S-doped mesoporous nanocomposite of HTiNbO5 nanosheets and TiO2 nanoparticles with enhanced visible light photocatalytic activity

The S-doped mesoporous nanocomposite (S-TNT) of HTiNbO5 nanosheets (NSs) and anatase TiO2 nanoparticles (NPs) with exposed {101} facets has been successfully synthesized by first mixing freeze-dried HTiNbO5 NSs with titanium isopropoxide and then calcination with thiourea in air. The exposed anatase {101} facets can act as a possible reservoir of the photogenerated electrons, yielding a highly reactive surface for the reduction of O-2 to O-2(center dot-). The partial substitution of Ti4+ by S6+ in the lattice of TiO2 NPs leads to a charge imbalance in S-TNT and the formation of Ti-O-S bonds. As a result, the formed cationic S-TNT favours adsorption of hydroxide ions (OHads-) and thus captures the photo-induced holes to form hydroxyl radicals ((OH)-O-center dot). Moreover, with the formation of Ti-O-S bonds, partial electrons can be transferred from S to O atoms and hence the electron-deficient S atoms might capture photo-induced electrons. The surface-adsorbed SO42- could also act as an efficient electron trapping center to promote the separation of charge carriers. In addition, the Ti3+ species due to the removal of oxygen atoms during calcination and the associated oxygen vacancy defects on the surface of S-TNT could act as hole and electron scavengers, respectively. Besides, the closely contacted interface is formed between HTiNbO5 NSs and anatase TiO2 NPs due to the common features of TiO6 octahedra in two components, resulting in a nanoscale heterojunction structure to speed up the separation rate of photogenerated charge carriers. The formation of a nano-heterojunction and the incorporation of Ti3+ and S dopants give rise to the visible and near-infrared light response of S-TNT. The combined effects greatly retard the charge recombination and improve the photocatalytic activity for the degradation of rhodamine B (RhB) and phenol solution under visible light irradiation. The corresponding photocatalytic mechanism was investigated via the active species capture experiments. The present work may provide an insight into the fabrication of delicate composite photocatalysts with excellent performance.