Recent advances in non-metals-doped TiO2 nanostructured photocatalysts for visible-light driven hydrogen production, CO2 reduction and air purification

Abstract

The generation of hydrogen and oxygen from the photocatalytic water splitting reaction under visible light is a promisingly renewable and clean source for H2 fuel. The transition metal oxide semiconductors (e.g. TiO2, WO3, ZnO, and ZrO2) are have been widely used as photocatalysts for the hydrogen generation. Because of safety, low cost, chemical inertness, photostability and other characteristics (bandgap, corrosion resistance, thermal and environmental stability), TiO2 is considered as a most potential catalyst of the semiconductors being investigated and developed. However, the extensive applications of TiO2 are hampered by its inability to exploit the solar energy of visible region. Other demerits are lesser absorbance under visible light, and recombination of photogenerated electron-hole pairs. In this review, we focus on the all the possible reactions taking place at the catalyst during photo-induced H2 from water splitting reaction, which is green and promising technology. Various parameter affecting the photocatalytic water splitting reactions are also studied. Predominantly, this review is focussed on bandgap engineering of TiO2 such as the upward shift of valence band and downward shift of conduction bands by doping process to extend its light absorption property into the visible region. Furthermore, the recent advances in this direction including various new strategies of synthesis, multiple doping, hetero-junction, functionalization, perspective and future opportunities of non-metals-doped TiO2-based nanostructured photocatalysts for various photocatalytic applications such as efficient hydrogen production, air purification and CO2 reduction to valuable chemicals have been discussed.