Polymer-capped

This chapter is organised as follows Following this introduction as section 1, a brief description of the synthesis and characterisation techniques used for the as-synthesised polymer capped selenide nanopartides is given as section 2. In section 3, the mechanism of the reaction, results and discussion of the different selenide nanocomposites obtained using different polymers are given. Section 4, the last section gives a summary of the whole process, followed by references. Acknowledgements are cited before references. 

The synthetic approach is very simple and does not require any special set up. In a typical room temperature reaction, 1.0 mL aqueous solution of cadmium chloride was added to 20 mL aqueous solution of soluble starch in a 50 mL one-necked round-bottom flask with constant stirring at room temperature. The pH of the solution was adjusted from 6 to 11 using 0.1 M ammonia solution. This was followed by a slow addition of 1.0 mL colourless selenide ion stock solution. The mixture was further stirred for 2 h and aged for 18 h. The resultant solution was filtered and extracted with acetone to obtain a red precipitate of CdSe nanoaprticles. The precipitate was washed several times and dried at room temperature to give a material which readily dispersed in water. The same procedure was repeated for the synthesis of PVA and PVP - capped CdSe nanoparticles by replacing the starch solution with the PVA and PVP polymers while the synthesis of elongated nanoparticles was achieved by changing the Cd Se precursor ratio from 1 1 to 1 2. The synthesis of polymer capped ZnSe nanoparticles also follows the same procedure except that ZnCb solution was used instead of CdCb solution. 

Scheme 2. Proposed chemical reactions involved in the formation of polymer capped MSe...

N. Toshima, Polymer-capped bimetallic nanoclusters as active and selective catalysts, in N. Ueyama, A. Harada (eds.) Macromolecular Nanostructured Materials, Kodansha/ Springer, Tokyo/Berlin, 2004, 182. 

Organic Species Surfactant or Polymer-Capping Agents... 

Lipowsky, P. Jia, S. Hoffmann, R. C. Jin-Phillipp, N. Y. Bill, J. Ruhle, M. 2006. Thin film formation by oriented attachment of polymer-capped nanocrystalline ZnO. Zeitschrift fur Metalllcunde 97(5) 607-613. 

Fig. 10.3. Effects of polymer capping ratios on quantum dot properties, (a) Fluorescence quantum yield blue curve) and polydispersity index red curve) of 2.5 nm CdTe quantum dots as a function of molar capping ratio. Polydispersity indices were calculated from gel filtration chromatograms, (b) Photostability data at various capping ratios (MCR = 1.5, 1.0, or 0.5) and in the absence of polymer (MCR = 0)...

Almost all metal-catalyzed living polymerizations give polymers capped with halogens that are stable after the usual workup. These terminal halogens would be undesirable, because they may lower the polymer s thermal stability. Dehalogenation by tribu-tyltin hydride (EC-15) is of importance in this respect and effectively works for the bromide terminals in polystyrene, PMMA, and poly(MA) in the presence of copper catalysts.277... 

Linear polymers are also obtained by elimination of n-BuCl through pyrolysis of n-BujNBClj, resulting in as many as nine n-BuNBCl units linearly assembled". Chain termination was assumed to be via loss of BClj, resulting in polymers capped with n-Bu and n-BujN moieties. 

Rao, Y. N., Banerjee, D., Datta, A., Das, S. K., Guin, R., and Saha, A. 2010. Gamma irradiation route to synthesis of highly re-dispersible natural polymer capped silver nanoparticles. Radiat. Phys. Chem. 79 1240-1246. 

Since a milestone paper in Science in 1996, the group of El-Sayed [238-240] has led the field of synthesis and applications of shape-specific nanoparticles. A classical example of the detailed study of metal-particle shape effects in catalysis was reported by Narayanan and El-Sayed using unsupported polyvinylpyrollidone (PVP) polymer-capped Pt shape-specific colloids (cubes, spheres, and tetrahedra) in a model electron transfer reaction between hexacyanoferrate(III) and thiosulfate... 

Polymer-capped Bimetallic Nanoclusters as Active and Selective Catalysts... 

In this section the preparation and catalytic properties of the colloidal dispersion of polymer-capped bimetallic nanoclusters will be discussed, emphasizing the importance of polymers for controlling the structure and stabilizing the dispersions of bimetallic nanoclusters in preparation processes as well as for the improvement of the activity and selectivity in catalyses. Although there are many reports on the preparation of industrial catalysts composed of bimetallic nanoclusters and inorganic supports, they are not included in this section. 

Preparation and Structure of Polymer-capped Bimetallic Nanoclusters... 

A polymer-capped metal nanocluster catalyst has not only the advantages similar to those of particles dispersed on an inorganic support but also new benefits in that... 

An alcohol reduction method in which alcohol like ethanol can work both as a reductant and a solvent has been applied to the synthesis of polymer-capped bimetallic nanoclusters. They have been prepared by the simultaneous reduction of the two corresponding metal ions with refluxing alcohol. For example, colloidal dispersions of Pd/Pt bimetallic nanoclusters can be prepared by refluxing... 

Polymer-capped bimetallic nanoclusters containing both light transition metal and precious metal can also be prepared by a modified alcohol reduction method. For example, Cu/Pd bimetallic nanoclusters were successfully prepared with various Cu Pd ratios by refluxing a glycol solution of the hydroxides of Cu and Pd in the presence of PVP or by the thermal decomposition of metal acetates. 

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