Other Layered Oxides

LiV02 is isostructural with IiCo02 and has the 03 layered structure. However, in de-lithiated Lii jV02 with - x) 0.67, the vanadium ions migrate from the octahedral sites of the vanadium layer into the octahedral sites of the Hthium layer because of the low OSSE of the vanadium ions [58]. Therefore, the kinetics of lithium transport and the electrochemical performance is very poor with UVO2, 

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Among these oxides, K4Nb60i7 has been studied in some detail although the structure is rather unique. Studies on this oxide will be introduced first, followed by those on other layered oxides. Tables 16.1 and 16.2 list the various systems studied for photocatalysis. 

Anhydride of chloric acid, Cl20, is unknown. Oxides with even number of oxygen atoms are mixed anhydrides. Other chlorine oxides such as the radicals CIO, CIO, and CIO are known. Chlorine monoxide [14989-30-17, CIO, plays a key role in depletion of the o2one layer. 

The Pourbaix diagram" for tin (Fig. 4.41) refers only to solutions in which formation of soluble tin complexes or protective layers of insoluble salts does not occur. There are few instances of the formation of protective layers other than oxide on tin, and although the formation of soluble complexes is more common, the diagram provides a useful general indication of the... 

Recently was estimated an expected impact on the global chemistry of the atmosphere of the indirect heterogeneous photocatalytic reactions under the much more abundant near ultraviolet, visible and near infrared solar light [2]. As photocatalysts may serve atmospheric aerosols, i.e. ultrasmall solid particles that sometimes are embedded into liquid droplets. Aerosols are known to contain Ti02, Fc203, ZnO and other natural oxides, as well as metal sulfides of volcanic or antropogenic origin, that may serve as semiconductor photocatalysts (see Fig.5). Aerosols are known to be concentrated mainly in the air layers near the surface of the Earth, i.e. in the troposphere, rather than stratosphere. 

Less, but still significant, information is available on the surface chemistry of other nitrogen oxides. In terms of N20, that molecule has been shown to be quite reactive on most metals on Rh(110), for instance, it decomposes between 60 and 190 K, and results in N2 desorption [18]. N02 is also fairly reactive, but tends to convert into a mixed layer of adsorbed NO and atomic oxygen [19] on Pd(lll), this happens at 180 K, and is partially inhibited at high coverages. Ultimately, though the chemistry of the catalytic reduction of nitrogen oxide emissions is in most cases controlled by the conversion of NO. 

Some impurities are converted into gases that are then released from the hot molten metal others are oxidized (converted into oxides), making up slag, the layer of useless matter on the upper surface of the molten, refined metal, from where it is removed. 

According to El-Mashri et al.,190 the A106 A104 ratio determines the hydration capacity of anodic oxides. Tetrahedral sites are hydrated easily to form a boehmite-like structure, which is known to be composed of double layers of Al-centered octahedra, weakly linked by water molecules to other layers.184 As the oxide formed in H3P04 contains about 70% tetrahedral aluminum bonds, its hydration ability should be higher than that of the oxide formed in tartrate solution. However, this has not been found in practice, which is interpreted by El-Mashri et al. as being due to some reduction of A104 by incorporated phosphate species. 

Figure 2.54 The geometry of one of the substrates employed by Murray and Allara in their spacer experiments. PMMA = polymelhyl methacrylate spacer of thickness J, PNBA = monolayer of p-nitrobcnzoic acid. The mass thicknesses of the other layers are CaF, = 800 A. Al = 2500 A. Al = oxide c. 30 A, Ag = 200 A. From Murray and Allara (1982).

In this chapter, we discuss double layer theory and how it can be incorporated into a geochemical model. We will consider hydrous ferric oxide (FeOOH //IFO), which is one of the most important sorbing minerals at low temperature under oxidizing conditions. Sorption by hydrous ferric oxide has been widely studied and Dzombak and Morel (1990) have compiled an internally consistent database of its complexation reactions. The model we develop, however, is general and can be applied equally well to surface complexation with other metal oxides for which a reaction database is available. 

The structures of ternary oxides such as spinels, perovskites, pyrochlores, layered cuprates (high-7 c superconductors), and other lamellar oxides are fascinating subjects by themselves and are beyond the scope of the present discussion. 

Examples of electroactive NP materials discussed in the review include Ti02, Mn02, iron oxides, other metal oxides, hydroxides and oxyhydroxides and Prussian Blue. We use the term electroactive N Ps to refer to the faradaic electroactivity in such materials and to distinguish them from NPs comprised of metals (such as Au, Ag, Pt, Co, etc.) or semiconductors (such as CdS, CdSe, etc.). This distinction is based on the ability of many electroactive NPs to undergo faradaic oxidation or reduction of all of the metal (redox) centers in the NP. This is in contrast to the behavior of many metal and semiconductor NPs for which oxidation or reduction is fundamentally an interfacial, double-layer process. This deflnition is somewhat arbitrary, since the smallest metal and semiconductor NPs behave molecularly, blurring the distinction... 

This report deals primarily with the origins and effects of ozone and other photochemical oxidants. It is limited, more or less, to the problem of urban pollution and to such closely related topics as natural background in the earth s boundary layer. No consideration is given to the stratospheric ozone layer and the effects produced by supersonic transport (sst) emission or halocarbons. 

The sites of action and effects of ozone and other photochemical oxidants are described in Chapters 8 and 9. Recent work with primates has suggested that ozone is absorbed along the entire respiratory tract, penetrates more into the peripheral nonciliated airways, and causes more lesions in the respiratory bronchioles and alveolar ducts as the inhaled ozone concentration increases from 0.2 to 0.8 ppm. The most common and most severe tissue damage was observed in the respiratory bronchioles. The ciliated cells in the terminal bronchioles and the Type 1 cells in the epithelial layer of the proximal alveoli of rats were the... 

Another vanadium oxide that has received much attention is LiVaOs, which has a layer structure composed of octahedral and trigonal bipyramidal ribbons that can be swelled just like other layered compounds and can intercalate lithium. Here again, the method of preparation is important to its electrochemical characteristics. West et al. made a systematic study of the impact of synthesis technique on capacity and cycling and showed that amorphous material increased the capacity above 2 V from 3—4 lithium per mole of LiVsOs at low current drains, 6—200 fiAlcm. ... 

The double layers of vanadium oxide found in the xerogel have been described in a number of other vanadium oxides by Galy ° and Oka ° they also form the double sheets described above for VeOis. These oxides, in which the vanadium is found in distorted VOe octahedra, show particularly attractive electrochemical capacities " exceeding 200 mAh/g in some cases, as shown in Figure 9. However, at the present time their rate capability appears somewhat limited. More recently vanadium oxide nanotubes have been synthesized, first by Spahr et these compounds also contain double sheets of vanadium oxide and again have interesting but complex... 

Polishing is also an important application area of the surface chemistry of solids. The surface layer produced after polishing may or may not remain stable after exposure to its surroundings (air, other gases, oxidation). The polishing industry is much dependent on surface molecular behavior. 

Magnetite differs from most other iron oxides in that it contains both divalent and trivalent iron. Its formula is written as Y[XY]04 where X = Fe , Y = Fe " and the brackets denote octahedral sites (M sites). Eight tetrahedral sites (T sites) are distributed between Fe" and Fe", i.e. the trivalent ions occupy both tetrahedral and octahedral sites. The structure consists of octahedral and mixed tetrahedral/octahedral layers stacked along [111] (Fig. 2.13a). Figure 2.13b shows the sequence of Fe- and O-layers and a section of this structure with three octahedra and two tetrahedra is depicted in Figure 2.13 c. 

Lepidocrocite is paramagnetic at room temperature. The Neel temperature of 77 K is much lower than that of the other iron oxides and is the result of the layer-like structure of this mineral. The sheets of Fe(0,0H)6 octahedra are linked by weak hydrogen bonds, hence magnetic interactions are relatively weak. The saturation hyperfine field is also lower than for any other iron oxide (Tab. 6.2). In the antiferromagnetic state, the spins are ordered parallel to the c-axis with spins in alternate layers having opposite signs. A decrease of T by 5 K was observed for Al-lepidocrocites with an Al/(Fe-i-Al) ratio of 0.1 (De Grave et al., 1995). 

Like other non-oxidic semiconductors in aqueous solutions, surface oxidized and photocorrosive InP is a poor photoelectrode for water decomposition [19,27,32,33], To enhance properties several efforts have focused on coupling of the semiconductor with discontinuous noble metal layers of island-like topology. For example, rhodium, ruthenium and platinum thin films, less than 10 nm in thickness, have been electrodeposited onto p-type InP followed by a brief etching treatment to achieve an island-like topology on the surface [27,28]. In combination with a Pt counter electrode, under AM 1.5 illumination of 87 mW/cm the metal (Pt, Rh, Ru) functionalized p-InP photocathodes [27] see a reduction in the threshold voltage for water electrolysis from 1.23 V to 0.64 V, and in aqueous HCl solution a photocurrent density of 24 mA/cm with a photoconversion efficiency of 12% [27]. 

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