Mesoporous Anatase Titania Hollow Nanostructures though Silica-Protected Calcination

The crystallization of nanometer-scale materials during high-temperature calcination can be controlled by a thin layer of surface coating. Here, a novel silica-protected calcination process for preparing mesoporous hollow TiO2 nanostructures with a high surface area and a controllable crystallinity is presented. This method involves the preparation of uniform silica colloidal templates, sequential deposition of TiO2 and then SiO2 layers through sol–gel processes, calcination to transform amorphous TiO2 to crystalline anatase, and finally etching of the inner and outer silica to produce mesoporous anatase TiO2 shells. The silica-protected calcination step allows crystallization of the amorphous TiO2 layer into anatase nanocrystals, while simultaneously limiting the growth of anatase grains to within several nanometers, eventually producing mesoporous anatase shells with a high surface area (∼311 m2 g−1) and good water dispersibility upon chemical etching of the silica. When used as photocatalysts for the degradation of Rhodamine B under UV irradiation, the as-synthesized mesoporous anatase shells show significantly enhanced photocatalytic activity with greater enhancement for samples calcined at higher temperatures thanks to their improved crystallinity.