Magnetically recoverable activated carbon/CMC-β-cyclodextrin composite sponge for high-performance Cr(VI) adsorption,...

Hexavalent chromium (Cr(VI)) is a dangerous and mobile contaminant with high toxicity that can threaten aquatic environments and human health. A magnetically recoverable activated carbon composite sponge (MACC) was synthesized by the in-situ growth of Fe₃O₄ NPs into activated carbon followed by encapsulation in a crosslinked carboxymethyl cellulose (CMC)/β-cyclodextrin (β-CD) biopolymer matrix. The structural characterization and physicochemical properties of the synthesized composite were carried out using XRD, BET surface area analysis, FTIR, SEM-EDS, XPS, and vibrating sample magnetometry. Batch adsorption tests indicated that the removal of Cr(VI) was significantly influenced by solution pH, adsorbent dosage, and contact time. The adsorption kinetics were best described by the pseudo-second-order model, suggesting that the mechanism was controlled by chemisorption. Equilibrium data fitted well to the Langmuir isotherm model, indicating monolayer adsorption onto homogeneously distributed active sites with a maximum adsorption capacity (qₘ) of 528.75 mg.g⁻¹. Process optimization was performed using response surface methodology based on Box-Behnken Design (BBD), where a quadratic polynomial regression model was developed to evaluate individual and interactive effects of operational variables; numerical optimization via desirability function revealed that optimal adsorption conditions were obtained at pH 4, adsorbent dosage 0.02 g, and contact time 100 min with a predicted adsorption capacity about 530 mg.g⁻¹ very close to experimental results. In addition, the MACC composite showed good regeneration ability and structural stability after repeated adsorption-desorption cycles without any detectable framework deterioration; these results confirmed that the MACC composite sponge is an efficient magnetically separable sustainable adsorbent for Cr(VI) remediation from aqueous environments.