Porous silica technology

The most commonly used base material is silica (SiOi), the most common substance on the Earth and thoroughly studied in the last two centuries. An excellent monograph on the properties of silica was published by Her [7]. Development of modern HPLC techniques promoted advancement in porous silica technology. Almost all sihca-based HPLC packings manufactured in the twenty-first century are very uniform spherical porous particles with narrow particle and pore size distribution. 

In order to probe the influence of Au and KOAc on the vinyl acetate synthesis chemistry, four different catalysts were synthesized. All of these catalysts were prepared in a manner exemplified in prior patent technology [Bissot, 1977], and each contained the same palladium loading in an egg-shell layer on the surface of a spherical silica support. The palladium content in the catalyst was easily controlled by adjusting the solution strength of palladium chloride (PdClj) added to the porous silica beads prior to its precipitation onto the support by reaction with sodium metasilicate (Na SiOj). The other two catalyst components (Au and KOAc) were either present or absent in order to complete the independent evaluation of their effect on the process chemistry, e.g., (1) Pd-i-Au-hKOAc, (2) Pd-i-KOAc, (3) Pd-hAu, and (4) Pd only. 

Applications exploiting porous silica to encapsulate sensor molecules, enzymes and many other compounds are developing rapidly. Nowadays, sol-gel technology is being used in various fields of modem technology, as for example the basis for optodes, integrated systems, fiber optics, lasers, and new materials. 

Adsorbents employed in this mode of chromatography are porous rigid materials with hydrophobic surfaces. In all modes of HPLC with positive analyte surface interactions (NP, RP, lEX) the higher the adsorbent surface area, the longer the analyte retention and in most cases the better separation. The majority of packing materials used in RP HPLC are chemically modified porous silica. The properties of silica have been studied for many years [15, 16], and the technology of manufacturing porous spherical particles of controlled size and porosity is well-developed. 

FI9. 31.6. (a) Zorbax porous silica microsphere particle, 50% porosity, 100-A pores, (b) Xerogel silica particle, 70% porosity, 100-A pores. (Courtesy of Agilent Technologies.)... 

Porous silica (or silica gel) is by far the most important adsorbent for liquid-solid chromatography and is also the substrate used to prepare most chemically bonded phases, giving it a preeminent position in modem column technology [3-15]. Silica particles are mechanically strong and easily prepared in a wide range of particle size ranges and pore diameters suitable for chromatography. As a substrate for the... 

H.G. Floch, J.J. Priotton I.M. Thomas, "Porous Silica Sol-Gel Coatings For Nd Glass High-Pbwer Pulsed Laser Uses", The Hiysics Technology of Amorphous Si02, edited by R. Devine, Plenum Press, 1988. 

Huang, X. Pelegri, A. A. Nanoindentation Measurements on Low-k Porous Silica Thin Films Spin Coated on Silicon Substrates. Journal of Engineering Materials and Technology 125, 361-367 (2003). 

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