Polyol methods

Nanoparticles of the noble metals have been prepared extensively by the polyol or the modified polyol methods because of the ease of reduction of their salts (Figure 9). 

TEM imugv uf Pt particles prepared via polyol method (wilhoul sarfaclanl)... 

PVP, a water soluble amine-based pol5mer, was found to be an optimum protective agent because the reduction of noble metal salts by polyols in the presence of other surfactants often resulted in non-homogenous colloidal dispersions. PVP was the first material to be used for generating silver and silver-palladium stabilized particles by the polyol method [231-233]. By reducing the precur-sor/PVP ratio, it is even possible to reduce the size of the metal particles to few nanometers. These colloidal particles are isolable but surface contaminations are easily recognized because samples washed with the solvent and dried in the air are subsquently not any more pyrophoric [231,234 236]. 

Similarly, Pd, Ag, and Pd-Ag nanoclusters on alumina have been prepared by the polyol method [230]. Dend-rimer encapsulated metal nanoclusters can be obtained by the thermal degradation of the organic dendrimers [368]. If salts of different metals are reduced one after the other in the presence of a support, core-shell type metallic particles are produced. In this case the presence of the support is vital for the success of the preparation. For example, the stepwise reduction of Cu and Pt salts in the presence of a conductive carbon support (Vulcan XC 72) generates copper nanoparticles (6-8 nm) that are coated with smaller particles of Pt (1-2 nm). This system has been found to be a powerful electrocatalyst which exhibits improved CO tolerance combined with high electrocatalytic efficiency. For details see Section 3.7 [53,369]. 

AuPt bimetallic nanoparticles, prepared by polyol method and stabilized with PVP, were studied by UV-Vis spectra [122]. In this preparation the reaction temperature... 

Recently characterization of bimetallic nanoparticles by EXAFS were extensively reported [122-124,176], Structural transformation of bimetallic Pd/Pt nanoparticles, which were prepared by a sequential loading of H2PtClg onto the Pd loaded catalyst, was investigated with EXAFS at high temperatures [176], The results of EXAFS at Pd K and Pt L-III edges showed that Pt was surface-enriched or anchored on the Pd metal core with an increase of the Pt content. The structure of the obtained bimetallic Pd/Pt nanoparticles seemed to be retained upon heating up to 1273 K under ambient condition [176], Pt/ Au bimetallic nanoparticles can be prepared by polyol method and stabilized by PVP [122], XANES and EXAFS studies were also performed on the samples and their results supported the idea of a Pt-core/Au-shell structure with the elements segregated from each other [122],... 

These routes rely on the direct transformation of soluble molecular species into supported metal (or mixed metal) particles. One method that has recently become popular is the "polyol" method. This takes a solution of metal salts, the carbon support, and a polyalcohol such as ethylene glycol. On heating, the polyol acts as both stabilizer and reductant, forming reduced metal particles on the carbon. It has been used successfully to prepare Ft and PtRu catalysts. ... 

The findings of combined elevation of C4, C5 and C7 polyols ( method 1) and/or erythritol, arabitol, ribitol, sedoheptitol and perseitol (method 2) indicate a deficiency of the enzyme TALDO. 

In contrast to aqueous methods, the polyol approach resulted in the synthesis of metallic nanoparticles protected by surface-adsorbed glycol, thus minimizing the oxidation problem The use of polyol solvent also reduces the hydrolysis problem of ultrafine metal particles, which often occurs in aqueous systems. Oxide nanoparticles can be prepared, however, with the addition of water, which makes the polyol method act more like a sol—gel reaction (forced hydrolysis). For example, 5.5-nm CoFe204 has been prepared by the reaction of ferric chloride and cobalt acetate in 1,2- propanediol with the addition of water and sodium acetate. 

A popular method for the synthesis of metal nanowires is the use of the polyol process,lal wherein the metal salt Is reduced in the presence of PVP to yield nanowires of the desired metal. For example, Ag nanowires have been rapidly synthesized using a microwave-assisted polyol method.161 CoNi nanowires are obtained by heterogeneous nucleation in liquid polyol.162 While Bi nanowires have been prepared employing NaBiO, as the bismuth source.161 Pd nanobars are synthesized by varying the type and concentration of reducing agent as well as reaction temperature.1 ... 

The IBM nanoparticle synthesis route is a combination of the polyol method and the thermolysis routes. The rapid injection of the organometallic precursor into a hot solution containing the polyol stabilizing agents allows for the immediate formation of nuclei. 

The polyol method is applied to obtain a series of inorganic nanopar-ficles including ceria (Feldmann, 2003). Yu ef al. reported the s)mthesis of ceria nanocrysfals through a polyol method. Thermal decomposition of (NH4)2Ce(N03)6 in refluxing ethylene glycol with PVP (ca. 190 °C) is carried out to produce sphere-like, rod-like, and spindle-like nanocrystals (Ho et al., 2005). 

Nonaqueous solution methods The syntheses of rare earth phosphate NCs in nonaqueous solutions mainly include the solvothermal method, polyol method, the synthesis in ionic liquids, and the synthesis in high-boiling coordinating solvents like TOPO or OA. 

The polyol method could be applied to synthesis LaP04 Ce,Tb and other rare earth orthophosphate NCs. The so-called polyol method is the precipitation of a solid while heating sufficient precursors in multivalent and high-boiling alcohol like diethylene glycol (DEG) with a boiling point of 246 °C. Therefore, spherical NPs of 20-300 nm in size, usually metal... 

Poly(methyl methacrylate) (PMMA), 310,328 Poly(sodium 4-styrenesulfonate) (PSS), 415 Polycyclic polyyne rings, 142 Polyol hydrolysis method, 409 Polyol method, 289, 291,405 Polyvinyl pyrrolidone (PVP), 291, 355, 392, 393, 407, 424, 429 Positive electrodes, 104 Pr(OH)3,326 Pr Cg2/126 PrFs, 408 Primary... 

Figure 11.26 Left SEM image of a sample of silver nanocubes produced by the polyol method with a trace amount of Na2S. Reprinted by permission from Macmillan Publishers Ltd Nature Protocols [81], (2007). Right UV—Vis spectra taken from silver nanocubes of different sizes. Reprinted from reference [80] (2006) with permission from Elsevier.

Tsuji, M., Miyamae, N., Lim, S., Kimura, K., Zhang, X., Hikino, S. and Nishio, M. (2006). Crystal structures and growth mechanisms of Au Ag core-shell nanoparticles prepared by the microwave-polyol method. Cryst. Growth Des. 6 1801-1807. 

Another microwave study yielded only the anatase phase [199]. In this work Ti02 was synthesized from the alkoxide by the polyol method using various polyols (1,4-butanediol, 1,5-pentanediol, or 1,6-hexanediol) under MW radiation. The authors demonstrated that the crystallite size, which was always less than 10 nm, could be controlled by the quantity of added water and by the nature of the polyol (see Table 1 in [199]). 

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