RESUMO
The natural highly charged lamellar silicate vermiculite was investigated as an exchanger matrix in doubly distilled water solution to exchange magnesium inside the lamella with the heavy cations copper, nickel, cobalt, and lead at the solid/liquid interface. The extension of each exchange reaction was dependent on time of reaction, pH, and cation concentration. The maximum time presented the following order Pb2+ < Ni2+ < Cu2+ < Co2+, which corresponds to 12, 24, 48, and 72 h, respectively. The best performance was observed for nickel, as represented by the exchange capacity Nf, which gave values 0.59, 0.76, 0.84, and 0.93 mmol g(-1) for Pb2+ < Co2+ < Cu2+ < Ni2+, respectively. This capacity is dependent on pH interval variation from 1 to 9, being significantly increased in alkaline condition. The isotherm data were adjusted to a modified Langmuir equation and from the data the spontaneous Gibbs free energy was calculated. Linear correlations were obtained through Gibbs free energy or the maximum capacity against the cationic radius plot, with the lowest values for the largest cation lead. An exponential correlation was also observed for the maximum capacity versus enthalpy of hydration plot, indicating a difficulty of the less hydrated cation, lead, in exchanging with magnesium inside the lamellar space, as suggested by the proposed mechanism. The saturated matrices with cations presented a decrease in interlayer distance in comparison with the original vermiculite, which can be related to the hydrated phases, characteristic for each cation, with a lowest value for lead.
RESUMO
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.
Assuntos
Etanol/química , Dióxido de Silício/química , Tioglicolatos/química , Adsorção , Calorimetria , Quelantes/farmacologia , Cromo/química , Entropia , Géis , Ferro/química , Espectroscopia de Ressonância Magnética , Modelos Químicos , Molibdênio/química , Temperatura , TermodinâmicaRESUMO
Silica gel was modified firstly with aminepropyltrimethoxisilane obtaining the matrix named as SILNH(2). The SILNH(2) silica reacted subsequently with thioglycolic acid Sil-Ntga. The elemental analysis showed the presence of 0.98mmolg(-1) of organic moieties immobilized on silica. Infrared and (13)C NMR spectroscopic data in conjunction with thermogravimetric measurements are in agreement with the suggested functionalization. The ion adsorption properties of the silica Sil-Ntga were studied using copper ions in aqueous/ethanolic solutions in concentrations ranging from 4.0x10(-3) to 5.0x10(-2)moldm(-3) at different temperatures. The new modified silica showed a good sorption ability for copper at lower temperatures and its reuse capacity was demonstrated.
RESUMO
Silica gel surface has been modified in two reaction steps: (i) the silylating agent 3-mercaptopropyltrimetoxysilane was firstly immobilized to give a surface Sil-SH and (ii) this precursor incorporated an ethylene sulfide molecule to obtain the surface denoted Sil-SSH. This material was characterized by elemental analysis, IR spectroscopy, thermogravimetry, solid state 13C and 29Si NMR, and surface area measurement. These materials were employed as adsorbents for divalent heavy cations from aqueous solutions at room temperature and the isotherms were adjusted to a modified Langmuir equation. The maxima number of moles adsorbed were 1.0, 1.5, 1.6, 2.2, 2.4 and 3.3 mmol g(-1) for Co, Cu, Ni, Cd, Pb, and Hg, respectively.
Assuntos
Metais Pesados/análise , Metais Pesados/química , Dióxido de Silício/química , Compostos de Sulfidrila/química , Adsorção , Monitoramento Ambiental/métodos , Géis/química , Sílica GelRESUMO
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.