Fcb., 1059
JNFRARICD STUDY OF
THE
WATER-SILICA GELSYSTEM
179
AN INFRARED STUDY OF THE WATER-SILICA GEL SYSTEM BY H. A. BENESIAND A. C. JONES Shell Development Company , Emeryville, California Received J u n e 19, 1968
An infrared study of bound and adsorbed water in silica gel has been made. It mas found that hydrogen in silica gel could be completely replaced by deuterium upon treatment with DzO a t room temperature. Deuteration of silica gel allowed unambiguous differentiation between absorption bands arising from silica itself and those arising from atomic groupings that contain hydrogen. It was found that “bound water” in silica gel consists entirely of SiOH groups located on the surface. The infrared spectrum of physically adsorbed water closely resembles that of liquid water. Dehydration of silica gel a t high temperatures removes surface SiOH groups; these can be reconstructed by reaction with adsorbed water a t room temperature.
The present study was undertaken with the expectatioii, since fulfilled, that the w e of infrared spectroscopy would lead to a better understanding of the state of bound and adsorbed water in the water-silica, gel system. As the first step, we made absorption hand nssignments which, in turii, enabled us to make an unambiguous interpretation of the nature and location of hydroxyl groups in silica gel. A.t this stage of the investigation, the information derived t)hrough observiLtion of the spectral changes that accoiiipnnietl silica gel deuteratioii was indispensable. We then iiivestigated the physical adsorpt,ion niid chemisorption of water 011 nilica gel, the present, study heing more nearly complete thaii t h a t reported by Pimeiitel, et n1.I The results obtaiiied are pieseiited and discussed below. Experimental Details Sample Preparation .-Silica gel samples consisting of particles having diameters less than one micron were obtained from Monsanto (Aerogel), Philadelphia Quartz (QUS.O), Godfrey Cabot (Cab-0-Sil), D?vison Chemical (Syloid 244) and Dow Corning Conipanieti. Such silica gel powders could be used, as received, for the preparation of sample films. Samples of Grade 3 5 , GI.adc: 70 and Grade 950 silica gel from Davison Chemical Company were ground and sedimented from isoliropyl alcohol suspension using tecliniques very similar to those developed by Hunt2 and by Keller and Picltett.a However, the material used in most of the present study was a sample of Davison’s Grade 950 silica gel that had been air-millec14 by use of n Sturtevant fi4icronizer. The above sample of Grade 950 silica gel, as it was received from Davison Chemical Company, contained only 0.002% aluminum, had a surface area of 745 m.”g. and a pore volume of 0.37 cc./g. The latter values dropped to 581 ni.2/g. and 0.31 cc./g., respectivelv, through the air-milling process. Most sample films were mounted on sodium chloride or barium fluoride windows by placing a quantity of silica gel of fine particle size on the window, adding enough isopropyl alcohol to make n slurry, wiping a microscope slide across the window, and allowing the nlcohol to evapornte. During the coume of our studies we developed a teclinique similar to that recently described by Yang rtnd Garland6) to prepare films that were much more unifoi.m than those prepared as described above. The technique consisted of spraying a suspension of tine particle size silica gel in isopropyl alcohol (0.1 g. per 100 ml. of suspension) onto a salt window t,liat was heated by cont.act with an aluminum block kept R t GO t’o 90”. The sprayer used was of the type suitable for the developnient of paper c,hromatograms. I t was ohtained from .RIicrocheinic,zl Specialties, h e . , Berkeley, California. (1) C:. C . Piiiieiilcl, C. \V. Gurlnnd :ind G . J u r a , .1..4m. Chain. SOC., 76, 803 ( 1 ~ 5 ~ ) . (2) J. 31. H u n t , API I ’ r o j r c t 49, Rept. No. 8, 1). 105 (1950). (3) \V. D. Rellet a n d E. E. Pickett. r e f . 2, p. 123. (4) Kindly furnished by Dr. I
