Hierarchical TiO sub(2) Nanospheres with Dominant {001} Facets: Facile Synthesis, Growth Mechanism, and Photocatalytic Activity

Hierarchical TiO sub(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 sub(2) nanospheres have a uniform size of 400-500nm 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 sub(2) nanostructures are formed by assembly of TiO sub(2) nanocrystals. Because of the high concentration of HF in the early stage, these TiO sub(2) nanostructures were etched, and hollow structures formed on the surface. After the F super(-) 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 sub(2) nanospheres are dissolved and TiO sub(2) nanospheres with dominant {101} facets are obtained. The photocatalytic activities of the hierarchical TiO sub(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 sub(2) nanospheres exhibit much enhanced photocatalytic efficiency (almost fourfold) compared to P25 TiO sub(2) as a benchmark material. This study provides new insight into crystal-facet engineering of anatase TiO sub(2) nanostructures with high percentage of {001} facets as well as opportunities for controllable synthesis of 3D hierarchical nanostructures. A one-pot hydrothermal method was used for facile synthesis of hierarchical TiO sub(2) nanospheres with controlled surface morphologies and up to 78% {001} facets (see figure). The influence of reaction temperature, reaction time, and HF concentration was systematically studied. A possible growth mechanism of the hierarchical TiO sub(2) nanostructures with exposed {001} facets was proposed. Owing to their hierarchical architecture and high percentage of exposed {001} facets, the hierarchical TiO sub(2) nanospheres exhibit much enhanced photocatalytic efficiency (almost fourfold