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.

Plate-like Bi 4 Ti 3 O 12 particles were synthesized using a one-step, molten-salt method from Bi 2 O 3 and TiO 2 nanopowders at 800 °C. The reaction parameters that affect the crystal structure and morphology were identified and systematically investigated. The differences between various Bi 4 Ti 3 O 12 plate-like particles were examined in terms of the ferroelectric-to-paraelectric phase transition and the photocatalytic activity for the degradation of Rhodamine B under UV-A light irradiation. The results encouraged us to conduct further testing of the as-prepared Bi 4 Ti 3 O 12 plate-like particles as templates for the preparation of plate-like SrTiO 3 perovskite particles using a topochemical conversion under hydrothermal conditions. The characteristics of the Bi 4 Ti 3 O 12 plates and the reaction parameters for which the SrTiO 3 preserved the shape of the initial Bi 4 Ti 3 O 12 template particles were determined.

The engineering of epitaxial, two-dimensional (2D) nano-heterostructures has stimulated great interest owing to an expectation of better functional properties (e.g., photocatalytic, piezoelectric). Hydrothermal topotactic epitaxy is one of the promising...