Poly (acrylamide-co-2-acrylamido-2-methylpropane sulfonic acid)-g-carboxymethylcellulose-Ca(II) hydrogel beads for efficient adsorption of Cd(II)

To address Cd(II) contamination in aquatic environments and the limitations of conventional adsorbents, such as poor mechanical strength, low adsorption capacity, and insufficient reusability, a novel hydrogel bead adsorbent with a semi-interpenetrating polymer network (semi-IPN) was developed using a simple physical and chemical crosslinking approach. The hydrogel beads, composed of poly(acrylamide-co-2-acrylamido-2-methylpropanesulfonic acid)-carboxymethyl cellulose-Ca(II) (P(AM-AMPS)-CMC-Ca(II)), exhibited a high compressive strength of 60.0 kPa. Their well-developed porous structure and abundant functional groups significantly enhanced their Cd(II) adsorption potential. Isothermal, kinetic, and thermodynamic adsorption experiments conducted at pH 5.65 indicated that Cd(II) adsorption onto the hydrogel beads followed the Freundlich isotherm model and the pseudo-second-order kinetic model, suggesting a non-spontaneous, endothermic, and heterogeneous multilayer adsorption process. The adsorption mechanism was governed by both physical and chemical interactions, with a maximum adsorption capacity of 275.13 mg/g. Characterization (SEM, FTIR, XPS) confirmed that Cd(II) adsorption was primarily driven by electrostatic attraction, complexation with functional groups, and ion exchange. After five adsorption-desorption cycles using 0.1 mol/L HCl as the desorption agent, the adsorption efficiency remained above 90 %. Overall, the hydrogel beads, with simple preparation method, high strength, and excellent regeneration, could be a promising eco-friendly adsorbent for Cd(II) removal.