Photoelectrochemical oxidation of phenol with nanostructured TiO2-PANI electrodes under solar light irradiation

Abstract

Abstract The photoelectrochemical removal of phenol from aqueous solution under solar light with polyaniline-modified TiO2 electrodes has been investigated. Nanotubular TiO2 electrodes (NTs) have been obtained by anodization of Ti; the coating with polyaniline (PANI) has been obtained with a three-step approach: (i) functionalization of NTs by electroreduction of 4-nitrobenzendiazonium salt, (ii) electrochemical reduction of the nitro group to amine, (iii) galvanostatic electropolymerisation of aniline. The results of galvanostatic electrolyses under simulated solar light are presented, degradation of phenol with TiO2 was achieved and the trends of concentration with time follow a pseudo-first order kinetics. As a comparison, also unmodified NTs have been tested. The results depend on the initial concentration of reactant, with 300 mg dm−3 of phenol and applying a current density i = 0.18 mA cm−2, the reaction rate with NT-PANI was more than double of that obtained with NTs. Moreover, the presence of PANI increases the conductivity of the electrode, which in turn depolarizes the cell. Hydroquinone and oxalic acid have been detected as main intermediates, which are distributed depending on the experimental conditions and kind of electrodes: the relevant data have been modelled assuming an in-series reaction scheme and pseudo first order kinetics.