Adsorption properties of silica surface-grafted with a salicylhydroxamic acid-functionalized polymer toward lead ions

Salicylhydroxamic acid (SHA), functionalized composite chelating adsorbing material SHA-PHEMA/SiO₂, was prepared through the nucleophilic substitution reaction of 5-chloromethyl-salicylhydroxamic acid with poly (2- hydroethyl methacrylate) (PHEMA) modified silica gel particles PHEMA/SiO₂. The SHA-PHEMA/SiO₂ composites were characterized by FT-IR, scanning electron microscopy, X-ray photoelectron spectroscopy and nitrogen absorption. The adsorption behavior, adsorption thermodynamic, and adsorption mechanism of SHA-PHEMA/SiO₂ for Pb2+ ions were studied, and the pH value of the medium on the adsorption property and chelating adsorption ability of SHA-PHEMA/SiO₂ for Pb2⁺ ions was also investigated. The experimental results show that SHA-PHEMA/SiO₂ possesses strong chelating adsorption ability for Pb2⁺ ions, and the adsorption capacity for Pb2⁺ ions at 308K reached 57 mg/g. The adsorption process is a chemical adsorption process driven by entropy, and the adsorption capacity increases with rising temperature. In pH range that can inhibit the hydrolysis of heavy metal ions, increasing the pH value of the medium strengthens the adsorption ability of SHA-PHEMA/SiO₂ toward Pb2⁺ ions. The adsorption behavior is monomolecular and follows Langmuir isotherm. The adsorption capacity is almost the same after ten consecutive adsorption- desorption experiments of SHA-PHEMA/SiO₂ for Pb2⁺ ions, indicating that SHA-PHEMA/SiO₂ has excellent elution property and reusability.