SrTiO 3 /Bi 4 Ti 3 O 12 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 ₃ on Bi ₄ Ti ₃ O ₁₂ platelets is studied as a new route for the formation of novel nanoheterostructural SrTiO ₃ /Bi ₄ Ti ₃ O ₁₂ platelets at an intermediate stage or (100)-oriented mesocrystalline SrTiO ₃ nanoplatelets at the completed stage of the TC reaction. The Bi ₄ Ti ₃ O ₁₂ platelets act as a source of Ti(OH) ₆ ^2- species and, at the same time, as a substrate for the epitaxial growth of SrTiO ₃ . The dissolution of the Bi ₄ Ti ₃ O ₁₂ platelets proceeds faster from the lateral direction, whereas the epitaxial growth of SrTiO ₃ occurs on both bismuth-oxide-terminated basal surface planes of the Bi ₄ Ti ₃ O ₁₂ platelets. In the progress of the TC reaction, the Bi ₄ Ti ₃ O ₁₂ platelet is replaced from the lateral ends toward the interior by SrTiO ₃ , while Bi ₄ Ti ₃ O ₁₂ is preserved in the core of the heterostructural platelet. Without any support from noble-metal doping or cocatalysts, the SrTiO ₃ /Bi ₄ Ti ₃ O ₁₂ platelets show stable and 15 times higher photocatalytic H ₂ production (1265 μmol·g ^-1 ·h ^-1 ; solar-to-hydrogen (STH) efficiency = 0.19%) than commercial SrTiO ₃ nanopowders (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.