Surface Chemistry of Silica

An understanding of the surface chemistry of silica is required to interpret its chromatographic properties. The silica surface consists of a network of silanol groups, some of which may. be hydrogen bonded to water, and siloxane groups, as shown in Figure 4.2. A fully hydroxylat silica surface contains about 8... 

ISO. Her, R. K., Surface Chemistry of Silica and Silcates, p. 242. Cornell Univ. Press, Ithaca, New York, 1955. 

The triol 16 can be deprotonated according to Scheme 6. The initial step involves met-allation and this is followed by a coproportionation on addition of two further equivalents of 16. Finally, addition of an ammonium or phosphonium salt gives 36. The stability of the ion has implications for the surface chemistry of silica where similar multiply hydrogen bonded anion sites are likely to be more acidic than isolated silanol groups144. The related cubic polyanion [SigOigtOHji]6- can be prepared directly from aqueous solutions of silica and a quaternary ammonium hydroxide derivative such as [NPhMe3]OH145 146. 

Surface chemistry of silica, edited by A. A. Chuiko (UkrINTEI, Kiev, 2001). 

Silica materials are thermally stable and exhibit ample chemical stability. They dissolve in strong basic solutions and hydrofluoric acid. The surface chemistry of silica... 

Jehng, J.M. et al., Surface chemistry of silica-titania-supported chromium oxide catalysts,, 7 Chem. Soc. Faraday Trans., 91, 953, 1995,... 

An account of the surface properties of silica powders has been given by Hockey (H7). Basila (B3) has studied the surface chemistry of silicas. In the diatomaceous earths, it is generally considered that the main forces responsible for adsorption of solutes are the weak van der Waals forces and the stronger forces due to hydrogen bonding. The van der Waals forces are neutralized by all liquid phases and so need not be considered here. In the diatomaceous support there will be both... 

The work of Her and his co-workers led to the creation of new materials and industries. His studies of the surface chemistry of silica led to the invention of unique organophilic and hydrophobic silica products termed estersils . Virtually a new industry was created when he rendered titania pigment particles in organic films and finishes photochemically inert by coating them with silica. 

The surface chemistry of silica was a subject of intensive study in the period between 1960 and 1970 as a consequence of the widespread industrial use of colloidal, pyrogenic, and precipitated silicas, as well as silica hydrogels and xerogels. Chemical surface reactions and IR spectroscopy were the most-applied methods in surface structure elucidation. Significant contributions to the understanding of the silica surface were made by Fripiat (I), Kiselev and co-workers (2), Hair (3), Little (4), Peri... 

Furlong Surface Chemistry of Silica Coatings of Titania... 

Chuiko, A.A. Gorlov, Yu.I. Surface Chemistry of Silica Surface Structure, Active Sites, Sorption Mechanisms Naukova Dumka Kiev, 1992 (in Russian). 

The history of investigation of the molecular surface chemistry of silica can be divided into three time periods. The period between 1960 and 1970 saw the introduction of IR spectroscopy and the use of chemical reactivity to follow reactions on a silica surface at a molecular level. The period between 1970 and 1980 was less active, but the advances in computer instrumentation that occurred in that decade (in particular Fourier transform IR and NMR spectroscopy) have led to the current revitalization of the subject. The chapters that follow will question some old interpretations and will reinterpret some old ideas. 

Vibrational spectroscopy has had a profound effect on our understanding of the surface chemistry of silica. Indeed, it has been the model system for the use of IR spectroscopy for probing the surface chemistry of oxides, the first studies having been carried out in late 1950. The books written by Hair [1] and Little [2] in the sixties have become classics with respect to the early use of IR spectroscopy for studying the surface properties of silica and adsorbed species thereon. 

This paper will only be concerned with the surface chemistry of silica in vacuum and/or in the presence of an adsorbate. The IR spectrum of a typical self-supporting disc of a pyrogenic or fumed sifica after heating under vacuum for 1 h at 150 C is shown in Figure 25.1 A. Pyrogenic or fumed silicas [some trade names are AerosU and Cab-O-Sil] are made by the flame hydrolysis of SiCLt at 1000°C. These non-porous silicas have a low bulk density and adsorbed water can be removed by evacuation at 20°C. However, the spectral properties are identical when evacuation is carried out at 150 C evacuation at the latter temperature is preferred in order to remove any trace impurities which may be present. The spectrum is characterized by a sharp absorption band at 3747 cm with a broad tail to low wavenumber having a maximum near 3550 cm . The sharp peak is due to the OH... 

The fundamental results achieved in the field of surface chemistry of silica formed the basis for the evolution of a novel direction of researches — chemical science of nanostmctural materials. Within the scope of this scientific direction over 200 new materials with designed properties have been developed which find... 

---