Infrared study of isolated hydroxyl groups on silica surfaces

Abstract

Publication costs assisted by Chevron Research CompanyA reinvestigation of isolated hydroxyl groups on silica surfaces shows the 3750-cm-l SiOH band to be structureless and asymmetric, for wafers prepared a t pressures _<200,000 lb/in.2. Band peak positions vary linearly with temperature with a temperature coefficient of 0.0176 cm-l/deg. The log of the band halfwidths varies linearly with 1/T above -100'. Hydroxyl group rotational activation energies are about 0.9 kcal/mol. Identical surface environments have been found for hydroxyl groups on two different silicas (Cab-0-Si1 and Aerosil) by the precise spectroscopic measurements reported here. * Address correspondence t o this author a t the Jet PropulsionLaboratory, Pasadena, Calif. 91103. observed in the OH region. More recently, Van ( k~+ &~r t and coworkers claim to have resolved the OH absorption

FT-IR Studies of Interaction between Zeolitic Hydroxyl Groups and Small Molecules. 2. Adsorption of Oxygen, Hydrogen, and Rare Gases on H-Mordenite at Low Temperatures

“…110 K in order to make the v(OH) band shift upward by 2 cm"1, according to Ryason and Russell. 37 In fact, as mentioned in the Results section, the v(OH) bands shifted upward by 1-2 cm"1 when the apparent sample temperature was decreased from 300 to 110 K. Such a large decrease in the sample temperature should be difficult to occur simply by the gas introduction. Another possible explanation is that the frequency of the vibrational-rotational transitions is increased by the collision effect, which has been reported for molecules in the gas phase.38 However, this effect should be dependent on the gas pressure and should be very small, in the range of MHz or kHz.38 As described in the Experimental Section, the upward shift caused by He is almost independent of the pressure and is much larger than the order of MHz or kHz.…”

Infrared study of low temperature adsorption. 1. Carbon monoxide on aerosil. An interpretation of the hydrated silica spectrum

“…The slight upward shift of the bands and their intensification is accounted for by the decrease in thermal agitation of the solid; the increase in the KOH) frequency is in agreement with what is already known. 19 Much more stimulating is the case of sample A. No low temperature spectrum of this or similar samples has, to our knowledge, even been reported.…”

Gas Phase Organic Functionalization of SiO2 with Propanoyl Chloride

“…The spectrum in Figure for the initial deposition of SiO 2 onto the bare ZnSe IRC shows two distinct features in the hydroxyl region: a very broad hydrogen-bonded −SiOH band over the range ∼3400–3700 cm –1 and isolated −SiOH groups at ∼3750 cm –1 . ,,,− However, as the deposition of SiO 2 is continued on top of the first film, the infrared spectra referenced to the SiO 2 -coated ZnSe IRC show an increase in absorbance related only to hydrogen-bonded −SiOH groups (blue and red spectra in the inset in Figure ). In addition, the absorbance for hydrogen-bonded −SiOH groups is nearly the same in all three spectra, which indicates that these −SiOH groups are almost entirely embedded in the SiO 2 bulk, and only a small fraction may be present on the top surface.…”