Silica sorbed

In the course of mixture separation, the composition and properties of both mobile phase (MP) and stationary phase (SP) are purposefully altered by means of introduction of some active components into the MP, which are absorbed by it and then sorbed by the SP (e.g. on a silica gel layer). This procedure enables a new principle of control over chromatographic process to be implemented, which enhances the selectivity of separation. As a possible way of controlling the chromatographic system s properties in TLC, the pH of the mobile phase and sorbent surface may be changed by means of partial air replacement by ammonia (a basic gaseous component) or carbon dioxide (an acidic one). 

Natural colloid particles in aqueous systems, such as clay particles, silica, etc. may serve as carriers of ionic species that are being sorbed on the particulates (pseudocolloids). It seems evident that the formation and transport properties of plutonium pseudocolloids can not yet be described in quantitative terms or be well predicted. This is an important area for further studies, since the pseudocolloidal transport might be the dominating plutonium migration mechanism in many environmental waters. 

The photochemical transformation of phenanthrene sorbed on silica gel (Barbas et al. 1996) resulted in a variety of products including c -9,10-dihydrodihydroxyphenanthrene, phenanthrene-9,10-quinone, and a number of ring fission products including biphenyl-2,2 -dicarboxaldehyde, naphthalene-l,2-dicarboxylic acid, and benzo[c]coumarin. 

Barbas JT, ME Sigman, R Dabestani (1996) Photochemical oxidation of phenanthrene sorbed on silica gel. Environ Sci Technol 30 1776-1780. 

As an example of composite core/shell submicron particles, we made colloidal spheres with a polystyrene core and a silica shell. The polar vapors preferentially affect the silica shell of the composite nanospheres by sorbing into the mesoscale pores of the shell surface. This vapor sorption follows two mechanisms physical adsorption and capillary condensation of condensable vapors17. Similar vapor adsorption mechanisms have been observed in porous silicon20 and colloidal crystal films fabricated from silica submicron particles32, however, with lack of selectivity in vapor response. The nonpolar vapors preferentially affect the properties of the polystyrene core. Sorption of vapors of good solvents for a glassy polymer leads to the increase in polymer free volume and polymer plasticization32. 

Conformations and aggregate structures of sorbed natural organic matter on muscovite and hematite. Geochim. Cosmo-chim. Ada 65 1047-1057 Nanzyo, M. Watanabe,Y. (1981) Material balance associated with phosphate sorption by amorphous clays, silica-alumina gel and synthetic goethite. Soil Sd. Plant Nutr. 27 329-337... 

This paper is devoted to the sorption of uranyl, which exhibits a complex aqueous and surface chemistry. We review briefly the sorption behaviour of An in the environment, and illustrate the variety of environmental processes using published data of uranyl sorption in the Ban-gombe natural reactor zone. After summarizing the general findings of the mechanisms of An sorption, we then focus particularly on the current knowledge of the mechanisms of uranyl sorption. A major area of research is the influence of the aqueous uranyl speciation on the uranyl surface species. Spectroscopic data of U(VI) sorbed onto silica and alumina minerals are examined and used to discuss the role of aqueous uranyl polynuclear species, U02(0H)2 colloids and uranyl-carbonate complexes. The influence of the mineral surface properties on the mechanisms of sorption is also discussed. 

SPME uses a polymer-coated fused-silica fiber, typically 1 cm 100 m, that is fastened into the end of a fine stainless steel tube contained in a syringelike device and protected by an outer stainless steel needle. In use, the plunger of the device is depressed to expose the fiber to the sample matrix so that the organic compounds to be sorbed onto the fiber. The plunger is retracted at the end of the sampling time, and then it is depressed again to expose the fiber to a desorption interface for analysis typically by GC or LC. In a recent variation of this technique, the so-called in-tube SPME, the polymer is not coated on a fiber but on the inside of a fused-silica capillary before analysis by LC. 

Chromo sorb-W/Tenax/silica Protection Agency... 

It must not, however, be forgotten that conventional techniques (e.g., 13C Fourier transform NMR) can be applied to certain solids of catalytic significance, such as sheet silicates since in many of these systems rapid motion of intercalated or otherwise sorbed organic species secures sharp absorption lines which provide much information about the individual atomic environments. Organic species attached to high surface area solids (such as zeolites, silica, alumina, magnesia, as well as other oxides and their mixtures) are specific examples (6). 

Next, let us consider the applicability of this unique wettability phenomenon. With Ti02 photocatalyst alone, this highly amphiphilic surface disappears soon after exposure of the surface to light. When the photocatalyst has been combined with a water-sorbing substance that can hold water within its structure (such as silicon dioxide or silica gel), the effect of the surface continues even in the dark. Fogging of the surfaces of mirrors and glass occurs when steam that has cooled on these surfaces form many water droplets. On a highly amphiphilic surface, no... 

The very high affinity of these zeolites for n-paraffins was confirmed by counterdiffusion studies, in which p-xylene was initially sorbed into the zeolite prior to n-nonane addition. The n-paraffin rapidly displaced virtually all of the sorbed p-xylene, as shown schematically in Figure 2. Similar results were obtained with both small ( 0.02y) and large (>ly) crystal forms of H-ZSM-5, as well as with a very high silica/alumina ratio (1670 1) form of H-ZSM-5. 

The high hydrophobicity of ZSM-5 permits the selective sorption of organic compounds dissolved in water. A high (1670 1) silica/alumina ratio ZSM-5 preferentially sorbed n-butyl alcohol (90.7% sorbed) from iso-butyl alcohol (17.3% sorbed) and tert-butyl alcohol ( 0% sorbed), all dissolved in water. 

With PCE transformation, the product (ethane) was the same for all supports but yields (measured by both ethane and Q production) varied 50-55% ethane yield was obtained on C, 68% yield on Pd/PEI/silica, and 80-85% yield on alumina. The possibility that lower yields resulted from PCE sorbed to the support was considered the C catalyst was therefore heated to 180°C in an attempt to desorb any species. However, only a few nanomoles of PCE (tenths of a percent of the original mass) and traces of lesser chlorinated ethylenes were detected. This suggests that the low ethane... 

The catalyst support impacts the rate of a catalyzed reaction, the reaction pathway (quantities and species of intermediates and products) and the resistance of the catalyst to deactivation. In DBCP reactions, powders had higher rate constants than beads, presumably due to reduced mass transfer limitations alumina yielded a faster rate than C, which had a faster rate than PEI/silica. Sorptive capabilities of the supports may also play an important role Kovenklioglu found that supports which sorbed 1,1,2-TCA more strongly had higher reaction rates, and Farrell concluded that TCE sorption to Fe cause higher reaction rates on Pd/Fe electrodes than on pure Pd electrodes. It is also clear that supports influence reaction products, but the correlation between a given support and pathways/products it promotes is not yet understood. The choice of support can also affect its resistance to deactivation this implies that catalyst supports may be tailored to maximize activity over the long term. 

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