Adsorption on Powders

Until the mid-1980s, the studies of adsorption on powders have been performed by transmission of pressed self-supporting disks [3-5]. Since then, in situ detection 

ULTRATHIN FILMS AT GAS-SOLID, GAS-LIQUID, AND SOLID-LIQUID INTERFACES 

In order to unravel adsorption mechanisms, a detailed knowledge of the composition and reactivity of the adsorption centers on the initial adsorbent is imperative [35-37]. It is well known [37-39] that fractured surfaces can be covered by cations and anions with unoccupied orbitals that act as Lewis acid and Lewis base centers, respectively. After adsorption of water molecules, with the evolution of hydroxyl and hydrogen species, the Lewis centers are transformed into Bronsted centers, which will influence surface properties. In many cases, characterizing the adsorption sites is complicated, and controversy stiU exists in the interpretation of IR spectra of functional groups, even for extensively studied oxides such as silica and alumina [6, 40, 41]. 

Mono- and bi-pillared smectites Montmorillonite Microcristalline T102 (anatase) 

Natural and synthetic quartz, y-Al203, feldspars Re207, Cr03, M0O3, V2O5, Xi02, Nb20s alumina supported 

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This description is traditional, and some further comment is in order. The flat region of the type I isotherm has never been observed up to pressures approaching this type typically is observed in chemisorption, at pressures far below P. Types II and III approach the line asymptotically experimentally, such behavior is observed for adsorption on powdered samples, and the approach toward infinite film thickness is actually due to interparticle condensation [36] (see Section X-6B), although such behavior is expected even for adsorption on a flat surface if bulk liquid adsorbate wets the adsorbent. Types FV and V specifically refer to porous solids. There is a need to recognize at least the two additional isotherm types shown in Fig. XVII-8. These are two simple types possible for adsorption on a flat surface for the case where bulk liquid adsorbate rests on the adsorbent with a finite contact angle [37, 38]. 

Protactinium can be recovered from an aqueous nitrate solution of fission products and protactinium by adding sodium chromate, which brings down protactiniiun on the aluminum chromate precipitate. After dissolution of the precipitate in acid, protactinium may be recovered by solvent extraction, or it may be allowed to decay to which is more easily extracted [G4]. Protactinium can also be recovered by adsorption on powdered Vycor glass. 

The data presented in Sections 1.8 and 2.5.4 show that immersion of the powder into a transparent liquid with a refractive index close to that of the IRE can substantially increase the SNR of the ATR spectrum of the interfacial layer due to the increase of the MSEF at the interface. This approach also reduces scattering and so is particularly effective in studying in situ adsorption on powders. If the r/k < 10 condition is met, the refractive index of the composite layer (powder plus the immersion medium) may be evaluated within the framework of the EMT (Section 1.9), which allows one to calculate the value of cpc and simulate the ATR spectrum [175, 176]. 

Harrelkas, R, Azizi, A., Yaacoubi, A., Benhammou, A., Pons, M. N. (2009). Treatment of textile dye effluents using coagulation-flocculation coupled with membrane processes or adsorption on powdered activated carbon. Desalination, 235, 330-339. 

In the case of n-hexane adsorption on powder sample, the concentration profiles (not shown) become perfectly rectangular after only 2 min (almost 7 min for benzene). The value... 

The first type of crucible is a quartz reactor that is designed for the investigation of gas adsorption on powders (Fig. 2.13). 

N2 as adsorbate, was quite similar to that for N2 on a directly prepared and probably amorphous ice powder [35, 141], On the other hand, N2 adsorption on carbon with increasing thickness of preadsorbed methanol decreased steadily—no limiting isotherm was reached [139]. 

Figure 3.26(a) and (h) gives results for nitrogen on a compact of silica. Curve (a) is a comparison plot in which the adsorption on the compact (ordinates) is plotted against that on the uncompacted powder (abscissae) there is a clear break followed by an increased slope, denoting enhanced adsorption on the compact, at p/p° = 0-15, far below the lower closure point ( 0-42) of the hysteresis loop in the isotherm (curve (b)). A second compact, prepared at 64 ton in" rather than 130 ton in", showed a break, not quite so sharp, at p/p° = 0-35. 

Low-pressure hysteresis is not confined to Type I isotherms, however, and is frequently superimposed on the conventional hysteresis loop of the Type IV isotherm. In the region below the shoulder of the hysteresis loop the desorption branch runs parallel to the adsorption curve, as in Fig. 4.26, and in Fig. 4.2S(fi) and (d). It is usually found that the low-pressure hysteresis does not appear unless the desorption run commences from a relative pressure which is above some threshold value. In the study of butane adsorbed on powdered graphite referred to in Fig. 3.23, for example, the isotherm was reversible so long as the relative pressure was confined to the branch below the shoulder F. 

Few studies have been made of benzene chemisorption by the volumetric method. Zettlemoyer et al. (8) have examined the adsorption of benzene vapor at 0°C on powders of nickel and of copper. First, the monolayer coverage of argon (vm) A, was measured. The argon was then removed by pumping and the amount of benzene required to form a monolayer, (vmi) Bz, was measured. Weakly adsorbed benzene was then removed by pumping, after which further benzene adsorption provided the value (vm2) Bz. Some results are reproduced in Table I. On the assumption that the same extent of surface is accessible both for argon and for benzene adsorption, it is clear that complete monolayers of benzene were not achieved, that some (Ni) or all (Cu) of the benzene was adsorbed reversibly. It was considered that only the irreversibly adsorbed benzene was chemisorbed, the remainder being physically adsorbed. Thus chemisorption of benzene on copper appeared not to occur. The heat of adsorption of benzene on nickel at zero... 

The overall distribution of lanthanides in bone may be influenced by the reactions between trivalent cations and bone surfaces. Bone surfaces accumulate many poorly utilized or excreted cations present in the circulation. The mechanisms of accumulation in bone may include reactions with bone mineral such as adsorption, ion exchange, and ionic bond formation (Neuman and Neuman, 1958) as well as the formation of complexes with proteins or other organic bone constituents (Taylor, 1972). The uptake of lanthanides and actinides by bone mineral appears to be independent of the ionic radius. Taylor et al. (1971) have shown that the in vitro uptakes on powdered bone ash of 241Am(III) (ionic radius 0.98 A) and of 239Pu(IV) (ionic radius 0.90 A) were 0.97 0.016 and 0.98 0.007, respectively. In vitro experiments by Foreman (1962) suggested that Pu(IV) accumulated on powdered bone or bone ash by adsorption, a relatively nonspecific reaction. On the other hand, reactions with organic bone constituents appear to depend on ionic radius. The complexes of the smaller Pu(IV) ion and any of the organic bone constituents tested thus far were more stable (as determined by gel filtration) than the complexes with Am(III) or Cm(III) (Taylor, 1972). 

S. Suzuki, Black tea adsorption on calcium carbonate a new application to chalk powder for brown powder materials. Coll. Surf. A Physicochem. Eng. Asp. 202 (2002) 81-91. 

This study presents catalytic properties of Pd and Pt for hydrogen adsorption. Metals were deposited by easy to perform procedure on powder materials. This method does not required use of hydrogen as reactant gas and can be easy scale-up. Presence of metal particles was verified by SEM experiment. Average size of noble metals was approximately 1pm. From experiment conditions amount of catalyst was found and it was revealed that mass of metal (Pt or Pd) do not exceed l %wt. 

Yoon Y, Westerhoff P, Snyder SA, Esparza M (2003) HPLC-fluorescence detection and adsorption of bisphenol A, 17P-estradiol, and 17a-ethynyl estradiol on powdered activated carbon. Water Res 37 3530-3537... 

Robertson, M.). and Angelid, R.J. (1994) Adsorption of aryl and alkyl isocyanides on powdered gold. Langmuir, 10,... 

Microcalorimetry has gained importance as one of the most reliable method for the study of gas-solid interactions due to the development of commercial instrumentation able to measure small heat quantities and also the adsorbed amounts. There are basically three types of calorimeters sensitive enough (i.e., microcalorimeters) to measure differential heats of adsorption of simple gas molecules on powdered solids isoperibol calorimeters [131,132], constant temperature calorimeters [133], and heat-flow calorimeters [134,135]. During the early days of adsorption calorimetry, the most widely used calorimeters were of the isoperibol type [136-138] and their use in heterogeneous catalysis has been discussed in [134]. Many of these calorimeters consist of an inner vessel that is imperfectly insulated from its surroundings, the latter usually maintained at a constant temperature. These calorimeters usually do not have high resolution or accuracy. 

Type II isotherms are most frequently encountered when adsorption occurs on nonporous powders or on powders with pore diameters larger than micropores. The inflection point or knee of the isotherm usually occurs near the completion of the first adsorbed monolayer and with increasing relative pressure, second and higher layers are completed until... 

Homogenization of sample (adding water if needed) and adsorption on activated Florisil to produce a free-flowing powder. Elution with ethyl acetate or methylene chloride. 

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