Synthesis of poly(acrylic acid)-bentonite-FeCo (PAA-B-FeCo) hydrogel nanocomposite via ultrasound assisted in situ emulsion polymerization was carried out. Addition of exfoliated bentonite clay platelets and Fe-Co increased the strength and stability of hydrogel and assisted the adsorption of an organic pollutant. The response of the nanocomposite hydrogel was evaluated using a cationic dye, crystal violet (CV) under different temperature, pH, and cavitation environment. The optimum temperature was found to be 35 degrees C and basic pH (optimum at 11) was responsible for the higher adsorption of dye due to dissociation of COO(-) ions at higher pH. Bimetallic components form the metal ions in hydrogel which shows repulsion at low pH resulting to lower response. Thermodynamic parameters for adsorption indicated that the dye adsorption onto PAA-B-FeCo hydrogel was spontaneous and endothermic in nature. (C) 2011 Elsevier B.V. All rights reserved.