P–N co-doping induced structural recovery of TiO 2 for overall water splitting under visible light irradiation

Doping nitrogen in TiO2 crystals is a simple and effective approach to extend the absorption spectrum of TiO2 to visible light range, but it leads to a serious decline in charge transfer and total loss of the catalytic ability for overall water splitting. Here, TiO2 was co-doped with phosphorus and nitrogen by high temperature method and found the sample of P–N–TiO2-I could realize overall water splitting under visible light while the samples of P–N–TiO2-II, P–N–TiO2-III and N–TiO2 cannot do it. The structures of the photocatalysts were described by various analytical techniques. Through XRD and HRTEM, lots of long-range defect such as twins and dislocations could be clearly observed for P–N–TiO2-II, P–N–TiO2-III and N–TiO2. But for P–N–TiO2-I, the long-range defect was decreased drastically. We proposed that because of various sizes and bonding modes of N, O, P and Ti, proper mole ratios of P to N replace Ti and O respectively can reduce the long-range defect, as that of P–N–TiO2-I. Furthermore, this co-doping effect results in a significant improvement in the separation of photo-excited electrons and holes and enables the nitrogen-doping TiO2 to catalyze the overall splitting of water into molecular hydrogen and oxygen under visible light irradiation, in the absence of sacrificial agents. These observations might arouse new strategies to mend the hybrid-atom-doping-induced structural damage in semiconductor crystals and to modulate their functional properties.