Thioglycolic acid grafted onto silica gel and its properties in relation to extracting cations from ethanolic solution determined by calorimetric technique.

Thioglycolic acid was immobilized onto silica gel surface using 3-aminopropyltrimethoxysilane as precursor silylating agent to yield silica. The amount of thioglycolic acid immobilized was 1.03 mmol per gram of silica. This new surface displayed a chelating moiety containing nitrogen, sulfur, and oxygen basic centers which are potentially capable of extracting cations from ethanolic solution, such as MCl3 ( M=Fe, Cr, and Mo). This process of extraction was carried out by the batch method when similar chemisorption isotherms were observed for all cations. The data were adjusted to a modified Langmuir equation. The sequence of the maximum retention capacity was Cr(III) > Mo(III) > Fe(III). The same adsorption was determined by calorimetric titration and the enthalpic values of -35.75 +/- 0.02, 32.90 +/- 0.15, and -84.08 +/- 0.12 kJmol(-1) for chromium, molybdenum, and iron, respectively, were obtained. From the calculated Gibbs free energy -23.4 +/- 0.2, -27.2 +/- 0.2, and -32.7 +/- 0.3 kJmol(-1), the variations in entropy obtained were 42 +/- 1, 201 +/- 1, 172 +/- 1 JK(-1)mol(-1) for the same sequence. All thermodynamic values are in agreement with the spontaneity of the proposed cation-basic center interactions for these chelating processes.

Chemisorption and thermodynamic data of the interaction between a chelate free acidic center with basic groups attached to grafted silicas.

The molecule 2-aminoethanethiol was added to the grafted silylant agent [(3-chlorosilylpropyl)trimethoxysilane] (cpts) onto silica gel(triple bond SilCl), obtaining a surface (triple bond SilSNH(2)) and giving 0.70 mmol g(-1) of nitrogen; the surface of silica was modified with [(3-mercaptosilylpropyl)trimethoxysilane] (mpts) with surface (triple bond SilSH), giving 0.78 mmol g(-1) of sulphur. Both matrices, (triple bond SilSNH(2)) and (triple bond SilSH), adsorb copper and cobalt acetylacetonates from ethanolic solution. Adsorption, using a batchwise process, showed that copper chelate was the most adsorbed. The interactions between the basic centers attached to organic chains of these modified silicas with the cations in the chelates Me(acac)(2) [M=Cu and Co] were followed through calorimetric titrations. Exothermic enthalpic results were obtained for the triple bond SilSNH(2) matrix. The spontaneity of these systems was reflected in negative free Gibbs energy and positive from entropic values.