Construction of an S-Scheme g-C3N4/In2S3 Heterojunction with a Boosted Interfacial Electric Field for Highly Efficient Photocatalytic Cr(VI) Reduction under Simulated Sunlight Irradiation

The limitations of traditional water treatment in Cr(VI) removal have spurred the development of solar-driven photocatalysis as a sustainable alternative for environmental remediation. Herein, an S-scheme g-C3N4/In2S3 heterojunction was synthesized via a hydrothermal strategy. Compared to its monocomponent counterparts, the obtained composite exhibits an extended light absorption edge and enhanced Cr(VI) reduction. Comprehensive microstructural and surface chemical analyses reveal that the Fermi-level offset between g-C3N4 and In2S3 triggers the formation of a strong internal electric field at the intimate interface, which promotes efficient spatial separation of photogenerated charges while preserving high-energy reductive electrons for photocatalytic reduction. Consequently, the obtained g-C3N4/In2S3 sample achieves a remarkable 99.5% Cr(VI) reduction efficiency within 20 min, with an apparent reaction rate approximately 2.3-fold higher than that of In2S3, respectively. Mechanistic studies confirm that charge transfer follows an S-scheme pathway, and that photogenerated electrons and superoxide radicals were found to play a dominant role in the reaction. This work not only provides a rational strategy for the architectural engineering of S-scheme composite photocatalysts but also opens up a highly promising pathway for using solar energy to eliminate diverse highly toxic pollutants in aqueous environments.