S-Scheme Heterostructured CdS/g-C₃N₄ Nanocatalysts for Piezo-Photocatalytic Synthesis of H₂O₂

Sustainability in catalysis is increasingly becoming the primary target in academic and industrial studies. Regarding the material perspective, designing heterojunction nanocatalysts to produce small molecules, such as hydrogen peroxide (H2O2), has been an attractive research theme in recent decades. Nonetheless, most reported materials suffer from a complicated synthetic process with various steps and using unbenign solvents, hindering practical applications on an industrial scale. This study proposed a facile one-step way to fabricate heterostructured CdS/g-C3N4 nanocatalysts to produce H2O2 from water and oxygen under light and ultrasound irradiation. The results showed that the formation of H2O2 mainly relies on oxygen radical species. Oxygen is initially converted into superoxide via excited electrons from CdS, followed by the formation of singlet oxygen from the oxidation process in g-C3N4 sites. Interestingly, the formation of H2O2 in an inert atmosphere is associated with the in situ evolution of oxygen from water oxidation due to the suitable electronic band position of g-C3N4 to drive multioxidation reactions. Charge transfer characterizations illustrate the S-scheme mechanism in the catalytic process, giving a better understanding of the charge transportation phenomenon, thus providing a critical pathway in designing and developing heterojunction materials for catalysis with easier catalyst preparation and operation processes.