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 with ethylenesulfide to yield 2-{2-{3-(trimethoxysilyl)propylamino}ethylthio}-ethanethiol, which was anchored on silica gel by using the sol-gel process. The new synthetic silylant agent displayed a chelating moiety containing one nitrogen and two sulfur basic centers, which are potentially favored for adsorbing divalent cations from aqueous solution. Thus. the similar chemisorption isotherms for all cations were obtained by batchwise method and the 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 cobalt 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 entropy were also obtained as 62 +/- 1, 42 +/- 1 and 100 +/- 1 J K-1 mol(-1) for 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.