Hierarchical TiO ₂ Nanosheets for High-Performance Photocatalytic Hydrogen Evolution

Two-dimensional single-crystal nanomaterials have been extensively studied in various fields due to their unique structure and crystalline properties. However, chemical synthesis methods have limitations in precisely controlling the crystal assembly structure. The inevitable stacking phenomenon in two-dimensional (2D) nanomaterials hinders the full utilization of advantages of highly exposed surfaces, thereby restricting the developmental potential in this field. In this work, we report a polyacid-induced solvothermal method for constructing highly (101)-exposed hierarchical single-crystal titanium dioxide (HSC-TiO 2 ) with a thickness of 25 nm and an average size of 2 μm in the anatase phase. By adjusting the mixed acid ratio and reaction time, the constituent units from 0D to 2D and the number of layers can be further modulated while maintaining crystal orientation. Such a combination of crystalline orientation and hierarchical spatial structure provides efficient mass and charge transfer that greatly promotes the hydrogen generation rate under sunlight with good stability. The study is envisaged to afford an exciting pathway for the design and synthesis of specific single-crystal structures, nanoarchitectures, and complex hierarchies toward future nanotechnologies.