A new organofunctionalized silica containing thioglycolic acid incorporated for divalent cations removal-A thermodyamic cation/basic center interaction

The silylating agent 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane was previously immobilized onto silica gel in heterogeneous route, followed by incorporation of thioglycolic acid. The elemental analysis for this final organofunctionalized silica has a degree of pendant chain of 0.27 mmol per gram of the inorganic support. Infrared spectroscopy, thermogravimetry and (CNMR)-C-13 data are in agreement with the covalent bond of organic moieties on silica, with increase in basic centers attached to these pendant chains, which adsorb divalent copper, nickel and cobalt cations from aqueous solution. The data from batch adsorption process were adjusted to a modified Langmuir equation, to give the maximum retention capacity Cu(II)>Ni(II)>Co(II). This same cation/basic centers interaction was calorimetrically followed through titration technique. The enthalpies of these processes are: -3.03 +/- 0.01, -3.73 +/- 0.02, and -2.75 +/- 0.01 kJ mol(-1) for Cu(II), Ni(II), and Co(II), respectively. The standard molar Gibbs free energies are in agreement with the spontaneity of the proposed reactions between cation and basic center. (C) 2008 Elsevier B.V. All rights reserved.