Metal-complexing ligand methacryloylamidocysteine containing polymer beads for Cd(II) removal

Abstract

Different metal-complexing ligands carrying synthetic and natural adsorbents have been reported in the literature for heavy metal removal. We have developed a novel and new approach to obtain high metal adsorption capacity utilizing 2-methacryloylamidocysteine (MAC) as a metal-complexing ligand and/or comonomer. MAC was synthesized by using methacryloyl chloride and cysteine. Spherical beads with an average size of 150–200 μm were obtained by the radical suspension polymerization of MAC and 2-hydroxyethylmethacrylate (HEMA) conducted in an aqueous dispersion medium. Poly(2-hydroxyethylmethacrylate–methacryloylamidocysteine) p(HEMA–MAC) beads have a specific surface area of 18.9 m2 g−1. p(HEMA–MAC) beads were characterized by swelling studies, FTIR and elemental analysis. The p(HEMA–MAC) beads with a swelling ratio of 72%, and containing 3.9 mmol MAC g−1 were used in the removal of cadmium(II) ions from aqueous solutions. Adsorption equilibrium was achieved in about 15 min. The adsorption of Cd(II) ions onto pHEMA beads was negligible. The MAC incorporation significantly increased the Cd(II) adsorption capacity. Adsorption capacity of MAC incorporated beads increased significantly with pH. Competitive heavy metal adsorption from aqueous solutions containing Cd(II), Cr(III), Pb(II), Hg(II) and As(III) was also investigated. The adsorption capacities are 254 mg g−1 for Cd(II); 90.9 mg g−1 for Cr(III); 150.4 mg g−1 for Hg(II), 91.2 mg g−1 for Pb(II) and 6.7 mg g−1 for As(III) ions. These results are an indication of higher specificity of the p(HEMA–MAC) beads for the Cd(II) ions compared with other ions. Consecutive adsorption and desorption operations showed the feasibility of repeated use for p(HEMA–MAC) chelating beads.