Acetilacetona, diacetamida e N-(2-piridil)-acetamida imobilizadas na superficie de silica gel - preparação, caracterização, adsorção, termoquimica e espectroscopia de complexos suportados

AUTOR(ES)

Edesio Fernandes da Costa Alcantara

DATA DE PUBLICAÇÃO

1993

RESUMO

The ligands acetyIacetone(ac), diacetamide(da) and N-(2-pyridyl)acetamide(pa) were immobilized on siIica gel surface, giving the products Si-ac, Si-da and Si-pa, respectively. These materiaIs were characterized through elemental analyses, infrared spectroscopy, surface area measurement, solid state carbon-13 NMR, thermogravimetry and differencial scanning calorimetry. The elemental analyses indicated the presence of 0.616, 0.286 and 0.345 mmol of bonded ac, da and pa groups per grama of silica gel. The functionalized materiaIs were equilibrated with divalent chloride solutions of Co, Cu, Ni, Zn, Cd and Hg in ethanol and acetone, and Cr(VI) in acidic medium at 298 K. The adsorption of those ions follow the Langmuir Equation, which was used to determine the maximum capacity (N)(molg) and the intensity of adorption (K )(lmol). The N values for a given metallic cation, indicate that the adsorption in acetone was always larger than in ethanol, as shown in the following sequencies: Si-da: Cu>Co>Zn in acetone and Cd>Hg>Zn>Ni>Co>Cu in ethanol; Si-pa: Cu>Co>Zn in acetone and HgCdZn>Co>Cu>Ni in ethanol; Si-ac: Cu>Co>Zn in acetone and Hg>Cd>Cu>Co>Zn>Ni in ethanol. The adsorption of Cr(VI) in the three surfaces follow the same trend as that of the surface functionalization. The calorimetric titrations of the suspended functionalized surfaces with cationic solutions in ethanol and acetone gave isotherms which obeyed the modified Langmuir Equation. The linearization of these Equations enable the determination of the thermochemical parameters Ke, DH, DG and DS for cation-ligand supported interactions. With exception of Co with the three surfaces, Zn with Si-da in acetone and Hg with the same surface in ethanol and Zn with Si-ac in both solvents, alI other DH values were exothermic. The enthalpy vaIues reveal that the processes are more exothermic with Cu in acetone, following the sequency: Cu>Zn>Co for alI the functionalized surfaces. The electronic absorption spectra of cation supported complexes suggest: a)a tetrahedral symmetry for Co and Ni and b)an octahedral symmetry with strong tetragonal distortions for Cu.

ASSUNTO(S)

analise espectral absorção silica gel

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