Physical adsorption forces

Above the critical temperature the thermal energy possessed by gas molecules is sufficient to overcome the forces leading to liquefaction. Because of the similarity between adsorption and liquefaction, the critical temperature can be used as an estimate of the maximum temperature at which significantly measurable amounts of physical adsorption can occur. 

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Activated carbon has the strongest physical adsorption forces or the highest volume of adsorbing porosity of any material known to mankind. 

Adsorption of the colorless form onto silicic acid57 or silica gel8 immediately produces a highly colored matrix which in certain cases, depending on the structure of the pyran, can be reversibly photobleached.7 The brightly colored matrix indicates that the open partly ionic form is the more stable in the highly polar silica gel environment undoubtedly physical adsorption forces also contribute to the stability of this form. 

The surface charge on the metal is defined by the position of free corrosion potential /icon °f the metal with respect to its potential of zero charge Ev/( . When Econ-EPZC is negative, cations are adsorbed and when it is positive, negative ions are adsorbed and this adsorption is electrostatic in nature. Physical adsorption forces are relatively weak and have low activation energy. Some data on the values of zero charge potentials of metals are given in Table 1.22. 

L. W. Bruch, M. W. Cole and E. Zaremba, Physical Adsorption Forces and Phenomena, Clarendon Press, Oxford, 1997, Chap. 2. 

Bruch L.W., Cole, M.W., and Zaremba, E. (1997). Physical Adsorption Forces and Phenomenon. Clarendon. 

Molecules adsorbed by physical adsorption forces on these surfaces will, consequently, be polarized to form dipoles pointing with their negative sides away from the surface. Polar molecules, possessing peripheric dipoles, such as OH-, NH2-, or COOH-groups, are selectively adsorbed with their positive ends in direct contact with the negative surface ions. It was recently shown (7) that the heat of innnersion of the clean solid surface of... 

The adsorbing of bromacil by soil organic matter relative to several other herbicides is shown in Figure 11. The compound was adsorbed in low amounts, probably as a result of its high solubility. The pH of the system was approximately 5.7, so bromacil was present predominantly in the molecular form and was probably adsorbed through hydrogen bonding or other physical adsorption forces. 

Adsorption onto activated carbon is considered as a very cost effective and technically viable method for air and liquid purification [14-15]. The chemical features of amorphous carbon combined with a high surface area and porosity makes it a supreme medium for the removal of wide spectrum of chemicals by mean of adsorption [16-17]. The adsorption process strongly depends on the physical form of an adsorbent and the pore diameter of the carbon, where a molecule can be accommodated. The physical adsorption forces associated with activated carbon are not always sufficient to adsorb a given compound. To overcome this problem, the internal surface of activated carbon may be used as a carrier for some active species to increase the uptake of specific adsorbates ly chemisorption and/or catalytic reaction (see section 2.2. 4. of this chapter). 

Bruch LW, Cole MW, Zaremba E (1997) Physical adsorption Forces and phenomena. Clarendon Press, Oxford... 

In gas-solid chromatography, the solute molecules interact with the surface of solid adsorbents through relatively weak physical adsorption forces. Such weak forces are desirable, because the adsorption process must be... 

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