Template synthesis of single-crystal-like porous SrTiO₃ nanocube assemblies and their enhanced photocatalytic hydrogen evolution.

Porous nanostructures of semiconductors are well-known for their ability to enhance the photocatalytic activity thanks to the large specific surface area and abundant active sites for the reactions, interfacial transport, and high utilization of light arising from multireflections in the pores. In this paper, we have successfully fabricated a special porous SrTiO3 three-dimensional (3D) architecture through a facile hydrothermal reaction at 150 °C, using layered protonated titanate hierarchical spheres (LTHSs) of submicrometer size as a precursor template. The SrTiO3 architecture is characterized by the 3D assembly of hundreds of highly oriented nanocubes of 60-80 nm by the partial sharing of (100) faces, thereby displaying porous but single-crystal-like features reminiscent of mesocrystals. Our experimental results have shown the key roles played by the template effect akin to that in topotactic transformation in crystallography and Ostwald-ripening-assisted oriented attachment in the formation of such nanocube assemblies. Compared to the solid SrTiO3 photocatalysts previously synthesized by high-temperature solid-state methods, the as-synthesized porous SrTiO3 nanocube assemblies have relatively large specific surface areas (up to 20.83 m(2)·g(-1)), and thus they have exhibited enhanced photocatalytic activity in hydrogen evolution from water splitting. Expectantly, our synthetic strategy using LTHSs as the precursor template may be extended to the fabrication of other titanate photocatalysts with similar porous hierarchical structures by taking advantage of the diversity of the perovskite-type titanate.