Surface oxide ions spectroscopic studies

X-ray photoelectron spectroscopic (XPS) studies of Ag63,64 and Pt6,56-62 films deposited on YSZ under positive current application conditions have confirmed the proposition2-4 that NEMCA with oxide ion conducting solid electrolytes is due to an electrochemically induced and controlled backspillover of oxide ions on the catalyst surface. 

Iron is the most abundant, useful, and important of all metals. For example, in the 70-kg human, there is approximately 4.2 g of iron. It can exist in the 0, I, II, III, and IV oxidation states, although the II and III ions are most common. Numerous complexes of the ferrous and ferric states are available. The Fe(II) and Fe(III) aquo complexes have vastly different pAa values of 9.5 and 2.2, respectively. Iron is found predominantly as Fe (92%) with smaller abundances of Fe (6%), Fe (2.2%), and Fe (0.3%). Fe is highly useful for spectroscopic studies because it has a nuclear spin of. There has been speculation that life originated at the surface of iron-sulfide precipitants such as pyrite or greigite that could have caused autocatalytic reactions leading to the first metabolic pathways (2, 3). 

Charlet, L. Manceau, A.A. (1992a) X-ray absorption spectioscopic study of the sorption of Cr(III) at the oxide/water interface. II. Adsorption, coprecpitation, and surface precipitation on hydrous ferric oxide. J. Colloid Interface Sd. 148 443-458 Charlet, L. Manceau, A.A. (1992) X-ray absorption spectroscopic study of the sorption of Cr(III) at the oxide-water interface. J. Colloid Interface Sd. 148 425-442 Chatellier, X. Fortin, D. West, M.M. Leppard, G.G. Ferris, F.G. (2001) Effect of the presence of bacterial surfaces during the synthesis of Fe oxides by oxidation of ferrous ions. Fur. J. Mineral. 13 705-714 Cheetham, A.K. Fender, B.E.F. Taylor, R.I. (1971) High temperature neutron diffraction study of Fei. O. J. Phys. C4 2160-2165 Chemical Week (1988) Glidderfs anti rust secret is out." 15 10... 

The spectroscopic study of the nature of vanadium oxide [VOx] supported on a high surface area Ti02 (anatase) indicated the formation of three different VOx structures [48] a) isolated V4+ ions, part of which was coordinatively unsaturated, strongly bonded to the surface hydroxy groups of the support b) bidimensional clusters of VOx with mainly V5+ after calcinations, reducible under mild conditions to V4+ and also to V3+ to some extent (these species weakly interact with the support surface) c) V205 appeared when cove-rage was about the monolayer and was presented as bulk multiplayer structures. The authors observed the existence of at least two different isolated surface V4+ species, which caused splitting of the low-field hfs lines in parallel orientation. 

Specific spectroscopic techniques are used for the analysis of polymer surface (or more correctly of a thin layer at the surface of the polymer). They are applied for the study of surface coatings, surface oxidation, surface morphology, etc. These techniques are typically done by irradiating the polymer surface with photons, electrons or ions that penetrate only a thin layer of the polymer surface. This irradiation is followed by the absorption of a part of the incident radiation or by the emission of specific radiation, which is subsequently analyzed providing information about the polymer surface. One of the most common techniques used for the study of polymer surfaces is attenuated total reflectance in IR (ATR), also known as internal reflection spectroscopy. Other techniques include scanning electron microscopy, photoacoustic spectroscopy, electron spectroscopy for chemical analysis (ESCA), Auger electron spectroscopy, secondary ion mass spectroscopy (SIMS), etc. 

VIBRATIONAL SPECTROSCOPY Infrared and Raman spectroscopies have proven to be useful techniques for studying the interactions of ions with surfaces. Direct evidence for inner-sphere surface complex formation of metal and metalloid anions has come from vibrational spectroscopic characterization. Both Raman and Fourier transform infrared (FTIR) spectroscopies are capable of examining ion adsorption in wet systems. Chromate (Hsia et al., 1993) and arsenate (Hsia et al., 1994) were found to adsorb specifically on hydrous iron oxide using FTIR spectroscopy. Raman and FTIR spectroscopic studies of arsenic adsorption indicated inner-sphere surface complexes for arsenate and arsenite on amorphous iron oxide, inner-sphere and outer-sphere surface complexes for arsenite on amorphous iron oxide, and outer-sphere surface complexes for arsenite on amorphous aluminum oxide (Goldberg and Johnston, 2001). These surface configurations were used to constrain the surface complexes in application of the constant capacitance and triple layer models (Goldberg and Johnston, 2001). 

Metals other than A1 have been successfully introduced in numerous zeolite frameworks. Aluminum substitution by other metals, such as Fe, Ga, Zn, Co or Cu in the zeolite framework results in modified acidity, and subsequently modified catalytic activity, for certain reactions such as selective catalytic reduction of NOx by hydrocarbons. For example, a calorimetric and IR spectroscopic study of the adsorption of N2O and CO at 303 K on Cu(II)-exchanged ZSM-5 zeolites with different copper loadings has been performed by Rakic et al. [92]. The active sites for both N2O and CO are Cu (I) ions, which are present on the surface as a result of the pre-treatment in vacuum at 673 K. The amounts of chemisorbed species adsorbed by the investigated systems and the values of the differential heats of adsorption of both nitrous oxide (between 80 and 30 kJ mof ) and carbon monoxide (between 140 and 40 kJ mol ) demonstrate the dependence of the adsorption properties on the copper content. 

Brown GE Jr (1990) Spectroscopic studies of chemisorption reaction mechanisms at oxide/water interfaces. In Mineral-Water Interface Geochemistiy. Hochella MF, White AF (eds), 23 309-63 Brown GE Jr, Parks GA, O Day PA (1995) Sorption at mineral-water interfaces macroscopic and microscopic perspectives. In Mineral Surfaces. Vaughan DJ, Patrick RAD (eds), 5 129-184 Birrgess J (1978) Metal Ions in Solution. Ellis Horwood, New York... 

It should be noted that minerals, and oxide minerals in particular, have different types of OH groups, depending on the coordination of the O atoms, as revealed by spectroscopic studies. Goethite (a-FeOOH) has four types of surface hydroxyls whose reactivities are a function of the coordination environment of the O in the FeOH group (Sposito 1984 Sparks 2002). The FeOH groups are A-, B-, or C-type sites, depending on whether the O is coordinated with 1,3, or 2 adjacent Fe(III) ions. The fourth type of site is a Lewis acid-type site, which results from chemisorption of a water molecule on a bare Fe(III) ion. Only A-type sites are basic (can bind H+), and, on the contrary, A-type and Lewis acid sites can release a proton. The B- and C-type sites are considered unreactive. Thus, A-type sites can be either a proton acceptor or a proton donor (i.e., they are amphoteric). Other spectroscopic studies have shown that boehmite (y-AlOOH) and lepidocrocite (y-FeOOH) have two types of OH, presumably associated with different crystal faces (Lewis and Farmer 1986). 

Investigations may be carried out on the tracer level, where solutions are handled in ordinary-sized laboratory equipment, but where the substance studied is present in extremely low concentrations. Concentrations of the radioactive species of the order of 10 m or much less are not unusual in tracer work with radioactive nuclides. A much larger amount of a suitably chosen non-radioactive host or carrier is subjected to chemical manipulation, and the behavior of the radioactive species (as monitored by its radioactivity) is determined relative to the carrier. Thus the solubility of an actinide compound can be judged by whether the radioactive ion is carried by a precipitate formed by the non-radioactive carrier. Interpretation of such studies is made difficult by the formation of radiocolloids, and by adsorption on glass surfaces or precipitates. Tracer studies provide information on the oxidation states of ions and complex-ion formation, and are used in the development of liquid-liquid solvent extraction and chromatographic separation procedures. Tracer techniques are not applicable to solid-state and spectroscopic studies. Despite the difficulties inherent in tracer experiments, these methods continue to be used with the heaviest actinide and transactinide elements, where only a few to a few score atoms may be available [11]. 

The shorter lifetime in the glass ceramic is probably due to the effect of the oxide matrix incorporating the nanoparticles. Indeed, several studies have proved that the oxide glassy matrix interacted with the rare-earth ions situated inside the nanosized crystallites and influenced their spectroscopic properties [65, 66]. Indeed, those Er ions close to the nanocrystallite/glass interface are in distorted sites. As the distortions lower the symmetry, this could result in an increase in the electric dipole transition probability and consequently decrease the radiative lifetime. Moreover, those Er " " ions close to the surface of the crystallites can be sensitive to the presence of oxide ions in their coordination polyhedron, inducing multiphonon nonradiative contribution to the Er " " de-excitation and lowering the lifetime. 

A silver-ion-exchanged HZSM-5 zeolite sample exhibited prominent catalytic performance in the partial oxidation of CH at temperatures above 573 K, exceeding by far the activity of nonzeolitic Ag/SiO -Al Oj and Ag/SiO catalysts. The spectroscopic studies showed that the simultaneous existence of Ag+ ions and small clusters of Ag particles leads to the partial oxidation of methane. The authors believe that dioxygen activated on small Ag metal clusters elaborates a surface oxide layer and the thus-formed species is decomposed and the oxygen activated in this way on the Ag metal spills over and reacts with methane activated hy the Ag+ ions. This catalyst may be promising in the conversion of natural gas into higher value-added chemicals and fuels. 

In spite of the development of physicochemical techniques for surface analysis, spectroscopic methods applicable to the study of bonding between adsorbed metal ion species and substrate are limited, especially those applicable to in situ measurement at interfaces between solid and aqueous phases (1,2). In previous papers, we showed that emission Mossbauer measurement is useful in clarifying the chemical bonding environment of dilute metal ions adsorbed on magnetic metal oxide surfaces (3,1 ) ... 

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