SrTiO3/Bi4Ti3O12Nanoheterostructural 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 SrTiO3on Bi4Ti3O12platelets is studied as a new route for the formation of novel nanoheterostructural SrTiO3/Bi4Ti3O12platelets at an intermediate stage or (100)-oriented mesocrystalline SrTiO3nanoplatelets at the completed stage of the TC reaction. The Bi4Ti3O12platelets act as a source of Ti(OH)62–species and, at the same time, as a substrate for the epitaxial growth of SrTiO3. The dissolution of the Bi4Ti3O12platelets proceeds faster from the lateral direction, whereas the epitaxial growth of SrTiO3occurs on both bismuth-oxide-terminated basal surface planes of the Bi4Ti3O12platelets. In the progress of the TC reaction, the Bi4Ti3O12platelet is replaced from the lateral ends toward the interior by SrTiO3, while Bi4Ti3O12is preserved in the core of the heterostructural platelet. Without any support from noble-metal doping or cocatalysts, the SrTiO3/Bi4Ti3O12platelets show stable and 15 times higher photocatalytic H2production (1265 μmol·g–1·h–1; solar-to-hydrogen (STH) efficiency = 0.19%) than commercial SrTiO3nanopowders (81 μmol·g–1·h–1; STH = 0.012%) in pH-neutral water/methanol solutions. A plausible Z scheme is proposed to describe the charge-transfer mechanism during the photocatalysis.