Controllable synthesis of porous TiO₂ with a hierarchical nanostructure for efficient photocatalytic hydrogen evolution

TiO₂ has been the most suitable candidate for commercial scale-up photocatalysts to date. However, the practical application of TiO₂ has been limited, due to its wide band gap (3.0 eV for rutile and 3.2 eV for anatase) and recombination of photoinduced charges. Herein, we report a simple and effective approach to resolve the limitations by manipulating the structure and size of TiO₂ to improve the photocatalytic efficiency. By adjusting the volume ratio of hydrochloric acid (HCl) and ethylene glycol (EG), porous TiO₂ hierarchical microspheres with controllable size of nanorods were obtained. The nanorods were several hundreds of nanometers long with different average widths, including 5 (TiO₂-5), 10 (TiO₂-10) and 15 nm (TiO₂-15). The band gap of TiO₂-5 was as low as 2.75 eV with a super large BET surface area of 216.607 m² g^-1. The rate of photocatalytic hydrogen generation for TiO₂-5 was 23.74 mmol g^-1 h^-1 under UV-visible light irradiation of 200 mW cm^-2.