CHEMISORPTION OF DIVALENT-CATIONS ON N-(2-PYRIDYL)ACETAMIDE IMMOBILIZED ON SILICA-GEL - A THERMODYNAMIC STUDY

N-(2-Pyridyl)acetamide covalently immobilized on silica gel (''=Si-pa'') has a great ability to chemisorb cations from propanonic or ethanolic solutions through the amount of substance divided by mass 1.57 . 10(-4) mol . g(-1) of bidentate groups attached to this inorganic support. The chemisorption isotherms obtained with MCl(2) (M: Ni, Co, Cu, Zn, Cd, Hg) in each solvent are similar and adjustable to a modified Langmuir equation. The sequence of the maximum capacity is Cu > Co > Zn in propanone and Hg > Cd > Zn > Co > Cu > Ni in ethanol. The enthalpies of chemisorption of the cations by ''=Si-pa'' at T = (298.15 +/- 0.02) K showed larger values in ethanol. With the exception of cobalt (Delta H-m = +(6.12 +/- 0.01) kJ . mol(-1)} in propanone, all other cation-surface interactions are enthalpically favourable in both solvents. The enthalpic sequence is Cu > Zn > Co in each solvent and the complete series Cu > Cd > Hg > Ni > Zn > Co was found in ethanol. The standard molar Gibbs free energies are in agreement with the spontaneity of the proposed reactions between a cation and a basic centre, which has a favourable enthalpic contribution to these chelating processes.