Iron oxyhydroxide, Mossbauer

Figure 1. Mossbauer spectra of the Fust seam, C, lignite. Pyrite (P), jarosite (J), and iron oxyhydroxide (0) are indicated. Key top, room temperature and bottom, 77 K.

Bauminger and Harrison reviewed studies of the process of iron core formation in human and horse spleen ferritins using Mossbauer spectroscopy. It was demonstrated that iron deposition within ferrihydrite core in human and horse spleen ferritin started with Fe(ll) oxidation. This process was associated with ferroxidase center of H-chains. Further, an Fe(lll) compound and Fe(lll) jL-oxo-bridged dimers in ferroxidase centers of H-chains were found, which were intermediate compounds in the process of iron oxyhydroxide core formation in horse spleen ferritin. The steps leading to ferrihydrite core formation in human L- and H-ferritins were also identified and transfer between ferritin molecules was established [M2]. 

Kaolinite is the basic dioctahedral 1 1 layer silicate. The ideal formula is Al2Si205(0H)4. It tends to contain very httle iron and it has been shown that ferric iron can substitute for A1 to a very small amount. Murad and Wagner [234] summarized the published Mossbauer data giving on the average = 0.34 mm/s and A = 0.52 mm/s for the ferric doublet. These hyperfine parameters are also representative for superparamagnetic iron oxyhydroxides and oxides which are commonly associated with kaolinite. Therefore spectra at very low temperatures (below the blocking temperatures of the oxides) are necessary to distinguish the... 

Three series of Au nanoparticles on oxidic iron catalysts were prepared by coprecipitation, characterized by Au Mossbauer spectroscopy, and tested for their catalytic activity in the room-temperature oxidation of CO. Evidence was found that the most active catalyst comprises a combination of a noncrys-taUine and possibly hydrated gold oxyhydroxide, AUOOH XH2O, and poorly crystalhzed ferrihydrate, FeH0g-4H20 [421]. This work represents the first study to positively identify gold oxyhydroxide as an active phase for CO oxidation. Later, it was confirmed that the activity in CO2 production is related with the presence of-OH species on the support [422]. 

In situ Mossbauer parameters for iron oxides and oxyhydroxides dispersed on high area Schawinigan Black carbon electrode... 

The presence of iron in nickel oxyhydroxide electrodes has been found to reduce considerably the overpotential for oxygen evolution in alkaline media associated with the otherwise iron free material.(10) An in situ Mossbauer study of a composite Ni/Fe oxyhydroxide was undertaken in order to gain insight into the nature of the species responsible for the electrocatalytic activity.(IT) This specific system appeared particularly interesting as it offered a unique opportunity for determining whether redox reactions involving the host lattice sites can alter the structural and/or electronic characteristics of other species present in the material. 

In situ Mossbauer parameters for an iron-nickel mixed oxyhydroxide... 

Bauer, Ph. Genin, J.M. Rezel, D. (1986) Mossbauer effect evidence of chlorine environments in ferric oxyhydroxides from iron corrosion in chlorinated aqueous solution. Hyperfme Interactions 28 757-760... 

De Endredy, A.S. (1963) Estimation of free iron oxides in soils and clays by a photolytic method. Clay Min. Bull. 5 209-217 de Faria, D.L.A. Venancio Silva, S. de Oliveira, M.T. (1997) Raman Microspectroscopy of some iron oxides and oxyhydroxides. J. Raman Spectrosc. 28 873-878 De Grave, E. Vandenberghe, R.E. (1986) 57Fe Mossbauer effect study of well-crystallized goethite (a-FeOOH) Hyp. Interact. 28 643-646... 

L.H. (1990) Magnetic properties of some selected, sod-related iron oxides and oxyhydroxides as probed by Fe Mossbauer spectroscopy. In Stanek, J. Pedziwiatr, A.T. (eds.) Condensed matter studies by nuclear methods. Proc. XXIV Zakopane School on Physics. 

As mentioned above, 57Fe is the most important isotope that exhibits the Mossbauer effect and Mossbauer spectra provide valuable information about the chemical environments of iron nuclei. At the trivial level it is able to provide quantitative discrimination between Fe11 and Fem non-invasively, a valuable technique particularly for unstable samples such as, for example, air-sensitive sediments. Also, because the technique is specific for individual isotopes, it is able to detect and identify small amounts of iron-rich phases in the presence of large quantities of other compounds. A good example here is the case of soil and mineral specimens, where the various oxide and oxyhydroxide species can all be distinguished from one another on the basis of their Mossbauer spectra at different temperatures (see e.g. Goodman, 1994). 

Direct methods for determining the combinational form of an element or its oxidation state include infrared absorption spectrometry, X-ray diffraction and, more recently, electron paramagnetic resonance - nuclear magnetic resonance -and Mossbauer spectrometry. With such techniques the combinational forms of major elements in soil components such as clay minerals, iron, manganese and aluminium oxyhydroxides and humic materials and the chemical structures of these soil components have been elucidated over the past 50 years. These direct, mainly non-destructive, methods for speciation are dealt with in some detail in Chapter 3 and are not further discussed here. 

Mossbauer spectroscopy of Fe has proven to be an extremely powerful tool for the analysis of iron containing corrosion products on steel and technical alloys. Depending on the corrosion conditions a variety of iron oxides and oxyhydroxides may be formed. Mossbauer spectroscopy enables one to differentiate between the various phases on the basis of their different magnetic behavior. Figure 14 illustrates this with six different corrosion products. The Fc304 (magnetite), shows the superposition of two six-line spectra as described in Section 19.7.1. 

TABLE IV. Ex Situ Mossbauer Parameters of Various Iron Oxides and Oxyhydroxides... 

TABLE V. In situ Mossbauer Parameters for Iron Oxides and Oxyhydroxides Dispersed on High-Area Shawinigan Black Carbon Electrode... 

TABLE VIII, In Situ Mossbauer Parameters for an Iron-Nickel Mixed Oxyhydroxide... 

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