In this study, cryogels containing imidazole functional groups were prepared by two different approaches and were used in the removal of Pb2+, Cd2+, Zn2+ and Cu2+ ions from aqueous solutions. In the first approach, poly(2-hydroxyethyl methacrylate-n-vinyl imidazole) [poly(HEMA-VIM)] cryogel was prepared using n-vinyl imidazole monomer. In the second approach, in order to increase the surface area, poly(HEMA-VIM)/poly(HEMA) composite cryogel was prepared by embedding the poly(HEMA-VIM) particles prepared with suspension polymerization into poly(2-hydroxyethyl methacrylate), poly(HEMA) cryogel. Both poly(HEMA-VIM)] cryogel and poly(HEMA-VIM)/poly(HEMA) composite cryogels were characterized by swelling studies, Fourier transform infrared spectroscopy, elemental analysis, surface area measurements and scanning electron microscopy. The surface area of poly(HEMA-VIM) cryogel was found to be 39.7 m(2)/g while the surface area of poly(HEMA-VIM)/poly(HEMA) composite cryogel was 78.6 m(2)/g as expected. The optimum adsorption conditions for metal uptake such as pH, metal ion concentration, and adsorption time were studied. Performed experiments showed that composite formation increased the adsorption capacity of the cryogel. The amounts of decreasing adsorption capacity were calculated as 38.5% for Cu2+, 39.1% for Pb2+, 66.9% for Zn2+ and 69.9% for Cd2+. The maximum adsorption capacities of the composite cryogel in the affinity order on mass basis were found to be Pb2+(7620 mu g/g) > Cd2+(5800/mu g) > Zn2+(4340 mu g/g) > Cu2+(2540 mu g/g) while on molar basis the order was Zn2+(66.4 mu mol/g) > Cd2+(51.6 mu mol/g) > Cu2+(40.0 mu mol/g) > Pb2+(36.8 mu mol/g). These results fitted well the Langmuir adsorption model. Competitive adsorption studies were performed with solutions containing the four heavy metal ions at 20 mg/L metal ion concentration. The binding capacities of the composite cryogel were found to be Pb2+(1498.2 mu g/g) > Cu2+(742.5 mu g/g) > Cd2+(550.4 mu g/g) > Zn2+(450.5 mu g/g) in competitive manner. It was observed that composite cryogels could be repeatedly used without significant loss in the adsorption capacity after ten repetitive adsorption-desorption processes. (C) 2011 Elsevier Ltd. All rights reserved.