Hierarchical TiO2 Nanospheres with Dominant {001} Facets: Facile Synthesis, Growth Mechanism, and Photocatalytic Activity

Abstract Hierarchical TiO 2 nanospheres with controlled surface morphologies and dominant {001} facets were directly synthesized from Ti powder by a facile, one‐pot, hydrothermal method. The obtained hierarchical TiO 2 nanospheres have a uniform size of 400–500 nm and remarkable 78 % fraction of {001} facets. The influence of the reaction temperature, amount of HF, and reaction time on the morphology and the exposed facets was systematically studied. A possible growth mechanism speculates that Ti powder first dissolves in HF solution, and then flowerlike TiO 2 nanostructures are formed by assembly of TiO 2 nanocrystals. Because of the high concentration of HF in the early stage, these TiO 2 nanostructures were etched, and hollow structures formed on the surface. After the F − ions were effectively absorbed on the crystal surfaces, {001} facets appear and grow steadily. At the same time, the {101} facets also grow and meet the {101} facets from adjacent truncated tetragonal pyramids, causing coalescence of these facets and formation of nanospheres with dominant {001} facets. With further extension of the reaction time, single‐crystal {001} facets of hierarchical TiO 2 nanospheres are dissolved and TiO 2 nanospheres with dominant {101} facets are obtained. The photocatalytic activities of the hierarchical TiO 2 nanospheres were evaluated and found to be closely related to the exposed {001} facets. Owing to the special hierarchical architecture and high percentage of exposed {001} facets, the TiO 2 nanospheres exhibit much enhanced photocatalytic efficiency (almost fourfold) compared to P25 TiO 2 as a benchmark material. This study provides new insight into crystal‐facet engineering of anatase TiO 2 nanostructures with high percentage of {001} facets as well as opportunities for controllable synthesis of 3D hierarchical nanostructures.