Surface titration experiment

Figure 10.3. Schematic representation of the typical results obtained from a surface titration experiment for the calculation of surface charge...

Here c = Cm + oic JKq and is equal to Ci when a = l. is calculated from surface titration experiments and Kq = Aocxpi-Uo/RT). Once nmax,Ko, n, and Uo are specified and the variation of tlto with pH known, then a plot of adsorption against pH can be constructed. Equation (80) reduces to Freundlich or Langmuir isotherms in given limiting cases, and when j/tq varies with pH in a manner parallel to the electrolyte dissociation curve the equation predicts adsorption curves that agree with the experimental observations of early workers. 

Figure Bl.22.1. Reflection-absorption IR spectra (RAIRS) from palladium flat surfaces in the presence of a 1 X 10 Torr 1 1 NO CO mixture at 200 K. Data are shown here for tluee different surfaces, namely, for Pd (100) (bottom) and Pd(l 11) (middle) single crystals and for palladium particles (about 500 A m diameter) deposited on a 100 A diick Si02 film grown on top of a Mo(l 10) single crystal. These experiments illustrate how RAIRS titration experiments can be used for the identification of specific surface sites in supported catalysts. On Pd(lOO) CO and NO each adsorbs on twofold sites, as indicated by their stretching bands at about 1970 and 1670 cm, respectively. On Pd(l 11), on the other hand, the main IR peaks are seen around 1745 for NO (on-top adsorption) and about 1915 for CO (tlueefold coordination). Using those two spectra as references, the data from the supported Pd system can be analysed to obtain estimates of the relative fractions of (100) and (111) planes exposed in the metal particles [26].

For the experiments shown in Fig. 5.30 the ratio Cdi2/Cdi] is on the average 2500, very close to the ratio NG/Ntpb ( 3570)54 where N0 is the gas-exposed electrode surface area and Ntpb is the surface area of the three phase boundaries. These quantities were measured via surface titration and via SEM and the techniques described in section 5.7.2, respectively. Thus once N0 has been measured, AC Impedance spectroscopy allows for an estimation of the three-phase-boundary (tpb) length via ... 

The potentiometric titration was carried out in order to determine the functional groups present in the biomass surface. During the titration experiments, the C02-free condition was always maintained to avoid the influence of inorganic carbon on the solution pH. Detailed potentiometric titration procedure and estimation method of functional groups are available in the previous reports [4,6]. 

Another important catalytic reaction that has been most extensively studied is CO oxidation catalyzed by noble metals. In situ STM studies of CO oxidation have focused on measuring the kinetic parameters of this surface reaction. Similar to the above study of hydrogen oxidation, in situ STM studies of CO oxidation are often conducted as a titration experiment. Metal surfaces are precovered with oxygen atoms that are then removed by exposure to a constant CO pressure. In the titration experiment, the kinetics of surface reaction can be simplified and the reaction rate directly measured from STM images. 

In situ CO titration experiments have also been conducted on multicomposition systems, that is, inverse model catalyst. Schoiswohl et al. [68] in their studies compared the CO titration reaction on three surfaces clean Rh(l 1 1) surface, Rh (111) surface covered with large 2D V309 islands (mean size >50 nm), and Rh(l 11) surface covered with small 2D V309 islands (meansize<15 nm). Prior to CO titration, the three surfaces were exposed to 10-7 mbar 02 to form a (2 x l)-0 phase at room temperature. In situ STM was used to follow the titration reaction in the presence of 10 x-10 7 m liar CO. CO titration on the clean Rh(l 1 1) surface or the Rh(l 1 1) surface with large V309 islands exhibits similar reaction kinetics. Figure 3.19 shows... 

In most applications we want to know the charge density of dispersed systems. To determine the surface charge of dispersed particles, titration methods can be used. Before we can do a quantitative titration experiment we need to know the specific surface area, that is the total... 

Figure 26. XPS data in the carbon 1 s region for a UHV cleaved graphite reference (HOPG) and a carbon black sample used in the titration experiments of Fig. 25. The arrow marks the position of the graphite surface plasmon. The top section of the modified spectrum in the high-binding energy side reveals several weak peaks for oxygen functional groups after removal of the asymmetric line profile from the main peak.

There are some studies that did not use in situ measurements. These include surface titration and desorption experiments in which surface cover-... 

The proton-promoted surface complexation model was applied to silicates by several research groups in the late 1980s (e.g., Blum and Lasaga, 1988, 1991 Brady and Walther, 1989, 1992 Schott, 1990). For example, Blum and Lasaga (1988, 1991) performed dissolution and titration experiments for albite and found that the surface charge under acid conditions. 

Titration experiments show that PL of semiconductor CdSe/ZnS and CdSe quantum dots is quenched by surfacely attached porphyrins (Fig. 2) [7] PL integrated intensity becomes smaller accompanied by PL non-exponential decay shortening upon the increase of the molar ratio x = [Cp]/[Cqd]. 

The amphoteric character of the hydroxylated Ti02 surface has been demonstrated by Boehm and co-workers in a series of potentiometric titration experiments performed both with anatase and rutile samples. Approximately half of the total amount of hydroxyls present on the Ti02 surface, which underwent neutralization with a diluted (0.01 M) sodium hydroxide solution, has been described as relatively strongly acidic, with a pK value of 2.9, and the remainder as weakly acidic with a pK of 12.7. However, the use of a Langmuir-type adsorption equation as a basis for estimating these acid dissociation constants has raised questions about the real significance of the above values. ... 

Morel, J.-P. et al.. Effect of temperature on the acid-base properties of the alumina surface Microcalorimetry and acid-base titration experiments, J. Colloid Interf. Sci., 298, 773, 2006. 

The titration experiments, the EM measurements, and the

complementary information about the properties of the carbon black as manifested in their interactions with the white reference solids. It is appropriate to ask what these results taken together say about the surface properties of carbon black. 

More detailed information on ion exchange involved in protein adsorption can be derived from titration experiments in systems where the charge of the protein and the sorbent can be varied independently. Currently, we are studying such systems, using bovine plasma albumin (BPA) and cytochrome c as the proteins and silver iodide (Agl) particles as the sorbent. In these systems there are two potential determining ion couples, the H" /oh" couple for the protein and the Ag" "/ " couple for the sorbent. They enable independent control of protein and surface charge. Below, we will briefly discuss some results obtained with the BPA - Agl system. 

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