Colloids alloys

Metal organo- and hydro-sols can be obtained with exceptionally high metal concentrations (preparative reproducibility in multi-gram amounts. Further, surfactant-stabilized metal alloy nanoparticles are easily accessible via the co-reduction of different metal salts. As shown in Fig. 2.1, even the inner structure of the colloidal alloy particles can be tailored by adjusting the reduction conditions and/or preparative pathways to prepare homogeneous [8, 36, 37], gradient [38-40] or egg-sheU type [41] nano-alloys. Reductive stabiHzation ... 

Adsorbed carbon monoxide can serve as a useful infrared probe of surface composition in bimetallic colloids if both metals bind CO. This is exemplified in the infrared spectrum of CO on a PVP stabilized colloidal alloy CutgPdjT, [38] Carbon monoxide adsorbs readily onto these PdCu particles (co. 45 A) in dichloro-methane at 25 °C, as shown by the infrared absorption spectrum in Figure 6-28. By comparing this to the IR spectrum of CO on a pure palladium colloid of similar size [34] in Figure 6-27d, it can be clearly seen that CO occupies both palladium and copper sites. Whereas the bands at 2046 cm" and 1936 cm" are in the frequency ranges found for linear and bridged CO on the pure palladium particles, the new band at 2089 cm corresponds to CO on surface copper atoms, thus demonstrating that both metals are present at the surfaces of the particles. 

Bonnemann H ef a/1996 Nanoscale colloidal metals and alloys stabilized by solvents and surfactants preparation and use as catalyst precursors J. Organometaii. Chem. 520 143... 

Let us add here that the fabrication of polycrystalline semiconductive films with enhanced photoresponse and increased resistance to electrochemical corrosion has been attempted by introducing semiconductor particles of colloidal dimensions to bulk deposited films, following the well-developed practice of producing composite metal and alloy deposits with improved thermal, mechanical, or anti-corrosion properties. Eor instance, it has been reported that colloidal cadmium sulfide [105] or mercuric sulfide [106] inclusions significanfly improve photoactivity and corrosion resistance of electrodeposited cadmium selenide. 

Turkevich, J. (1985) Colloidal gold. Partll. Colour, coagulation, adhesion, alloying and catalytic properties. Gold Bulletin, 18, 125-131. 

Xin and co-workers modified the alkaline EG synthesis method by heating the metal hydroxides or oxides colloidal particles in EG or EG/water mixture in the presence of carbon supports, for preparing various metal and alloy nanoclusters supported on carbon [20-24]. It was found that the ratio of water to EG in the reaction media was a key factor influencing the average size and size distribution of metal nanoparticles supported on the carbon supports. As shown in Table 2, in the preparation of multiwalled carbon nanotube-supported Pt catalysts... 

The alkaline EG synthesis method described in this chapter is highly efficient for preparing colloidal solutions of small and narrowly distributed unprotected noble metal or alloy nanoclusters with high metal concentration. 

The alkaline EG S5mthesis method is a very effective technology for the chemical preparation of unprotected metal and alloy nanoclusters stabilized by EG and simple ions. This method is characterized by two steps involving the formation of metal hydroxide or oxide colloidal particles and the reduction of them by EG in a basic condition. The strategy of separating the core formation from reduction processes provides a valid route to overcome the obstacle in producing stable unprotected metal nanoclusters in colloidal solutions with high metal concentrations. Noble metal and alloy nanoclusters such as Pt, Rh, Ru, Os, Pt/Rh and Pt/Ru nanoclusters with small particle... 

The emphases of future investigation on these unprotected metal nanoclusters should be mainly placed on (1) further controlling the size, composition and shape of the unprotected metal or alloy nanoclusters (2) better understanding the stabilizing mechanism of the unprotected metal nanoclusters in colloidal solutions prepared by the alkaline EG synthesis method (3) developing novel catalytic and other functional systems for real applications. 

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... 

An important eonelusion was that the best catalyst is not the alloyed one as expected, nor the mixture of Pt/XC 72 and Ru/XC 72 powders, but one eonsisting of a dispersion of Pt colloid and Ru colloid on the same carbon support, i.e., the Pt + Ru/XC 72 eatalyst. The latter leads to higher current densities for the eleetro-oxidation of methanol than the other catalysts with the same atomic ratio for potentials lower than 0.5 V versus a reversible hydrogen electrode (RHE) (Fig. 11.3). This result... 

Schmidt TJ, Gasteiger HA, Behm RJ. 1999. Methanol electrooxidation on a colloidal PtRu-alloy fuel-cell catalyst. Electrochem Commun 1 1-4. 

Schmidt TJ, Noeske M, Gasteiger HA, Behm RJ, Britz P, Boennemann H. 1998a. PtRu alloy colloids as precursors for fuel cell catalysts. J Electrochem Soc 145 925-931. 

Colloids embedded in a silica sol-gel matrix were prepared by using fully alloyed Pd-Au particles. The Mossbauer data have yielded evidence that alloying Pd with Au in bimetallic colloids leads to enhanced catalytic hydrogenation and also to improved selectivity [426]. 

Zinc electrowinning Zinc in a sulfuric acid/ aqueous solution, lead-silver alloy anodes, aluminum cathodes, barium carbonate, or strontium, colloidal additives... 

Proper lubrication of the dies is essential in forging aluminum alloys. Colloidal graphite in either water or an oil medium is usually sprayed onto the dies for this purpose. 

This mechanism is based on the known importance of hydroxides in other deposition reactions, such as the anomalous codeposition of ferrous metal alloys [38-39], Salvago and Cavallotti claim an analogy with the mechanism of Ni2 + reduction from colloids in support of their proposed mechanism. There is no direct evidence for the hydrolyzed species, however. Furthermore, the mechanism does not explain two experimentally observed facts Ni deposition will proceed if the Ni2 + and the reducing agent are in separate compartments of a cell [36, 37] and P is not deposited in the absence of Ni2 +. The chemical mechanism does not take adequate account of the role of the surface state in catalysis of the reaction. It has no doubt been the extreme oversimplification, by some, of the electrochemical mechanism that has led other investigators to reject it. 

Chen YH, Yeh CS (2001) A new approach for the formation of alloy nanoparticles laser synthesis of gold-silver alloy from gold-silver colloidal mixtures. Chem Commun 371-372... 

Brayner, R., Coradin, T., Vaulay, M.-J., Mangeney, C., Livage, J. and Fievet, F. (2005) Preparation and characterization of metal (Au)- and bimetallic alloys (AuNi)-gelatin nanocomposites. Colloids and Surface Science A, 256, 191-197. 

Choi J, Konno T, Matsuno R et al (2008) Surface immobilization of biocompatible phospholipid polymer multilayered hydrogel on titanium alloy. Colloids Surf B Biointerfaces 67 216-223... 

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