title: Thioglycolic acid grafted onto silica gel and its properties in relation to extracting cations from ethanolic solution determined by calorimetric technique.
abstract: 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.
authors.affiliation: Departamento de Química, CCEN, Universidade Federal da Paraíba, 58051-900 João Pessoa, Paraíba, Brazil. arakaki@labpesq.quimica.ufpb.br
authors.forename: Luiza N H
authors.initials: LN
authors.lastname: Arakaki
authors.forename: José G P
authors.initials: JG
authors.lastname: Espínola
authors.forename: Maria G
authors.initials: MG
authors.lastname: da Fonseca
authors.forename: Severino F
authors.initials: SF
authors.lastname: de Oliveira
authors.forename: Antonio N
authors.initials: AN
authors.lastname: de Sousa
authors.forename: Tomaz
authors.initials: T
authors.lastname: Arakaki
authors.forename: Claudio
authors.initials: C
authors.lastname: Airoldi
mesh_terms: D000327:Adsorption; D002151:Calorimetry; D002614:Chelating Agents / Q000494:pharmacology; D002857:Chromium / Q000737:chemistry; D019277:Entropy; D000431:Ethanol / Q000737:chemistry*; D005782:Gels; D007501:Iron / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008982:Molybdenum / Q000737:chemistry; D012822:Silicon Dioxide / Q000737:chemistry*; D013696:Temperature; D013816:Thermodynamics; D013864:Thioglycolates / Q000737:chemistry*
chemical_list: D002614:Chelating Agents; D005782:Gels; D013864:Thioglycolates; D002857:Chromium; D000431:Ethanol; D012822:Silicon Dioxide; D008982:Molybdenum; D007501:Iron