Organized media surfaces

The use of an organic medium yields an increase in the surface area of the VOHPO O.5H2O (70,126). This increase in surface area is carried over to the resulting vanadyl pyrophosphate phase (123) and is desirable because a concurrent increase in activity toward butane oxidation is observed (70). 

An additional effect of the use of an organic medium in the catalyst preparation is creation of mote defects in the crystalline lattice when compared to a catalyst made by the aqueous route (123). These defects persist in the active phase and are thought to result in creation of strong Lewis acid sites on the surface of the catalysts (123,127). These sites ate viewed as being responsible for the activation of butane on the catalyst surface by means of abstraction of a hydrogen atom. 

Most studies of ORR catalysis by metalloporphyrins have been carried out using water-insoluble catalysts absorbed on a graphite electrode in contact with aqueous solution. In a limited number of cases, four other approaches have been used catalysts imbedded in an inert film (i.e., Nafion or lipid) on the electrode surface self-assembled monolayers of catalysts catalysts in aqueous or mixed organic/aqueous solutions in contact with an electrode and catalysis in mixed aqueous/organic medium using... 

Let us consider the uptake of a given species, either a nutrient or a pollutant heavy metal or an organic (macro)molecule, etc., which will be referred to as M. M is present in the bulk of the medium at a concentration, c, ar d we assume that the only relevant mode of transport from the medium to the organism s surface is diffusion. The internalisation sites are taken to be located on the spherical surface of the microorganism or in a semi-spherical surface of a specialised region of the organism with radius ro (see Figure 1). Thus, diffusion prescribes ... 

The Chi in the hairy roots and parent plant organs was extracted with a mixture of 80% acetone and 20% phosphate buffer (2.5 mol m 3,pH 7.8), and analyzed according to the method described by Porra et al. [17]. The activities of SOD and POD in the hairy roots and parent plant organs were spectrophoto-metrically determined using ferricytochrome C [18] and o-aminophenol [19], respectively. Fructose in the medium was analyzed by the Somogyi-Nelson method [20] or was determined using an HPLC with a refractive index detector. Light intensity was measured with a thermopile on the outer walls of flasks at the level of the medium surface or at the top of the Petri dish, and expressed as the mean of values determined at several positions. 

The organofunctional portion bonds with the resin in the adhesive or the organic medium, and the silane portion bonds to the inorganic or substrate surface. Silane coupling agents are commonly used between the adhesive and the adherend, between resin matrix and reinforcing fibers in composites, and between resin matrix and mineral fillers in compounds. The resulting interface provides... 

Table 23.3 shows also that there is not any tight correlation between the capacitance in aqueous or organic medium and the BET specific surface area [76, 78]. On the contrary, in Fig. 23.14, a good linear relationship can be observed between the capacitance values for both media and the micropore volume... 

In liquids of low dielectric constant, dispersants tend not to form ionic species in solution, but can form ions in adsorbed films on particle surfaces where acid-base interactions and proton transfer occurs between the particle surface and the dispersant. Particle potentials develop when adsorbed dispersant ions desorb into the organic medium where they become the counter-ions. Zeta-potentials well over a hundred millivolts result from the stronger acid-base interactions. Debye lengths in concentrated dispersions are typically 5 to 20 nm, and the DLVO energy barriers, of ten exceed 25 kT with stability ratios of 10° or more. 

Furthermore, in the case of petroleum products, the high surface area of the substrate in the furnace can be wet easily and homogeneously by the organic medium. 

Fig. 8. Specific capacitance vs BET specific surface area for different activated carbons in (a) organic medium (Et4NBF4 in propylene carbonate or acetonitrile) (b) in aqueous medium (6 mol L KOH) [34]. Reprinted with permission horn H. Shi, Electrachun. Acta, 41 (1995) 1633.

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