Efficient selective adsorption of Cu2+ and Cd2+ by poly(hydroxyethyl methacrylate) polymer modified by polyfunctional groups

A novel polyfunctional group-modified poly(hydroxyethyl methacrylate) polymer, termed PFG-PHEMA, was synthesized for adsorption of Cu²⁺ and Cd²⁺. Material characterization confirmed that the surface functional groups facilitated efficient adsorption of these ions. pH optimization experiments demonstrated that the adsorption capacities of Cu²⁺ and Cd²⁺, reaching 162.2 and 150.3 mg·L⁻¹ respectively, were maximized at a pH of 5, with an initial heavy metal concentration of 200 mg·L⁻¹. Kinetic and isotherm studies indicated that the adsorption process conformed to a monolayer, homogeneous, and chemisorption model, achieving equilibrium within 60 min. The maximum adsorption capacities were determined to be 500 mg·g⁻¹ for Cu²⁺ and 384.6 mg·g⁻¹ for Cd²⁺. Competitive adsorption experiments showed that PFG-PHEMA exhibited superior selectivity for Cu²⁺ over other metal ions. This selectivity was corroborated by X-ray photoelectron spectroscopy (XPS) analysis, which identified the sulfhydryl group as the crucial functional moiety responsible for Cu²⁺ selectivity. Furthermore, the presence of low concentrations of fulvic acid (FA) enhanced adsorption via ternary complex formation, whereas higher concentrations impeded adsorption by forming FA-metal complexes that competed with the polymer. Overall, the strategic incorporation of multiple functional groups into PFG-PHEMA conferred a high adsorption capacity for Cu²⁺ and Cd²⁺. The analysis further indicated that sulfhydryl groups exhibit high selectivity toward Cu²⁺, whereas amine and oxygen-containing groups preferentially bind to Cd²⁺, reinforcing the potential of PFG-PHEMA as a highly effective adsorbent for heavy metals.