Properties of Oxide Surfaces

While the bulk properties of simple binary oxides are well understood, rather little is known about the surfaces of oxides, even the most simple ones. Only recently, if compared with the 30 years of surface science that have passed by [8], researchers have started to study the surface science of oxides. There is a very useful book by V. E. Henrich and P. A. Cox that marks the first milestone in this effort entitled The Surface Science of Oxides [9]. Since the publication of this book, several reviews have appeared that have covered the field up to the present date [10-16]. It is understood that there are classes of technologically very important oxides exhibiting external and internal surfaces, that is, zeolites and mesoporous materials, which will not be discussed here. We refer the reader to a recent article by Thomas et al. [17]. This chapter will treat the properties of single crystalline oxide surfaces in terms of their geometric and electronic structure. 

Surface and Interface Science Properties of Composite Surfaces Alloys, Compounds, Semiconductors, 

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The chemical properties of oxide surfaces have been studied by several methods, including oxygen exchange. This method has been used to investigate the mechanisms of heterogeneous reactions for which oxides are active catalysts [36]. The dimerization step does not necessarily precede desorption and Malinin and Tolmachev [634], in one of the few reviews of decomposition kinetics of solid metal oxides, use this criterion to distinguish two alternative reaction mechanisms, examples being... 

Redox properties of oxide surfaces and their relationships to catalytic activity. 

Beside its use for the direct characterization of solids, PL has been applied in combination with probe molecules, luminescent or not, to investigate the acidic and basic properties of oxide surfaces (Section 3). In relation to catalysis, the investigation of the formation of hydroxyl groups from hydrogen-containing reactants (such as hydrocarbons or alcohols) or reaction products (notably water) is an important step forward. Various types of hydroxyl group can be formed upon adsorption of such molecules. In the case of water adsorption on MgO, this can be illustrated schematically by the following reaction ... 

The technological and commercial interest in metal oxide surfaces and interfaces has also continued to grow. For decades, oxide surfaces have played a key role in corrosion protection, catalysis, sensors, fuel cells, ceramics, etc. Over the last few years, totally new devices and technologies that rely on the properties of oxide surfaces and interfaces have emerged. Non-volatile ferroelectric field-... 

IV. Study of the Acid-Base Properties of Oxide Surfaces... 

Most of the recent adsorption literature has emphasized the importance of the acid-base properties of oxide surfaces when explaining or estimating their sorption behavior. However, Sveijensky (1993) has shown that log values for the adsorption of a specific cation by multiple mineral sorbents are a simple linear function of l/e, where e is the dielectric constant of each mineral. He has used this approach to estimate CC and TL model K"" values for the adsorption of up to 18 cations on 7 oxide and silicate mineral surfaces. 

Acid-base properties of oxide surfaces are employed in many fields and their relationship with PZC has been often invoked. Adsorption and displacement of different organic molecules from gas phase was proposed as a tool to characterize acid-base properties of dry ZnO and MgO [341]. Hammet acidity functions were used as a measure of acid-base strength of oxides and some salts [342]. Acidity and basicity were determined by titration with 1-butylamine and trichloroacetic acid in benzene using indicators of different pAg. There is no simple correlation between these results and the PZC. Acid-base properties of surfaces have been derived from IR spectra of vapors of probe acids or bases, e.g. pyridine [343] adsorbed on these surfaces. The correlation between Gibbs energy of adsorption of organic solvents on oxides calculated from results obtained by means of inverse gas chromatography and the acceptor and donor ability of these solvents was too poor to use this method to characterize the donor-acceptor properties of the solids [344],... 

The key properties of oxide surface are the chemical bonding feature, coordination environment, oxidation state and acidic or redox properties of surface cations, and the basicity of surface anions. The longer term challenge to oxide surface chemistry is to address important issues in selectivity in catalytic oxidation and acid-base reactions, in particular the principle of tuning of metal reactivity by oxide ligands. In the development of new catalysts, new chemical concepts regarding structure or composition are conceived. The requirements... 

We will only treat the cluster approach in the present review. We further refer the reader to a series of text bool [ 1-4] and review articles [5-11 ] in which the geometrical and electronic properties of oxide surfaces and the theoretical treatment of the adsorption on such surfaces are covered in more detail. 

Basic Centres on Oxide Surfaces.- Species responsible for the basic properties of oxide surfaces are ... 

Oxides are very common in nature and play a fundamental role in corrosion, friction, electronic devices and superconductivity. The study of the properties of oxide surfaces has an interdisciplinary nature, being included in several fields of research - not only solid-state chemistry and physics, but also electrochemistry, catalysis, electronics and even geophysics and geology. Nowadays, nanostructured surfaces are used as substrates for growing artificial structures, for example, to make quantum wires or size-controlled clusters. 

Lima, E., Charles de Menorval, L., Tichit, D., Lasperas, M., Graffin, P., and Fajula, F. Characterization of acid-base properties of oxide surfaces by C CP/MAS NMR using adsorption of nitromethane. J. Phys. Chem. B 2003,107, 4070-4073. 

Oxide surfaces are influeneed to a large degree by the molecular composition of the bulk solid oxide. The strueture and properties of oxide surfaces as they are influeneed by the eomposition of the eontiguous phases of solution and solid oxide are discussed in Chapters 5 and 6. 

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