Infrared spectra of geminal and novel triple hydroxyl groups on silica surface

We investigated the O---H stretching frequencies of geminal and triple hydroxyl groups on silica surface by FT-IR spectroscopy. The geminal and triple hydroxyl groups were individually prepared by the chemical reaction of alkylchlorosilane with surface isolated hydroxyl groups which are separated enough and following hydroxylation of surface chlorine groups. The O---H stretching frequencies of these generated geminal and triple hydroxyl groups were observed at frequencies by 2 and 3 cm⁻¹ lower than that of isolated ones, respectively. By heat treatment the triple hydroxyl groups are firstly eliminated, and secondly the geminal hydroxyl groups disappear. Lastly only isolated hydroxyl groups remain on silica surface.