Novel Anatase TiO<sub>2</sub> Boxes and Tree-like Structures Assembled by Hollow Tubes: d,l-Malic Acid-Assisted Hydrothermal Synthesis, Growth Mechanism, and Photocatalytic Properties

Novel anatase TiO<sub>2</sub> hollow boxes and tree-like structures assembled by hollow tubes with a surface area as high as 241.89 m<sup>2</sup>/g can be synthesized in large scale by a simple hydrothermal method. A distinctive growth mechanism taking advantage of the gaps and cracks in rectangular particulates with a composition of (TiO<sub>2</sub>)<sub>2</sub>·C<sub>4</sub>H<sub>6</sub>O<sub>5</sub>·6H<sub>2</sub>O as template has been proposed, which results in a particular structure with a double-layer wall and several inserted layers or separated rooms in the anatase TiO<sub>2</sub> hollow boxes. The effects of the reaction time, temperature, and molar ratio between d,l-malic acid and TiCl<sub>4</sub> on the formation of anatase TiO<sub>2</sub> have been investigated in detail. The results demonstrate that a larger molar ratio of d,l-malic acid and TiCl<sub>4</sub> benefits the formation of TiO<sub>2</sub> hollow boxes with larger aspect ratios. Anatase TiO<sub>2</sub> tree-like structures assembled by hollow tubes can be obtained when the molar ratio is kept at 5.4. Moreover, these distinctive structures show excellent photocatalytic properties, which would find potential applications in photocatalytic fields.