Nickel nanoparticles inside poly(2-acrylamido-2-methyl-1-propansulfonic acid) (p(AMPS)) hydrogel were prepared by reduction of Ni(II) ions absorbed within hydrogel network. TEM images confirmed that in situ formed nickel particle in p(AMPS) hydrogel networks are about 100 nm. These nickel metal nanoparticles containing hydrogel-composites were utilized as catalysts and reaction media for the reduction reactions of aromatic nitro compounds, 2- and 4-nitrophenols with aqueous NaBH(4). The reduction rate constants at four different temperatures (30, 40,50 and 60 degrees C) and activation parameters were calculated. The activation energies (E(a)) for 4- and 2-nitrophenols are 25.70 and 38.69 kJ mol(-1), respectively. It was found that these types of hydrogel-composite catalyst systems can be used repetitively up to five times with 100% conversion and only with 25% reduction in the initial reduction rate. (c) 2010 Elsevier B.V. All rights reserved.