Green synthesis of ZnO and CuO nanoparticles and ZnO-CuO nanocomposites: Characterization and photocatalytic dyes removal efficiency's determination

This study reports the green biogenic synthesis of zinc oxide (ZnO) and copper oxide (CuO) nanoparticles, as well as ZnO–CuO nanocomposites, using an aqueous extract of Capparis spinosa L. leaves. The prepared nanomaterials were extensively characterized, and their photocatalytic performance was assessed under simulated solar light irradiation and ambient conditions for the degradation of anionic (Rose Bengal) and cationic (Rhodamine B) dyes as model of wastewater pollutants. The crystal structure of the photocatalysts was examined using X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) was employed to disclose the powder's morphology, and Fourier-transform infrared spectroscopy (FTIR) highlighted the role of plant-derived biomolecules as capping and stabilizing agents. Thermogravimetric analysis (TGA) allowed the evaluation of the nanoparticles’ stability, while optical and electrochemical measures were performed to study the electronic behavior of the photocatalysts. After 2 h of irradiation in the presence of 0.3 g/l of ZnO, CuO, or ZnO–CuO, the conversion of Rose Bengal reached 97.1 %, 87.8 %, and 99.9 %, respectively, while 27.5 %, 17.8 %, and 33.9 % were the values obtained for Rhodamine B. This finding demonstrates the effectiveness of our synthesis method as a green and sustainable approach in developing highly active photocatalysts for environmental remediation.