identified by using the in situ spectroelectrochemical technique. the two new waves at 419 nm and 477 nm should be ascribed to the new-formed dimers/oligomers intermediates: phenazine-type structureand and PANI-like backbone structure. The copolymer was further characterized by Fourier transform infrared spectroscopy(FT-IR).3. Cyclic voltammetry(CV) technique was used to investigate the homo-/co-copolymerization of o-phenylenediamine(OPD) and m-methoxy aniline(MA). The voltammetric characteristics show the dependence of the copolymerization on the concentrations ratios of OPD and MA. The in situ ultraviolet-visible(UV-Vis) spectroelectrochemical study on the copolymerization of OPD and MA has been performed at a constant potential of 0.8 V using indium tin oxide(ITO)-coated glass electrodes as working electrode. And also, as a comparison, the electrochemical homopolymerizations of OPD and MA have been investigated by using the in situ spectroelectrochemical technique. The results reveal the formation of an intermediate in the initial stage of copolymerization through the cross-reaction of the cation radicals of OPD and MA, and the absorption peak located at 417 nm and 479 nm in the UV–Vis spectra is assigned to the intermediates...