Adsorption on silica

The absolute nitrogen isotherm has been analysed by several investigators all using local isotherms that do not allow for lateral 

Other investigations of the silica surface have been completed including systems such as nitrogen/Fransil (77.5 nitrogen, krypton/aerosil (77 nitrogen, krypton/aeroal (77 K), benzene/silica gel (303 cyclohexane, 

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As stated earlier, these hydrocarbons are difficult to quantify with accuracy. The FIA method, which is a chromatographic adsorption on silica, gives volume percentages of saturated hydrocarbons, olefins and aromatics. 

Adsorption on Silica Surfaces, edited by Eugene Papirer... 

Ozone is strongly endothermic (A(g) +142.2 kJ/mol, 2.96 kJ/g) and the pure solid or liquid materials are highly explosive. Evaporation of a solution of ozone in liquid oxygen causes ozone enrichment and ultimately explosion [1], Organic liquids and oxidisable materials dropped into liquid ozone will also cause explosion of the ozone [2], Ozone technology and hazards have been reviewed [3], a safe process to concentrate ozone by selective adsorption on silica gel at low... 

Copper Adsorption on silica modified with 8-quinolol Flow injection AAS - [868]... 

The /V-BOC group in 148 is readily removed on mild heating after adsorption on silica gel (92% yield). 

With the RPA model it has been possible to simulate many sets of CPA/alumina data mentioned in the literature [18], with the same set of unadjusted parameters (PZC, K and K2, OH density). Since pH shifts in the presence and the absence of CPA adsorption on alumina [23] and PTA adsorption on silica [19] are similar, it can be concluded that metal and proton transfer are independent in these systems. Thus the pH shift model can be used in concert with the RPA model not only to predict metal uptake, but also to compute final pH from the initial pH of the contacting solutions [18,28],... 

A separation of myoglobin and lysozyme has been presented by Nicoud [44]. This purification was performed on SMB containing 8 columns using ACA 54 (Biosepra, France) as support. Very pure extracts (>98%) and raffinates (>98%) were obtained from a 50-50 mixture. An internal profile is given in Fig. 7. Another recently presented example is the separation of cyclosporine A from cyclic oligopeptide and other impurities in the reversed phase mode or by adsorption on silica gel presented by Schulte et al. [10]. 

The formation of silicon-flvxyride bonds on the surface of silica after treatment with hydrogen fluoride was never proven directly. However, there is a pronounced change in the adsorption and wetting properties. The silica becomes hydrophobic as was mentioned in a patent to Kimberlin (279a). Neimark and collaborators (279b) found a type V isotherm in the methanol adsorption on silica gel which had been treated with a solution of SiF in absolute alcohol. Wilska (280) obtained a water-repellent silica when solutions of HaSiPg were precipitated with ammonia. The Si—F bond is hydrolyzed only slowly. A considerable fluorine content of 7-10% F was reported in an older patent (281) for a silica that had been prepared by hydrolysis of SiF. ... 

Fig. 36 Schematic diagram of surfactant-adsorption on silica surface as monomer, hemimicelle, and at surfactant concentration above CMC where pyrene is bound to micelle...

To illustrate adsorption on silica immobilization of Upases on macioporous silica will be described. 

Cyclohexadienones. The perturbation of the electronic absorption spectra by adsorption on silica gel can have a significant effect on subsequent photochemical reactions. For example, Hart has shown that 2,4-cyclo-hexadienones photochemically degrade cleanly in nonpolar solvents to a ketene (1) but in highly polar solvents or adsorbed on silica gel bicyclic ketone (2) is the predominant product.33 The absorption spectra indicate that in nonpolar solvents the lowest singlet state is the n,n state, from which the formation of the ketene proceeds. This n -n band is obscured by the band in polar media, inversion of the energy levels of the n,n, and the first... 

Normal-phase adsorption on silica gel with a relatively less polar mobile phase is the most widely used mode in conventional TLC. To improve separations, silica gel may be impregnated with various solvents, buffers, and selective reagents. Other commercial precoated layers include alumina, florisil, polyamide, cellulose, and ion exchangers. 

Table I. Contributions to the Second Central Moment— Adsorption on Silica Gel at 50°C.

In general, there is a wide variety of chromatographic modes (types) that can be employed for the HPLC determination of food components, but only a few have been used for the determination of NOC. These include partition/adsorption on silica gel, liquid-liquid partition on polar-bonded phase (e.g., cyano, amino) or nonpolar hydrophobic-bonded phase (e.g., reversed-phase), and anion-exchange chromatography. Macrae (61) discussed the theories behind the various modes of chromatography. 

Mello et al. [76] Polyphenols Tea Peroxidase (HRP)/ adsorption on silica-titanium and cross-linking with glutaraldehyde, then mixed with carbon paste Carbon paste electrode/-50 mV vs. Ag/ AgCl... 

Inoue, U. and Tochiyama, O. (1977) Determination of the oxidation states of neptunium at tracer concentrations by adsorption on silica gel and barium sulphate./. Inorg. Nucl. Chem., 39, 1443-1447. 

In these terms, the ammonia adsorption is not entirely reversible. Figure 12.1 shows the total and irreversible ammonia adsorption (at room temperature) on Kieselgel 60, thermally pretreated at 473, 673 and 973 K. The adsorption capacity is exceptionally expressed as /nm2. The figure clearly demonstrates that the total ammonia adsorption on silica is determined by the silanol number, in a 1 1 relationship. This means that ammonia adsorption on silica involves an attachment (by a hydrogen bond) of 1 NH3 molecule to 1 silanol group. Such species produce an infrared band at 3419 cm1, assigned by Peri1 to the v3 valence vibration of ammonia. 

Figure 12.1 Total and irreversible ammonia adsorption on silica gel, thermally pretreated at 473, 673 and 973 K.

Careful infrared study of CO chemisorbed by Pd/Si02 catalysts in an SMSI versus a non-SMSI state verified that after HTR, silicon species are distributed in the Pd surface layer. For the catalysts reduced at 300°C (LTR), the B/L intensity ratio (B = bridging CO L = linearly bound CO) is a monotonic function of Pd particle size (Fig. 17). On the other hand, the B/L ratios for Pd/Si02 catalysts that experienced HTR show considerable departure from this universal curve (Fig. 17) (208). Of course, a relatively higher proportion of linearly bound CO for Pd/Si02 catalysts in the SMSI state is believed to follow from the existence of silicon, rather uniformly interdispersed in the metal surface, resembling the case of CO adsorption on silica-supported Pd-Ag alloys (209). 

H. van Damme, in Adsorption on Silica Surfaces, E. Papirer, (editor), Marcel Dekker, New York, 2000, p. 119. 

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