Adsorption measurements, procedures

Adsorption environments, TSLS complex, 120,12 Adsorption measurements, procedures, 90 Adsorption sites, distinguishing between, 93-94 Aging, effect on particle size of titanium dioxide sols, 200-201,203/... 

Mercury porosimetry is generally regarded as the best method available for the routine determination of pore size in the macropore and upper mesopore range. The apparatus is relatively simple in principle (though not inexpensive) and the experimental procedure is less demanding than gas adsorption measurements, in either time or skill. Perhaps on account of the simplicity of the method there is some temptation to overlook the assumptions, often tacit, that are involved, and also the potential sources of error. 

The results of chemical analysis show that all samples have similar values of Si/Al ratio and confirm that the recrystallization procedure doesn t lead to any significant changes in chemical composition. On the contrary, the adsorption measurements point to remarkable changes in zeolite texture (Fig.l). 

Special care must always be exercised in the study of parts-per-billion concentrations of organics in water to ensure minimal losses due to sample degradation, adsorption or absorption to process materials, and other similar losses. These issues were addressed by dividing the measurement procedures into two parts (1) sample preparation and (2) analytical method, or finish. Because well-defined sample preparation steps were not available from the literature for the quantitative determination of parts-per-billion concentration levels of most of the model organic compounds in water, a considerable amount of effort was placed on the development of appropriate procedures for such measurements. In particular, each method was developed with the indent to have a procedure that could verify the presence of appropriate concen-... 

Table 24.1 Representative Adsorptive Stripping Procedures for Measurements of Trace Metals...

With a small loss of accuracy, the straight-line BET plot (Figure 5.13) can be assumed to pass through the origin and Vm can be calculated on the basis of a single gas-adsorption measurement (usually with p/pa between 0.2 and 0.3). This procedure is frequently adopted for routine surface area measurements. 

It is essential to take into account a number of potential sources of experimental error in the determination of an adsorption isotherm. In the application of a volumetric technique involving a dosing procedure it must be kept in mind that any errors in the measured doses of gas are cumulative and that the amount remaining unadsorbed in the dead space becomes increasingly important as the pressure increases. In particular, the accuracy of nitrogen adsorption measurements at temperatures of about 77 K will depend on the control of the following factors ... 

Labelled polystyrene-14C (PS-14C) was the adsorbate. Two batches were prepared by an identical procedure with only one of them containing radioactive 14C. The labelled polymer was used for the adsorption measurements, whereas the unlabelled polymer was used for the determination of the solution properties. The polystyrene was prepared by emulsion polymerization of redistilled styrene. In order to remove unreacted monomer the polystyrene was freeze-dried from benzene solution. 

The adsorption up to 50 bars was carried out by means of a Tian-Calvet type isothermal microcalorimeter built in the former CNRS Centre for Thermodynamics and Microcalorimetry. For these experiments, around 2 g of sample was used which were outgassed by Controlled Rate Thermal Analysis (CRTA) [7]. The experiments were carried out at 30°C (303 K). Approximately 6 hours is required after introduction of the sample cell into the thermopile for the system to be within 1/100 of a degree Celsius. At this point the baseline recording is taken for 20 minutes. After this thermal equilibrium was attained, a point by point adsorptive dosing procedure was used. Equilibrium was considered attained when the thermal flow measured on adsorption by the calorimeter returned to the base line. For each point the thermal flow and the equilibrium pressure (by means of a 0-70 bar MKS pressure transdueer providing a sensitivity of 0.5% of the measured value) were recorded. The area under the peak in the thermal flow, Q eas, is measured to determine the pseudo-differential... 

Norit Row activated carbon (type 0.8 supra) is supplied by Norit Company (USA) in the form of 0.8 mm (diameter) cylindrical extrudate. The physical and structural properties of the adsorbent and the measurement procedures of adsorption isotherm and kinetics were given in our previous work [16]. 

HPLC measurements of plasma catechols are usually limited to dopamine, norepinephrine, and epinephrine. However, with an alumina adsorption extraction procedure it is also possible to simultaneously measure several other catechols by HPLC or microchip electrophoresis. These catechols include DHPG, the deaminated metabolite of norepinephrine and epinephrine DOPAC, the deaminated metaboHte of dopamine and 3,4-dihydroxyphenylalanine (r-dopa), the immediate precursor of dopamine. All are present in plasma at concentrations many fold higher than the catecholamines, making their detection relatively simple once appropriate chromatographic separation is achieved. 

Procedures. Procedures were developed for measuring plutonium distribution coefficients for batch equilibrium adsorption measurements and for measuring plutonium breakthrough concentrations for column flow-through adsorption experiments. 

In theory, the adsorption measurements can be made with a number of different gases. However, it has been found that even when values of a are calculated from Eq. (8-14) for each gas the results are somewhat different (see Example 8-3). Therefore it has become standard procedure to employ N2 at its normal boiling point (—195.8°C). The reason for the variation in areas obtained with different gases is not well understood. Nevertheless, if the measurements are carried out with one gas at one temperature, the results for different catalysts may be compared with confidence. 

Alumina supported nickel, cobalt and iron catalysts containing 10, 30 and 50 wt % of metal were prepared by co-precipitation method at constant pH conditions (pH = 8 for Ni and Co and pH = 7 for Fe) as described earlier [7], Hydrogen and oxygen adsorption measurements were carried out over the catalysts using a conventional high vacuum system according to the procedure described elsewhere [7]. BET surface area was measured... 

Iler DS coatings have been a major success in the pigment world, and the Iler process may well be of value in the world of useful photocatalysis. Studies of silica adsorption on titania, via uptake and electrophoresis measurements and gas adsorption characterization procedures, have enabled an explanation of the nature of specific interactions between aqueous silica and titania. Binding is proposed to occur preferentially via hydrated cation sites on titania, and the occurrence of such binding is concluded to provide the basis for the subsequent surface polymerization necessary for the buildup of coherent multilayer silica. 

On the other hand, results are also presented to show the experimental limitations of methods and measuring procedures. As mentioned above, the knowledge of an adsorption isotherm of a surfactant is of fundamental importance for the study of adsorption dynamics. For the surfactants discussed in this chapter, the parameters of the Frumkin isotherm are summarised in the tables of Appendix 5D. In case the interfacial interaction parameter a is zero, the Frumkin isotherm changes into a Langmuir isotherm. 

Rates of adsorption measured by the flash-filament technique are summarized in Fig. 3. These data are based on a knowledge of three related parameters A(dn/dt), the absolute rate of adsorption occurring on a sample of geometrical area A, p the pressure in the system, and n the instantaneous surface concentration. Procedures for determining these parameters are outlined in the next few pages. 

The detailed procedure involved in making the adsorption measurements is being omitted from this chapter because it has already been published several times (Emmett, 28,33) and is, in addition, very little different from standard gas adsorption techniques that have been described in the literature for many years. 

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