Photoelectrocatalytic degradation of the insecticide imidacloprid using TiO2/Ti electrodes

The photoelectrocatalytic degradation and mineralization of the chlorinated nicotinoid insecticide imidacloprid in aqueous solution has been investigated. Experiments were carried out using as working electrodes TiO2 P-25 coatings, prepared by the dip coating method, on Ti substrates (TiO2/Ti). After annealing at 500 degrees C for 1.5 h, the surface morphology of the TiO2 film electrodes was examined by scanning electronic microscopy (SEM) and X-ray diffraction (XRD). From capacity measurements the flat band potential has been calculated (V-fb = -0.54 V vs Ag/AgCl, pH = 5.6), as well as the donor density of the deposited TiO2 film electrodes. Photocurrents vs applied potential curves was used for their preliminary photoelectrochemical characterization. The photoelectrocatalytic efficiency (PEC) of the TiO2/Ti electrodes, concerning the imidacloprid oxidation has been evaluated in terms of degradation and mineralization under various experimental conditions. The selected pollutant was effectively degraded following the first order kinetics model. The degradation efficiency increased with increasing of applied potential bias up to + 1.5 V vs Ag/AgCl and is more favourable in acidic than in alkaline environments. The results of the photoelectrocatalytic experiments were compared to those of photochemical and photocatalytic (PC) degradation of the insecticide and showed a significant synergy effect in the case of the PEC degradation, leading at +1.5 V to an 249% increase of the apparent rate constant, k(o), in comparison to the simple photocatalytic process. (C) 2009 Elsevier B.V. All rights reserved.