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 MX(2) (M=Co(2+), Ni(2+), Cu(2+), and X=Cl(-), NO(3)(-)) 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 Ni(2+)>Cu(2+)>Co(2+) 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 DeltaG values are in agreement with the spontaneity of the proposed reactions and the complexation is entropically favored. Copyright 2000 Academic Press.