SrTiO/BiTiO Nanoheterostructural Platelets Synthesized by Topotactic Epitaxy as Effective Noble-Metal-Free Photocatalysts for pH-Neutral Hydrogen Evolution.

Low-temperature hydrothermal epitaxial growth and topochemical conversion (TC) reactions offer unexploited possibilities for the morphological engineering of heterostructural and non-equilibrium shape (photo)catalyst particles. The hydrothermal epitaxial growth of SrTiO on BiTiO platelets is studied as a new route for the formation of novel nanoheterostructural SrTiO/BiTiO platelets at an intermediate stage or (100)-oriented mesocrystalline SrTiO nanoplatelets at the completed stage of the TC reaction. The BiTiO platelets act as a source of Ti(OH) species and, at the same time, as a substrate for the epitaxial growth of SrTiO. The dissolution of the BiTiO platelets proceeds faster from the lateral direction, whereas the epitaxial growth of SrTiO occurs on both bismuth-oxide-terminated basal surface planes of the BiTiO platelets. In the progress of the TC reaction, the BiTiO platelet is replaced from the lateral ends toward the interior by SrTiO, while BiTiO is preserved in the core of the heterostructural platelet. Without any support from noble-metal doping or cocatalysts, the SrTiO/BiTiO platelets show stable and 15 times higher photocatalytic H production (1265 μmol·g·h; solar-to-hydrogen (STH) efficiency = 0.19%) than commercial SrTiO nanopowders (81 μmol·g·h; STH = 0.012%) in pH-neutral water/methanol solutions. A plausible Z scheme is proposed to describe the charge-transfer mechanism during the photocatalysis.