Constructing an S-Scheme NiO/SrTiO3 Heterojunction for Highly Enhanced Visible-Light Photocatalytic Removal of Methylene Blue

Organic dye pollution in industrial wastewater poses a serious environmental challenge, with methylene blue (MB) serving as a typical persistent pollutant due to its stable chemical structure, recalcitrance to degradation, and eco-toxicity. Conventional physical, chemical, and biological treatment methods suffer from limitations such as insufficient efficiency, high cost, or the tendency to generate secondary pollution. Based on green and sustainable photocatalysis technology, this study designed and prepared a NiO/SrTiO₃ p-n heterojunction photocatalysts, aiming to broaden the light-response range and enhance charge-carrier separation efficiency. The optimal sample (NiO (10%)/SrTiO₃) achieved complete photocatalytic degradation of MB within 9 min, with an apparent rate constant 34.6 times that of pure SrTiO₃. It also showed good cyclic stability. Trapping experiments confirmed that •OH and •O₂^- were the key active species in the degradation process. Combined with band structure and PL analyses, an S-scheme charge-transfer mechanism was proposed, clarifying the critical role of the built-in electric field at the heterojunction interface in promoting carrier separation while maintaining high redox capability. This work not only provides a new pathway for developing efficient and stable SrTiO₃-based photocatalysts but also offers theoretical and experimental support for the practical application of p-n heterojunction photocatalysts in environmental pollution control.