Formation of nanopartides

A pioneer in the application of ultrasound to the formation of nanopartides of noble metals is Y. Maeda. In an earlier study his group [17] synthesized sonochemically metallic nanopartides of metals such as Ag, Pd, Au, Pt and Rh with a fairly narrow distribution (e.g., about 5 nm for Pd particles obtained from a 1.0 mM Pd(II) solution in polyethylene glycol monostearate solution). They suggested three different reduction pathways under sonication (i) reduction by H atoms, (ii) reduction by secondary reducing radicals formed by hydrogen abstraction from... 

Xylan-based micro- and nanoparticles have been produced by simple coacervation (Garcia et al., 2001). In the study, sodium hydroxide and chloride acid or acetic acid were used as solvent and non-solvent, respectively. Also, xylan and surfactant concentrations and the molar ratio between sodium hydroxide and chloride acid were observed as parameters for the formation of micro- and nanoparticles by the simple coacervation technique (Garcia et al., 2001). Different xylan concentrations allowed the formation of micro- and nanoparticles. More precisely, microparticles were found for higher concentrations of xylan while nanopartides were produced for lower concentrations of the polymer solution. When the molar ratio between sodium hydroxide and chloride acid was greater than 1 1, the partides settled more rapidly at pH=7.0. Regarding the surfactant variations, an optimal concentration was found however, at higher ones a supernatant layer was observed after 30 days (Garda et al., 2001). 

Bimetallic nanoparticles, either as alloys or as core-shell structures, exhibit unique electronic, optical and catalytic properties compared to pure metallic nanopartides [24]. Cu-Ag alloy nanoparticles were obtained through the simultaneous reduction of copper and silver ions again in aqueous starch matrix. The optical properties of these alloy nanopartides vary with their composition, which is seen from the digital photographs in Fig. 8. The formation of alloy was confirmed by single SP maxima which varied depending on the composition of the alloy. 

Scheme 1. Proposed chemical reactions involved in the formation of starch capped MSe nanopartides...

Qi, H. and Hegmann, T. (2006) Formation of periodic stripe patterns in nematic liquid crystals doped with functionalized gold nanopartides. Journal of Materials Chemistry, 16, 4197-4205. 

The formation of nanopattemed functional surfaces is a recent topic in nanotechnology. As is widely known, diblock copolymers, which consist of two different types of polymer chains cormected by a chemical bond, have a wide variety of microphase separation structures, such as spheres, cylinders, and lamellae, on the nanoscale, and are expected to be new functional materials with nanostructures. Further modification of the nanostructures is also useful for obtaining new functional materials. In addition, utilization of nanopartides of an organic dye is also a topic of interest in nanotechnology. 

Mo03 (bipy)] [Mo03 (H20) ] Inorganic Chemistry, 49, 6865—6873. Moreno-Manas, M. and Pleixats, R. (2003) Formation of carbon-carbon bonds under catalysis by transition-metal nanopartides. Accounts of Chemical Research, 36, 638—643. 

A nonmetallic element, silicon, was prepared sonodiemically by reducing tetraethyl orthosilicate (TEOS) with a colloidal solution of sodium. The product was obtained as 2-5 nm sized, highly aggregated partides. The silicon exhibited a luminescence similar to that of porous silicon. This procedure is suggested as a general sonochemical reduction leading to the formation of metallic nanopartides [26]. 

Wizel later extended her study and included another metallic nanopartide, cobalt, and an additional polymer, poly(methylmethacrylate), in her metal-polymer composite research [58]. A significant difference in the solubility of the iron-poly(methylacrylate) and cobalt-poly(methylacrylate) in various solvents was observed. While the iron-poly(methylacrylate) composite (FePMA) and iron-poly(methylmethacrylate) composite (FePMMA) dissolved in chloroform, acetone, and toluene at room temperature, the corresponding cobalt-poly(methylacrylate) composite (CoPMA) was insoluble in these solvents at room temperature. At elevated temperatures (45 °C), dissolution of CoPMA in these solvents was observed. This difference is accounted for by the stronger interaction existing between the cobalt and the surrounding polymer. For iron-poly(methylacrylate) this interaction is weakened due to the formation of an iron complex. The Mw of the various polymers and composites as a function of the metal-to-monomer weight ratio was measured and reported. 

One paper by the same group reports on the sonochemical insertion of palladium nanopartides loaded within mesoporous silica [111]. The formation of Pd nanopartides (5-6 nm in diameter) was restricted by the coalescence of the so-nochemically reduced Pd atoms inside the confined volumes of the porous solid. 

The en molecules play an important role in controlling the nucleation and growth of the CdS nanorods. As a bidentate ligand, en molecules may react with Cd + ions and form relatively stable complexes. Under appropriate solvothermal conditions, the complexes become unstable and decompose, which results in the formation of CdS nanorods [lOOj. A mono-dentate ligand, n-butylamrne, was found to be a shape controller for nanorods of CdS and MSe (M = Zn, Cd or Pb) [101]. Similarly, the precursor of ZnE(en)o.s (E = S, Se) could also form in en which then is converted to ZnSe nanopartides via pyrolysis in solvothermal conditions [102]. The coordinating ability of the solvent was found to play an important role in the nucleation and growth of nanocrystallites [103]. 

Propylene carbonate-stabilized palladium nanopartides were also shown to be active catalysts for the Heck reaction [116, 117]. The formation of olefins from aldehydes and ketones via McMurry-type coupHng reactions was reported using Bu4NBr-stabihzedTi colloids (3nm) [22]. TheTHF-protectedTi,3-nanocluster (Fig. 

To form Pt nanopartides, HPS was impregnated in an inert atmosphere with a solution of H2PtCl6 in THF followed by reduction with H2. It is noteworthy that incorporation of the THF solution of platinic acid in microporous HPS results in partial reduction of the Pt(IV) species and formation of Pt(II) complexes where the ligands are the THF oxidation products [89]. The accumulation of Pt(II) complexes, as well as subsequent Pt nanoparticle formation, is effectively restricted by... 

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