Oxyhydroxides hydroxides

Nanoparticles and the Environmenf targets naturally occurring, finely particulate minerals, many of which form at low temperature. Thus, many of the compounds of interest are those of the clay fraction . Of course, there have been decades of critical work on the structures, microstructures, and reactivity of finely crystalline or amorphous minerals, especially oxides, oxyhydroxides, hydroxides, and clays. We will not summarize what is known in general about these (for this, the reader is referred to earlier Reviews in Mineralogy volumes). Rather, our goal is to focus on the features of these materials that stem directly or indirectly from their size. 

Oxyhydroxides/ Hydroxides O2 + H2O Fused silica, glass, alumina... 

Secondary minerals. As weathering of primary minerals proceeds, ions are released into solution, and new minerals are formed. These new minerals, called secondary minerals, include layer silicate clay minerals, carbonates, phosphates, sulfates and sulfides, different hydroxides and oxyhydroxides of Al, Fe, Mn, Ti, and Si, and non-crystalline minerals such as allophane and imogolite. Secondary minerals, such as the clay minerals, may have a specific surface area in the range of 20-800 m /g and up to 1000 m /g in the case of imogolite (Wada, 1985). Surface area is very important because most chemical reactions in soil are surface reactions occurring at the interface of solids and the soil solution. Layer-silicate clays, oxides, and carbonates are the most widespread secondary minerals. 

In addition to effects on the concentration of anions, the redox potential can affect the oxidation state and solubility of the metal ion directly. The most important examples of this are the dissolution of iron and manganese under reducing conditions. The oxidized forms of these elements (Fe(III) and Mn(IV)) form very insoluble oxides and hydroxides, while the reduced forms (Fe(II) and Mn(II)) are orders of magnitude more soluble (in the absence of S( — II)). The oxidation or reduction of the metals, which can occur fairly rapidly at oxic-anoxic interfaces, has an important "domino" effect on the distribution of many other metals in the system due to the importance of iron and manganese oxides in adsorption reactions. In an interesting example of this, it has been suggested that arsenate accumulates in the upper, oxidized layers of some sediments by diffusion of As(III), Fe(II), and Mn(II) from the deeper, reduced zones. In the aerobic zone, the cations are oxidized by oxygen, and precipitate. The solids can then oxidize, as As(III) to As(V), which is subsequently immobilized by sorption onto other Fe or Mn oxyhydroxide particles (Takamatsu et al, 1985). 

Powell AK (1997) Polyiron Oxides, Oxyhydroxides and Hydroxides as Models for Biomineralisation Processes. 88 1-38... 

Addition of sufficient base to give a > 3 to a ferric solution immediately leads to precipitation of a poorly ordered, amorphous, red-brown ferric hydroxide precipitate. This synthetic precipitate resembles the mineral ferrihydrite, and also shows some similarity to the iron oxyhydroxide core of ferritin (see Chapter 6). Ferrihydrite can be considered as the least stable but most reactive form of iron(III), the group name for amorphous phases with large specific surface areas (>340 m2 /g). We will discuss the transformation of ferrihydrite into other more-crystalline products such as goethite and haematite shortly, but we begin with some remarks concerning the biological distribution and structure of ferrihydrite (Jambor and Dutrizac, 1998). 

Table l.i Oxides, hydroxides and oxyhydroxides of iron. Reprinted with permission from Jambor and Dutrizac, 1998. Copyright (1998) American Chemical Society. 

First of all let us consider the morphological structure of an agglomerate electrode [6] by way of example of the model shown in Figure 1. This schematic represents a multiphase system with no fixed connection between its components. As a rule, the active mass of an electrode is a mixture of Nickel hydroxide (oxyhydroxide) with conductive carbon or a metal, which are well dispersed mechanically in the matrix. 

Hsu PH (1989) Aluminum hydroxides and oxyhydroxides. In Dixon JB, Weed SB (ed) Minerals in soil environments, 2nd edn, pp 331-378 Inskeep WP, McDermott TR, Fendorf S (2002) Arsenic (V)/(III) cycling in soils and natural waters chemical and microbiological processes. In Frankenberger WT Jr (ed) Environmental chemistry of arsenic. Marcel Dekker, New York, pp 183-215... 

The intensities for the high mass manganese ions for the pH 10 Co(II)-birnessite material are reduced compared to intensities in Na-birnessite, or in the pH 7 Co(II)-birnessite sample, while the cobalt-containing species are the dominant ions. The results indicate a surface coating of cobalt-containing species, perhaps cobalt hydroxide or cobalt oxyhydroxide. A comparison of the pH 10 Co(II)-birnessite results with data for the reference cobalt compounds reveals ions similar to those found in Co(0H>2 and CoOOH... 

The hydroxyl (OH) group is the dominant reactive functional group on the surface of many solid phase particles, amorphous silicate minerals, metal oxides, oxyhydroxides, and hydroxides [17,25,160]. In the case of various organic pol-... 

Next we explore using the 5 Fe value of the ferric oxide/oxyhydroxide precipitate as a proxy for 5pe(ni)aq, which allows Equation (21) to be used to calculate the Ape(ni)-Fe(n) fractionation from the measured 5 Fe values for the ferric precipitate and Fe(II)aq. This approach is valid when the molar proportion of Fe(III)3q is very small. However, if there is a significant Fe isotope fractionation between Fe(III)3q and ferric hydroxide precipitate, this must be taken into account. As discussed in the previous chapter (Chapter 10A Beard and Johnson 2004), at low... 

A nicad cell has a cadmium electrode and another electrode that contains nickel(lll) oxyhydroxide, NiO(OH). When the cell is discharging, cadmium is the anode. When the cell is recharging, cadmium is the cathode. The electrolyte is a base, sodium hydroxide or potassium hydroxide. 

Using coprecipitation methods with a suitable mixture of solutions described above, the resulting LDH materials are often poorly crystallized and exhibit compositional fluctuations due mainly to the difference in the values of the pH at which the precipitation of M(II)(OH)2 and M(III)(OH)3 hydroxides occurs. Consequently, the chemical formula of the final material may not reflect the composition of the solution prior to the precipitation as noted in Chapter 1. Controlling the amount of anion incorporated under such conditions is very difficult. A "chimie douce method has been proposed by Delmas et al. in an effort to overcome this problem [181,182]. The process is illustrated schematically in Fig. 8. Since the synthesis starts from a highly crystalline layered y-oxyhydroxide precursor, it was suggested that this favored the formation of very crystalline LDHs with controllable M(1I)/M(III)... 

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... 

Oxyhydroxides Amorphous precipitates of oxides and hydroxides that form in alkaline solutions such as seawater. These precipitates usually contain a variety of caUons, such as trace metals. 

A1 is thermodynamically unstable, with an oxidation potential at 1.39 V. Its stability in various applications comes from the formation of a native passivation film, which is composed of AI2O3 or oxyhydroxide and hydroxide.This protective layer, with a thickness of 50 nm, not only stabilizes A1 in various nonaqueous electrolytes at high potentials but also renders the A1 surface coating-friendly by enabling excellent adhesion of the electrode materials. It has been reported that with the native film intact A1 could maintain anodic stability up to 5.0 V even in Lilm-based electrolytes. Similar stability has also been observed with A1 pretreated at 480 °C in air, which remains corrosion-free in LiC104/EC/ DME up to 4.2 However, since mechanical... 

For removing low levels of priority metal pollutants from wastewater, using ferric chloride has been shown to be an effective and economical method [41]. The ferric salt forms iron oxyhydroxide, an amorphous precipitate in the wastewater. Pollutants are adsorbed onto and trapped within this precipitate, which is then settled out, leaving a clear effluent. The equipment is identical to that for metal hydroxide precipitation. Trace elements such as arsenic, selenium, chromium, cadmium, and lead can be removed by this method at varying pH values. Alternative methods of metals removal include ion exchange, oxidation or reduction, reverse osmosis, and activated carbon. 

Silca, crystalline-quartz, 628 Chromyl chloride, 175 Fthylidene norbornene, 335 Methomyl, 443 Cobalt hydrocarbonyl, 182 Decaborane, 203 Benomyl, 67 Diborane, 211 Pentaborane, 555 Osmium tetroxide, 546 Cesium hydroxide, 131 Alumina trihydroxide, 38 Aluminum oxyhydroxide, 38 Vinyl toluene, 738 Nonylphenol, 541 2,4-Dinitrotoluene, 279 Trimethyl benzene, 712 Methylcyclohexanol, 465 Terphenyls, 656 Isooctyl alcohol, 409 Anisidine, 52... 

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