Estrutura de ions complexos adsorvidos sobre superficie de silica gel modificada com 1,4-diazabiciclo (2.2.2.) octano

AUTOR(ES)
DATA DE PUBLICAÇÃO

1991

RESUMO

Silica gel having 242 mg specific surface area, average diameter pore of 100 Å, was chemically modified with 3-[1-onio-4-azabicyclo(2.2.2)octane]propyl trimetoxisilane chIoride, resulting in 0.35 mmol g functionalization degree. Adsorption of Cu(II), Co(II), Ni(II), Zn(II), Cd(Il) and Hg(Il) were carried out in absolute ethanol. Although the amina monoquaternization which could reduce the free nitrogen basicity, the coordination ability was preserved. In fact, the specific adsorption capacities were respectively (in mmol g) 0.29, 0.30, 0.08, 0.24, 0.33 and 0.26. Replacing the Cl¨ counterion by ClO4¨ through exchange reaction, Cu(II) and Co(Il) adsorption were affected, decreasing to 0.21 and 0.19 mmol g, due to the compIex species symmetry influence on the surface. In addition to the metal adsorption by functional group sites, an invasion of MCl2 was also observed. It was clear that the invasion was a function of metal ion concentration, increasing the adsorption capacities of the material more than its real capacity. The Cu(II), Co(Il) and Ni(Il) ions on the surface were able to adsorb gaseous ammonia. This adsorption resulted for Cu(II), a Iigand replacement in the coordination sphere with symmetry change of the absorved species, descending from tetrahedral to square planar structure. The visible and UV region eletronic spectra of Cu(II), Co(Il) and Ni(II) showed that these metals are tetracoordinated on the surface. Cu(Il) and Co(II) are immersed in a tetrahedral symmetry while Ni(II) in a square planar (D4h) symmetry. Other complex species having different symmetries were also detected. The ammonia adsorption by Cu(II) resulted in a square planar complex, identified by electron spin resonance and eletronic spectra. For chloro- and amin complexes species, the structure was shown to be dependent of the surface counterion. The complex was shown to be thermically very stable, an evidence of strong metal-to-nitrogen bond.

ASSUNTO(S)

ions complexos quimica adsorção

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