Synthesis and characterization of SiO2–Nb2O5systems prepared by the sol–gel method: structural stability studies

Abstract

X-Ray diffraction (XRD), N2 absorption (BET specific surface area), transmission electron microscopy (TEM), Raman and Fourier infrared (FT-IR) spectroscopic techniques have been applied to characterize the texture, structure and niobia–silica interaction of SiO2–Nb2O5 systems prepared by the sol–gel method containing different amounts of Nb2O5 and calcined at temperatures between 393 and 1473 K. For a small loading of niobia, amorphous niobium species were well dispersed in the silica up to 1273 K. Crystallization is observed only after thermal treatment at 1473 K, with the T-phase predominating as observed by XRD and TEM analyses and confirmed by Raman spectra. For samples with a higher amount of niobia, the formation of a T-Nb2O5 phase was observed at 1273 K, and the H-Nb2O5 phase predominates at 1473 K. FT-IR results indicate the presence of Si–O–Nb linkages at the silica–niobia interface, formed during preparation, which are responsible for the higher structural stability of the SiO2–Nb2O5 system. The stability of the SiO2–Nb2O5 system is confirmed by obtaining high specific surface areas even after the high temperature of calcination.