Remarkably fast and reusable photocatalysis by UV annealed Cu₂O–SnO₂ p−n heterojunction

Powdered micro- or nano-particles photocatalyst has separation and recovery challenges, which may create a second pollution to environment and harmful to animals. To address those issues, SnO₂, Cu₂O and Cu₂O–SnO₂ p-n heterojunction thin films are formed on glass substrates using efficient co-sputtering method that is commonly employed for large-area high-definition display panel. Using first-order kinetics, 100 °C ultraviolet (UV) annealed Cu₂O–SnO₂ p-n heterojunction shows the superb fast degradation rate constant of 0.21 and 0.16 min⁻¹ for methylene blue (MB) and methyl orange (MO) organic dyes, respectively, as photogenerated electron-hole pairs is increased. Record best degradation rate constants of 0.19 and 0.11 min⁻¹ for respective MB and MO are still achieved even after four repeated cycles. The 100 °C UV annealed Cu₂O–SnO₂ film catalyst displays greater degradation efficiency in both dyes, reaching 100% degradation at room temperature after 30 and 35 min of illumination for MB and MO respectively. The scavenger experiments show that hydroxyl (·OH) and superoxide radicals (·O₂⁻) are the major active species in the degradation of dye. The 100 °C UV annealed Cu₂O–SnO₂ film catalyst showed stability as well as reusability towards the dye degradation. As a result, the present work delivers an effective way to enhance the photocatalytic performance and also an easy recovery of the catalyst, which can be explored for various emerging pollutants.