Sulfur-vacancy-induced charge density redistribution for efficient photocatalytic Cr(VI) reduction in an S-scheme AgIn₅S₈/Bi₂S₃ heterojunction

The rapid recombination of photogenerated charge carriers and the poor stability of metal sulfides remain bottlenecks limiting their practical applications. In this study, sulfur vacancies were introduced into an S-scheme AgIn5S8/Bi2S3 heterojunction via an in situ hydrothermal method. The sulfur vacancies induced charge density redistribution within the heterojunction and generated efficient active sites for electrons, thereby creating a localized electron-rich environment. The synergistic effects of the sulfur vacancies, internal electric field, and defect energy levels accelerated the separation and transfer of photogenerated charge carriers via the S-scheme pathway, thereby enhancing the visible-light photocatalytic performance, by achieving a Cr(VI) reduction efficiency of 99.6%. More importantly, the long-term stability and excellent anti-interference capability of the S-scheme AgIn5S8/Bi2S3 heterojunction demonstrate its practical application potential, achieving 98.9% Cr(VI) removal from real electroplating wastewater and meeting discharge standards. This work provides a theoretical basis for constructing highly-catalytic S-scheme heterojunctions and serves as a promising solution for Cr(VI)-containing electroplating wastewater treatment.