Solvent-Free Synthesis of an Oxidized β-Cyclodextrin–Phytic Acid Copolymer for the Dual Removal of Heavy Metals and Organic Pollutants from Wastewater

In this study, a novel water-insoluble copolymer of oxidized β-cyclodextrin (β-CDO) and phytic acid (PA) was designed, synthesized, and evaluated for the dual adsorption of heavy metals and organic pollutants from wastewater. β-CD was oxidized using the TEMPO/NaOCl system to yield β-CD containing carboxyl functional groups (β-CDO). The copolymer was synthesized via a solvent-free esterification method by heating the reactants at 120 °C, thereby forming phosphate ester linkages between the hydroxyl groups of β-CDO and PA. Five polymers with different ratios were prepared and characterized by FTIR, SEM, and TGA, confirming linkage formation, porous morphology, and good thermal stability of the β-CDO-co-PA copolymer. Polymer E, with a β-CDO-to-PA ratio of 3:1, exhibited outstanding adsorption capabilities. Polymer E removed 99.0% of Pb(II) from a 50 mg/L solution at pH 5 and 30 °C, reaching equilibrium within 30 min. For methylene blue (MB), it showed a removal efficiency greater than 98%, with a Qe value of 196 mg/g at pH 7.0 through β-CD inclusion complexation and electrostatic interactions with PA. In real wastewater, polymer E efficiently removed several heavy metals, including Pb (99.5%), Cr (98.6%), Cu (98.8%), and As (98.5%), through synergistic adsorption, with PA phosphate groups chelating metal ions and β-CD cavities capturing organic contaminants. The adsorption behavior followed pseudo-second-order kinetics, indicating the predominance of chemisorption, and the Langmuir isotherm, indicating monolayer coverage. Polymer E also retained more than 90% efficiency after six regeneration cycles.