Energetics of the interaction of ethylamine and acidic sites of immobilized complexes on SH-modified silica gel

Interactions of ethylamine from aqueous solutions on Sil-SM [thiol-modified silica gel containing complexed cations, where M = Ag(I), Hg(II), Zn(II), Cu(II) and Ni(II)] have been investigated. Using an isoperibolic calorimetric titration technique, the enthalpies evolved at different surface coverages were obtained with the corresponding interacting amount of ethylamine (n(int(i))) determined by using an isothermal calorimetric titration technique, specially developed for this purpose. The maximum capacities of interaction (N-s), molar enthalpies of interactions at different surface coverages (Delta(int(i))H(m)) and molar integral enthalpies of interaction for a monolayer (Delta(mon)H(m)) have been determined. The Delta(mon)H(m) values, taking into account the investigation of the interaction strengths between ethylamine and Sil-SM, suggest that the Pearson concept is the predominant mechanism in the behavior of the Sil-SM/amine adsorption processes. It is shown that the Delta(int(i))H(m) values are not constant with the surface coverage, thus the general tendency found earlier has been confirmed. (C) 2000 Elsevier Science B.V. All rights reserved.