Surface traps

Pulse radiolysis results (74) have led other workers to conclude that adsorbed OH radicals (surface trapped holes) are the principal oxidants, whereas free hydroxyl radicals probably play a minor role, if any. Because the OH radical reacts with HO2 at a diffusion controlled rate, the reverse reaction, that is desorption of OH to the solution, seems highly unlikely. The surface trapped hole, as defined by equation 18, accounts for most of the observations which had previously led to the suggestion of OH radical oxidation. The formation of H2O2 and the observations of hydroxylated intermediate products could all occur via... 

In addition, the results of adsorption experiment in Fig. 4 revealed that H2O2 promotes the adsorption of 4-NP on the Cr-Ti-MCM-41 surface. From considering above results, it can be said that H2O2 increases the reaction rate by the promotion of adsorption of reactant and the removing of surface-trapped electrons. 

R. (2001) Bioreduction of AuCLt- ions by the fungus VerticiUium sp. and surface trapping of the gold nanopartides formed. Angewandte Chemie-Intemational Edition, 40, 3585-3588. 

The surface characteristics of excipients have also been studied and related to the dispersion and dissolution of poorly soluble drugs [58]. It was found that excipients with rough surfaces (such as Emcompress, with a porous surface) trap the drug particles in the indentations, which can then be blocked by fine excipient particles and decrease dissolution. Smooth surfaces (such as spherical sugar beads), however, produced high dissolution efficiency of the poorly soluble drugs. 

While it has not been studied, it is probable that there exists a range of crystal sizes, possibly quite wide, where both surface trapping and space charge layer effects contribute to the PEC functioning of the photoelectrode. 

Surface O- species have also been generated via X-ray irradiation of polycrystalline MgO14 as well as via the reaction of surface trapped electrons with N2015,16 according to ... 

As discussed earlier, surface trapped electrons are not only important as paramagnetic surface probes but, being localized at a solid-gas interface, they are extremely reactive and can act as powerful reducing agents leading to surface stabilized radicals. An account of these radicals has been given in the past volume of this series1 and we limit ourselves here to report on the 1702 radical stabilized on the surface of MgO for which the hyperfine tensor was fully... 

Energy levels corresponding to electrons localized near the surface may also be present. These are termed surface states. For example, adsorbed ions are one type of surface state they may be of the form of donors, such as hydrogen, which yield electrons to the material, or in the form of acceptors, such as oxygen, which accept, or trap electrons from the material. In Fig. 1, surface traps of the acceptor type are shown, and it is indicated that there are two possible levels present. Other possibilities are impurity atoms at the surface, which are introduced in the preparation of the sample or diffuse from the interior during heat treatment, or nonstoichiometry of the surface layers of the compound. Surface... 

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