Reduction stabilization

Waste management is a field that involves tlie reduction, stabilization, and ultimate disposal of waste. Waste reduction is tlie practice of minimizing file amount of material tliat requires disposal. Some of the common ways in which waste reduction is accomplished are incineration, compaction, and dewatering. The object of waste disposal is to isolate tlie material from tlie biosphere, and in the case of radioactive wtiste, allow it time to decay to sufficiently safe levels. 

A key criterion for selection of a solvent for electrochemical studies is the electrochemical stability of the solvent [12]. This is most clearly manifested by the range of voltages over which the solvent is electrochemically inert. This useful electrochemical potential window depends on the oxidative and reductive stability of the solvent. In the case of ionic liquids, the potential window depends primarily on the resistance of the cation to reduction and the resistance of the anion to oxidation. (A notable exception to this is in the acidic chloroaluminate ionic liquids, where the reduction of the heptachloroaluminate species [Al2Cl7] is the limiting cathodic process). In addition, the presence of impurities can play an important role in limiting the potential windows of ionic liquids. 

The mechanism of formation of Pt particles by the or-ganometallic reduction route, however, was found to proceed differently, for example in the reductive stabilization of Pt nanoparticles produced by reacting Pt-acetylacetonate with excess trimethylaluminium. Here, derivates of aluminium alkyls act as both reducing agents and colloidal stabilizers. As was shown by a combination... 

Figure 4. Nanoscopic Pt colloids in the embryonic state during reductive stabilization [86,94], (Reprinted from Ref. [53], 2007, with permission from Wiley-VCH.)...

Reductive Stabilization of Metal Colloids by Aluminium Alkyls... 

Bifunctional spacer molecules of different sizes have been used to construct nanoparticle networks formed via self-assembly of arrays of metal colloid particles prepared via reductive stabilization [88,309,310]. A combination of physical methods such as TEM, XAS, ASAXS, metastable impact electron spectroscopy (MIES), and ultraviolet photoelectron spectroscopy (UPS) has revealed that the particles are interlinked through rigid spacer molecules with proton-active functional groups to bind at the active aluminium-carbon sites in the metal-organic protecting shells [88]. 

The formation of nanometal colloid via reductive stabilization using aluminum organic reagent operates with a different mechanism as is depicted in Figure 3.2. The mechanism has been elucidated based on various physical and analytical data [37],... 

Bonnemann, H. et al., The reductive stabilization of nanometal colloids by organo-aluminum compounds, Rev. Roum. Chim., 44,1003, 1999. 

The removal of potassium cations makes the results of the liquid-phase and electrode reactions similar. In the presence of crown ether, the eight-membered complex depicted in Scheme 2.16 is destroyed. The unprotected anion-radicals of azoxybenzene are further reduced by cyclooctatet-raene dianion, losing oxygen and transforming into azodianion. The same particle is formed in the electrode reaction shown in Scheme 2.13. In the chemical reduction, stabilization of azodianion is reached by protonation. Namely, addition of sulfuric acid to the reaction results in the formation of hydrazobenzene, which instantly rearranges into benzidine (4,4 -diamino-l,l"-diphenyl). The latter was isolated from the reaction, which proceeded in the presence of crown ether. 

Organoaluminum compounds have been used for the reductive stabilization of mono- and bimetallic nanoparticles, presenting an interesting new method for the preparation of these colloids [see Eq. (5) and Table 2] [43]. 

Volatiles removal Waste recovery Calcincation Reduction Stabilization... 

Nappstruaured Pt-Cofhid Fig. 2.2 Nanoscopic Pt colloids In the embryonic state during reductive stabilization [43, 44]. Applied Methods NMR, MS, XANES, EXAFS, ASAXS. 

Table 2.2 summarizes some typical examples of mono- and bi-metallic organosols prepared via the reductive stabilization pathway. 

I 2 Colloidal Nanoparticles Stabilized by Surfactants or Organo-Aluminum Derivatives Table 2.2 Mono- and bimetallic nanocolloids prepared via reductive stabilization . 

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