Optimized size and stability of composite CuO – ZnO metal oxide nanoparticles for efficient removal of Reactive Black 5 dye

Abstract BACKGROUND The increasing contamination of water bodies with industrial dyes necessitates efficient remediation strategies. CuO–ZnO composite nanoparticles (NPs) have shown promise as adsorbents due to their high surface area, stability, and tunable properties. This study focuses on optimizing the synthesis conditions of CuO‐ZnO NPs via a co‐precipitation method and evaluating their performance for the removal of Reactive Black 5 (RB5) dye. RESULTS CuO–ZnO composite NPs were synthesized with varied precursor ratios, pH values, temperatures, and reagent addition times to achieve optimal size and stability. Characterization using ultraviolet–visible spectroscopy, fluorescence, X‐ray diffraction, Fourier transform infrared spectroscopy, dynamic light scattering, vibrating‐sample magnetometry, and Brunauer–Emmett–Teller analysis confirmed the structural, optical, and physical properties of the optimized composite. The smallest size and highest stability for a concentration ratio of 50:50 was obtained at pH 11, 80 °C, and a reagent addition time of 5 min. Composite NPs show ferromagnetic behavior. The adsorption efficiency of RB5 dye was studied under different operational parameters, revealing that maximum removal (92%) occurred at pH 2 with a contact time of 60 min. Adsorption kinetics followed the  pseudo‐first‐order model, while equilibrium data aligned with the Freundlich isotherm, indicating multilayer adsorption. Thermodynamic analysis confirmed the endothermic and spontaneous nature of the process. CONCLUSION The optimized CuO–ZnO composite NPs demonstrated high efficiency for RB5 dye removal and maintained significant reusability across multiple adsorption–desorption cycles. These findings highlight the potential of CuO–ZnO NPs as an effective and sustainable adsorbent for wastewater treatment. © 2025 Society of Chemical Industry (SCI).