Adsorption, apparent specificity

It is assumed that the quantity Cc is not a function of the electrolyte concentration c, and changes only with the charge cr, while Cd depends both on o and on c, according to the diffuse layer theory (see below). The validity of this relationship is a necessary condition for the case where the adsorption of ions in the double layer is purely electrostatic in nature. Experiments have demonstrated that the concept of the electrical double layer without specific adsorption is applicable to a very limited number of systems. Specific adsorption apparently does not occur in LiF, NaF and KF solutions (except at high concentrations, where anomalous phenomena occur). At potentials that are appropriately more negative than Epzc, where adsorption of anions is absent, no specific adsorption occurs for the salts of... 

Simply calculating specific surface areas from the values in Tables 3-5 leads to apparent specific surface areas of approximately 400-500 m2/g [49,51], Specific surface areas obtained from similar analyses of nonpolar gas (nitrogen or krypton) adsorption studies, however, are typically in the range of 1 m2/g, independent of sample pretreatment. 

Lignite GAC This presents a total surface area of 650 m2/g and an apparent density of 0.50 g/cm3, approximately. It is usually used for liquid-phase adsorption, and specifically, in decolorizing applications because it has a higher percentage of meso (transitional) and macro pores than bituminous GAC, and therefore is appropriate for larger molecules. 

In the absence of more detailed information about the actual magnitude of the adsorption in specific instances, it is at least worth while to see what regularities, if any, reveal themselves when the apparent value of E is used as an approximation for the true value. Nevertheless it is most desirable that experimental investigation should be made of reaction rates in conjunction with actual adsorption measurements, in order to leave no uncertainty about this matter. 

Values of apparent specific micropore volume, vp, of VPI-5 evaluated from the uptakes determined by Kenny et al. (1992) of various adsorptives at p/pa = 0.4 are recorded in Table 12.7. As before, the adsorbate densities are assumed equal to the respective liquid densities at the operational temperatures. Also included in Table 12.7 are values of vp derived from the measurements of Davis etal. (1989b), Schmidt et al. (1992) and Reichert et al. (1994). The complexity of the behaviour of VPI-5 is... 

Pine charcoal. A fine easily scattered black powder, which has an apparent specific gravity of about 0.37 g/cc. The adsorption power of dye in water is quite small which may show that it is not so porous. 

Paulownia charcoal. A light powder, which is easily scattered and has an apparent specific gravity of 0.12 g/cc. This value is the lowest for all the kinds of charcoal at present available. The dye adsorption power in water lies between pine charcoal, and hemp coal which has the largest. One analysis showed that it contained. 9% moisture and 2.5% ash. The pH value of the wash water(5 grams of charcoal / 30cc of water) was 7 5 A mixture of the paulownia charcoal, sulphur and potassium nitrate burns as well as the pine charcoal, but it produces less fire dust than the pine charcoal. 

A black fine powder which has a somewhat hygroscopic feeling. The apparent specific gravity is 0.22g/cc. The dye adsorption power is the ... 

The microporous gel may have a fraction of micropores so narrow that nitrogen molecules cannot enter and cover the total silica particle surface. This would result in the smaller apparent specific surface area than the real area because we use nitrogen molecule as the probe. This shows that the surface area estimated by the gas adsorption method is dependent on the size of the probe molecule even in case of nitrogen. 

One of the approaches found most suitable to explain the sensorial properties of sweet, bitter, and sweet-bitter substances proves to be the physico-chemical approach especially as concerns hydration and surface properties (DeSimone and Fleck, 1980 Funasaki et al., 1996 Fimasaki et al., 1999 Mathlouthi and Hutteau, 1999). Thus, solution properties of sweet and bitter molecules were found informative on their type of hydration (hydrophobic or hydrophilic) and on the extent of the hydration layer (Fiutteau et al., 2003). Physico-chemical properties (intrinsic viscosity, apparent specific volume, and surface tension) and NMR relaxation rates of the aqueous solutions of sucrose, caffeine, and sucrose-caffeine mixtures were used in the interpretation of the taste modalities of these molecules and to explain the inhibition of caffeine bitterness by sucrose (Aroulmoji et al., 2001). Caffeine molecules were found to form an adsorption layer whereas sucrose induces a desorption layer at the air/water interface. The adsorption of caffeine gradually increases with concentration and is delayed when sucrose is added in the caffeine solution (Aroulmoji et al., 2004). 

A black fine powder which has a somewhat hygroscopic feeling. The apparent specific gravity is 0.22g/cc. The dye adsorption power is the largest of all the kinds of plant coal. A mixture of hemp coal, sulphur and potassium nitrate burns to produce a violet flame and less fire dust than pine charcoal. It is used to obtain a large force of explosion as a component of black powder or in combination with potassium chlorate or perchlorate for the bursting charge of chrysanthemum shells. 

A quite different technique is necessary when a stabilising adsorption layer on the particle surface is formed. Apparently it is necessary to provide reversibility of surfactant adsorption so that a decrease of surfactant concentration in the bulk results in desorption. This decrease is used in water purification technology based on adsorption methods. Specifically, if a surfactant stabilises the adsorption layers on particles and also adsorbs at the water-air interface, a preliminary flotation of surfactant can decrease their adsorption and thus destabilise the particles. Then microflotation can be applied to extract destabilised particles. 

The apparent specific surface area of hypercrosslinked polystyrenes is much higher than that of traditional macroporous styrene-DVB copolymers. However, when discussing this subject, we have to pay attention to the fact that the adsorption and desorption branches of the isotherm given in Fig. 7.26 do not coincide in the whole range of relative pressures, including the range of very small pressures. The sorption hysteresis at low p/p is... 

With respect to the values of the apparent specific surfiice area, we have to note here that modem instmmentation permitting the measurement of nitrogen adsorption isotherms is usually provided with software permitting surface area calculation according to several mathematical models, including the BJH (corresponding to the names of Barrett, Joyner, Halenda) method, Langmuir adsorption isotherms, and the BET theory these methods may provide for the same sample of a porous material, values that may differ by as much as 30%. 

Concluding the book, we state once again that there is every good reason to consider hypercrosslinked polystyrene as the first representative of a whole new class of polymeric materials with an intrinsic nanoporosity. They are characterized by a rigid open-framework structure that remains accessible to small molecules both in the dry and solvated state. Because of that structure, on the one hand, extremely large apparent specific surface areas are measured for hypercrosslinked materials by conventional gas adsorption techniques, and, on the other hand, the materials actively respond to mechanical forces and to wetting with any liquid media, irrespective of their nature and thermodynamic quality. 

In the absence of specific interactions of the receptor - ligand type the change in the Helmholtz free energy (AFadj due to the process of adsorption is AFads = yps - ypi - Ysi, where Yps, YPi and ys, are the protein-solid, protein-liquid and solid-liquid interfacial tensions, respectively [5], It is apparent from this equation that the free energy of adsorption of a protein onto a surface should depend not only of the surface tension of the adhering protein molecules and the substrate material but also on the surface tension of the suspending liquid. Two different situations are possible. 

A correlation between the amount of adsorbed ions and the electrode potential, in particular E. , has been identified apparently for the first time by Frumkin and Obrutschewa [26Fru]. A minimum of ionic adsorption was found at E, this is equivalent to the absence of specific adsorption at Ep c- The measurement of the amount of adsorbed ions was performed by measuring the ionic concentration in the solution as a function of the electrode potential or by measuring the surface concentration of adsorbed ions by e.g. radiotracer techniques (see also 4.2). (Data obtained with this method are labelled lA). 

DRIFT spectroscopy was used to determine Av0h shifts, induced by adsorption of N2 and hexane for zeolite H-ZSM-5 (ZSM-a and ZSM-b, Si/Al=15.5 and 26), H-mordenite (Mor-a and Mor-b, Si/AI— 6.8 and 10) and H-Y (Y-a and Y-b, Si/Al=2.5 and 10.4) samples. Catalysts were activated in 02 flow at 773 K in situ in the DRIFTS cell and contacted than with N2 at pressures up to 9 bar at 298 K or with 6.1% hexane/He mixture at 553 K, i.e., under reaction conditions. Catalytic activities of the solids were measured in a flow-through microreactor and kapp was obtained as slope of -ln(l-X0) vs. W/F plots. The concentration of Bronsted acid sites was determined by measuring the NH4+ ion-exchange capacity of the zeolite. The site specific apparent rate constant, TOFBapp, was obtained as the ratio of kapp and the concentration of Bronsted acid sites. 

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