Ethyleneimine anchored on thiol-modified silica gel surface - Adsorption of divalent cations and calorimetric data

Activated silica gel was previously modified by the silylant agent 3-mercaptopropyltrimethoxysilane. The organofunctionalized silica gel containing pendant groups ended with the -SH functions reacted with the three-member cyclic ethyleneimine molecules to yield the new ligand attaching sulfur and nitrogen basic centers available to complex cations. This final anchored surface adsorbs MX2 (M = Co2+, Ni2+, Cu2+, and X = Cl-, NO3-) at 298 +/- 1 K. A considerable increase in adsorption capacity was observed for nitrate counteranions. This process of extraction was followed by the batch method and the order of the maximum capacities found was Ni2+ > Cu2+ > Co2+ for both series of salts. The pendant immobilized groups-cation interaction processes showed exothermic enthalpies. Those values are more pronounced for chlorides, with the largest values obtained for cobalt. The calculated Delta G values are in agreement with the spontaneity of the proposed reactions and the complexation is entropically favored. (C) 2000 Academic Press.