2D/2D S-scheme heterojunction photocatalysts: fundamentals, engineering modification strategies, and applications

Two-dimensional/two-dimensional (2D/2D) S-scheme heterojunctions provide an effective route to combining efficient charge separation with strong redox capability in photocatalysis. Their planar interfaces shorten carrier transport distances, strengthen interfacial coupling, and facilitate the formation of internal electric fields. Meanwhile, the S-scheme pathway promotes the recombination of low-energy carriers while preserving highly reductive electrons and strongly oxidative holes. This review summarizes recent advances in 2D/2D S-scheme photocatalysts, emphasizing band alignment, interfacial charge transfer, structural advantages, and material selection. Major construction routes, including mixing-assisted assembly, surface chemical regulation, and in-situ growth, are compared in terms of interface formation and coupling strength. The discussion then examines how microscopy, spectroscopy, surface potential mapping, transient spectroscopy, and theoretical calculations resolve interfacial structures and verify charge transfer pathways. Recent advances in interfacial bonding, multidimensional coupling, doping, defect engineering, cocatalyst integration, single atom engineering, strain modulation, and facet control are further assessed for their effects on carrier dynamics, redox activity, and surface reaction kinetics. Finally, representative applications in H₂ evolution, CO₂ reduction, pollutant degradation, and H₂O₂ production are surveyed, and the review concludes by identifying key challenges and outlining future priorities for rational interface design.