Easily recyclable magnetic polyacrylamide/sodium alginate/Fe₃O₄@ZIF-8 hydrogel beads for effective removal of Congo Red

Direct discharge of Congo red (CR) dye wastewater can cause environmental pollution. Herein, magnetic polyacrylamide/sodium alginate/Fe₃O₄@ZIF-8 (PAM/SA/Fe₃O₄@ZIF-8) hydrogel beads with semi-interpenetrating polymer network (SIPN) structure were prepared by combining the properties of PAM/SA hydrogel and Fe₃O₄@ZIF-8 for removal of CR. The magnetic hydrogel beads were characterized by SEM, EDS, FTIR, XRD, and BET. The effect of different factors on the adsorption of CR by magnetic hydrogel beads was investigated. The results showed that the addition of Fe₃O₄@ZIF-8 improved the adsorption capacity of PAM/SA hydrogel beads and the maximum adsorption amount of CR by magnetic PAM/SA/Fe₃O₄@ZIF-8-8 was 234.69 mg g⁻¹. The adsorption of CR on PAM/SA/Fe₃O₄@ZIF-8-8 complied with the Pseudo-second-order kinetic model and Freundlich model. Thermodynamic analyses indicated that the adsorption process was endothermic and spontaneous. The adsorption mechanism of PAM/SA/Fe₃O₄@ZIF-8 on CR was based on electrostatic attraction, metal coordination, hydrogen bonding, and π-π stacking. PAM/SA/Fe₃O₄@ZIF-8-8 had excellent selective adsorption and cyclic regeneration performance for CR removal. This study showed that magnetic PAM/SA/Fe₃O₄@ZIF-8 hydrogel beads can be used as a new effective adsorbent for the recovery of CR in wastewater.