The hierarchical structure of cubic K_0.5La_0.5TiO₃ layers and enhanced photocatalytic hydrogen evolution after surface acidification

Transition-metal perovskite oxides possess rich functionalities in the fields of ferroelectrics, piezoelectrics, superconductors, dielectrics, fuel cells and photocatalysis. Nano-facet control of the cubic ATiO₃ (A: a divalent cation) phase, a typical perovskite oxide, may result in new properties or phenomena not observable in the bulk material. Herein, we first report a puzzle-like 3D hierarchical structure constructed with K_0.5La_0.5TiO₃ nanosheets. Surprisingly, K_0.5La_0.5TiO₃ has a cubic symmetry similar to a SrTiO₃ perovskite. The unusual phase is synthesized by a simple one-pot hydrothermal strategy without using any structure-directing agent. After modest acidification, the assembled 3D hierarchical structure is etched into a core-shell nanostructure which consists of a crystalline K_0.5La_0.5TiO₃ core and an amorphous TiO₂ shell. The acid-treated sample exhibits remarkably enhanced photocatalytic H₂ production, which is over 60 times higher than the pristine sample.