Electrodispersion technique

The same dependence between concentration of M nanoparticles (Ns) on a surface of a dielectric substrate and their catalytic activity has been also found out in the investigation of an amorphous films of M nanoparticles [117], prepared by laser electrodispersion technique and deposited on Si02 dielectric surface layer of thermally oxidized Si (see Chapter 15). It has been shown that in various reactions of chlorinated hydrocarbons catalyzed by so prepared nanostructured Cu film with growth Ns the value of Y increases firstl, reaches a maximum at Ns 4 x 1012 particles/cm2, and then quickly falls. 

By now, the possibility of deposition of granulated Cu, Ni, Pd, Pt, and Au films by laser electrodispersion has been experimentally verified. The structural parameters of the films being formed were studied by various diagnostic techniques, with the most informative results obtained with TEM, atomic-force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). 

All the metallic nanostructures deposited by laser electrodispersion on both types of silicon substrates were found to be exceedingly active in the above processes. The activity was orders of magnitude higher than that of typical supported catalysts prepared by the standard techniques. Such a high activity is presumably due not only to the small size and amorphous state of nanoparticles, but also to the influence exerted by the charge effects discussed above. 

Another specific feature of the catalytic behavior of the structures under study consists in that the chemical nature of a metal becomes a factor less important for catalysis as the surface nanoparticles density increases. This is well seen in Figure 15.14, which shows the results obtained in measurements of the activity of copper- and nickel-based catalysts in the reaction of carbon tetrachloride addition to olefins. Presented in this figure are the activities of catalysts prepared by laser electrodispersion and the conventional deposition techniques. Two important features are worth noting. First, the activity... 

Indirect detection techniques with UV-absorbing buffer components and non-absorbing analytes are widely applied in CZE of small molecules. To diminish electrodispersion, i.e. to achieve symmetrical peaks, the mobilities of analyte ions and background electrolyte should match closely [2]. In this case the sieving effect will dominate and peak broadening is only due to polydispersity. When mobility differences are large, electrodispersion rules... 

Laser electrodispersion (LED) method makes possible to fabricate dense nanostmctured catalysts with unique catalytic properties. In contrast to earlier laser ablation techniques, where nanoparticles were synthesized from vaporized matter, LED is based on the cascade fission of hquid metalhc drops. Fabricated catalysts consist of ensembles of nanoparticles that are uniform in size and shape, amorphous and stable to coagulatioa The catalytic activity of these self-assembled Pt, Ni, Pd, Au and Cu catalysts with extremely low metal content (<10 mass.%) in hydrogenation and hydrodechlorination is several orders of magnitude higher compared to that for separated metal clusters, highly loaded metal films and supported catalysts prepared by usual methods. 

This technique is performed using a sacrificial anode experimental set-up, and is referred to as sacrificial anode electrolysis. During the process, the stabihzing effect can occur either at the anode or at the cathode. In the former case, the anode is made from the metal to be electrodispersed as nanostructures when the applied potential is sufficiently high, the anode dissolves into metal ions that subsequently are precipitated due to the presence of hydroxides or other anions [316]. 

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