Poly(hydroxyethyl methacrylate) nanobeads containing imidazole groups for removal of Cu(II) ions

Poly(hydroxyethyl methacrylate) (PHEMA) nanobeads with an average size of 300 nm in diameter and with a polydispersity index of 1.156 were produced by a surfactant free emulsion polymerization. Specific surface area of the PHEMA nanobeads was found to be 996 m(2)/g. Imidazole containing 3-(2-imidazoline-1-yl)propyl (triethoxysilane) (IMEO) was used as a metal-chelating ligand. IMEO was covalently attached to the nanobeads. PHEMA-IMEO nanobeads were used for the removal of copper(H) ions from aqueous solutions. To evaluate the degree of IMEO loading, the PHEMA nanobeads were subjected to Si analysis by using flame atomizer atomic absorption spectrometer and it was estimated as 973 mu mol IMEO/g of polymer. The PHEMA nanobeads were characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. Adsorption equilibrium was achieved in about 8 min. The adsorption of Cu2+ ions onto the PHEMA nanobeads was negligible (0.2 mg/g). The IMEO attachment into the PHEMA nanobeads significantly increased the Cu2+ adsorption capacity (58 mg/g). Adsorption capacity of the PHEMA-IMEO nanobeads increased significantly with increasing concentration. The adsorption of Cu2+ ions increased with increasing pH and reached a plateau value at around pH 5.0. Competitive heavy metal adsorption from aqueous solutions containing Cu+, Cd2+, Pb2+ and Hg2+ was also investigated. The adsorption capacities are 61.4 mg/g (966.9 mu mol/g) for Cu2+; 180.5 mg/g (899.8 mu mol/g) for Hg2+; 34.9 mg/g (310.5 mu mol/g) for Cd2+ and 14.3 mg/g (69 mu mol/g) for Pb2+. The affinity order in molar basis is observed as Cu2+ > Hg2+ > Cd2+ > Pb2+. These results may be considered as an indication of higher specificity of the PHEMA-IMEO nanobeads for the Cu2+ comparing to other ions. Consecutive adsorption and elution operations showed the feasibility of repeated use for PHEMA-IMEO nanobeads. (C) 2009 Elsevier B.V. All rights reserved.