A critical review on green synthesis of copper oxide nanoparticles: characterization and its application in wastewater treatment

Green synthesis of copper oxide nanoparticles (CuO NPs) using biological sources represents a sustainable, cost-effective alternative to traditional physicochemical methods, leveraging natural reducing agents under mild conditions. This approach utilizes diverse biological entities, including yeasts, bacteria, and plant extracts, to produce CuO NPs with unique structural and functional characteristics that are well-suited for environmental applications, particularly in wastewater treatment. This review synthesizes the latest methodologies in green CuO NPs production, focusing on the distinct intra- and extracellular mechanisms in microorganisms like Saccharomyces cerevisiae and Candida utilis and the role of plant-derived phytochemicals in nanoparticle stability and activity. Key characterization techniques such as TEM, SEM, XRD and FTIR are highlighted for their importance in understanding particle morphology, size and surface chemistry, which directly impact CuO NPs performance in pollutant degradation. In addition, this review addresses crucial challenges, including the scalability of green synthesis processes and the need for standardization to ensure consistent industrial application. The novelty of this work lies in the systematic evaluation of green-synthesized CuO NPs from various biological sources, emphasizing the correlation between synthesis methods, physicochemical properties, and wastewater remediation efficiency – an aspect largely overlooked in previous studies.