Highly efficient CuO/In₂O₃ multilayer thin films as photocatalysts under solar irradiation

In this work, multilayer CuO and In₂O₃ thin films were fabricated on glass substrates via a polymeric precursor sol–gel dip-coating route to investigate the effect of thermal treatments (300 °C and 500 °C) on their structural and photocatalytic properties. The results demonstrated that calcination at 500 °C triggered a solid-state dewetting process, resulting in a hydrophilic surface (contact angle < 90°) with increased roughness and specific surface area. XPS confirmed the formation of a p–n heterojunction characterized by significant interfacial charge transfer. Under natural sunlight, the optimized CuO/In₂O₃/CuO heterostructure degraded over 75% of cationic dyes (methylene blue and malachite green) within 120 min, maintaining high efficiency over 10 reuse cycles. Mott–Schottky and photocurrent measurements verified that the p–n heterojunction establishes a favorable potential gradient to suppress charge recombination, while EPR evidenced a high density of oxygen vacancies acting as active sites. Finally, phytotoxicity assays using Phaseolus vulgaris seeds confirmed the detoxification of the treated effluent, validating the conversion of pollutants into non-toxic inorganic constituents. These findings establish the engineered CuO/In₂O₃/CuO multilayer architecture as a highly stable and eco-friendly photocatalyst for solar-driven wastewater remediation.