Chemically Synthesized Copper-Tin Oxide Heterojunction Photocatalysts for Hydrogen Evolution and CO₂ Methanation

Abstract

The urgent demand for sustainable energy solutions has motivated the design of multifunctional photocatalysts that couple renewable hydrogen production with carbon utilization. In this work, copper oxide nanoparticles and copper–tin oxide heterojunction nanocomposites were synthesized through a chemical precipitation–calcination approach. Structural and optical characterization using XRD, FTIR, SEM, and UV–Vis spectroscopy confirmed the successful formation of crystalline nanostructures with strong interfacial contact and enhanced visible-light absorption. The heterojunction nanocomposites exhibited a reduced bandgap of 1.42 eV compared to 2.35 eV for pristine copper oxide, favoring improved charge excitation under solar irradiation. Photocatalytic hydrogen evolution under Xe lamp illumination reached 690 μmol g⁻¹ within 10 hours, significantly higher than copper oxide alone (540 μmol g⁻¹). Systematic studies revealed
optimal conditions at 45 mg catalyst loading and 70 °C, yielding up to 710 μmol g⁻¹. For CO₂ methanation, the nanocomposites achieved 96.9% conversion with 98.2% methane selectivity at 390 °C, outperforming pure copper oxide. The superior activity is attributed to efficient charge carrier separation and stable p–n heterojunction formation, as confirmed by reusability tests. These findings highlight chemically synthesized copper–tin oxide heterojunction nanocomposites as promising dual-function photocatalysts for solar-driven hydrogen generation and carbon utilization.