A recyclable guar gum/β-cyclodextrin composite hydrogel with phosphorylated ginkgo charcoal for stable and high-capacity removal of cationic pollutants

In this study, phosphoric acid-modified ginkgo leaf charcoal (PGC) was prepared, and a β-cyclodextrin (β-CD)/guar gum (GG)/PGC composite hydrogel was synthesized via free radical polymerization. Synthesis conditions were optimized by response surface methodology to achieve optimal adsorption performance. Adsorption kinetics and isothermal studies revealed that the adsorption process follows the Langmuir isothermal model and pseudo-second-order kinetic model, indicating a combination of physical and chemical adsorption. Based on the Langmuir model, the hydrogel exhibited maximum adsorption capacities of 1086.49 mg·g^-1 for Pb²⁺, 385.19 mg·g^-1 for Co²⁺, and 879.41 mg·g^-1 for MB. Zeta potential and XPS analyses demonstrated that oxygen- and carbon-containing functional groups in the hydrogel interact with pollutants primarily through electrostatic adsorption. Additionally, the adsorbent maintained favorable adsorption performance during five consecutive adsorption-desorption cycles. In summary, this work develops a facile, sustainable, and economical hydrogel-based adsorbent with high removal capacities for both organic dyes and inorganic heavy metal ions in aqueous systems.