Oxido de niobio (v) enxertado sobre silica gel : estabilidade termica, acidez e reatividade de especies absorvidas

AUTOR(ES)
DATA DE PUBLICAÇÃO

1994

RESUMO

Silica gel was chemically modified with niobium(V) oxide was obtained reacting silanol groups of the silica gel surface with niobium pentachlorite, in organic solvent. The amount of niobium(V) oxide grafted on silica gel surface was 0.89 x 10mol.g. Only Nb(v) ion in the SiNb material were observed by XPS analysis. The binding energy values found for Nb were 3d =210.0 eV and Nb 3d =207,3 eV. The SiNb showed to be highly stable under thermal treatment. Reduction of the specific surface area was observed only for samples pre-calcined to temperatures over than 1273K at which too weak difractions peaks were observed, indicating structure change. Vibracional spectra, Raman and infrared (transmition and Photoacustic) were obtained for SiNb. SiO2 and Nb2O5 pre-treated at diferent temperatures. A high stability of the dispersed oxide on the silica gel surface was verified. This behaviour was attributed to the Si-O-Nb bond formation on the surface. Using pyridine as a probe molecule, the infrared spectroscopy was used to determine the acid property of grafted oxide. It observed an increase of the thermal stability of the Lewis acid site on the support. SiNb was used as sorbent of metalic ions such as Cu, Co and Ni. The exchange capacity increased as the pH solution increased. However, a inflection point at pH=5.3 was observed in the exchange isotherms for the three cations, suggesting that the grafted niobium(V) oxide is an ionic exchanger more acid than free Nb2O5 in which inflection point is observed at pH=8.0. The reactivity of the adsorbed copper ions on SiNb, SiNbCu, was characterized by ciclic voltammetry (CV). It was observed that the mid point potential of the electrode surface was influenced by the supporting electrolityte solution. Oxiamons blocked of the electrochemical response. However this electrochemical response was reversible.

ASSUNTO(S)

oxidos metalicos silica gel voltametria

ACESSO AO ARTIGO

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