In this work, low-density vanillin-modified thin chitosan membranes were synthesized and characterized. The membranes were utilized as adsorbent for the removal of Cu(II) from aqueous solutions. The experimental data obtained in batch experiments at different temperatures were fitted to the Langmuir and Freundlich isotherms to obtain the characteristic parameters of each model. The adsorption equilibrium data fitted well with the Langmuir model (average R-2 > 0.99). Interactions thermodynamic parameters (Delta H-int, Delta(int)G, and Delta S-int), as well as the interaction thermal effects (Q(int)) were determined from T = (298 to 333) K. The thermodynamic parameters, the Dubinin-Radushkevick equation and the comparative values of Delta H-int for some Cu(II)-adsorbent interactions suggested that the adsorption of Cu(II) ions to vanillin-chitosan membranes show average results for both the diffusional (endothermic) and chemical bonding (exothermic) processes in relation to the temperature range studied. (c) 2005 Elsevier Ltd. All rights reserved.