Monolayer surface coverage

Figure 5.11 Voltammetric response for a 5 pm platinum electrode modified with a monolayer of [(pOp)Os(bpy)2(4-tet)Os(bpy)2Cl]3+, measured at a scan rate of 10 V s 1. The supporting electrolyte is 1.0 M LiCICh in acetonitrile, and the monolayer surface coverage is 9.8 x 10 n mol cm-2. The cathodic currents are shown as up, while the cathodic currents are shown as down. Reprinted with permission from R. J. Forster and T. E. Keyes, /. Phys. Chem., B, 105, 8829 (2001). Copyright (2001) American Chemical Society...

FIGURE 2.6. VSF spectra of the symmetric stretch region for alkyl chains in SDS at the CCI4/D2O interface. The spectra are for 0.1 mM ( ) and 10 mM ( ) aqueous SDS concenu-ation, corresponding to low and high (monolayer) surface coverage. The spectra were acquired under ssp polarization. From Ref. [6]. 

The Langmuir-adsorption model predicts an asymptotic approach to monolayer surface coverage as adsorbate partial pressure approaches saturation this is the Type-I isotherm of Figure 5.7. The Langmuir model, though proven for many ultraclean, well-ordered surfaces interacting with small-molecule adsorbates, is oversimplified for many real-world systems. Nonetheless, it is the foundation upon which much of adsorption theory is built and as such provides a useful con-... 

V—0-Support (930cm ) and V—O—V (625 cm ) bonds. Similar distributions of monomeric and polymeric surface VO4 species are found on other oxide supports with the exception of Si02 [30]. For the supported V20s/Si02 catalyst system, only isolated surface VO4 species are present below the maximum dispersion limit (<3 V atoms/nm ). For all supported vanadium oxide catalysts, crystalline V2O5 NPs are also present above the monolayer surface coverage or maximum dispersion limit [31]. 

Since the gram molecular weight of Nj is 28, the values of X are multiplied by 28 to obtain grams of Nj adsorbed. A plot of (P/Po)/[25( 1 — P/Po)] versus P/Po should give a straight line with slope S - (c — 1)1 cX and intercept I = l/cAT , where X is the mole quantity of N2 adsorbed at monolayer surface coverage, based on the conversion of equation 10.26... 

This finding is consistent with the rule of thumb of electrokinetics that the isoelectric point of a mixed surface is the surface-area-weighted average of the isoelectric point values of the components (15). Hence it appears that this surface concentration regime corresponds to the completion of silica monolayer surface coverage of titania particles. This... 

The adsorption of nonionic cellulose derivatives (HPMC 2910, HEC, and HPC) and their stabilizing effect on suspensions of polystyrene latices and of the antirheumatismal ibuprofen have been examined by Law and Kayes [117, 118]. Adsorption isotherms (see Fig. 20 for HPMC and ibuprofen) are of a sigmoidal type rapid initial adsorption, then a plateau corresponding to monolayer adsorption and finally a further increase in adsorption. At the same time, a gradual reduction in the sedimentation volume (decreased flocculation) is observable, while the redispersibility tends to be optimum (minimum number of revolutions necessary) at values of HPMC corresponding to a monolayer surface coverage. 

BET monolayer surface coverage on -y-alumina is completely resolved, with separate resonances for each of the three types of carbon present. Within experimental error the line positions coincide with the values for liquid pyridine. The lines are noticeably broad (3-4 ppm). The use of N enriched (90%) material results in a partial reduction (approximately 30%) in linewidth relative to the isotopically normal (>99.7% N) spectrum, presumably because the N quadrupole effect interferes with MAS averaging of dipolar interactions. 

Number of methanol molecules adsorbed per surface vanadia species at monolayer surface coverages (adsorption temperature of 100 C)... 

The volume of gas A per initial mass of catalyst that is required for complete monolayer surface coverage (i.e., va, monolayer) has been determined from the chemisorption/physisorption crossover on a graph of va vs. Pa-... 

Surface analysis techniques specifically probe the surface of a material and are capable of detecting sub-monolayer surface coverage. However, charging in polymeric systems and the chemical similarity between the graft polymer and the substrate complicate the analysis in entirely polymeric systems. 

Because quartz crystal microbalances are compact and sensitive, a large literature has developed on their use as sensors of both chemical and biomolecular reactions and processes at surfaces. A current review of this literature, with 176 references, is by Marx [44]. To quote from the abstract of this review The technique possesses a wide detection range. At the low mass end, it can detect monolayer surface coverage by small molecules or polymer films. At the upper end, it is capable of detecting. ..complex arrays of biopolymers and biomacromolecules, even whole cells. Another important and unique feature of the technique is the ability to... 

The Langmuir theory describes the quantitatively formation a monolayer adsorbate on the outer surface of the adsorbent without further adsorption taken place [3]. This model assumes an adsorption homogeneity, which includes the equally available adsorption sites, monolayer surface coverage and no mutual interactions. The equation of Langmuir adsorption isotherm is expressed in Equation (11.1) ... 

The most abundant surface species are COads (65% of monolayer surface coverage) and Co, ads + Cp ds (25%). The surface concentration of hydrocarbon chains decreases fast with a C-number and is only 0.3% for the C3-C20 hydrocarbons. COads does not change with H2/CO ratio, C(,ads + Cp,ads decreases, while the surface concentrations of free surface sites increase. 

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