S-scheme GQDs/Bi24O31Br10 heterojunction boosts photocatalytic H2O2 production and tetracycline degradation

Abstract

GQDs/Bi₂₄O₃₁Br₁₀ S-scheme heterojunction composite was successfully constructed via a hydrothermal method and its bifunctional performance in photocatalytic tetracycline (TC) degradation and hydrogen peroxide (H₂O₂) production was systematically evaluated. Results demonstrate that the optimized composite exhibits excellent activity in both reactions. It achieves a TC degradation rate of 88.5% within 20 min, and a H₂O₂ production yield of 104.53 μM within the same time, which is 4.2 times that of pure Bi₂₄O₃₁Br₁₀. Mechanism studies reveal that the superoxide radical serves as the key reactive species, acting as both a crucial intermediate for H₂O₂ synthesis and the dominant active species for TC degradation. The built-in electric field at S-scheme heterojunction interface enables efficient spatial separation of photogenerated carriers. Highly reductive electrons accumulate on graphene quantum dots (GQDs) to promote the two-step single-electron reduction of O₂ for H₂O₂ generation, while strongly oxidative holes remain on Bi₂₄O₃₁Br₁₀ to maintain degradation capability. This work not only develops an efficient and stable bifunctional photocatalyst but also elucidates at the microscopic scale how the S-scheme heterojunction synergistically drives different reactions through precise regulation of charge transfer pathways. It thus provides a theoretical foundation and practical guidance for designing novel photocatalytic systems for environmental remediation and green synthesis.