Preparation and Application of a Novel S-Scheme Nanoheterojunction Photocatalyst (LaNi_0.6Fe_0.4O₃/g-C₃N₄)

Rapid recombination of photogenerated electrons and holes affects the performance of a semiconductor device and limits the efficiency of photocatalytic water splitting for hydrogen production. The use of an S-scheme nanoscale heterojunction catalyst for the separation of photogenerated charge carriers is a feasible approach to achieve high-efficiency photocatalytic hydrogen evolution. Therefore, we synthesized a three-dimensional S-scheme nanoscale heterojunction catalyst (LaNi_0.6Fe_0.4O₃/g-C₃N₄) and investigated its activity in photocatalytic water splitting. An analysis of the band structure (XPS, UPS, and Mott-Schottky) indicated effective interfacial charge transfer in an S-scheme nanoscale heterojunction composed of two n-type semiconductors. X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) spectroscopy confirmed that the light-induced charge transfer followed the S-scheme mechanism. Based on the capture test (EPR) of •OH free radicals, it can be seen that the enhanced activity is attributed to the S-scheme carrier migration mechanism in heterojunction, which promotes the rapid adsorption of H⁺ by the abundant amino sites in g-C₃N₄, thus effectively generating H₂. The 2D/2D LaNi_0.6Fe_0.4O₃/g-C₃N₄ heterojunction has a good interface and produces a built-in electric field, improving the separation of e^- and h⁺ while increasing the oxygen vacancy. The synergistic effect of the heterostructure and oxygen vacancy makes the photocatalyst significantly better than LaNi_0.6Fe_0.4O₃ and g-C₃N₄ in visible light. The hydrogen evolution rate of the composite catalyst (LaNi_0.6Fe_0.4O₃/g-C₃N₄-70 wt %) was 34.50 mmol·h^-1·g^-1, which was 40.6 times and 9.2 times higher than that of the catalysts (LaNiO₃ and g-C₃N₄), respectively. After 25 h of cyclic testing, the catalyst (LaNi_0.6Fe_0.4O₃/g-C₃N₄-70 wt %) composite material still exhibited excellent hydrogen evolution performance and photostability. It was confirmed that the synergistic effect between abundant active sites, enriched oxygen vacancies, and 2D/2D heterojunctions improved the photoinduced carrier separation and the light absorption efficiency of visible light. This study opens up new possibilities for the logical design of efficient photodecomposition using 2D/2D heterojunctions combined with oxygen vacancies.