Immobilization of ethylenesulfide on silica surface through sol-gel process and some thermodynamic data of divalent cation interactions

The silylant precursor agent 3-aminopropyltrimethoxysilane (APTS) reacted w ith ethylenesulfide to yield 2-{2-{3-(trimethoxysilyl)propylamino}ethylthio }-ethanethiol, which was anchored on silica gel by using the sol-gel proces s. The new synthetic silylant agent displayed a chelating moiety containing one nitrogen and two sulfur basic centers, which are potentially favored f or adsorbing divalent cations from aqueous solution. Thus. the similar chem isorption isotherms for all cations were obtained by batchwise method and t he data were adjusted to a modified Langmuir equation to give the sequence of the maximum retention capacity as Cu > Co > Ni. The same adsorption was followed by calorimetric titration and the enthalpic values of -7.40 +/- 0. 01, -1.50 +/- 0.10 and -0.98 +/- 0.02 kJ mol(-1) for copper, nickel and cob alt respectively, were obtained. From the calculated Gibbs free energy -25. 8 +/- 0.1. -35.1 +/- 0.1 and -30.8 +/- 0.1 kJ mol(-1), the variation in ent ropy were also obtained as 62 +/- 1, 42 +/- 1 and 100 +/- 1 J K-1 mol(-1) f or the same above sequence. All thermodynamic values are in agreement with the spontaneity of the proposed cation-basic center interactions for these chelating processes. (C) 2001 Elsevier Science Ltd. All rights reserved.