Abstract: The photocatalytic synthesis of hydrogen peroxide (H₂O₂) using water and oxygen represents an economically viable, environmentally benign, and sustainable pathway. However, single-component photocatalysts are constrained by limited light-harvesting ranges, rapid carrier recombination, and insufficient redox capacities. In this study, the CdIn₂S₄/poly (barbituric acid) (CdInS/PBA) inorganic/organic S-scheme heterojunction photocatalyst was fabricated via ultrasonic self-assembly. The as-formed internal electric field and band bending in the prepared CdInS/PBA heterojunction not only accelerate the transfer of interface photogenerated charges, but also retain the strong reduction ability of electrons in CdIn₂S₄ and the strong oxidation ability of holes in PBA. In addition, the inorganic/organic composite systems can synergistically utilize the advantages of each component in photocatalytic generation of H₂O₂, in which the inorganic CdIn₂S₄ acts as a reaction site to promote the hydrophobic oxygen reduction process, while the organic PBA acts as an oxidation reaction site to promote the hydrophilic H₂O oxidation process. The as-prepared CdInS/PBA heterojunction demonstrates a high H₂O₂ production rate under visible light irradiation that is 4.5 times and 2.4 times higher than pristine CdIn₂S₄ and PBA, respectively. Finally, the rotating ring-disk electrode (RRDE) measurements and in-situ FTIR spectroscopy verify that the H₂O₂ generation by CdInS/PBA heterojunction follows a two-step single-electron oxygen reduction reaction (ORR) mechanism.

Key words: Photocatalysis, Cadmium indium sulfide, Poly (barbituric acid), S-scheme heterojunction, H₂O₂ production