Two different hydrogels, prepared from N-vinyl-2-pyrrolidone/acrylic acid (NVP/AAc) and N-vinyl-2-pyrrolidone/acrylamide (NVP/AAm), were studied for the separation and extraction of some heavy-metal ions from wastewater. The hydrogels were prepared by the gamma-radiation-induced copolymerization of the aforementioned binary monomer mixtures. Further modification was carried out for the NVP/AAc copolymer through an alkaline treatment to improve the swelling behavior by the conversion of the carboxylic acid groups into its sodium salts. The thermal stability and swelling properties were also investigated as functions of the N-vinyl-2-pyrrolidone content. The characterization and some selected properties of the prepared hydrogels were studied, and the possibility of their practical use in wastewater treatment for heavy metals such as Cu, Ni, Co, and Cr was investigated. The maximum uptake for a given metal was higher for a treated NVP/AAc hydrogel than for an untreated NVP/AAc hydrogel and was higher for an untreated NVP/AAc hydrogel than for an NVP/AAm hydrogel. (C) 2004 Wiley Periodicals, Inc.