Adsorption properties affecting

Activated carbons contain chemisorbed oxygen in varying amounts unless special cate is taken to eliminate it. Desired adsorption properties often depend upon the amount and type of chemisorbed oxygen species on the surface. Therefore, the adsorption properties of an activated carbon adsorbent depend on its prior temperature and oxygen-exposure history. In contrast, molecular sieve 2eohtes and other oxide adsorbents are not affected by oxidi2ing or reducing conditions. 

Figure 4 illustrates the dependence of on Aq for the case when r = 1 at several different values of [Fig. 4(a)] and when = 0.5 and at several different values of r [Fig. 4(b)]. From Fig. 4(a), one can see that takes a maximum around y = 0, i.e., Aq The volume ratio affects strongly the value of as shown in Fig. 4(b), which is ascribed to the dependence of the equilibrium concentration on r through Eq. (25). This simple example illustrates the necessity of taking into account the variation of the phase-boundary potential, and hence the adsorption of i, when one tries to measure the adsorption properties of a certain ionic species in the oil-water two-phase systems by changing the concentration of i in one of the phases. A similar situation exists also in voltammetric measurements of the transfer of surface-active ions across the polarized O/W interface. In this case, the time-varying thickness of the diffusion layers plays the role of the fixed volume in the above partition example. The adsorption of surface-active ions is hence expected to reach a maximum around the half-wave potential of the ion transfer. 

The order of the mobilities of alachlor, butylate, and metolachlor in columns of various soils was metolachlor > alachlor > butylate. This correlates directly with the water solubilities and inversely to the adsorption coefficients and octanol/water partition coefficients of these compounds. Diffusion of these compounds in soil thin-layers was as follows butylate > alachlor > metolachlor, which correlates directly with the vapor pressures of these compounds. Significant soil properties affecting diffusion appeared to be bulk density and temperature. Soil moisture is also probably important, but its effect on the diffusion of these compounds was not determined. 

On the other hand, irreversible changes in the PZC can be effected in some surfaces. The oxidation of carbon surfaces, for example, changes the PZC and does affect the adsorptive properties. Carbon will be discussed in a later section. 

One of the most signiflcant variables affecting zeolite adsorption properties is the framework structure. Each framework type (e.g., FAU, LTA, MOR) has its own unique topology, cage type (alpha, beta), channel system (one-, two-, three-dimensional), free apertures, preferred cation locations, preferred water adsorption sites and kinetic pore diameter. Some zeolite characteristics are shown in Table 6.4. More detailed information on zeolite framework structures can be found in Breck s book entitled Zeolite Molecular Sieves [21] and in Chapter 2. 

The chemical composihons of the zeolites such as Si/Al ratio and the type of cation can significantly affect the performance of the zeolite/polymer mixed-matrix membranes. MiUer and coworkers discovered that low silica-to-alumina molar ratio non-zeolitic smaU-pore molecular sieves could be properly dispersed within a continuous polymer phase to form a mixed-matrix membrane without defects. The resulting mixed-matrix membranes exhibited more than 10% increase in selectivity relative to the corresponding pure polymer membranes for CO2/CH4, O2/N2 and CO2/N2 separations [48]. Recently, Li and coworkers proposed a new ion exchange treatment approach to change the physical and chemical adsorption properties of the penetrants in the zeolites that are used as the dispersed phase in the mixed-matrix membranes [56]. It was demonstrated that mixed-matrix membranes prepared from the AgA or CuA zeolite and polyethersulfone showed increased CO2/CH4 selectivity compared to the neat polyethersulfone membrane. They proposed that the selectivity enhancement is due to the reversible reaction between CO2 and the noble metal ions in zeolite A and the formation of a 7i-bonded complex. 

Hi. Zeolites exchanged with transition metal ions. In the first row, scandium-, titanium-, cobalt-, and nickel-exchanged zeolites have been the most studied. Cobalt-exchanged zeolites are discussed in Section IV,E since they lead to oxygen adducts on adsorption of oxygen. There are several cases where copper and particularly iron ions are found as impurity cations which affect the oxygen adsorption properties of the zeolite. 

The reactivity of C=C bonds depends on the number and nature of substituents attached to the sp2 carbon atoms. Substituents affect the reactivity by affecting the rate constant of reaction and the adsorption properties. 

Physical / chemical properties affect the rate of biodegradation mostly by affecting bioavailability. Compounds which are sparingly soluble in water tend to be more resistant to biodegradation, possibly due to an inability to reach the microbial enzyme site, a reduced rate of availability due to solubilization, or sequestration due to adsorption or trapping in inert material (Alexander, 1973 Alexander, 1994). 

SURFACE PROPERTIES AFFECTING PROTEIN ADSORPTION HYDROPHILICITY/HYDROPHOBICITY TOPOGRAPHY ENERGY CHARGE ETC. 

Abstract. The influence of an inert impregnant (NaCl) on the adsorption properties of activated carbon Norit R 0.8 Extra was studied on breakthrough dynamics of tert-butylbenzene (TBB) and dimethylmethylphosphonate (DMMP). Pre-adsorbed NaCl (5-20 wt.%) strongly affects both structural (e.g. volume of nanopores and mesopores) and adsorption (adsorption potential, breakthrough time, kinetic saturation capacity, etc.) characteristics. 

Until a few years back, the crystal shape of solid materials was of academic curiosity only and shape was not considered to have an effect on the chemical properties and reactivities of a material. However, recent studies clearly indicate that the shape of nanocrystals does indeed affect the chemistry. For example, it has been shown that 4 nm nanocrystalline MgO particles adsorb six molecules of S02 per nm2 at room temperature and 20 Torr pressure.30 However microcrystalline MgO adsorbs only 2 molecules of S02 per nm2 under similar conditions. Similarly, the nanocrystalline aerogel prepared, AP-MgO material adsorbs four times as much C02 as the microcrystals. There are not only differences in the amounts of gaseous molecules adsorbed on these surfaces, but also the mode of surface binding can also be different. S02 binds more predominantly as a monodentate species on the AP-MgO crystal but favors a bidentate geometry on conventionally prepared, CP-MgO microcrystals. Clearly, these results indicate that the shape and size of the crystals affect the adsorptive properties of the MgO surfaces. The high reactivities of the... 

Although structural charges do not reside at the surface, they produce an electric field that emanates in all the directions affecting the surface potential.20 This potential, which is negative with respect to that of the solution bulk, drives the particular cation adsorption properties of basal surfaces. As mentioned previously,2 Figure 4.6... 

---