Spectroscopic studies of adsorbed complexes of water and hydrogen fluoride on the surface of dispersed silicas

Abstract

Important information about the nature of the active centers of a sil ica surface can be provided by IR spectroscopic studies of adsorption p rocesses in the region of the oxygen s i l i con stretching vibrations. However, for compressed pure powders of dispersed silicas complex absorption is usually observed in the range of frequencies below 1200 cm -1. In the few ea r l i e r studies of this region of the spect rum a suspension of the sil ica in liquid paraffin was used, small weighed samples of SiO 2 were compressed with KBr [1], a finely ground sil ica powder in suspension was deposited [2-4], or hydrolysis of a liquid film of te t raalkoxysilane [3] was ca r r i ed out on plates which were t ransparent in the IR region. Using the methods just indicated gives r i se to ser ious exper imental difficulties. As a consequence, interpretat ion of a number of the absorption bands of sil icas in the 1200-800-cm -1 region is ambiguous. In par t icular , three different absorption bands, 870 [2, 4], 950 [1, 5, 6], and 1120 cm -1 [31, have been assigned to the deformation frequencies of the OH vibrations in the silanol surface groups.