Fundamental photoelectrocatalytic and electrophoretic mobility studies of TiO2 and v-doped TiO2 thin-film electrode materials

Titanium dioxide and vanadium-doped titanium dioxide prepared by the sol-gel method showed a quantum-size effect in the form of a 0.19 eV blue shift in the band gap energy compared to bulk TiO2. The presence of vanadium as a dopant did not affect the band gap energy of TiO2. However, concentrations of this dopant up to 1% atom ratio increased the pH of the isoelectric point (IEP) above the value of 5.8 found for pure TiO2. When the vanadium concentration surpassed 1%, the IEP began to decrease, dropping below the IEP of pure TiO2 at dopant concentrations greater than ca. 2%. Thin-film electrodes fabricated from TiO2 and V-doped TiO2 coated on titanium foil showed different performances in degrading formic acid and oxalic acid depending on the V content in the catalyst. Using the 5% V-doped TiO2 electrode, 82% of TOC was removed from an aqueous solution containing oxalic acid (25 mg L-1 in C) against 74% removed by the pure TiO2 thin-film electrode in 1 h. In degrading formic acid, 79% of TOC was removed using the 1% V-doped photoelectrode against 77% removed using the plain TiO2 in 1 h. Additionally, the influence of the bias potential on photoelectrocatalytic oxidation using these thin-film electrodes is discussed as well as the effect of metal doping on the flat band potential of the electrodes.