Absorção na interface N-(2-aminoetil) (3-aminopropil) silica/soluções dos catons divalentes de cobalto, niquel cobre e zinco em alcool e acetona

AUTOR(ES)
DATA DE PUBLICAÇÃO

1984

RESUMO

Various features concerned with the metal-ligand interactions involving some divalent cations of the firt transition series and silica gel anchored with N-(2-aminoethyl) (3-aminopropil)trimetoxi-silane were studied both in acetone and ethanol. The material was characterized through various techniques as elemental analysis, support geometrical properties measurements, near infrared, infrared and visible regions spectroscopy, adsorption measurements in solution and calorimetric titration. With the zinc compound as an exception, alI other compounds are colored, and they also present a stability enough accentuated, being only destroyed in a relatively strong acid medium. The elernental analysis results showed that 0.57 mol of ligand groups were anchored per gram of modifyed silica gel. Reflecting this fixation, it was verifyed through surface area measurements a decrease of 155m per gram of silica. Through elemental analysis and cations adsorption measurements in solution it was observed that the complexes, formed in the adsorvent material surface, present different stoichiometries in accordance of the employed solvent. For example, in acetone it was observed s-LMCl2, where s representd a silicon atom in the adsorvent material surface plane, L is the anchored ligand group and M the Co, Cu and Zn cations. In alcohol, it follows the formulation: a) s-L2MCl2 for M = Ni and Zn b) s-LMCl2 for M = Co and Cu The data, related to electronic spectroscopy measurements, suggest for cobalt, nickel and copper complexes the tetrahedral, octahedral and distorted tetragonal symmetries, respecti vely. The studies of the equilibria: s- L(suspension) + MCl2 (solution) s-LnMCl2 (suspension) where n= 1 or 2 and M = cation, through calorimetric titrations, provided the equilibrium constant, K, as well as, the variation of the enthalpy, DH , for each reaction K values are in the order of 10 and DH value is exothermic for the cooper salt, and endothermic for the zinc and cobalt salts, for acetone as the solvent. In ethanol, it was only observed the enthalpy variation for the copper salt, whose DH value is exothermic. The equilibria constant enable us to establish the following order for the stability of the formed complexes: Co >Cu >Zn.

ASSUNTO(S)

cations absorção alcool acetona

ACESSO AO ARTIGO

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