UV-switchable polyoxometalate sandwiched between TiO2 and metal nanoparticles for enhanced visible and solar light photococatalysis

To improve the photocatalytic efficiency of TiO2-based nanomaterials, we demonstrate a facile, generalized, highly localized reduction approach to the decoration of TiO2-polyoxometalate composites with a range of metal nanoparticles including Cu, Ag, Pt, and Au. The synthesis of nanocomposite photococatalysts reported in this study has been achieved by utilizing the unique ability of the TiO2-bound PTA (phosphotungstic acid) molecules (a polyoxometalate, POM) to act as a highly localized UV-switchable reducing agent that specifically reduces metal ions to their nanoparticulate forms directly and only onto the TiO2 surface. This leads to the metal contaminant-free synthesis of TiO2-PTA-metal nanocomposites, which is a significant advantage of the proposed approach. The study further demonstrates that polyoxometalates are regenerable photoactive molecules with outstanding electron-transfer ability and the deposition of metal nanoparticles on the TiO2-PTA cocatalytic surface can have a dramatic effect on increasing the overall photocatalytic performance of the composite system. Moreover, it is observed that the photococatalytic performance of the TiO2-PTA-metal nanoparticles can be fine tuned by choosing the composition of metal nanoparticles in the nanocomposite. Interestingly, the photococatalysts reported here are found to be active under visible and simulated solar-light conditions. The underlying reaction mechanism for enhanced solar-light photococatalysis has been proposed.