B. A. Morrow

Bio: B. A. Morrow is an academic researcher from University of Ottawa. The author has contributed to research in topics: Silanol & Fumed silica. The author has an hindex of 6, co-authored 6 publications receiving 602 citations.

Surface vibrational modes of silanol groups on silica

Abstract: Infrared spectroscopy has been used to study the vibrational modes associated with free (isolated) silanol groups on an aerosil silica and a precipitated silica which have been activated in vacuum in the temperature range from 450 to 800 o C. Both silicas exhibit two Si-O-H angle deformation modes at 760 and 840 cm -1 , indicative of two types of isolated silanol species, called type I and II, respectively

Chemical reactions at silica surfaces

Abstract: Chemical modification of the silica surface can provide a powerful method for probing the nature of the surface hydroxyl groups and how these might be modified via thermal activation. In the present paper, it is shown how vibrational spectroscopic methods (infrared and Raman) can be used to study silanol groups which have been modified after reaction with a variety of very reactive hydrogen sequestering agents (D2O, ZnMe2, BCl3, TiCl4, AlMe3, GaMe3, BEt3 and (SiMe3)2NH), having differing steric dimensions and it is demonstrated that a nearly complete vibrational spectrum for some of the corresponding new surface species can be obtained. With the use of fast scanning FTIR spectroscopy, spectra were able to be recorded in less than a second and the application of these time-resolved methods has been used to probe differences in the reactivity of isolated and H-bonded silanol groups. The spectroscopic evidence suggests that the ability of a reactant to react bifunctionally, i.e. to react with more than one SiOH group, is important in determining the initial reactivity of the H-bonded silanols relative to those that are isolated or non-H-bonded. Further, the number of inaccessible and H-bonded silanols that do not react increases as the apparent size of the reactant molecule increases, regardless of whether the reactant can react bifunctionally. Finally, for the larger probe molecules used ((SiMe3)2NH and BEt3), the new chemisorbed surface species block other H-bonded silanols and prevent them from reacting with either of these probes.

Infrared evidence for two isolated silanol species on activated silicas

Abstract: Infrared spectroscopy has been used to study the OH stretching vibration of isolated silanol groups on an aerosil and a precipitated silica which have been activated under vacuum at 450, 600 or 800°C. When the 450°C activated samples are cooled to −191°C, the normally asymmetric OH peak splits into two components having a peak maximum near 3750 or 3746 cm −1 for the aerosil and precipitated silica, respectively, and a shoulder near 3738 cm −1

Trimethyl phosphite adsorbed on silica: an NMR and infrared study

Abstract: Infrared spectroscopy and phosphorus-31 magic angle spinning nuclear magnetic resonance spectroscopy have been used to study the adsorption of trimethyl phosphite (TMP) on silica. At 23 C TMP reacts rapidly with surface silanol groups to give SiOCH{sub 3} as a chemisorbed product and liquid dimethyl phospite (DMP). However, formation of DMP ceases when about half of the SiOH groups have been consumed because DMP strongly hydrogen bonds to the remaining silanols thereby inhibiting further reaction between TMP and SiOH. TMP also undergoes isomerization to dimethyl methylphosphonate (DMMP) which is catalyzed by SiOH. As the number of initial silanol groups is decreased (by using higher temperatures of vacuum activation) the quantity of DMP produced decreases whereas that of DMMP increases. A mechanism for formation of DMP and DMMP has been suggested. At 100C isomerization does not occur, all SiOH groups are consumed, and the major product is DMP/SiOCH{sub 3} accompanied by a small quantity of a chemisorbed phosphorus-containing species having the proposed structure (SiO){sub 2}P-H({double bond}O). The latter is stable up to 400C. If TMP is heated with silica from 100 to 400C, in addition to SiOCH{sub 3}, the major new chemisorbed product of the reaction which can be identified bymore » IR and NMR is (SiO){sub 2}P-Me({double bond}O) (Me = CH{sub 3}). The advantages of a combined IR-NMR approach is discussed.« less

Infrared spectroscopy of sol–gel derived silica-based films: a spectra-microstructure overview

Abstract: Infrared (IR) spectroscopy is one of the most popular analytical techniques used to characterize sol-gel silica materials in their different stages. The method represents, in particular, a simple and versatile tool to investigate the microstructural evolution in gels and films, as a function of temperature and synthesis parameters. Several studies have shown that sol-gel IR absorption spectra exhibit, with respect to silica melt glass spectra, some specific features closely related to the peculiarities of sol-gel processing. Furthermore, because of the differences between silica bulk gels and films the spectra- microstructure correlation must be especially evaluated for thin films. IR spectroscopy has been used to evaluate residual porosity, Si-O-Si bonding rearrangements during drying and firing stages and to model the microstructure evolution during film processing. Some questions are still, however, arising around the interpretations of the IR spectra, in particular about the presence of cyclic species in the microstructure and disorder-induced vibrational modes. An attempt is made here to present an overview of the different relationships existing between IR spectra and microstructure of sol-gel silica films as they actually appear from current literature.