An infrared study of the silica gel surface. 1. Dry silica gel

Abstract

Transparent plates of silica aerogel were studied by infrared spectroscopy. Experiments with D exchange, silanization, and heat treatment showed that dry silica gel, degassed at 875 K, has four absorption bands in the O-H stretching region. These bands are assigned to four different types of surface hydroxyl groups, viz. isolated single and geminal silanols (absorbing at 3749 and 3742 cm'1, respectively), and asymmetric H-bridged vicinal silanol pairs (absorbing at about 3720 and 3500-3700 cm™1). Interfering water vapor proved not to cause the observed spectral features. It is concluded that silica powders (Cabosil, Aerosil), having only one absorption at 3748 cm™1 after vacuum treatment at the same temperature, and silica gel do not have identical surfaces.

Water Adsorption on Pyrogenic Silica Followed by1H MAS NMR

“…In from silicas prepared in a liquid medium by their small order to better understand and control the properties of silica particle size (10-20 nm), their nonmicroporous surface, and much work has therefore been devoted to the study of surface their lower hydroxyl density (5). Moreover, prepared at protons, most noticeably by IR (3)(4)(5)(6), { 1 H- 29 Si} CP MAS-high temperature followed by rapid quenching, they are only NMR (5,(7)(8)(9)(10)(11), and , MAS, partially hydrated and present numerous unstable strained CRAMPS (7,8), and multiple coherence (13)). Surface siloxane bridges susceptible to relaxation by hydroxylation hydroxyl groups have been classified according to their coor-(21).…”

Surface photochemistry: the effect of surface modification on the photophysics of naphthalene and pyrene adsorbed on silica gel

“…The terminal oxygen functions -the silanols -have been shown by infrared studies to be geminal, vicinal, or isolated (15)(16)(17)(18)(19)(20)(21)(22)(23). These functions, in an amorphous framework, serve to render the silica gel surface inhomogeneous.…”

“…Heat treatment of silica gel first induces loss of the physically adsorbed water molecules and, subsequently, dehydroxylation of the silanol groups. The number of hydroxyl groups on the silica gel surface depends strongly on the temperature of pretreatment of the samples studied (15)(16)(17)(18)(19)(20)(21)(22)(23)(24). Measurements performed by Fripiat and Uytterhoeven (21), amongst others, indicate that the amount of free water rapidly decreases with increasing temperature and, for temperatures higher than about 250°C, it is ' Publication 315 from the Photochemistry Unit.…”

Estimating the relative acid site density of silica‐alumina by infrared spectroscopy using a selective reactant poison

“…This is the expected result if a = I , since the area of this peak is described by Eq. Mol, 1978). Infrared spectroscopy of the catalysts confirms this by the generation of C-H relaxations and the complete disappearance of 0 -H relaxations in the spectra of the HMDS-.treated catalyst (Rosenthal, 1985).…”