In today’s world, water is a highly valued resource, and enhancing the quality of this natural endowment is a significant concern and a worldwide endeavor. This study sought to purify real wastewater and water tainted with methylene blue (MB) by immobilizing ZnO nanoparticles onto an alginate matrix using a straightforward approach and a three-dimensional structure. After analyzing the impact of \({\text{H}}_{2}{\text{O}}_{2}\) , it was determined that 93.84% of MB was successfully removed (time = 120 min, dye concentration = 15 mg/L, catalyst amount = 2.5 g). The effects of inorganic ions and water types were investigated to simulate real wastewater conditions, and the catalyst performed satisfactorily. Alginate played a significant role in selectively removing dye, and the catalyst effectively removed 80.36% of MB and, in contrast, 20% of methyl orange (MO). The practical application of the catalyst was evaluated in textile wastewater treatment, and the catalyst showed satisfactory performance. An average 2.49% reduction in dye removal was observed after five stages of using the catalyst, demonstrating the beads’ excellent stability. The composites were subjected to free radical trapping experiments to ascertain the active species. According to the results, \({\text{h}}^{+}\) and \(\cdot \text{OH}\) acted as the main reaction species in the degradation of MB. At the end, the synergistic mechanism of adsorption and degradation in MB removal was presented.
