TiO_2-X mesoporous nanospheres/BiOI nanosheets S-scheme heterostructure for high efficiency, stable and unbiased photocatalytic hydrogen production

The efficiency of hydrogen production via semiconductor photocatalysts is currently limited by poorly light adsorption, rapid recombination of photogenerated carriers, ineffective surface catalytic behavior, and field-instability. Herein, a hierarchical S-scheme photocatalyst composite of BiOI nanosheets (NS) with Ti³⁺ self-doped black TiO_2-X mesoporous nanospheres (MS) was prepared, from which we observed an improve light utilization, as well as the accelerated separation and migration of photogenerated carriers. Furthermore, the optimized TiO_2-X/BiOI heterostructure exhibited a robust H₂ evolution rate of 794.28 μmol g⁻¹h⁻¹, which was approximately 9.2 and 3 times that of pure BiOI NS and TiO₂ MS, respectively. The photocatalytic mechanism of S-scheme heterostructure between black TiO_2-X and BiOI was proposed by combining upconversion spectrum, low temperature photoluminescence spectrum and theoretical calculations. This work provides not only a facile synthetic method to prepare the heterojunction structures with high catalytic activity, but also establishes a platform for future materials-by-design with S-scheme energy band structures.