Metal nanoparticles, synthesis steps

The synthesis of bimetallic nanoparticles is mainly divided into two methods, i.e., chemical and physical method, or bottom-up and top-down method. The chemical method involves (1) simultaneous or co-reduction, (2) successive or two-stepped reduction of two kinds of metal ions, and (3) self-organization of bimetallic nanoparticle by physically mixing two kinds of already-prepared monometallic nanoparticles with or without after-treatments. Bimetallic nanoparticle alloys are prepared usually by the simultaneous reduction while bimetallic nanoparticles with core/shell structures are prepared usually by the successive reduction. In the preparation of bimetallic nanoparticles, one of the most interesting aspects is a core/shell structure. The surface element plays an important role in the functions of metal nanoparticles like catal5dic and optical properties, but these properties can be tuned by addition of the second element which may be located on the surface or in the center of the particles adjacent to the surface element. So, we would like to use following marks to inscribe the bimetallic nanoparticles composed of metal 1, Mi and metal 2, M2. 

Recently, Somorjai reported the hydrothermal synthesis of SBA-15 in the presence of PVP-stabilized Pt nanoparticles [22]. This is a one-step synthesis of composites of metal nanoparticles and mesoporous silica. 

This method ensures the deposition of very reactive metal nanoparticles that require no activation steps before use. We shall review here the following examples of catalytic reactions that are of interest in line chemical synthesis (a) the hydrogenation of substituted arenes, (b) the selective hydrogenation of a, 3-unsaturated carbonyl compounds, (c) the arylation of alkenes with aryl halides (Heck reaction). The efficiency and selectivity of commercial catalysts and of differently prepared nanosized metal systems will be compared. 

Sakai T, Alexandridis P (2004) Single-step synthesis and stabilization of metal nanoparticles in aqueous Pluronic block copolymer solutions at ambient temperature. Langmuir 20 8426-8430... 

The asymmetric hydrogenation of prochiral ketones is often an important step in the industrial synthesis of fine and pharmaceutical products. Several noble metal nanoparticles have been investigated for asymmetric catalysis of prochiral substrates but platinum colloids have been the most widely studied and relevant enantiomeric excesses have been reported (>95%). Nevertheless, the enantioselec-tive hydrogenation of ethyl pyruvate catalyzed by PVP-stabilized rhodium nanocluster modified by cinchonidine and quinine was reported by Li and coworkers (Scheme 11.7) [68]. 

In the E/C synthesis, the first step in which metal nanocrystals are deposited on the substrate is critical. The semiconductor particles grow from the metal particles on a particle-by-particle basis (i.e. each metal particle is chemically transformed to the corresponding semiconductor). The size and size distribution, therefore, in the first step determine the final size of the semiconductor particles. For that reason, it is important to achieve an understanding of the growth mechanism of the metal nanocrystal deposition. Penner and associates studied the electrodeposition of various metal nanoparticles (Ag, Pt, Zn, Cu, Cd) mainly onto basal plane-oriented graphite and also onto Si electrodes [6-11]. The depositions were carried out from dilute aqueous solutions of metal ions using a potentiostatic pulse regime. A short (typically tens of ms) potential pulse was applied followed by open[Pg.174]

Pringle, J. M., Winther-Jensen, 0., Lynam, C., Wallace, G. G., Forsyth, M., and MacFarlane, D. R. (2008). One-step synthesis of conducting polymer-noble metal nanoparticle composites using an ionic liquid. Adv. Fund Mater., 18, pp. 2031-2040. 

Single step synthesis of transition metal nanoparticles in aqueous phase for catalytic applications... 

Pure metal nanoparticles have shown exceptional catalytic properties which have motivated modem researchers to come up with innovative ideas to synthesize nanoparticles in a cost effective manner. Apart from catalysis, potential applications of metal nanoparticles ate well known in other fields such as pigments, electronic and magnetic materials, dmg deUvery etc. Here we report solution combustion synthesis method to synthesize transition metals (Ni, Cu and Co) in a single step process. Metal nitrates and glycine are used as synthesis precursors and dissolved in water to make a homogeneous aqueous solution which is combusted to produce metal nanoparticles with desired composition. 

In any case, it is clear that, for its own nature, sol-gel material is suitable for the formation of many different composite materials [207] inorganic and organic polymers, as well as many different kinds of nano-objects possessing effective electrocatalytic properties, can find stable inclusion into a host matrix possessing all the characteristics previously listed. The most simple approach consists of adding the filler to the siliceous matrix after sol-gel formation. However, composite materials can also be obtained by synthesizing the sol-gel film in the presence of the precursor of the filler, e.g., a monomer [227] or a metal complex [228]. The synthesis of the composite material is finalized in a subsequent step, e.g. by a chemical oxidation or reduction, leading to polymer chains or metal nanoparticles, respectively, included inside the sol-gel matrix. 

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