Well-crystallized mesoporous TiO2 shells for enhanced photocatalytic activity: prepared by carbon coating and silica-protected calcination

Abstract

Mesoporous anatase-phase TiO₂ hollow shells were successfully fabricated by the solvothermal and calcination process. This method involves preparation of SiO₂@TiO₂ core–shell colloidal templates, sequential deposition of carbon and then silica layers through solvothermal and sol–gel processes, crystallization of TiO₂ by calcination and finally removal of the inner and outer silica to produce hollow anatase TiO₂ shells. The prepared samples were characterized by transmission electron microscopy, X-ray diffraction, N₂ adsorption–desorption isotherms and UV-vis absorption spectroscopy. The results show that a uniform carbon layer is coated on the core–shell particles through the solvothermal process. The combustion of carbon offers the space for the TiO₂ to further grow into large crystal grains, and the outer silica layer serves as a barrier against the excessive growth of anatase TiO₂ nanocrystals. Furthermore, the initial crystallization of TiO₂ generated in the carbon coating step and the heat generated by the combustion of the carbon layer allow the crystallization of TiO₂ at a relatively low temperature without changing the uniform structure. When used as photocatalysts for the oxidation decomposition of Rhodamine B in aqueous solution under UV irradiation, the hollow TiO₂ shells showed enhanced catalytic activity. Moreover, the TiO₂ hollow shells prepared with optimal crystallinity by this method showed a higher performance than commercial P25 TiO₂.