Reduction of metal ions

Medical Uses. A significant usage of chelation is in the reduction of metal ion concentrations to such a level that the properties may be considered to be negligible, as in the treatment of lead poisoning. However, the nuclear properties of metals may retain then full effect under these conditions, eg, in nuclear magnetic resonance or radiation imaging and in localizing radioactivity. 

Samples of high area powders and of supported metals may be applied to the CaF2 support plate by a spraying technique, previously described In detall(ll). In Figure 1, we show a half plate design In which a supported metal deposit, produced by H2 reduction of metal Ions held on the support, occupies one half of the plate while the pure support occupies the other half. 

Noble metal ions can be easily reduced to the corresponding zero-valent metal atoms. Therefore, bimetallic nanoparticles consisting of two different noble metals have been extensively investigated for purpose of novel catalysts and optical materials. A simultaneous reduction of two noble metal ions with alcohol is a simple and useful technique to prepare bimetallic nanoparticles. The alcohol reduction of metal ions M + is followed by Equation (1). 

A strategy to solve this problem is to separate the core formation process from the reduction of metal ions in the cores as shown in Scheme 1, and use solvent (EG) and simple ions (OH , etc.) as the stabilizers [11]. In the first step of this process, metal salts hydrolyzed in the alkaline solution of EG to give rise to metal hydroxide or oxide colloids, which were then reduced by EG at elevated temperature to produce colloidal metal nanoclusters in the... 

Ru(bipy)3 formed in this reaction is reduced by the sacrificial electron donor sodium ethylenediaminetetra-acetic acid, EDTA. Cat is the colloidal catalyst. With platinum, the quantum yield of hydrogenation was 9.9 x 10 . The yield for C H hydrogenation was much lower. However, it could substantially be improv l by using a Pt colloid which was covered by palladium This example demonstrates that complex colloidal metal catalysts may have specific actions. Bimetalic alloys of high specific area often can prepared by radiolytic reduction of metal ions 3.44) Reactions of oxidizing radicals with colloidal metals have been investigated less thoroughly. OH radicals react with colloidal platinum to form a thin oxide layer which increases the optical absorbance in the UV and protects the colloid from further radical attack. Complexed halide atoms, such as Cl , Br, and I, also react... 

In the past, the reduction of metallic ions and certain diazotised organic compounds by hindered phenols has served as the basis for colorimetric methods of analysis [112-114],... 

On the other hand, if 02 existed in the reaction system, the reaction mechanism would be affected by the reactions with 02 the reaction mechanism is dependent on the types of dissolved gases in the sample solution. The details for the effects of various parameters on the reduction of metal ions and formation of metal nanoparticles are described in the following sections. 

Effects of Various Parameters on the Rates of Reduction of Metal Ions... 

The effects of various parameters on the rates of sonochemical reduction of metal ions were described in the previous sections. From this section, the effects of such parameters on the properties of metal nanoparticles are described in relation to the rates of reduction. 

It has been reported that bimetallic nanoparticles with core/shell structure can be prepared by ultrasonic irradiation. Mizukoshi et al. reported the formation of bimetallic nanoparticles of Au core/Pd shell structure [42,43] from the sonochemical reduction of Au(III) and Pd(II), where the stepwise reduction of metal ions was observed to proceed during ultrasonic irradiation. That is, the reduction of Pd(II) started after the reduction of Au(III) finished. Vinodgopal et al. reported... 

Abstract A convenient method to synthesize metal nanoparticles with unique properties is highly desirable for many applications. The sonochemical reduction of metal ions has been found to be useful for synthesizing nanoparticles of desired size range. In addition, bimetallic alloys or particles with core-shell morphology can also be synthesized depending upon the experimental conditions used during the sonochemical preparation process. The photocatalytic efficiency of semiconductor particles can be improved by simultaneous reduction and loading of metal nanoparticles on the surface of semiconductor particles. The current review focuses on the recent developments in the sonochemical synthesis of monometallic and bimetallic metal nanoparticles and metal-loaded semiconductor nanoparticles. 

Some of the reports are as follows. Mizukoshi et al. [31] reported ultrasound assisted reduction processes of Pt(IV) ions in the presence of anionic, cationic and non-ionic surfactant. They found that radicals formed from the reaction of the surfactants with primary radicals sonolysis of water and direct thermal decomposition of surfactants during collapsing of cavities contribute to reduction of metal ions. Fujimoto et al. [32] reported metal and alloy nanoparticles of Au, Pd and ft, and Mn02 prepared by reduction method in presence of surfactant and sonication environment. They found that surfactant shows stabilization of metal particles and has impact on narrow particle size distribution during sonication process. Abbas et al. [33] carried out the effects of different operational parameters in sodium chloride sonocrystallisation, namely temperature, ultrasonic power and concentration sodium. They found that the sonocrystallization is effective method for preparation of small NaCl crystals for pharmaceutical aerosol preparation. The crystal growth then occurs in supersaturated solution. Mersmann et al. (2001) [21] and Guo et al. [34] reported that the relative supersaturation in reactive crystallization is decisive for the crystal size and depends on the following factors. 

The previous models were developed for Brownian particles, i.e. particles that are smaller than about 1 pm. Since most times particles that are industrially codeposited are larger than this, Fransaer developed a model for the codeposition of non-Brownian particles [38, 50], This model is based on a trajectory analysis of particles, including convective mass transport, geometrical interception, and migration under specific forces, coupled to a surface immobilization reaction. The codeposition process was separated in two sub-processes the reduction of metal ions and the concurrent deposition of particles. The rate of metal deposition was obtained from the diffusion... 

Metal nanoparticles are synthesized by reduction of metal ions using reducing agents such as borohydride, amines, and 1,2-diols in the presence of stabilizing agents, typically long-chain alkyl thiols (e.g., dodecanethiol), amines,... 

Preparation of amalgams electrochemical reduction on an Hg cathode According to Guminski (2002), the electrochemical reduction of metallic ions on an Hg cathode from aqueous or non-aqueous solvents (as well as from molten salts) allows the introduction of both soluble and insoluble metals into the Hg phase. Some amalgams may be prepared by simultaneous reduction of Hg2+ and Men+ from their solutions. On the other side, noble metal (Pd, Pt, Ag, Au) amalgams may by obtained by reduction of Hg2+ on noble metal electrodes. 

So far, the reduction of metal ions into the metallic state was discussed involving a complete removal of the coordinated solvent molecules in the reduction process. We shall now consider such redox-systems in which both the oxidized and the reduced species are solvated. The polarographic reduction of Eu(III) to Eu(II) in different solvents occurs at such halt-wave potentials which are again related to the donicity of the solvent molecules118). In the Ei/j-DN plot a straight line is observed. Analogous results were obtained for the redox complexes Sm(III)-Sm(II) and Yb(III>Yb(II) 118> 120> (Fig. 27). 

Choi, H.C., et al., Spontaneous reduction of metal ions on the sidewalls of carbon nanotubes. Journal of the American Chemical Society, 2002.124(31) p. 9058-9059. 

The anaerobic reduction of metal ions, including ferric iron (Fe(III)) to ferrous iron (Fe(II)) by microorganisms, has been observed for >80 years (Harders 1919) and was reviewed several times from various viewpoints (Jones 1986 Lovley 1991, 1995 Nealson and Saffarini 1995). In general terms the process can be described by ... 

Reversible Reduction of Metal Ions on Stationary Electrode... 

Electrochemical deposition of metals and alloys involves the reduction of metal ions from aqueous, organic, and fused-salt electrolytes. In this book we treat deposition from aqueous solutions only. The reduction of metal ions in aqueous solution is... 

The specificity of the radiation-induced reduction of metal ion precursors into metal atoms, which then coalesce into clusters, is attributable to strong reducing agents such as the... 

A number of rate constants for reactions of transients derived from the reduction of metal ions and metal complexes were determined by pulse radiolysis [58]. Because of the shortlived character of atoms and oligomers, the determination of their redox potential is possible only by kinetic methods using pulse radiolysis. In the couple Mj/M , the reducing properties of M as electron donor as well as oxidizing properties of as electron acceptor are deduced from the occurrence of an electron transfer reaction with a reference reactant of known potential. These reactions obviously occur in competition with the cascade of coalescence processes. The unknown potential °(M /M ) is derived by comparing the action of several reference systems of different potentials. 

This process has been used to make nanosized material by either chemical reduction of metallic ions or coprecipitation reactions. These various factors (water content, intermicellar potentials) control the size of the particles. 

When we consider the metals of nanoscopic size, fine metal particles from micrometer to nanometer size can be synthesized by both physical and chemical methods. The former method provides the fine metal particles by decreasing the size by addition of energy to the bulk metal, while in the latter methods, fine particles can be produced by increasing the size from metal atoms obtained by reduction of metal ions in solution. Since chemical reactions usually take place in homogeneous solution in any case, this chapter includes most of the cases of synthesis and growth of fine metal particles. However, the polyol process, reaction in microemulsions, and formation in the gas phase are omitted, since they are described in later chapters by specialists in those fields. 

Colloidal dispersions of fine metal particles can usually be prepared by reduction of metal ions. The first scientific report to synthesize colloidal dispersion of metals was presented by Faraday, who prepared metal colloids without stabilizers (5). In his case counteranions may have played the role of the stabilizer. In most recent cases, however, stabilizers are usually added to the system to stabilize the colloidal dispersions. 

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