Sodium alginate‐based hydrogel loaded with <scp> <i>in situ</i> </scp> generated magnesium hydroxide was used for the treatment of copper ions in wastewater

Abstract BACKGROUND Copper ion contamination in wastewater presents significant environmental and health challenges. Hydrogels, particularly those with three‐dimensional networks based on sodium alginate (SA), are promising adsorbents. This study aimed to develop an enhanced hydrogel adsorbent by crosslinking SA with Ca 2+ (forming SC hydrogel) and subsequently modifying it via in situ formation of magnesium hydroxide (Mg(OH) 2 ) to create SC‐Mg(OH) 2 , specifically targeting efficient Cu 2+ removal. RESULTS The formation mechanism and structure of SC‐Mg(OH) 2 were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, Brunauer–Emmett–Teller measurements and X‐ray photoelectron spectroscopy. Under optimized conditions (pH = 5, 298.15 K, adsorbent dosage 1 g L −1 , initial Cu 2+ concentration 100 mg L −1 , contact time 480 min), the composite hydrogel achieved a high Cu 2+ removal efficiency of 95.75% and a maximum adsorption capacity of 253.37 mg g −1 . The adsorption kinetics conformed to the pseudo‐second‐order kinetic model ( R 2 = 0.99977). When adsorption reached equilibrium, it fitted the Langmuir isotherm model ( R 2 = 0.99128) with a negative Δ G , which indicated that the reaction involved spontaneous chemical adsorption and monolayer adsorption. CONCLUSION The novel SC‐Mg(OH) 2 hydrogel, synthesized by in situ loading of Mg(OH) 2 on SC, demonstrates exceptional efficacy for Cu 2+ adsorption. The high removal efficiency (&gt;95%) and substantial adsorption capacity (253.37 mg g −1 ) surpass those of many conventional adsorbents. The adsorption process, well characterized by pseudo‐second‐order kinetics and the Langmuir model, confirms the material's potential. This work presents SC‐Mg(OH) 2 as a highly effective and advanced adsorbent, significantly contributing to the development of functional hydrogel materials for remediating heavy metal pollution in wastewater. © 2025 Society of Chemical Industry (SCI).