One pot synthesis and characterization of visible light responsive ZnO/CuO composites for efficient photocatalytic degradation of methylene blue

Industrial wastewater is a major contributor to water pollution, posing significant health risks and necessitating effective purification to prevent resource contamination. Organic dyes, widely used in textile, leather, paper, and pulp industries, as well as in academic research, can pollute water bodies if discharged untreated. This study utilized a biogenic approach to synthesize ZnO/CuO composite photocatalysts with varying CuO loadings (10%, 20%, 30%; denoted ZnO/CuO-10, ZnO/CuO-20, ZnO/CuO-30) using Laggera tomentosa plant extract, selected for its abundant phytochemicals, as a reducing and capping agent. These catalysts were characterized using scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and diffuse reflectance spectroscopy. The photocatalytic performance was evaluated by degrading methylene blue (MB) under visible light. Results showed enhanced efficiency compared to pristine ZnO (65%), with ZnO/CuO-30 (70%), ZnO/CuO-20 (79%), and ZnO/CuO-10 (87%) degrading MB effectively. The superior performance of ZnO/CuO-10 is attributed to its optimized p-n heterojunction between ZnO (n-type) and CuO (p-type), which enhances charge separation and reduces electron-hole recombination, as evidenced by its high pseudo-first-order rate constant. The ZnO/CuO-10 catalyst also demonstrated stability over five reuse cycles. Overall, these biogenically synthesized composites, particularly ZnO/CuO-10, offer a viable and sustainable option for water remediation. KEY WORDS: Photocatalysis, ZnO/CuO composite, Plant extract, Methylene blue degradation, Reusability Bull. Chem. Soc. Ethiop. 2025, 39(10), 2095- 2110. DOI: https://dx.doi.org/10.4314/bcse.v39i10.15