Multicycle Adsorption of Malachite Green Using ZnO-Embedded SA/AC Hydrogel: Structural Characterization and Performance Evaluation

In this study, a sodium alginate/acrylic acid (SA/AC) hydrogel and its nanocomposite variant incorporating zinc oxide nanoparticles (SA/AC/ZnO-NPs) were synthesized via a copolymerization method. The incorporation of ZnO-NPs was aimed at enhancing the functional performance of the hydrogel. Morphological and structural analyses were conducted using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), confirming the successful formation and nanoscale dispersion of the composite materials. The adsorption efficiency of both adsorbents was evaluated through batch adsorption experiments for the removal of malachite green (MG) dye under varying operational parameters. The SA/AC/ZnO-NPs nanocomposite exhibited superior dye removal efficiency, achieving a maximum removal of ۹۰.۳۱% at pH ۸.۰, ۲۵ °C, ۰.۰۹ g adsorbent dosage, and ۴۰ minutes of contact time-significantly outperforming the individual components (SA, AC, and ZnO-NPs). Additionally, regeneration studies demonstrated that the nanocomposite retained high adsorption capacity over four consecutive adsorption-desorption cycles, particularly when regenerated in acidic media. Among the acidic, basic, and neutral regenerants tested, the acidic condition most effectively restored surface activity. These findings suggest that the SA/AC and SA/AC/ZnO-NPs hydrogels represent cost-effective, eco-friendly, and efficient adsorbents for treating dye-contaminated wastewater. The results indicate that the hydrogel exhibits good reusability for at least three cycles, with minimal loss of efficiency. However, by the fourth cycle, the adsorption capacity significantly decreases, likely due to some factors such as irreversible binding of dye molecules, structural fatigue or collapse of the hydrogel network, and reduced accessibility to active functional groups. While the hydrogel demonstrates promising reusability, its adsorption efficiency decreases progressively with each regeneration cycle, highlighting the need for the optimization of regeneration methods or structural enhancement for long-term applications.

کلیدواژه ها:

Hydrogel ، Polymeric Adsorbent ، Malachite Green ، Regeneration ، Dye removal ، Adsorption