S-scheme heterojunctions: Emerging designed photocatalysts toward green energy and environmental remediation redox reactions

The implication of photocatalytic reactions based on semiconductor heterojunction are critical for impacting both environment and energy. Scientists are passionate for developing their photocatalytic competence. The high recombination rates of photoinduced charge carriers beside their limited oxidation and reduction abilities for solely semiconductor lead to the construction of heterojunctions by several approaches. Ranging from type-I, type-II, Schottky, and Z-scheme heterojunctions, the Step-Scheme (S-Scheme) heterojunction composed of two independent semiconductors with different band energies was emerged. A brief discussion on the difference between previously studied heterojunction types compared to the newly proposed S-Scheme is presented in this review in terms of charge-transfer mechanism and key characterization tools are presented. The current design strategies and perspective applications of S-scheme heterojunction photocatalysts in fuel production, carbon cycling (namely oxidation of organic compounds and reduction of carbon dioxide), as well as other important redox reactions are selectively highlighted as emerging green approach for clean energy and environmental remediation. Moreover, another related environmental reactions such as oxidation of nitrous oxide to green products and reduction of heavy metal ions to less toxic chemicals are discussed including our current research. The current challenges and perspectives for S-Scheme photocatalysis are also summarized.