Generic Adsorbents

Splitting the countercharge into the diffuse (ct ) and Stem layer (cr ) contributions is carried out from the observation that the Na ion adsorbs generically so that, from. V niay be computed, and hence o, and af, using (3.5.25 and 13). 

The chemical complexity of most natural systems often requires that adsorption reactions be described using semi-empirical, macroscopic models. A common approach is to describe the net transfer of an adsorbate from the solution phase to the solid/water interface with a single stoichiometric expression. Such stoichiometries include a generic relationship between the adsorption of a solute and the release or consumption of protons. 

The three generic classifications of hydrogen storage materials are reversible metal hydrides, non-reversible chemical hydrides, and adsorbent materials. Reversible metal hydride materials and adsorbents can be recharged with hydrogen without removing them from the vehicle, while non-reversible chemical hydride materials must be removed from the vehicle in order to be recharged. 

Folate is the generic name used to refer to a family of vitamers with related biological activity. Instead, folic acid (pteroylglutamin acid, PGA) (Fignre 19.16) refers to the most oxidized, stable, and easily adsorbable synthetic form (monoglutamate). It is commonly nsed in food supplements and in food fortification because of its stability and becomes biologically active after redaction. 

Another attractive application of polymer brushes is directed toward a biointerface to tune the interaction of solid surfaces with biologically important materials such as proteins and biological cells. For example, it is important to prevent surface adsorption of proteins through nonspecific interactions, because the adsorbed protein often triggers a bio-fouling, e.g., the deposition of biological cells, bacteria and so on. In an effort to understand the process of protein adsorption, the interaction between proteins and brush surfaces has been modeled like the interaction with particles, the interaction with proteins is simplified into three generic modes. One is the primary adsorption. 

The theoretical description of photochemistry is historically based on the diabatic representation, where the diabatic models have been given the generic label desorption induced by electronic transitions (DIET) [91]. Such theories were originally developed by Menzel, Gomer and Redhead (MGR) [92,93] for repulsive excited states and later generalized to attractive excited states by Antoniewicz [94]. There are many mechanisms by which photons can induce photochemistry/desorption direct optical excitation of the adsorbate, direct optical excitation of the metal-adsorbate complex (i.e., via a charge-transfer band) or indirectly via substrate mediated excitation (e-h pairs). The differences in these mechanisms lie principally in how localized the relevant electron and hole created by the light are on the adsorbate. 

Since it is not known whether the gas-phase oxygen molecules or weakly adsorbed oxygen (which is present only in the presence of gas-phase oxygen) is responsible for the degradation of the surface intermediates, we shall refer to it generically as gas-phase oxygen. 

Adsorption The adherence of a solute, gas, or liquid onto the surface of a solid substance (the adsorbent). Also, adsorption refers to a treatment technology for liquids and gases that primarily uses adsorption to remove contaminants. Some researchers use the generic term sorption to refer to a natural or artificial process where both adsorption and absorption may be involved or if adsorption and absorption cannot be distinguished (compare with absorption and sorption). 

When a gas or vapour is brought into contact with a clean solid surface, some of it will become attached to the surface in the form of an adsorbed layer. The solid is generally referred to as the adsorbent, adsorbed gas or vapour as the adsorbate and non-adsorbed gas as the adsorptive. It is possible that uniform absorption into the bulk of the solid might also take place, and, since adsorption and absorption cannot always be distinguished experimentally, the generic term sorption is sometimes used to describe the general phenomenon of gas uptake by solids. 

Equation 4.3 is formally similar to a complexation reaction between SR(s) and the aqueous solution species on the left side. Indeed, the solid-phase product on the right side can be interpreted on the molecular level as either an outer-sphere or an inner-sphere surface complex. The latter type of adsorbed species was invoked in connection with the generic adsorption-desorption reactions in Eqs. 3.46 and 3.61, which were applied to interpret mineral dissolution processes. In general, adsorbed species can be either diffuse-layer ions or surface complexes,7 and both species are likely to be included in macroscopic composition measurements based on Eq. 4.2. Equation 4.3, being an overall reaction, does not imply any particular adsorbed species product, aside from its stoichiometry and the electroneutrality condition in Eq. 4.4. 

An example of a speciation calculation involving metals and ligands that adsorb to form only inner-sphere surface complexes ( specific adsorption ) is shown in Table 4.2 for a soil solution at pH 7.5. The generic adsorption reactions for these metals and ligands are exemplified by the third and tenth rows in Table 4.1 ... 

The film diffusion process provides a supply of adsorptive molecules at the adsorbent surface to engage in a chemical reaction leading to adsorption (Eq. 4.3). The rate law for this reaction is developed, for example, in conjunction with the adsorption step in the sequential reaction schemes that appear in Eqs. 3.46, 3.56, and 4.51. Prototypical expressions are in Eqs. 3.47, 3.57, and 4.52a a generic rate law for reaction-controlled adsorption is in Eq. 4.17. For the present example the rate of adsorption can be described by the equation... 

The matrix plays a critical role in the selective cracking of the bottoms fraction when resid-containing feedstock is processed (9). The generic roles of the matrix are to pre-crack large molecules and adsorb Ni and V preferentially to protect the zeolite component of the FCC particle. In an ideal situation, macropores should lead to mesopores and these to the (zeolitic) micropores. The features and catalytic effects of the various levels of porosity are as follows ... 

In recent years, we have seen an explosive interest in nanomaterials, in particular in nanofibers, nanofilaments, and nanotubes of the very different chemical composition. The interest arises from the specific mechanical and physicochemical properties of these nano objects, which allow them to be used, for example, as specific adsorbents, catalyst supports, reinforcing components of composite materials, and so on. The most cited generic types of nanomaterials are carbon nanofilaments and nanotubes. Numerous methods for preparing these carbon materials are known. However, the simplest method seems to be thermal pyrolysis of various carbon contain ing precursors (e.g., carbon monoxide, saturated and unsaturated hydro carbons, etc.) in the presence of special catalysts that are typically nanosized particles of nickel, cobalt, iron metals, or their alloys with different metals. 

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