Monomolecular coverage

For a typical monomolecular coverage, T — 10 10 mol/cm2, an electrode roughness factor r = 1000 and an extinction coefficient ads = 107 cm2/mol, the light-harvesting efficiency is, in comparison to the preceding case, very high, intimate contact with the semiconductor surface, hence the conditions for charge injection from S into the semiconductor are almost ideal (q9j—>100 per cent). 

Of further interest is the fact that when the BET equation (4.38) is solved for the relative pressure corresponding to monomolecular coverage, W = iV ), one obtains... 

When O fi, the isotherm resembles the monomolecular coverage and m = mmax. 

With regard to the sulfur bound on the catalyst surface, differences exist between the various types of ammonia catalysts, especially between those that contain alkali and alkaline earth metals and those that are free of them. Nonpromoted iron and catalysts activated only with alumina chemisorb S2N2 and thiophene. When treated with concentrations that lie below the equilibrium for the FeS bond, a maximum of 0.5 mg of sulfur per m2 of inner surface or free iron surface is found this corresponds to monomolecular coverage [382], [383], The monolayer is also preserved on reduction with hydrogen at 620 °C, whereas FeS formed by treatment above 300 °C with high H2S concentrations is reducible as far as the monolayer. For total poisoning, 0.16-0.25 mg S/m2 is sufficient. Like oxygen, sulfur promotes recrystallization of the primary iron particle. 

It follows from Figure 3 that the film pressure values increase with surfactant concentration tending to nearly constant values at large concentrations, which correspond to monomolecular films reflecting complete monomolecular coverage. The concentrations of the latter films are about (1.5-2) mg m 2. 

Some differences between the isotherms and the elasticity curves in Figures 3 and 4 are worth noting. In particular, the concentrations reflecting monomolecular coverage appear to be a little smaller than for the isotherms in Figure 3, the elasticity values in Figure 3 are also smaller than those in Figure 4. This can be connected with enhanced diffusion of surfactants dissolved in ethanol from the surface to the subsurface microlayer due to parametrically excited surface waves and container vibrations. 

Monomolecular coverage of the active sites ( ) with the species A and B... 

The specific surface area (in m /g) of a catalyst or a support material can be determined by the proven BET method. The volume of a gas (usually N2) that gives monomolecular coverage is measured, allowing the total surface area to be calculated. The equiUbrimn isotherms are of the form shown in Figure 5-43. 

X-ray diffraction studies of metal tris(2,2 -bipyridine) complex-smectite intercalation compounds, prepared by conventional ion exchange, show basal spacings of ca. 1.8 nm when the complexes substitute the interlayer exchangeable cation quantitatively (75). Considering the size and shape of the complexes, the intercalated tris(2,2 -bipyridine) complexes are arranged as monomolecular coverage of the silicate sheets, with their threefold axis perpendicular to the silicate sheets. IntCTsalation is also possible (75,76). 

Internal surface area of microporous adsorbents is often used as one of the measures to describe the degree of development of pores. The concept of B.E.T. adsorption isotherm (Eq. 3-12), where the amount adsorbed by monomolecular coverage, q , is defined, gives the specific surface area by assuming the molecular sectional area of nitrogen to be 16.2 A /molecule, which corresponds to 9.76X 10 m / mol or 4.35 m / Ncc. 

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