Charge different metal oxides

Rutile pigments, prepared by dissolving chromophoric oxides in an oxidation state different from +4 in the mtile crystal lattice, have been described (25,26). To maintain the proper charge balance of the lattice, additional charge-compensating cations of different metal oxides also have to be dissolved in the mtile stmcture. Examples of such combinations are Ni " + Sb " in 1 2 ratio as NiO + Sb202, + Sb " in 1 1 ratio as Cr202 + Sb O, and Cr " +... 

The main difference between the proton adsorption behavior of clays carrying structural charge and metal oxides with no structural charge is the effect of the electrolyte concentration on the proton adsorption curves. In clays, the pH where proton adsorption is zero decreases as the electrolyte concentration increases, whereas in metal oxides this pH value does not change by changing the electrolyte concentration and a crossing point is observed (PZC). 

However, the nature, crystallinity (Kinniburg and Jackson, 1976, 1981 McKenzie, 1980), crystal size, and surface charge of metal oxides and mixed metal oxides (e.g., Fe-Al oxides Violante et al., 2003) also play an important role in the sorption selectivity of trace elements in cationic form. McBride (1982) compared the sorption behavior of different Al precipitation products of different crystallinity. The Cu sorption capacity followed tlie order noncrystalline Al-hydroxide > poorly crystalline boehmite > gibbsite. Iron and Mn oxides are... 

Parks review [1] introduced several ideas in the field of surface charging of metal hydr(oxides) that seem obvious now but at the time were revolutionary. Examples include the collection of PZC/IEP data from different sources, inert electrolytes (Section 1.3), and the possible correlation between PZC and well-established physical quantities such as the bond valence and the degree of oxidation or hydration. Not surprisingly [1] has been a source and an inspiration for many followers, and with over 2000 citations it is one of the most successful papers in the field of colloid chemistry ever published. Figure 1.13 presents the history of citations of [1]. Even now, the knowledge of many scientists about pH-dependent surface charging of metal oxides is chiefly based upon that... 

The unique properties of small Au particles responsible for the low-temperature catalytic activity have not been given a definitive explanation . Neutral and negatively and positively charged gold particles have been identified on different metal oxide supports and speculated in catalyzing different reactions. The formation of neutral and positively and... 

The proposed approach to the design of the calorimetry experiments, concerning charging of metal oxide surfaces, resulted in the difference of standard enthalpies of deprotonation and protonation reactions (2) and (1). As already demonstrated for anatase [5], the calorimetry result for hematite agrees with the corresponding measurements of the p.z.c. dependence on temperature. The obtained value also agrees with other published data [10, 11]. 

The simple picture of the MOS capacitor presented in the last section is compHcated by two factors, work function differences between the metal and semiconductor and excess charge in the oxide. The difference in work functions, the energies required to remove an electron from a metal or semiconductor, is = —25 meV for an aluminum metal plate over a 50-nm thermally grown oxide on n-ty e siUcon with n = 10 cm . This work... 

Pseudocapacitance is used to describe electrical storage devices that have capacitor-like characteristics but that are based on redox (reduction and oxidation) reactions. Examples of pseudocapacitance are the overlapping redox reactions observed with metal oxides (e.g., RuO,) and the p- and n-dopings of polymer electrodes that occur at different voltages (e.g. polythiophene). Devices based on these charge storage mechanisms are included in electrochemical capacitors because of their energy and power profiles. 

The question arises as to which metal is dissolved, and which one is deposited, when combined in an electrochemical cell. The electrochemical series indicates how easily a metal is oxidized or its ions are reduced, i.e., converted into positively charged ions or metal atoms respectively. The standard potential serves for the comparison of different metals. 

Certain three-dimensional electrodes, also known as slurry or fluidized-bed electrodes, are sometimes used as well in order to have a strongly enhanced working surface area. Electrodes of this type consist of fine particles of the electrode material (metal, oxide, carbon, or other) kept in suspension in the electrolyte solution by intense mixing or gas bubbling. A certain potential difference is applied to the system between an inert feeder elecnode and an auxiliary electrode that are immersed into the suspension. By charge transfer, the particles of electrode material constantly hitting the feeder electrode acquire its potential (fully or at least in part), so that a desired electrochemical reaction may occur at their surface. In this reaction, the particles lose their charge but reacquire it in subsequent encounters with the feeder electrode. 

In fact, one of the peculiar properties of the title class of compounds is the ability of the molecular entity to carry a charge which can vary considerably, also assuming fractional values in non-integral oxidation state (NIOS) salts. The different molecular oxidation states are reversibly accessible by chemical or electrochemical means. A good example is the case of fe(l,2-dithiolene) complexes of ds metal ions [such as Ni(II), Pd(II), Pt(II), Au(III)], whose charge can assume values typically ranging between —2 and 0 (see Scheme 4). 

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