Control of the crystallinity in TiO2 microspheres through silica impregnation

Abstract

The crystal grain size as well as the crystallinity in nanoscale TiO₂ have been determined to be of importance to the photocatalytic activity, however it is difficult to control while maintaining a high surface area. Here we demonstrate the synthesis of anatase titania microspheres with controllable grain sizes, which are obtained by impregnating the porous networks of amorphous titania microspheres with silicate oligomers through the addition and hydrolysis of the precursor tetraethyl orthosilicate (TEOS) and calcining the obtained composite. Varying the amount of TEOS added controls to the degree of silicate impregnation, which restricts the anatase grain growth during calcination and enables the tuning of the grain size from 4–25 nm while maintaining a spherical morphology. The silica is then removed through base etching in order to utilize the microspheres. The photocatalytic performance of microspheres with enhanced crystallinity is tested using the model system of the degradation of Rhodamine B under UV irradiation and the rate constants determined are compared against the surface area and grain size of the microspheres to determine optimal conditions.