Controllable Synthesis of Mesoporous TiO 2 Hollow Shells: Toward an Efficient Photocatalyst

TiO 2 hollow shells with well‐controlled crystallinity, phase, and porosity are desirable in many applications. In photocatalysis in particular, they can provide high active surface area, reduced diffusion resistance, and improved accessibility to reactants. Here, the results from studies of the causes for the failure of a prior etching and calcination scheme to make such shells and on a newly‐developed simple yet robust process for producing uniform mesoporous TiO 2 shells with precisely controllable crystallinity and phase are reported. The key finding is that base etching of the SiO 2 @TiO 2 core‐shell particles leads to the formation of sodium titanate species, which, if not removed, promote substantial crystal growth during calcination and destroy the structural integrity of the TiO 2 shells. A simple acid treatment of the base‐etched samples may convert the sodium titanates into protonated titanates, which not only prevent the formation of the impurity phases, but also help to maintain the structural integrity of the shell and allow precise control of the TiO 2 phase and crystallinity. This new development affords convenient optimization of the structure of the hollow TiO 2 shells toward efficient photocatalysts, which outperform the commercial P25‐TiO 2 in the photocatalytic decomposition of organic dye molecules.