Mechanistic insights into 2,4-D photoelectrocatalytic removal from water with TiO2 nanotubes under dark and solar light irradiation

Removal of recalcitrant pollutants from water is a major challenge, to which the photoelectrocatalytic processes may be a solution. Applied potential plays a key role in the photocatalytic activity of the semiconductor. This paper investigated the effect of applied potential on the photoelectrocatalytic oxidation of 2,4-Dichlorophenoxyacetic acid (2,4-D) with TiO2 nanotubular anodes under solar light irradiation. The process was investigated at constant potentials in different regions of the polarization curve: the ohmic region, the saturation region and in the region of the Schottky barrier breakdown. PEC tests were performed in aqueous solutions of 2,4-D, and in the presence of methanol or formic acid, as scavengers of OH center dot radicals and holes. Results showed the main mechanism is oxidation by OH center dot radicals from water oxidation, while runs with hole scavenger revealed a second mechanism of direct oxidation by holes photogenerated at the electrode surface, with high removal rates due to current doubling effect.

Automated summary

This study investigated the effect of applied potential on the photoelectrocatalytic oxidation of 2,4-D using TiO2 nanotubular anodes under solar light irradiation. Results showed that oxidation by OH radicals from water oxidation is the main mechanism, while direct oxidation by photogenerated holes at the electrode surface is a secondary mechanism with high removal rates due to current doubling effect.