Inverse Opal Sn2– x TiO4/TiO2 S-Scheme Heterojunction with Slow Photon Effect for Photocatalytic Hydrogen Production and Degradation

Abstract Photocatalytic water splitting for hydrogen production is a crucial pathway for renewable energy conversion. However, conventional photocatalysts commonly face challenges such as low light absorption efficiency and severe recombination of photogenerated charge carriers. In this study, a Sn2–xTiO4/TiO2 S-scheme heterojunction photocatalyst with an inverse opal structure was designed and constructed. The inverse opal structure provides continuously interconnected macropores and a high effective reaction interface, while promoting multiple light scattering and the slow photon effect within the material, thereby improving light harvesting efficiency. Meanwhile, the intimate heterojunction interface between TiO2 and Sn2–xTiO4 establishes the construction of charge transfer pathways, enabling efficient separation and utilization of photogenerated electron–hole pairs, thus accelerating surface redox reactions. The results demonstrated that the heterojunction achieved nearly 100% degradation of methyl orange (MO) within 4 min under UV irradiation, and exhibited a hydrogen evolution rate of 19.64 mmol g–1 h–1 under 300 W xenon lamp irradiation, about 11 times higher than that of IO TiO2, indicating outstanding photocatalytic performance. This study demonstrates that the synergistic effect between the optical properties of inverse opal structures and charge regulation at heterojunction interfaces is an effective strategy for constructing highly efficient photocatalytic materials with both environmental purification and energy conversion.