Extraction of Pb(II), Cd(II), and Hg(II) from aqueous solution by nitrogen and thiol functionality grafted to silica gel measured by calorimetry

The reaction of ethylene sulfide with 3-aminopropyltrimethoxysilane gave a new silylating agent, which was anchored onto a silica surface via the sol-gel procedure. This surface displayed a chelating moiety containing nitrogen and two sulfur basic centers potentially capable of extracting cations from aqueous solutions. The process of metal extraction was followed by a batch method, and fitted to a modified Langmuir equation. The maximum adsorption capacities found were: 2.06 +/- 0.01, 3.72 +/- 0.02, and 5.14 +/- 0.02 mmol g(-1) for Pb(II), U(II), and Hg(II), respectively. The enthalpies of bending are: -1.16 +/- 0.04, -3.60 +/- 0.10, and -8.94 +/- 0.03 kJ mol(-1) for Cd(II), Pb(II), and Hg(II), respectively. The Gibbs free energies of binding agree with the spontaneity of the proposed reactions between cations and basic centers. (c) 2006 Elsevier B.V. All rights reserved.