Preparation and characterization of the newly synthesized metal-complexing-ligand N-methacryloylhistidine having PHEMA beads for heavy metal removal from aqueous solutions

Abstract

The aim of this study was to investigate in detail the performance for removal of heavy metal ions of beads composed of poly(2-hydroxyethyl methacrylate) (pHEMA) to which N-methacryloyhistidine (MAH) was copolymerized. The metal complexing ligand MAH was synthesized by using methacryloyl chloride and histidine. Spherical beads with an average size of 150-200 mum were obtained by the radical suspension polymerization of MAH and HEMA conducted in an aqueous dispersion medium. Owing to the reasonably rough character of the bead surface, p(HEMA-MAH) beads had a specific surface area of 17.6 m(2)/g. The synthesized MAH monomer was characterized by NMR; p(HEMA-MAH) beads were characterized by swelling studies, FTIR and elemental analysis. The p(HEMA-MAH) beads with a swelling ratio of 6.5% and containing 1.6 mmol MAH/g, were used in the adsorption/desorption experiments. Adsorption capacity of the beads for the selected metal ions, i.e., Cu(II), Cd(II), Cr(III), Hg(II) and Pb(II), were investigated in aqueous media containing different amounts of these ions (10-750 mg/L) and at different pH values (3.0-7.0). Adsorption equilibria were established in about 20 min. The maximum adsorption capacities of the p(HEMA-MAH) beads were 122.7 mg/g for Cu(II), 468.8 mg/g for Cr(III), 639.4 mg/g for Cd(II), 714.1 mg/g for Pb(II) and 1234.4 mg/g for Hg(II). pH significantly affected the adsorption capacity of MAH incorporated beads. The chelating beads can be easily regenerated by 0.1 M HNO3 with high effectiveness. These features make p(HEMA-MAH) beads a potential candidate for heavy metal removal at high capacity.