Stabilized Gold Nanoparticles

While ligands have a beneficial influence on the stability of gold nanoparticles, they exert a negative influence from the catalytic activity point of view, reducing 

Still interact with those substrates that can enter through the cucurbituril portals. 

Influence of the Support on the Catalytic Activity of Supported Cold Nanoparticles 

In other cases, it has been proposed that one condition of a suitable solid support should be a metal oxide in which the metal is able to undergo redox processes in such a way that cooperate with the catalytic oxidation [33,63,69,74—76]. Iron oxide, ceria and even titania are examples of supports in which the metal atoms can swing their oxidation state. In this context it would be of interest to use Mn02 and CrOs as supports since these oxides have themselves been widely used as stoichiometric oxidizing reagents due to their ability to become reduced. 

In fact, in contrast to the role ascribed to nanoparticulated ceria contributing to the overall catalytic activity of gold in solventless alcohol oxidation, naked  

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Figure 7.7 Colloidal crystal formed from oleylamine-stabilized gold nanoparticles, Reproduced with permission from Harris etal.

The preparation and study of metal nanoparticles constitutes an important area of current research. Such materials display fascinating chemical and physical properties due to their size [62, 63]. In order to prevent aggregation, metal nanoparticles are often synthesized in the presence of ligands, functionalized polymers and surfactants. In this regard, much effort has focused on the properties of nanoparticles dispersed into LCs. In contrast, the number of nanoparticles reported that display liquid crystal behavior themselves is low. Most of them are based on alkanethiolate stabilized gold nanoparticles. 

Figure 4. Preparative procedure of alkene thiol-stabilized gold nanoparticles. 50% of hexenethiol bounded to the particle surface is hydrogenated to hexanethiol [11b].

C5 - and Cll -stabilized gold nanoparticles were prepared by the same procedure, that is, reducing AUCI4 in the presence of the corresponding ot, co-alkenethiols by NaBH4 (Figure 4). 

On such very useful hydrogen-terminated surfaces, immobilization of a,(B-alkenethiol-stabilized gold nanoparticles was carried out. The thermal hydrosilylation was selected for this immobilization. Under dry nitrogen... 

Gold nanoparticles can be clearly observed as white dots and silicon wafers are black in HR-SEM images of the gold nanoparticles-immobilized silicon surface. When immobilizing the allylthiol (C3, HS-CHj-CH = CHj)-stabilized gold nanoparticles, even the reaction temperature was as low as 50 °C, the white dots with diameters about lO Onm are observed (Figure 5A). 

Figure 2.6 TEM images and size distributions of CXL fractionated DDT-stabilized gold nanoparticles using C02-expanded hexane.

Figure 2.7 Effect of various factors on nanoparticle dispersion (as determined by tracking the absorbance oTIspr) as a function of applied C02 pressure, (a) effect of temperature on DDT-stabilized gold nanoparticles dispersed in hexane (b) effect of solvent on DDT-stabilized gold nanoparticles at room temperature (c) effect of ligand on gold...

Figure 2.9 DDT-stabilized silver nanoparticle films deposited via (a) hexane evaporation and (b) CXL nanoparticle deposition. Adapted from [15] 2005 American Chemical Society. DDT-stabilized gold nanoparticle...

Figure 2.12 OATS phase separation of a THF-water mixture (left) containing dodecanethiol-stabilized gold nanoparticles. Pressurization of the mixture with C02 induces a phase separation where the nanoparticles remain in the C02-expanded THF (right).

Evans SD, Johnson SR, Mahon SW, Ulman A (1997) Synthesis and Characterization of Surfactant-Stabilized Gold Nanoparticles. Supramol Sci 4 329-333... 

Ligand-stabilized metal nanoparticles such as triphenylphosphine-stabilized gold nanoparticles were usually synthesized by reduction of the corresponding metal ions or complexes with excess diborane. Tetraalkylammonium salts of hydro-... 

An improved synthesis of this type of phosphine-stabilized gold nanoparticle was necessary to make them convenient for use as synthetic intermediates in materials applications. We developed a safer, more convenient, and more versatile synthesis of phosphine-stabilized nanoparticles analogous to those originally reported by Schmid. The synthesis described here eliminates the use of diborane and can be carried out quickly with minimal concern for inert conditions. The nanoparticle product is comparable to that prepared by the Schmid procedure, possessing a core diameter of 1.5 0.4 nm and the same reactivity. In addition, the new synthesis can be adapted to permit the use of a variety of phosphines as passivating ligands and provide control over particle core size. ... 

Purification yields 200-300 mg of triphenylphosphine-stabilized gold nanoparticles, which should be stored cold (—20°C) in the sofid state, or immediately converted to thiol- or amine-stabilized nanoparticles through subsequent reaction with the appropriate ligand. The particles decompose in solution thus manipulation of the product in solution should be minimized. 

A one-pot method for the synthesis of amine-stabilized gold nanoparticles using... 

In a recent report, new nanocomposites of Au NPs and poly(4-vinylpyridine) were obtained through surface-initiated atom-transfer radical polymerization (SI-ATRP). The citrate-stabilized gold nanoparticles were first modified by the disulfide initiator [BrC(CH3)2COO(CH2)iiS]2 for ATRP initiation, and the subsequent polymerization of 4-vinylpyridine occurred on the surface of the gold particles. The assembled Au PVP nanocomposites are pH-responsive because of the pyridyl groups, which are facially protonated and positively charged. The micrographs show Au N Ps of around 15 nm size [92] (Scheme 3.14). 

Moores, A., Goettmann, F., Sanchez, C. and Le Floch, P. Phosphinine stabilized gold nanoparticles synthesis and immobilization on mesoporous materials, Chem. Commun. 2004, 2842-2843. 

So-called superlattices of 5mn alkylthiolate protected silver particles having truncated octahedral shapes as well as thiol-stabilized 5 6 mn gold particles can be obtained from solution. Fractional crystallization is a very usual method to separate chemical compounds from other compounds and impurities. Mixtures of thiolate stabilized gold nanoparticles between 1.5 and 3.5 nm could successfully be fractioned into real monodisperse species containing 140, 225, 314, and 459 atoms. 2D assemblies have also become available of these fcc-structured nanoparticles. The decisive criterion to successhilly fraction and crystallize metal nanoparticles is to protect them perfectly by strongly bound ligand molecules in order to avoid coalescence. 

Figure 6.42. Schematic of the controlled spacing between individually stabilized gold nanoparticles by the formation of fullerene inclusion complexes. Reproduced with permission from Yonezawa, T. Matsune, H. Kunitake, T. Chem. Mater. 1999,11, 33. Copyright 1999 American Chemical Society.

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