Study of xerogel-glass transition of CuO/SiO2

The xerogel-glass transition of SiO2 containing various amounts of CuO was studied by thermogravimetry, differential thermal analysis, Fourier transform infrared spectroscopy, diffuse UV-VIS-NIR reflectance, electron spin resonance spectroscopy, and X-ray photoelectron spectroscopy. The samples were prepared by the sol-gel process from tetraethoxysilane, and copper(II) acetate monohydrate. Significant structural changes were observed during the various stages of glass formation. It was concluded that copper(II) ions exist in two different enviroments, i.e., isolated and clustered. The results indicate that the former remains entrapped (doped) in the xerogel and glass, and that the clustered copper(II) ions were transformed into highly dispersed CuO by calcination. The relative amounts of these species depend on the copper(II) concentration and, except for the sample with 0.5% CuO, the amount of isolated copper(II) ions is lower than that of the clustered ions. (C) 1996 Academic Press, Inc.