Acetylacetone was covalently immobilized on silica gel to produce a new surface (Sil-ac), having 0.62 mmol of ligand attached per gram of silica, which was characterized by means of elemental analysis and physical measurements, before being submitted to calorimetric measurements. Thus, a suspension of this anchored surface in ethanol or acetone was calorimetrically titrated with divalent cations (Co, Ni, Cu, Zn, Cd, Hg). The resulting isotherms conformed to a modified Langmuir equation. After linearization of these isotherms, the enthalpies of cation/surface adsorption and the interfacial equilibrium constant, as well as the variation of free energies and entropies, were calculated. In acetone, adsorption of copper gives rise to an exothermic ΔH of - 93.38 ± 0.94 kJ mol-1, while cobalt, 41.80 ± 0.42 kJ mol-1, and zinc, 2.38 ± 0.02 kJ mol-1, give an endothermic adsorption. In ethanol, the endothermic ΔH of 52.64 ± 0.53 kJ mol-1 for zinc contrasts with the exothermic enthalpies of adsorption observed for other cations, especially for mercury, - 102.20 ± 1.02 kJ mol-1 and nickel, -137.70 ± 1.38 kJ mol-1. © 1995.259195102Iler, (1979) The Chemistry of Silica, , Wiley, New YorkD'Hamers, Philippaerts, der Voort, Vansant, Siloxane bridges as reactive sites on silica gel. Fourier transform infrared?photoacoustic spectroscopic analysis of the chemisorption of diborane (1990) Journal of the Chemical Society, Faraday Transactions, 86, p. 3747Deschler, Kleinschmit, Panster, 3-Chloropropyltrialkoxysilanes?Key Intermediates for the Commercial Production of Organofunctionalized Silanes and Polysiloxanes (1986) Angewandte Chemie International Edition in English, 25, p. 236Bogart, Leyden, Wade, Schafer, Carr, (1989) J. Chromatogr., 483, p. 209Kurusu, Synthesis and Reaction of a Silica-Supported Catalyst with Ammonium Groups. Immobilized Ammonium Groups on Silica (1990) Journal of Macromolecular Science: Part A - Chemistry, 27, p. 1389Simonzadeh, Schilt, Chelation Properties of Silica-Bound 1,10-Phenanthroline (1989) Journal of Coordination Chemistry, 20, p. 117Airoldi, Alcântara, Chemisorption of some metal(II) chlorides on silica-immobilized acetylhydrazine (1989) Colloids and Surfaces, 39, p. 219Kudryavtsev, Bernadyuk, Lisichkin, Ion exchangers based on modified mineral carriers (1989) Russian Chemical Reviews, 58, p. 406Kallury, Lee, Thompson, (1993) Anal. Chem., 65, p. 2459Haan, van den Bogarert, Bongeé, van der Ven, Characterization of modified silica powders by fourier transform infrared spectroscopy and cross-polarization magic angle spinning NMR (1986) Journal of Colloid and Interface Science, 110, p. 591Lisichkin, Kudryavtsev, Nesterenko, (1993) J. Anal. Chem. USSR, 38, p. 1288Airoldi, Alcântara, Nakamura, Paixão, Vargas, (1993) J. Mater. Chem., 3, p. 479Gona̧lves, Airoldi, (1989) Polyhedron, 8, p. 2901Pyell, Stork, (1992) Fresenius J. Anal. Chem., 343, p. 576Airoldi, Gushikem, Espínola, Adsorption of divalent cations on the silica-gel surface modified with N-(2-aminoethyl-3-aminopropyl) groups (1986) Colloids and Surfaces, 17, p. 314Spokenko, Trofimchuk, Zaitsev, (1982) Russ. J. Inorg. Chem., 27, p. 1458Gushikem, Silva, (1985) J. Colloid Interface Sci, 107, p. 81Gona̧lves, Airoldi, Immobilized 3-aminopyridine on silica: Adsorption of some metal (II) chlorides in non-aqueous solutions (1987) Colloids and Surfaces, 28, p. 199Airoldi, Santos, (1994) J. Mater. Chem., 4, p. 1479Tavares, O'Sullivan, Hauser, (1962) J. Org. Chem., 27, p. 1251Joshi, Pathak, (1977) Coord. Chem. Rev., 22, p. 37Breitmaier, Voelter, 13C NMR Spectroscopy: Methods and Applications in Organic Chemistry (1987) 13C NMR Spectroscopy: Methods and Applications in Organic Chemistry, , 2nd edn., New YorkTanamushi, (1983) Adsorption from Solution, , Academic Press, New YorkJednacak-Biscan, Pravdic, (1980) J. Colloid Interface Sci., 75, p. 322Jednacak-Biscan, Pravdic, Adsorption phenomena on glass surfaces. III. a microcalorimetric study of adsorption of n-butanol on heat treated surfaces of controlled pore glass (1982) Thermochimica Acta, 53, p. 203Airoldi, Santos, Jr., (1986) Thermochim. Acta, 104, p. 111Airoldi, Chagas, (1992) Coord. Chem. Rev., 119, p. 29