Five first generation ionic liquids (RTILs: BMImCl, OMImCl, AMImCl, BPyBr and OPyBr) were intercalated into the layered structure of a Na-montmorillonite by dispersion in aqueous solutions ([RTIL] <= 20 mmol L-1). For all ionic liquids, the intercalation expanded the spacing of the silicate layers, as measured by X-ray diffraction. FTIR, thermogravimetric analyses and sodium titrations of the solutions after intercalation proved the adsorption of the RTILs through a cation exchange mechanism. Adsorption isotherms, done at pH = 7 and at 25 degrees C, displayed that the maximum adsorption capacity of the substrates was closely linked to the nature of the organic cation and the length of the alkyl chain (BPyBr > OPyBr similar to AMImCl similar to BMImCl > OMImCl). For the five RTILs, calculated parameters obtained from the adsorption isotherms studied at three temperatures (25 degrees C, 40 degrees C and 55 degrees C) concluded to an endothermic and spontaneous adsorption reaction. (C) 2012 Elsevier B.V. All rights reserved.