Synthesis of rutile–anatase core–shell structured TiO2 for photocatalysis

Abstract

The crystal phases, surface states and hydroxyl groups of TiO₂ can intrinsically determine its performance in the applications of photocatalysis and dye-sensitized solar cells. Here we developed a unique rutile–anatase core–shell structured nanocrystalline TiO₂ with controlled surface states and hydroxyl groups for photocatalytic applications via a simple phase conversion method, where the semi-crystalline TiO₂ embedded in the caramelized sucrose matrix following the hydrothermal process was first converted to a composite of TiO_xC_y/C by calcining in a nitrogen atmosphere, and this composite was subsequently converted to TiO₂ by calcining in an oxygen atmosphere. It was found that the rutile phase exists within anatase particles, and the depth of rutile core in the anatase shell particles can be tuned by adjusting the thickness of TiO_xC_y (x < y) and TiO_xC_y (x > y) in the precursor composite TiO_xC_y/C simply through changing the calcination temperature. More interestingly, the amount of surface adsorbed water and hydroxyl groups and the abundance of surface states in such core–shell structured TiO₂ can be controlled by changing the size of the rutile and anatase phases. Finally, photocatalytic degradation reaction as an example clearly demonstrates the substantial role of the surface states in determining photocatalytic activity of the TiO₂ in desired applications.