Semi-interpenetrating networks (semi-IPN) composite cryogels synthesized by radical cross-linking polymerization of acrylamide (AAm) with N,N'-methylenebisacrylamide (BAAm), at (-18 degrees C), in the presence of an anionic polyelectrolyte (PA) derived from potato starch were tested in the sorption of methylene blue (MB) from aqueous solution, compared with the same cryogel subjected to controlled hydrolysis. The effect of contact time, temperature, and the initial dye concentration on the adsorption capacity of the composite gels was investigated, using a batch adsorption technique. The shape of the experimental isotherms was of "L" type in the case of the pristine cryogel, and "H" shape for the hydrolyzed cryogel, which support a very high affinity of the hydrolyzed cryogel for MB. Three isotherm models, Langmuir, Freundlich and Sips, were fitted on the experimental data by a non-linear regression method. It was found that both Langmuir and Sips model isotherm fitted the adsorption data of MB onto the composite cryogel, both before and after the controlled hydrolysis, the correlation coefficient (R-2) being higher, and the Chi-square test (chi(2)) being lower for Sips isotherm than for Langmuir isotherm. The maximum adsorption capacity, q(m), evaluated by the Langmuir model, was of 443.7 mg MB/g gel, before hydrolysis, and 667.7 mg MB/g gel, after hydrolysis, indicating the increase of the density of anionic sites after the controlled hydrolysis. The pseudo-first order equation described well the sorption kinetics, both for cryogels and the conventional hydrogel with the same composition, indicating the physisorption as the main driving force of the dye sorption. (C) 2013 Elsevier B.V. All rights reserved.