Charcoal physical adsorption

Physical adsorption is a readily reversible process, and alternate adsorption and desorption stages can be carried out repeatedly without changing the character of the surface or the adsorbate. Chemisorption may or may not be reversible. Often one species may be adsorbed and a second desorbed. Oxygen adsorbed on charcoal at room temperature is held very strongly, and high temperatures are necessary to accomplish the desorption. CO and/or C02 are the species that are removed from the surface. Chemical changes like these are prima facie evidence that chemisorption has occurred. 

Exception to this inert adsorbent assumption has been taken by Cook et at 101) and by Brunauer 24, 102). It has been stated 24), The theoretical arguments advanced in favor of this assumption were inadequate, and experimental data wholly lacking. The dimensional changes which take place when rare gases are adsorbed on to rigid adsorbents provide conclusive evidence that the assumption of inert adsorbents (for physical adsorption) is invalid. Many of the experiments on dimensional changes are not relevant here, in some cases because of the lack of heats of adsorption and in others because of the somewhat ill-defined nature of carbon and charcoal surfaces, a small amount of chemisorption may have taken place. It is generally accepted that adsorbents are not inert when chemisorption occurs. 

Type I isotherms (e.g. ammonia on charcoal at 273 K) show a fairly rapid rise in the amount of adsorption with increasing pressure up to a limiting value. They are referred to as Langmuir-type isotherms and are obtained when adsorption is restricted to a monolayer. Chemisorption isotherms, therefore, approximate to this shape. Type I isotherms have also been found for physical adsorption on solids... 

Physical adsorption of these gases on charcoal, therefore, must be regarded as being caused by the cooperative action of a polarization by the field of the charcoal nonpolar van der Waals forces and repulsion forces. 

As we discussed in Sec. VI,1 physical adsorption on charcoal and on metal surfaces is caused by the polarization of the adsorbed molecules in the electronic field over the surface of the conducting adsorbent (Sec. V,7), together with the nonpolar van der Waals forces between the adsorbent and the adsorbed molecules (Sec. V,2). As mentioned in Sec. V,12, the magnitude of the polarization of the adsorbed molecules by the electronic field is not seriously influenced by so-called active spots or by surface heterogeneity. The contribution by the nonpolar van der Waals forces, however, is more influenced by a heterogeneous character of the surface of the adsorbent. As those forces cooperate and as the surface of a metallic... 

All the aforementioned points about peculiarities of adsorption in micropores show that special attention is needed when microporous solids (i.e., activated carbons, ACFs, nanotubes, CMSs, charcoals, etc.) are characterized by the physical adsorption methods. 

We have examined several carrier matrices for their ability to immobilize p-glucosidase, including activated charcoal, nylon, chitosan, bentonite, kaolin, silica gel, and titanium dioxide. The results indicated that immobilization by covalent binding on silica gel and by physical adsorption on kaolin were the most prospective methods for improvement of the economic parameters of enzymatic hydrolysis of cellulose. Here, we report on these two supports. 

Moderate amounts of acidic pesticides were adsorbed to organic soil colloids, such as are present in muck soils, (51,143,147,175, 179) and to charcoal (53, 57,147,182,183). For both adsorption depended upon pH, being greater under acid conditions where the pesticides were adsorbed in the molecular form. The compounds were readily desorbed from the adsorbents with water (51, 57). Adsorption probably occurred through hydrogen bonding or weak physical adsorption. 

The effectiveness of modern masks depends on both physical adsorption and chemical inactivation of the threat agent. For example, in the M17 protective mask the adsorbent, known as ASC Whetlerite charcoal, is charcoal impregnated with copper oxide and salts of silver and chromium.6 The M40 protective mask uses an ASZ impregnated charcoal, which substitutes zinc for the hexavalent chromium (CrVI). The Centers for Disease Control and Prevention and the National Institute for Occupation... 

Bone Char. Bone charcoal is a carbonaceous substance derived from the carbonization of selected grades of animal bones by heating dry bones in an airtight iron retort at 500-700°C for about four to six hours. Comparing the capacity of metal ions removal with aetivated carbon, bone charcoal provides not only a porous carbon surface for physical adsorption, but also a hydroxyapatite lattice—Ca,o(P04)g(OH)2 for ion exchange of metal ions. Based on these properties, this sorbent should have excellent adsorption capacities for metal ions. The charaeteristies of typieal bone char are shown in Table 15.9. 

In 1923 F. Aston searched for the new gas in common air He let as much as 400 tonnes of air pass over a bed of charcoal for adsorption of radon. After that a mass spectrographic analysis was carried out. The result was negative, indicating that stable or very long-lived isotopes of radon do not exist. Considerations of nuclear physical character also suggest that radon should not have stable isotopes. 

Physical adsorption involves the attraction and retention of one or more layers of molecules of a gas on a solid surface. This technique finds considerable application in the removal of gaseous impurities near their condensation temperature. Materials such as silica gel, alumina gel, charcoal, and synthetic zeolite (molecular sieves) are widely used as adsorbents because their porous physical structures create large effective surface areas. Most of the gel and carbon adsorbents have pores of varying sizes in a given sample, but the synthetic zeolites are manufactured with closely controlled pore size openings ranging from 4 to about 13 A. This makes them even more selective than other adsorbents since it permits separation of gases on the basis of molecular size. 

Adsorption may in principle occur at all surfaces its magnitude is particularly noticeable when porous solids, which have a high surface area, such as silica gel or charcoal are contacted with gases or liquids. Adsorption processes may involve either simple uni-molecular adsorbate layers or multilayers the forces which bind the adsorbate to the surface may be physical or chemical in nature. 

Charcoal Tubes Reference has been made earlier to adsorption, which is the property of some solid materials, such as activated charcoal, to physically retain solvent vapors on their surfaces. In environmental health testing, the adsorbed vapors are removed, generally with a solvent, in a laboratory. The solvent is then analyzed by physical methods (gas chromatography, etc.) to determine the individual compounds whose vapors, such as benzene, were present in the sampled air. Industrial atmospheric samples can be collected in small glass tubes (4 mm ID) packed with two sections of activated charcoal, separated and retained with fiberglass plugs. To obtain an air sample, the sealed ends of the tube are broken off, and air is drawn through the charcoal at the rate of 1 liter per minute by means... 

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