S-scheme C3N5/Fe2TiO5 heterojunction for enhanced photocatalytic H2 evolution: Synergistic contribution of dipole field and internal electric field

Solar-driven photocatalytic water splitting provides a sustainable route for producing green H₂, but there are still several challenges in its practical application, including severe recombination of photogenerated charge carriers, low separation and transfer efficiency of photogenerated electron and hole pairs, and inefficient photocatalysts. To address these issues, we successfully constructed an S-scheme CN/FTO (C₃N₅/Fe₂TiO₅) heterojunction photocatalyst system based on C₃N₅ (CN) and Fe₂TiO₅ (FTO) nanoparticles by simple hydrothermal assembly of two pre-fabricated semiconductors. Under simulated solar irradiation, the CN/FTO heterojunction exhibits significantly improved photocatalytic H₂ production rate, reaching 607.7 μmol g⁻¹ h⁻¹, which is 9.5- and 7.1-fold higher than pure CN and FTO, respectively. The improvement in photocatalytic efficiency is attributed to synergistic modulation of photogenerated charge transfer by the internal electric field (IEF) formed at the CN/FTO interface and intrinsic structural and electronic features of the nitrogen-rich CN. This collaboration significantly accelerates the separation and directional transfer of photogenerated charge carriers between the CN and FTO interface and within the CN itself. Based on experimental characterizations, an S-scheme photogenerated charge carrier transfer mechanism is proposed. The combined effects of the CN/FTO heterojunction IEF and the CN structural features induce favorable band bending and facilitate efficient charge separation and transfer via the S-scheme pathway, thereby enhancing photocatalytic activity. This study emphasizes the crucial role of the interfacial IEF and the intrinsic structural and electronic properties of CN in synergistically regulating the directional migration of photogenerated charge carriers. It presents insights into the dynamics of photogenerated charge migration and photocatalytic reaction control through S-scheme heterojunction engineering, particularly utilizing nitrogen-rich carbon nitrides.