Crystallinity control of TiO2 hollow shells through resin-protected calcination for enhanced photocatalytic activity

Abstract

We report a novel resin-protected calcination process for preparing hollow TiO₂ nanoshells with controllable crystallinity and phase. This method involves coating a template core with TiO₂ and then a protection layer through sol–gel processes and then crystallization of the TiO₂ shell by calcination. Through a systematic study on the crystallization behaviour of the TiO₂ hollow shells with variation in core template and outer protection layer, we find that the grain growth and phase transformation of TiO₂ is determined by several parameters such as the protection material, core composition, and calcination conditions. In particular, the use of a crosslinked polymer as the protection layer for calcination, enables the production of TiO₂ shells with high crystallinity and controllable anatase–rutile mixed phases, which show significantly enhanced photocatalytic activity compared to those produced by SiO₂-protected calcination. The photocatalytic activity could be further improved by improving the water dispersity of TiO₂ shells through base treatment. With the ease of achieving photocatalytic activity comparable to commercial Degussa-P25 TiO₂, it is expected that the TiO₂ shells with controllable crystallinity and phase could be further engineered by incorporating more active components for producing highly active composite photocatalysts.