Nanoparticle production processes control

Supported metal catalysts are used in a large number of commercially important processes for chemical and pharmaceutical production, pollution control and abatement, and energy production. In order to maximize catalytic activity it is necessary in most cases to synthesize small metal crystallites, typically less than about 1 to 10 nm, anchored to a thermally stable, high-surface-area support such as alumina, silica, or carbon. The efficiency of metal utilization is commonly defined as dispersion, which is the fraction of metal atoms at the surface of a metal particle (and thus available to interact with adsorbing reaction intermediates), divided by the total number of metal atoms. Metal dispersion and crystallite size are inversely proportional nanoparticles about 1 nm in diameter or smaller have dispersions of 100%, that is, every metal atom on the support is available for catalytic reaction, whereas particles of diameter 10 nm have dispersions of about 10%, with 90% of the metal unavailable for the reaction. 

In a continuous system, it was seen that the same trend of size and charge data occurred. The continuous data displayed much clearer trends, however. Continuous processing is thus the preferred method of nanoparticle production, enabling a better quality control. 

The problem of impurity trapping in growing nanoparticles during their formation in a deposition from the gas phase is of interest for both different kinds of atmospheric processes and processes of modem technology (e.g., manufacture of nanoparticles). 11 i s well known that e ven a very small concentration of impurity molecules in a condensed phase can substantially change certain physicochemical properties of the product. The control of the concentration of impmity molecules in the substance is of paramount significance in the production of microelectronics elements. 

Controlled thermolysis of metal carbonyls in the presence of aluminium alkyls is a special case of nanoparticle formation via the decomposition of zerovalent metal complexes. This led to a production process for monodisperse, magnetic Co-, Fe/Co, and Fe-nanocolloids having particle sizes adjustable between 2 and... 

Co using their respective metal nitrate and glycine mixture. Nickel was chosen as a model to successfully verify the thermodynamic predictions. It can be concluded from the results and discussion that the fuel to oxidizer ratio, (p, is an important parameter in SCS systems and significantly influences the synthesized nanoparticles. The q> value not only affects the combustion temperature but also the nature of the solid product (metal or metal-oxide), porosity and crystalhte size. It is anticipated that the other metal-systems (Cu and Co) will also follow a similar trend. The properties of the synthesized nanoparticles can be controlled and fine-tuned by adjusting the fuel to oxidizer ratio in SCS processes. 

Nickel has been known to be one of the important catalytic, magnetic, and conductive materials. A one-step facile synthesis was devised for preparation of well-dispersed AgNi coreshell nanoparticles with uniform and intact shells [66]. The process is performed by a reduction of silver nitrate and nickel nitrate with sodium borohydride in water-in-oil (W/0) microemulsions of wa-ter/polyoxyethylene (4) nonylphenol (OP-4] and polyoxyethylene [7] nonylphenol (0P-7]/n-heptane. TEM (see Fig. 8.10], X-ray diffraction (XRD], X-ray photoelectron spectroscopy (XPS], and UVvis absorption are utilized to characterize the AgNi coreshell nanoparticles. The thickness of Ni layers on the surface of Ag nanoparticles could be controlled by the dosage of Ni + and Ag+. The AgNi coreshell nanoparticles showed a high catalytic activity for degradation reaction of eosin Y (see Fig. 8.11]. The product may also... 

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