Surface functional group oxide

The elemental composition, oxidation state, and coordination environment of species on surfaces can be determined by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques. Both techniques have a penetration depth of 5-20 atomic layers. Especially XPS is commonly used in characterization of electrocatalysts. One common example is the identification and quantification of surface functional groups such as nitrogen species found on carbon-based catalysts.26-29 Secondary Ion Mass spectrometry (SIMS) and Ion Scattering Spectroscopy are alternatives which are more surface sensitive. They can provide information about the surface composition as well as the chemical bonding information from molecular clusters and have been used in characterization of cathode electrodes.30,31 They can also be used for depth profiling purposes. The quantification of the information, however, is rather difficult.32... 

How could one distinguish experimentally in the interaction of a hydrous oxide surface with a fatty acid, whether the interaction is due to hydrophobic bonding or to coordinative interaction (ligand exchange of the carboxyl group with the surface functional groups of the hydrous oxide) ... 

The main, currently used, surface complexation models (SCMs) are the constant capacitance, the diffuse double layer (DDL) or two layer, the triple layer, the four layer and the CD-MUSIC models. These models differ mainly in their descriptions of the electrical double layer at the oxide/solution interface and, in particular, in the locations of the various adsorbing species. As a result, the electrostatic equations which are used to relate surface potential to surface charge, i. e. the way the free energy of adsorption is divided into its chemical and electrostatic components, are different for each model. A further difference is the method by which the weakly bound (non specifically adsorbing see below) ions are treated. The CD-MUSIC model differs from all the others in that it attempts to take into account the nature and arrangement of the surface functional groups of the adsorbent. These models, which are fully described in a number of reviews (Westall and Hohl, 1980 Westall, 1986, 1987 James and Parks, 1982 Sparks, 1986 Schindler and Stumm, 1987 Davis and Kent, 1990 Hiemstra and Van Riemsdijk, 1996 Venema et al., 1996) are summarised here. 

Adsorption of cations on iron oxides (Table 11.3) may be specific or non specific. With non specific adsorption, there is at least one water molecule between the adsorbing species and the surface functional group. Specific adsorption involves interaction with deprotonated surface hydroxyl groups to form mono- and bi-nuclear, inner sphere complexes, i.e. 

Iron oxides in the finely divided form have the power to promote (catalyse) a range of redox and photochemical reactions (Tab. 11.7). The preliminary step is the adsorption of the reacting species on the iron oxide. This may be followed either by direct reaction with the Fe surface atoms or surface functional groups or the surface may promote reaction between the adsorbed species and a solution species such as dissolved oxygen. 

Bargar, J. R., Brown, G. E. Jr, and Parks, G. A. 991b). Surface complexation of Pb(ll) at oxide water interfaces II. XAFS and bond valence determination of mononuclear Pb(II) sorption products and surface functional groups on iron oxides. Geochim. Cosmochim. Acta 61, 2639-52. 

The multisite surface complexation model (MS-SCM) by Hiem-stra, Van Riemsdijk, and Bolt (27) was the first effort directed at understanding the reactivity of an oxide surface in terms of heterogeneous array individual surface functional groups. These authors... 

Grazing incidence EXAFS spectroscopic studies of Pb(II)aq adsorption on metal oxide surfaces - effect of differences in surface functional groups on reactivity... 

Diamond surfaces after anodic oxidation treatment involve oxygen-containing surface functional groups. The electron-transfer kinetics for ions and polar molecules are expected to be quite different. Fe(CN)l /4 was highly sensitive to the surface termination of diamond. For an anionic reactant, there was an inhibition of the electron transfer for the oxygen-terminated diamond electrodes compared with the hydrogen-terminated diamond electrodes, and there was also an acceleration of the electron transfer for oxygen-terminated diamond for some cationic reactants such as Ru(NH3) +/3+ and Fe2+/3+. These results can be explained by electrostatic effects, which interact between the ionic... 

In the surface complexation approach, sorbing ions from solution are considered to react chemically with surface functional groups on the solid phase surface. For the hydrous oxide minerals these surface sites will be surface hydroxyls, and are represented by the symbol =S—OH0 where =S could be Fe, Al, Mn or Si. 

The reactivity of the solid substrates is determined by the surface functional groups. Immobilization of the biomolecules to the substrates can be performed via several routes. Immobilization can be done by a direct attachment of the molecule to the functionalized or nonfunctionalized surface, or by the employment of a cross-linker (homobifunctional, heterobifunctional, or multifunctional) between the functionalized surface and the biomolecule. Generally, the selection of the substrate and the chemistry is crucial for the successful immobilization of biomolecules and application of that substrate. Here, the reaction between the biomolecule and the reactive surface groups is described for both types of substrates silicon oxide/glass and gold. 

Because surface functional groups influence the adsorption properties and the reactivity of activated carbons, many methods, including heat treatment, oxidation, animation, and impregnation with various inorganic compounds, have been developed in order to modify activated carbons [183], These modifications can alter the surface reactivity, as well the structural and chemical properties of the carbon, which can be characterized using various methods, as described in detail elsewhere [176],... 

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