C. Airoldi et Efc. Alcantara, CHEMISORPTION OF DIVALENT-CATIONS ON N-(2-PYRIDYL)ACETAMIDE IMMOBILIZED ON SILICA-GEL - A THERMODYNAMIC STUDY, Journal of Chemical Thermodynamics, 27(6), 1995, pp. 623-632
N-(2-Pyridyl)acetamide covalently immobilized on silica gel (''=Si-pa'
') has a great ability to chemisorb cations from propanonic or ethanol
ic solutions through the amount of substance divided by mass 1.57 . 10
(-4) mol . g(-1) of bidentate groups attached to this inorganic suppor
t. The chemisorption isotherms obtained with MCl(2) (M: Ni, Co, Cu, Zn
, Cd, Hg) in each solvent are similar and adjustable to a modified Lan
gmuir equation. The sequence of the maximum capacity is Cu > Co > Zn i
n 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 (Del
ta H-m = +(6.12 +/- 0.01) kJ . mol(-1)} in propanone, all other cation
-surface interactions are enthalpically favourable in both solvents. T
he 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 th
e proposed reactions between a cation and a basic centre, which has a
favourable enthalpic contribution to these chelating processes.