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-mercap topropyltrimethoxysilane. The organofunctionalized silica gel containing pe ndant groups ended with the -SH functions reacted with the three-member cyc lic ethyleneimine molecules to yield the new ligand attaching sulfur and ni trogen basic centers available to complex cations. This final anchored surf ace adsorbs MX2 (M = Co2+, Ni2+, Cu2+, and X = Cl-, NO3-) at 298 +/- 1 K. A considerable increase in adsorption capacity was observed for nitrate coun teranions. This process of extraction was followed by the batch method and the order of the maximum capacities found was Ni2+ > Cu2+ > Co2+ for both s eries of salts. The pendant immobilized groups-cation interaction processes showed exothermic enthalpies. Those values are more pronounced for chlorid es, with the largest values obtained for cobalt. The calculated Delta G val ues are in agreement with the spontaneity of the proposed reactions and the complexation is entropically favored. (C) 2000 Academic Press.