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Type: Artigo de periódico
Title: Thioglycolic acid grafted onto silica gel and its properties in relation to extracting cations from ethanolic solution determined by calorimetric technique
Author: Arakaki, LNH
Espinola, JGP
da Fonseca, MG
de Oliveira, SF
de Sousa, AN
Arakaki, T
Airoldi, C
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 kJ mol(-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 kJ mol(-1), the variations in entropy obtained were 42 +/- 1, 201 +/- 1, and 172 +/- 1 J K-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. (C) 2004 Elsevier Inc. All rights reserved.
Subject: silica gel
thioglycolic acid
calorimetric titration
thermodynamic data
Country: EUA
Editor: Academic Press Inc Elsevier Science
Citation: Journal Of Colloid And Interface Science. Academic Press Inc Elsevier Science, v. 273, n. 1, n. 211, n. 217, 2004.
Rights: fechado
Identifier DOI: 10.1016/j.jcis.2004.01.006
Date Issue: 2004
Appears in Collections:Unicamp - Artigos e Outros Documentos

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