Eco-friendly CuO@SnO₂ photocatalysts for solar hydrogen evolution and CO₂ methanation

Abstract

In this study, CuO nanoparticles (NPs) and CuO@SnO₂ nanocomposite (NC) were synthesized via a green method using Moringa oleifera leaf extract, aiming to develop efficient and sustainable photocatalysts for hydrogen (H₂) production and CO₂ methanation. Comprehensive characterization techniques (FTIR, XRD, SEM, UV–Vis) confirmed the successful formation of nanocomposite with enhanced structural and optical features. The CuO@SnO₂ NC showed a significant bandgap reduction (1.81 eV) compared to CuO NPs (2.14 eV), leading to improved charge separation and light absorption. Photocatalytic H₂ production was systematically investigated under three variables: reaction time, catalyst mass, and temperature. The CuO@SnO₂ NC produced 665 µmol/g of H₂ after 10 h, increasing to 816.34 µmol/g at an optimal mass of 60 mg, and peaking at 722 µmol/g at 75 °C. In CO₂ methanation, the CuO@SnO₂ NC achieved a remarkable 99.7% CO₂ conversion and 99.9% CH₄ selectivity at 400  °C and 5 MPa, outperforming the CuO NPs (88.1% conversion, 95.2% selectivity). These improvements highlight the synergistic interaction between CuO and SnO₂ and demonstrate the potential of biogenic CuO@SnO₂ NC as dual-function photocatalysts for clean energy production and carbon utilization.