Black TiO2/g-C3N4 films as a Z-scheme heterojunction for enhanced photocatalytic hydrogen evolution

Titanium dioxide (TiO₂) is a widely used photocatalyst, but its large band gap (~3.2 eV) and rapid charge recombination limit the solar-driven efficiency. Black TiO₂ (b-TiO₂) with oxygen vacancies and Ti³⁺ defects can extend absorption into the visible region. In this work, black TiO₂ films decorated with graphitic carbon nitride (g-C₃N₄) nanoparticles were fabricated via a simple and efficient one-step solvothermal impregnation method for photocatalytic hydrogen evolution from water splitting. Morphological characterization by scanning and transmission electron microscopy reveals reveal that the films consist of aggregated TiO₂ nanowires, with g C₃N₄ uniformly wrapping around the nanowires to form an intimate heterojunction interface. X-ray photoelectron spectroscopy confirmed the presence of Ti³⁺ species and oxygen vacancies in the composite. Ultraviolet-visible diffuse reflectance spectroscopy demonstrated significantly enhanced visible-light absorption with a narrowed band gap of 1.82 eV. Under simulated sunlight irradiation (350 W xenon lamp), the optimized b-TiO₂/g-C₃N₄ composite exhibited a hydrogen evolution rate 1.64 times higher than that of the pristine white TiO₂. This remarkable improvement is attributed to the synergistic effects of a large specific surface area, abundant defect states, and a Z-scheme heterojunction charge transfer mechanism, which collectively extend the light-harvesting range and promote the efficient spatial separation of electron–hole pairs, thereby boosting the overall photocatalytic performance. These findings provide a facile strategy for designing high-efficiency, defect-engineered heterojunction photocatalysts for solar‑driven H₂ generation.