Steering the Bi4Ti3O12-to-SrTiO3 hydrothermal transformation for controlling the functionality of two-dimensional (2D) SrTiO3 nanoplatelets for photocatalytic H2 evolution

The Aurivillius-Phase Bi₄Ti₃O₁₂ platelets are not only important functional materials in their own right, but also serve as valuable two-dimensional (2D) templates for converting into 2D ATiO₃ (A = Sr, Ba, Ca) perovskite platelets with a favourable (100) orientation. The transformation under low-temperature (200 °C) hydrothermal conditions has recently been demonstrated; however, the process remains underexplored regarding the mechanistic control of the final product properties. This study sheds light on the steering of the Bi₄Ti₃O₁₂-to-SrTiO₃ hydrothermal transformation to precisely control the surface roughness and photocatalytic properties of the 2D epitaxial heterostructural SrTiO₃/Bi₄Ti₃O₁₂ and SrTiO₃ nanoplatelets. A higher excess of Sr (Sr/Ti = 15), smaller Bi₄Ti₃O₁₂ template nanoplatelets, and pre-reaction etching of the template with hot NaOH promote the formation of high-surface-area SrTiO₃/Bi₄Ti₃O₁₂ and SrTiO₃ nanoplatelets (BET >60 m 2 /g), which show more than 50 times higher H₂ evolution rates compared to smooth, low surface area platelets (BET~10 m 2 /g). This study demonstrated that higher surface roughness facilitates effective surface trapping of bismuth species, which, through in-situ reduction to metallic Bi° single atoms, acted as a co-catalyst and enhanced photocatalytic H 2 evolution. Both SrTiO₃/Bi₄Ti₃O₁₂ and SrTiO₃ nanoplatelets exhibited stable photocatalytic responses, but only SrTiO₃ maintained structural and chemical integrity under illumination. This study presents a new strategy for engineering the surface and functional properties of 2D SrTiO₃ perovskite nanoplatelets through the hydrothermal transformation of Aurivillius phase Bi₄Ti₃O₁₂ nanoplatelets, thereby expanding possibilities for the functional engineering of other 2D perovskite nanostructures. Higher surface roughness of SrTiO 3 nanoplatelets enhances photocatalytic H 2 evolution • Tailored surface roughness of 2D SrTiO 3 , derived from Bi 4 Ti 3 O 12 nanoplatelets. • Rough SrTiO 3 surface facilitates trapping of bismuth single atom co-catalysts. • Rough-surface SrTiO 3 nanoplatelets show 50-times higher H 2 evolution than smooth ones. • High photocatalytic and chemical stability of SrTiO 3 . • Inner Bi 4 Ti 3 O 12 part of heterostructures changes during photocatalysis into Bi°.