Methacrylated alginate hydrogels for water absorption and metal ion removal in environmental applications

Water contamination by heavy metals poses significant environmental risks, requiring efficient remediation strategies. In this study, methacrylated alginate hydrogels were synthesized and photocrosslinked under UV radiation to develop an effective adsorbent material. A design of experiments (DOE) approach was used to evaluate the effects of alginate concentration (20-30 g L^-1) and UV exposure time (1-3 h) on swelling capacity and metal adsorption. The hydrogels exhibited tunable swelling behavior (135 ± 0.4% to 442.9 ± 26.2%) that was influenced by polymer network density. Adsorption tests revealed a preferential affinity for divalent metal ions, following the order Cu²⁺ > Cd²⁺ > Zn²⁺ > Ni²⁺ > Mn²⁺ > Cr⁶⁺, with Cu²⁺ removal reaching 54.7%. Optimal Cu²⁺ removal was achieved at pH 5.0 and a hydrogel dosage of 1.0 g L^-1. Kinetic adsorption followed a pseudo-second-order model (R² = 0.985), suggesting chemical interactions supported by FTIR, EDX, and pH-dependent results. The Sips isotherm model (R² = 0.989) best described the adsorption process, confirming a hybrid mechanism. These results highlight the potential of photocrosslinked alginate hydrogels as sustainable adsorbents for water purification. Future studies should focus on evaluating regeneration, long-term stability, and scalability under realistic conditions.