Green-synthesized CuO/Cu2O-supported g-C3N4 p–n junction photocatalyst for photo(electro)catalytic hydrogen evolution

In this study, an environmentally friendly CuO/Cu2O nanoparticle (NPs) production method was developed using waste rosehip seed plant extracts as reducing and stabilizing agents. Automatic solvent extraction (ASE) with a green 60% (v/v) ethanol/water solvent combination produced polyphenol-rich solutions for biogenic nanoparticle production. Green CuO/Cu2O NPs were loaded onto n-type graphitic carbon nitride (g-C3N4, CN) at 5%, 10%, and 15% weight percentages to form p-n heterojunction photocatalysts (5CuO/Cu2O@CN, 10CuO/Cu2O@CN, and 15CuO/Cu2O@CN). Structural and morphological analyses and material characterizations performed using XRD, FTIR, SEM-EDS, TEM, XPS, UV–vis DRS, Zeta Sizer, and DLS confirmed the successful formation and homogeneous distribution of CuO/Cu2O on the CN surface. Optical and photoelectrochemical characterizations revealed that the formation of p–n type junction significantly increased visible light absorption and supported efficient charge carrier dissociation. Photoelectrochemical (PEC) measurements yielded consistent results for photocatalytic hydrogen (H2) evolution, with a consistent H2 evolution relationship; pure CN produced 125 μmol g− 1 h− 1 H2, while the 10CuO/Cu2O@CN sample produced 937 μmol g− 1 h− 1 H2, increasing performance by approximately 7.5-fold. Furthermore, this study aimed to contribute to a more environmentally friendly and sustainable approach by using lactic acid as a sacrificial material to facilitate hole consumption. In addition to photocatalytic activity, the antioxidant properties of the photocatalysts were evaluated using 2,2-diphenyl-1-picrylhydrazil (DPPH) free radical scavenging method, and composition-dependent radical scavenging efficiencies were determined.