Electron transfer mineral-water interface

This book deals only with the chemistry of the mineral-water interface, and so at first glance, the book might appear to have a relatively narrow focus. However, the range of chemical and physical processes considered is actually quite broad, and the general and comprehensive nature of the topics makes this volume unique. The technical papers are organized into physical properties of the mineral-water interface adsorption ion exchange surface spectroscopy dissolution, precipitation, and solid solution formation and transformation reactions at the mineral-water interface. The introductory chapter presents an overview of recent research advances in each of these six areas and discusses important features of each technical paper. Several papers address the complex ways in which some processes are interrelated, for example, the effect of adsorption reactions on the catalysis of electron transfer reactions by mineral surfaces. 

Here the intervention of the hydrocarbon radical cation seems possible. Hydrocarbon photocatalyzed oxidations seem to depend significantly on the relative positions of the valence-band edge of the active photocatalyst and the oxidation potential of the substrate. For example, in contrast to the photocatalytic oxidation of toluene described above, lower activity was observed in neat benzene, despite the fact that its oxidation potential lies at or slightly below the valence-band edge. This observation implies the importance of radical cation formation (by photoinduced electron transfer across the irradiated interface) as a preliminary step to hydrocarbon radical formation. If the benzene is dispersed into a benzene-saturated aqueous solution into which the semiconductor is suspended, complete mineralization is attained [158]. Thus, to observe selective photoelectrochemistry, it is necessary to avoid primary formation of the highly reactive, nonselective hydroxyl radical (formed by water oxidation) by the use of an unreactive, but polar, organic solvent. 

For interfacial systems, potential functions should ideally be transferrable from the gas-phase to the condensed phase. Aqueous-mineral interfaces are not in the gas phase (although they may be close, see (7)), but both the water molecules and the atoms/ions in the substrate are in contact with an environment that is very different from their bulk environment. The easiest different environment to test, especially when comparing with electronic structure calculations, is a vacuum, so there is likely to be a great deal of information available on either the surface of the solid or the gas-phase polynuclear ion or the gas-phase aquo complex (i.e., Fe(H20)63+, C03(H20)62-). The gas-phase transfer-ability requirements on potential functions are challenging, but it is difficult to imagine constructing effective potential functions for such systems without using gas-phase systems in the construction process. This means that any water molecules used on these complexes must also transfer from the gas phase to the condensed phase. A fundamental aspect of this transferability is polarization. 

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