Bioinspired Fabrication of Ca-ZnO/CuO/Alginate Beads for Enhanced Wastewater Treatment and Antibacterial Applications

This study focuses on optimizing the photochemical degradation of methylene blue (MB) using calcium-functionalized zinc oxide–copper oxide–alginate (ZnO/CuO/Alg) nanocomposite hydrogel beads under sunlight irradiation. Pure ZnO and CuO nanoparticles (NPs) were synthesized via a green co-precipitation method employing plant extracts and were subsequently embedded into an alginate polymer matrix. Various characterization techniques, including powder X-ray diffraction (PXRD), ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy-dispersive X-ray analysis (SEM–EDX), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA), were employed to analyze the structure and morphology of the catalysts. The photocatalytic performance of the nanocomposites was evaluated by studying the effects of pH, catalyst dose, irradiation time and MB concentration. Mathematical modeling was used to determine the optimal degradation conditions, achieving a maximum photocatalytic efficiency of 77.86% under the following parameters: MB concentration of 20 mg/L, catalyst dose of 50 mg, irradiation time of 75 min and pH 8. The model fit the experimental data well, showing a coefficient of determination (R2) of 0.963, confirming its reliability. Additionally, the antibacterial potential of the nanocomposite powders was investigated. Tests were conducted using equal concentrations of pure ZnO, ZnO/CuO and ZnO/CuO/Alg nanocomposites on Petri dishes inoculated with both Gram-positive and Gram-negative bacterial cultures. The results revealed significant bacterial growth inhibition, with the ZnO/CuO/Alg nanocomposite exhibiting the largest inhibition zone of 20 mm, compared to 14 mm for pure ZnO, indicating superior antibacterial efficacy.