Photocatalytic and photoelectrochemical studies on N-doped TiO₂ photocatalyst

One of the commercial N-doped TiO₂ powders (Sumitomo Chemicals, TPS 201) was studied as a model material by photocatalytic and photoelectrochemical methods in order to evaluate the photoactivity of N-doped TiO₂ materials and the possibility of their applications in solar photocatalysis. The N-doped TiO₂ powder (TPS) was able to degrade and mineralize phenol under solar or visible light (VL) irradiation, and the degradation rate was strongly dependent on the suspension concentration. Photoelectrochemical studies showed that the VL-irradiated TPS electrode was able to oxidize water, phenol, as well as maleic acid, an open-ring oxidized product of phenol, consistent with the results of photocatalytic studies. Calcining the TPS powder at/over 773 K was found to lower the absorption in the VL region and the photocatalytic activity under VL irradiation, but improve the photocatalytic activity under solar irradiation, suggesting that the mid-gap states introduced by nitrogen doping also worked as recombination centers. Deposition of Pt (0.2 wt%) on the TPS photocatalyst thus greatly increased the degradation rate of phenol under either solar or VL irradiation due to the suppression of charge recombination, and the degradation rate was found to be higher than a pristine TiO₂ photocatalyst (ST-01, anatase) either with or without loading of Pt. The potential application of the N-doped TiO₂ in solar photocatalysis was discussed on the basis of above-mentioned studies.