Rapid adsorption

For a macroporous sorbent the situation is slightly more complex. A differential balance on a shell element, assuming diffusivity transport through the macropores with rapid adsorption at the surface (or in the micropores), yields... 

Rapid Adsorption-Desorption Cycles For rapid cycles with particle diffusion controlling, when the cycle time is much smaller than the time constant for intraparticle transport, the LDF approximation becomes inaccurate. The generalized expression... 

There is a clinical need for non-natural, functional mimics of the lung surfactant (LS) proteins B and C (SP-B and SP-C), which could be used in a biomimetic LS replacement to treat respiratory distress syndrome (RDS) in premature infants [56]. An effective surfactant replacement must meet the following performance requirements (i) rapid adsorption to the air-liquid interface, (ii) re-spreadabihty... 

MacDonald, W.R. and Hayes, K.E. (1970) Comparative study of the rapid adsorption of oxygen by silver and gold. Journal of Catalysis, 18, 115-118. 

Metal sorption on Fe/Al oxides is an inner sphere complexion. The formation of a surface-metal bond releases protons for every metal ion adsorbed. Heavy metal sorbed on Fe oxides can be exchanged only by other metal cations having a similar affinity or by H (McBride, 1989). Metal adsorption on Fe oxides is an initial rapid adsorption reaction, followed by slow diffusion (Barrow et al., 1989). Metal ions (Ni2+, Zn2+ and Cd2+) slowly... 

It is, of course, not necessary to use a heat-flow microcalorimeter in order to determine the heat released by rapid adsorption phenomena. Dell and Stone (74), for instance, using an isoperibol calorimeter of the Garner-Veal type, found an initial heat of 54 4 kcal mole-1 for the adsorption of oxygen on nickel oxide at 20°C. The agreement with the value (60 2 kcal mole-1) in Fig. 19 is remarkably good, particularly if it is considered that very different methods were used for the preparation of the nickel-oxide samples (19, 74)-... 

PVA Particles. Dispersions were prepared in order to examine stabilization for a core polymer having a glass transition temperature below the dispersion polymerization temperature. PVA particles prepared with a block copolymer having M PS) x 10000 showed a tendency to flocculate at ambient temperature during redispersion cycles to remove excess block copolymer, particularly if the dispersion polymerization had not proceeded to 100 conversion of monomer. It is well documented that on mixing solutions of polystyrene and poly(vinyl acetate) homopolymers phase separation tends to occur (10,11), and solubility studies (12) of PS in n-heptane suggest that PS blocks with Mn(PS) 10000 will be close to dissolution when dispersion polymerizations are performed at 3 +3 K. Consequently, we may postulate that for soft polymer particles the block copolymer is rejected from the particle because of an incompatibility effect and is adsorbed at the particle surface. If the block copolymer desorbs from the particle surface, then particle agglomeration will occur unless rapid adsorption of other copolymer molecules occurs from a reservoir of excess block copolymer. 

As conclusion, bifunctional fibers having both phosphonic acid and sulfonic acid groups exhibit the characteristic metal ion selectivity and high breakthrough capacities in addition to the extremely fast adsorption rates. Studies on behavior of FPS-f in adsorption of other heavy metals like Fe(III) are now in progress. The bifunctional fiber developed in this work is attractive to application to the protection of the environment because of its extremely rapid adsorption rates and characteristic metal ion selectivity. 

The redox cycling of these elements have pronounced effects on the adsorption of trace elements onto oxide surfaces and trace element fluxes under different redox conditions. The hydrous Mn(III,IV) oxides are important mediators in the oxidation of oxidizable trace elements e.g., the oxidation of Cr(lll), As(III) and Se(III) is too slow with 02 however, these elements subsequent to their relatively rapid adsorption on the Mn(III,IV) oxide are rapidly oxidized by MnfUI.IV). 

The components of the starting mixture are in rapid adsorption-desorption interaction with the surface. For example, a part of adsorbed -hexane desorbs as -hexane another part reacts to give benzene. If benzene formation involves an n-hexene surface intermediate, this hexene—the concentration of which may be eventually so small that it does not appear in the gas phase—interacts with the inactive hexene in the starting material and increases its specific radioactivity. 

Another example of rate-selective adsorption is the separahon of diisopropylbenzene isomers using a silicalite adsorbent. Figure 6.12 shows the adsorption rates of 1,3-diispropylbenzene and 1.4-di-isopropylbenzene into silicalite adsorbent. In particular, it illustrates the more rapid adsorption of 1,4-di-isopropylbenzene compared to 1,3-di-isopropylbenzene. 

The column should permit the modulation of retention behavior over a very wide range of conditions. This requirement in fact means that the stationary phase is inert, that is it does not facilitate specific interactions with certain molecular functions of solute molecules with the concomitant advantage of a relatively clean and rapid adsorption-desorption kinetics. Preferably then the stationary phase has no functional groups such as fixed charges that would have strong affinity to counterionic solutes and exclude solutes of co-ionic nature. In this regard the properties of well-prepared hydrocarbonaceous bonded phases indeed approach those that we would expect from an ideal phase. 

SMF and SNF superplasticizers are adsorbed rapidly onto hydrating cement but this net effect is made up of very rapid adsorption by C3A and slower adsorption by the silicate phases, as shown in Fig. 2.9. [39],... 

From Figure 5 it can be clearly seen that nitrosobenzene totally inhibited nitrobenzene hydrogenation. The rapid adsorption and formation of azoxybenzene indicated that nitrosobenzene was more strongly adsorbed than nitrobenzene and that, given its high surface concentration, the principal surface reaction was coupling to form azoxybenzene with loss of water as shown in the reaction sequence ... 

Based on experiments carried out with small catalyst particles under vigorous stirring, experimental data representing intrinsic kinetics were obtained. Rate expressions based on the principle of an ideal surface, rapid adsorption and desorption, but rate-limiting hydrogenation steps were derived. The competiveness... 

Ford and coworker [104] have studied HIPEs of water-in-xylenes, stabilised by a variety of surfactants, and postulated three properties which an emulsifier should possess in order to form stable w/o HIPEs of high volume fraction a) a lowering of the interfacial tension between water and oil phases, b) the formation of a rigid interfacial film and c) rapid adsorption at the interface. 

Fig. 21. Series of field emission patterns as oxygen is adsorbed on a tungsten crystal at a pressure of 3.0 X 10 mm. On each photograph the upper numbers give the time and temperature of treatment the lower numbers give the applied voltage, the field emission current, and the exposure time. The upper three pictures show the rapid adsorption of the first layer the lower three show the slower adsorption of the second layer.

Current spikes that are attributable to rapid adsorption or desorption of an adsorbate are sometimes observable for strongly adsorbing but electroinactive species such as camphor at a mercury electrode. The spike is a nonfaradaic current caused by the change in capacitance resulting from the sudden alteration in double-layer structure when the molecule adsorbs or desorbs. 

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