Metal nanocomposites

This chapter describes two important and diverse roles played by polysaccharides in development of biocomposites viz. as reinforcing agents in polymers matrix and second as matrix for synthesis of green metal nanocomposites... 

Fig. 16. FT-IR spectra of pure waxy starch and waxy starch metal nanocomposites...

PHOTO-LUMINESCENCE PROPERTIES OF DENDRIMER METAL NANOCOMPOSITES... 

While the linear absorption and nonlinear optical properties of certain dendrimer nanocomposites have evolved substantially and show strong potential for future applications, the physical processes governing the emission properties in these systems is a subject of recent high interest. It is still not completely understood how emission in metal nanocomposites originates and how this relates to their (CW) optical spectra. As stated above, the emission properties in bulk metals are very weak. However, there are some processes associated with a small particle size (such as local field enhancement [108], surface effects [29], quantum confinement [109]) which could lead in general to the enhancement of the fluorescence efficiency as compared to bulk metal and make the fluorescence signal well detectable [110, 111]. 

Ultrafast emission measurements are possible with the dendrimer metal nanocomposites. The gold and silver internal dendrimer nanocomposites showed a fast emission decay of approximately 0.5 ps, which was followed by a slower decay process. The fast decay emission is attributed to decay processes of the gold (or silver) metal nanoparticles. Ultrafast emission anisotropy measure-... 

Sekino, T., Niihara, K., Microstructural characteristics and mechanical properties for Al203/metal nanocomposites, Nanostruc Mater., 1995, 6(5-8) 663. 

Previous paragraph was dedicated to the description of spontaneous magnetization of granular metal nanocomposite. In this section, behavior of this material at paramagnetic state (T> Tb) will be discussed. Magnetic moment of a granular metal in this temperature range is induced by the external... 

Dawson A., Kamat P.V. (2001) Semiconductor-metal Nanocomposites. Photoinduced Fusion and Photocatalysis of Gold-Capped Ti02 (Ti02/Gold) Nanoparticles, J. Phys. Chem. B. 105(5), 960-966. 

Cozzoli, P.D., R. Comparelli, E. Fanizza, M.L. Curri, A. Agostiano and D. Laub (2004a). Photocatalytic synthesis of silver nanoparticles stabilized by Ti02 nanorods A semiconductor/metal nanocomposite in homogeneous nonpolar solution. Journal of the American Chemical Society, 126(12), 3868-3879. 

The kinetics of 4-nitrophenol reduction in presence of microgel-metal nanocomposite particles was studied by UV/Vis spectroscopy. Figure 9 shows the UV spectra for the reduction of 4-nitrophenol measured at different times. For a typical measurement, successive decrease of peak intensity at 400 nm with time can be utilized to obtain the rate constant [59, 72, 73]. This peak is attributed due to the presence of 4-nitrophenate ions in the system. The formation of 4-nitrophenate ions... 

Fig. 13 Test reaction (oxidation of benzyl alcohol to benzaldehyde) used for the analysis of the catalytic activity of microgel-metal nanocomposite particles. All runs were done at room temperature...

Metal nanoparticles embedded in thermosensitive core-shell microgel particles can also work efficiently as catalyst for this reaction. Figure 13 shows the oxidation reaction of benzyl alcohol to benzaldehyde in aqueous media by using microgel-metal nanocomposite particles as catalyst. All reactions were carried out at room temperature using aerobic conditions. It is worth noting that the reaction conditions are very mild and no phase transfer catalyst is needed. It has been found that microgel-metal nanocomposites efficiently catalyze the aerobic oxidation of benzyl alcohol at room temperature. No byproducts have been detected by GC after the reaction, and water is the only product formed besides the aldehyde. 

Figure 15 shows the influence of temperature on the catalytic activity in an Arrhenius plot of the TOFs. These data can be compared to data obtained for the reduction of 4-nitrophenol with an excess of NaBkLt in presence of the metal nanocomposite particles. From Fig. 15, a nonlinear relationship between In (TOF) and T l can be seen. The TOF increase more than exponentially with increased temperature. Only in the immediate vicinity a significantly smaller TOF is monitored. 

Goodson,T., et al. (2004), Optical properties and applications of dendrimer-metal nanocomposites, Int. Rev. Phys. Chem., 23,1. 

FIGURE 13.5 Two preparation routes used in making ceramic-metal nanocomposites. Method (a) solution mixing of all components simultaneously. Method (b) uses a premade sol to which a further solution is added before gelation. (From Roy, R.A., and Roy, R., Mater. Res. Bull, 19, 169, 1984. With permission.)... 

A. Dawson P. V. Kamat, Semiconductor-metal nanocomposites. Photo-induced fusion and photocatalysis of gold-capped Ti02 (Ti02/Au) nanopartides./. Phys. Chem. B 2001, 105, 960-966. 

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