Cu-Zn coupled heterojunction photocatalyst for dye degradation: Performance evaluation based on the quantum yield and figure of merit

[Display omitted] •The biological preparation of a CuO-ZnO is demonstrated.•A p-n-type semiconductor composed of copper oxide and zinc oxide is fabricated.•Efficient photocatalyst activity was observed for Congo red dye degradation.•Photocatalytic degradation kinetics followed a pseudo-first-order reaction. This study reports the production of a heterojunction copper oxide-zinc oxide nano-photocatalyst based on lemon leaf extract, which acted as both a stabilizer and a capping and reducing agent. The fabricated photocatalyst had a smooth surface with numerous functional groups, and its energy band gap was measured to be 3.14 eV, which is suitable for photocatalytic applications. Toxic Congo Red dye was used as a model pollutant to investigate the photocatalytic degradation performance of the proposed CuO-ZnO nano-photocatalyst. The photocatalyst exhibited a rapid degradation rate under sunlight irradiation, reducing the concentration of the dye by almost 70 % within 50 min and exhibited pseudo-first-order kinetics. The performance of the photocatalyst was also evaluated based on its quantum yield and figure of merit, which were found to be 6.63 x 10−9 molecules photon−1and 3.31 x 10−4, respectively. In addition, the proposed catalyst displayed good stability for up to 5 cycles. Based on these results, the fabricated CuO-ZnO nano-photocatalyst outperformed previously reported photocatalysts. The mechanisms associated with the dye degradation were also explained by an interfacial charge transfer reaction.