0D/2D Sulfur-doped ZnO QDs/g-C₃N₄ nanosheets S-scheme heterojunction for visible-light-driven CO₂ reduction and environmental remediation

Rational design of dual-functional photocatalysts capable of concurrently driving CO₂ photoreduction and environmental remediation holds significant promise for addressing global energy shortages and environmental pollution challenges. Herein, we successfully fabricated a novel 0D/2D S-doped ZnO quantum dots/g-C₃N₄ nanosheets (SZ-QDs/CNNS) S-scheme heterojunction through a facile self-sacrificing template approach. Structural characterization reveals that the S-doped ZnO QDs are homogeneously dispersed across the g-C₃N₄ nanosheets, leading to the enhancement in visible-light harvesting capability of the composite system. Through combined density functional theory calculations and experimental investigations, we elucidated the interfacial charge transfer mechanism, revealing electron transfer from g-C₃N₄ to S-doped ZnO that establishes an internal electric field (IEF) oriented from g-C₃N₄ to S-doped ZnO. Electron spin resonance analysis under visible light irradiation confirmed that the IEF effectively drives photoexcited electrons from S-doped ZnO to g-C₃N₄, validating the formation of an S-scheme charge transfer pathway that significantly enhances electron-hole pair separation efficiency. The SZ-QDs/CNNS heterojunction demonstrates remarkable photocatalytic performance, achieving a CO evolution rate of 34.5 μmol·g⁻¹·h⁻¹ under visible light irradiation, which is 2.4 and 4.8 times higher than pristine g-C₃N₄ and S-doped ZnO, respectively. Furthermore, the SZ-QDs/CNNS also exhibits outstanding degradation efficiency for NO (56.5 % in 40 min), RhB (100 % in 40 min) and tetracycline (90 % in 180 min) compared to individual components. This work provides valuable insights into the rational design of efficient S-scheme photocatalysts for sustainable energy conversion and environmental applications.