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|Type:||Artigo de periódico|
|Title:||Host lamellar silicic acid magadiite for some heterocyclic amine inclusions and quantitative calorimetric data|
|Abstract:||Both synthesized crystalline lamellar phylosilicate sodic magadiite and its converted acidic nanomaterial present inorganic layers maintained through weak interactive forces, containing orthosilicate units, with sodium or silanol groups between the layers. The protons from the silanol groups interact directly with the basic nitrogen atoms of the cyclic amines through hydrogen bonding formation in the intercalation process. The extension of intercalation was followed through a batch technique to give the maximum amounts of 7.13 +/- 0.01, 3.03 +/- 10.04, 4.71 +/- 0.03, 5.07 +/- 0.02 and 4.67 +/- 0.07 mmol g(-1), for pyridine, 2-, 3- and 4-picolines and 2,6-lutidine, respectively. The synthesized magadiite and all intercalated nanocompounds were characterized by infrared vibrational spectroscopy, X-ray diffraction patterns, Si-29 nuclear magnetic resonance in the solid state, thermogravimetry, electronic scanning microscopy, surface area and porosity. The nuclear magnetic resonance and X-ray diffraction techniques enabled understanding how the guest molecules are accommodated inside the lamellar cavity, as well as revealing the crystallinity of these nanocompounds. Calorimetric titrations in heterogeneous conditions enabled simultaneous determination of the exothermic enthalpies: -7.45 +/- 0.06, -1.18 +/- 0.03, -0.94 +/- 0.01, -0.72 +/- 0.01 and -5.57 +/- 0.05 kJ mol(-1) for the above amine sequence, and the equilibrium constant. The spontaneity of these interaction are reflected in the negative Gibbs free energy, and the positive entropic values to complete the favorable set of thermodynamic data for this intercalation system at the solid/liquid interface, which is strongly dependent on the position of the methyl group attached to the amine heterocyclic ring. (c) 2006 Elsevier Inc. All rights reserved.|
|Editor:||Elsevier Science Bv|
|Appears in Collections:||Artigos e Materiais de Revistas Científicas - Unicamp|
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