Engineering S-Scheme Heterojunction of Bi ₂ S ₃ and Zn _0.5 Cd _0.5 Se Quantum Dots for Superior Photocatalytic Activity

The photocatalytic O2 reduction reaction to produce H2O2 has received a lot of attention as a potential approach for energy conversion owing to its economical and sustainable pathway. Here, we have synthesized the Zn0.5Cd0.5Se (ZCSe)/Bi2S3 S-scheme heterojunction by decorating ZCSe QDs over the Bi2S3 nanoflower. The optimized ZCSe/Bi2S3 (ZB100) composite sample yield was 2.54 mmol g–1 h–1 with ethanol as the sacrificial agent under visible light irradiation, and it was stable for up to four cycles and achieved a solar to chemical conversion efficiency of 0.11% in pure water. The S-scheme mechanism facilitated interfacial charge transfer owing to the interfacial electric field between ZCSe QDs and Bi2S3. The energy band alignment in the ZCSe/Bi2S3 S-scheme heterojunction was determined from X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, Tauc plot, and Mott–Schottky analysis. The incorporation of Bi2S3 and ZCSe QDs diminished the recombination rate of excitons and enhanced the light absorption capacity. The active radical trapping experiments and NBT test corroborated that superoxide radicals were the dominant intermediate species produced during the H2O2 production reaction following a two-step single-electron pathway.