Enhanced Photocatalytic H2O2 Production over CuO@g-C3N4 Heterojunctions: Interfacial Effects with DFT Insights

Abstract

Photocatalytic H₂O₂ production offers a promising sunlight-driven pathway toward sustainable oxidant synthesis, but its performance is constrained by slow interfacial redox kinetics, insufficient proton availability, and rapid recombination of photoinduced carriers. Herein, g-C₃N₄ was prepared by thermally calcining melamine and ammonium fluoride at equal mass, and CuO@g-C₃N₄ composites were subsequently constructed via ultrasound-assisted dispersion and hydrothermal treatment. The morphology, phase structure, surface chemistry, optical response, charge-transport behavior, carrier lifetime, and electronic structure were investigated by SEM-EDS, XRD, XPS, BET, UV–vis DRS, PL, photoelectrochemical measurements, TPV, and DFT simulations. Benefiting from optimized interfacial electronic interaction, the 30% CuO@g-C₃N₄ composite delivered H₂O₂ generation productivity reaching 2120 μmol g^–1 h^–1 in air using a water/isopropanol mixed solvent (9:1, v/v), 3.66 times the value for pristine soft-templated g-C₃N₄. Under pure O₂, the productivity further increased to 3700 μmol g^–1 h^–1 with cycling durability. PL, EIS, and TPV analyses confirm that CuO incorporation suppresses charge recombination, promotes carrier transport, and extends the carrier lifetime from 414 to 7117 μs. Combined evidence from XPS, band-structure analysis, photoelectrochemical measurements, reactive-species quenching, DMPO-trapping EPR spectroscopy, and DFT calculations reveals that interfacial chemical bonding constructs a type-II heterojunction, enabling directional charge migration and stabilizing •O₂^– intermediates for a successive one-electron ORR pathway toward H₂O₂ evolution. Overall, this study provides mechanistic insight into interfacial charge regulation in CuO@g-C₃N₄ heterojunctions and offers guidance for the rational development of efficient photocatalysts.