Copolymer hydrogels were prepared by gamma-radiation copolymerization of N-vinyl-2-pyrrolidone (NVP) and methylmethacrylate (MMA) or acrylonitrile (AN). The effect of NVP/MMA and NVP/AN compositions and irradiation dose on the gel fraction yield in the prepared hydrogels was determined. It was found that as the content of NVP increased, the gel fraction yield decreased. The increase in irradiation dose resulted in increasing the crosslinked network structure and, consequently, the gel percentage increased. The thermal stability and swelling properties were also investigated as a function of comonomer composition. The nitrile groups (-CN) in the prepared copolymer were converted into their respective amidoxime groups by treating with NH2OH-hydrochloride. Such a process resulted in improving both the swelling behavior and adsorption capacity. Characterization and some selected properties of the prepared hydrogels were studied and accordingly the possibility of its practicable use in the treatment of industrial waste dyes was determined. The thermodynamic parameters for the adsorption process were calculated. The effect of treatment time, pH of feed solution, effect of initial feed concentration, and temperature on the dye uptake was also investigated. The maximum uptake for investigated dyes was higher for treated NVP/AN hydrogel than that for untreated NVP/AN and NVP/MMA ones. (c) 2005 Wiley Periodicals, Inc.