The nature of metal oxide-aqueous solution interfaces some basics

The nature of metal oxide-aqueous solution interfaces - some basics 

Geochemistry of Mineral Surfaces and Factors Affecting Their Chemical Reactivity 

Macroscopic experiments allow determination of the capacitances, potentials, and binding constants by fitting titration data to a particular model of the surface complexation reaction [105,106,110-121] however, this approach does not allow direct microscopic determination of the inter-layer spacing or the dielectric constant in the inter-layer region. While discrimination between inner-sphere and outer-sphere sorption complexes may be presumed from macroscopic experiments [122,123], direct determination of the structure and nature of surface complexes and the structure of the diffuse layer is not possible by these methods alone [40,124]. Nor is it clear that ideas from the chemistry of isolated species in solution (e.g., outer-vs. inner-sphere complexes) are directly transferable to the surface layer or if additional short- to mid-range structural ordering is important. Instead, in situ (in the presence of bulk water) molecular-scale probes such as X-ray absorption fine structure spectroscopy (XAFS) and X-ray standing wave (XSW) methods are needed to provide this information (see Section 3.4). To date, however, there have been very few molecular-scale experimental studies of the EDL at the metal oxide-aqueous solution interface (see, e.g., [125,126]). 

One approach commonly used to study how strongly an aqueous ion binds to a sohd surface is measurement of adsorption isotherms as a function of pH, ionic strength, and total metal-ion concentration, in the presence or absence of other ions or organic coadsorbents, ft is often assumed that significant inhibition of adsorption with increasing ionic strength at a given pH indicates that the sorption complexes are dominantly of the weakly bound, outer-sphere type [123]. In contrast, when there is 

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