Preparation of titania with double band structure derived from a quantum size effect: Drastic increase in the photocatalytic activity

Titania is a competent photocatalyst widely used in environmental purification. Unfortunately, its photocatalytic ability to generate hydrogen by water decomposition without a co-catalyst is poor. Here, an efficient enhancement of noble-metal-free photocatalytic activity was studied on the basis of titania prepared in a supermicroporous silica template using TiCl₃ aqueous solution as a precursor. The amount of evolved hydrogen increased sharply by 37 times as the concentration of TiCl₃ was increased from 5 to 10 wt%. The existence of two species of titania was determined by XAFS analysis at concentrations of 10 wt% or greater. It is suggested that titania quantum dots inside the supermicropores and titania particles outside the supermicropores were prepared at the optimum precursor concentration and the resultant composite band structures suppressed electron–hole recombination.