Nanocrystalline oxide

Sunstrom et al. [38] have also used hydrodynamic cavitation generated, with the use of high-pressure fluid system for the generation of the nanocrystalline oxides. The precipitant stream is subjected to a large pressure drop (21,000 psi) across the interaction chamber. Due to the large pressure drops, bubbles are formed and collapse, causing localized heating of the solvent. In addition, the precipitate... 

Sunstrom JE, Moser WR, Marshik-Guerts B (1996) General route to nanocrystalline oxides by hydrodynamic cavitation. Chem Mater 8 2061-2067... 

Wu N.L. Nanocrystalline oxide supercapacitors. Mater Chem Phys 2002 75 6-11. 

In the case of ethanol, Pd-based electrocatalysts seem to be slightly superior to Pt-based catalysts for electro-oxidation in alkaline medium [87], whereas methanol oxidation is less activated. Shen and Xu studied the activity of Pd/C promoted with nanocrystalline oxide electrocatalysts (Ce02, C03O4, Mn304 and nickel oxides) in the electro-oxidation of methanol, ethanol, glycerol and EG in alkaline media [88]. They found that such electrocatalysts were superior to Pt-based electrocatalysts in terms of activity and poison tolerance, particularly a Pd-NiO/C electrocatalyst, which led to a negative shift of the onset potential ofthe oxidation of ethanol by ca 300 mV compared... 

A. V. Chadwick and G. E. Rush, Characterization of Nanocrystalline Oxides by EXAFS Spectroscopy, Kluwer, Norwell, MA, 2002. 

Abstract. Destructive adsorption of halocarbons on nanocrystalline oxides has been studied. The effect of nanoparticle size and phase composition on the reaction kinetics is discussed. The reactivity of nanocrystalline oxides has been found to increase after deposition of a permeable carbon coating. The possibility of synthesis of new nanocrystalline halogenated materials using nanoscale oxides as precursors has been demonstrated. 

Keywords nanocrystalline oxides aerogels destructive sorbents halocarbons MgO TiCh titanium oxydifluoride carbon coating... 

According to the XRD data, the particle size of reaction product TiOF2 is similar to that of the nanoparticles of the initial Ti02. The surface area of the material also does not change much. These results prove that such reactions can be used for synthesis of new halogenated nanocrystalline materials using nanocrystalline oxides as precursors. 

Nanocrystalline oxides have exceptionally high reactivity with respect to halocarbons. First of all, the temperature of their reaction with halocarbons is much lower than observed for bulk analogs. It is thus possible to carry out destructive adsorption reactions at fairly low temperatures. This is especially important for the development of effective destructive sorbents for neutralization of toxic compounds at mild temperatures. We have also demonstrated that nanocrystalline oxides can be used as precursors for the synthesis of novel halogenated nanocrystalline materials. 

Of special interest are composite materials consisting of carbon-coated nanocrystalline oxides. Such permeable carbon coating not only provides high stability of the destructive sorbents under atmospheric conditions, but in some cases shown in this publication considerably increases their reactivity. Elucidation of the mechanism of this interesting phenomenon will require further research. 

The aerogel-prepared metal oxide nanoparticles constitute a new class of porous inorganic materials because of their unique morphological features such as crystal shape, pore structure, high pore volume, and surface areas. Also, it is possible to load catalytic metals such as Fe or Cu at very high dispersions on these oxide supports and hence the nanocrystalline oxide materials can also function as unusual catalyst supports. Furthermore, these oxides can be tailored for desired Lewis base/Lewis acid strengths by incorporation of thin layers of other oxide materials or by preparation of mixed metal oxides. 

Photovoltaic cells based on the sensitization of mesoporous titanium dioxide by Ru(II) complex dyes in conjunction with the I.3 /U redox couple as a mediator have proved very efficient at exploiting this principle. In such systems, the ionic mediator travels back and forth by diffusion from the working electrode to the counterelectrode, to shuttle to the sensitizer the electrons that have gone through the electrical circuit [18, 21, 84]. Recently, solid-state devices have been described where the liquid electrolyte present in the pores of the nanocrystalline oxide film is replaced by a large-bandgap p-type semiconductor acting as a hole-transport medium [85 88]. 

This method may provide a convenient route for the synthesis of nanocrystalline oxide materials from alkoxide using only one reaction vessel however, because this method uses water dissolved from the gas phase, configuration of the reaction apparatus, that is, the ratio of the surface area of the liquid to the bulk volume of the liquid, may affect the physical properties of the product. 

Toupin M., Brousse T., Belanger D. Influence of microtexture on the charge storage properties of chemically synthesized manganese dioxide, Chem Mater 2002 14 3946-52. Wu N.L. Nanocrystalline oxide supercapacitors. Mater Chem Phys 2002 75 6-11. Frackowiak E., Metenier K., Bertagna V., Beguin F. Supercapacitor electrodes from multiwalled carbon nanotubes. Appl Phys Lett 2000 77 2421-3. 

Porous materials with large internal surface areas have attracted considerable attention in surface chemistry, catalysis and chromatography. In principle, a vast choice of porous materials is available. While some inspiration can indeed be drawn from chemical applications, the choices for useful photovoltaic substrate materials are considerably narrowed by the requirement to have thin-film constituency, transparency and electronic conductivity. Indeed, these requirements are so stringent that only a few substrate types and materials have so far been found suitable. Sintered nanocrystalline oxide films are one major class of these. Much development work on these materials has been reported in the context of dye-sensitised cells, and this is... 

Finally, complex nanocrystalline oxide-based materials such as Gdo gSro jCoO [98]... 

In this section, attention will be focused on the preparation and characterization of nanocrystals, paying particular attention to methods that probe the microstructure and the atomic transport. It should be noted that an excellent review of the chemistry of nanocrystalline oxides, together with coverage of many of the characterization methods employed, is available [137]. 

Spray pyrolysis has been widely used to prepare nanocrystalline metal oxides such as AI2O3, ZnO, and ZrO2 [138], and involves dispersing a solution of a chemical precursor as an aerosol. The droplets are transported to a hot zone where they decompose to form the required nanocrystalline oxide particles. 

The application of nanocrystalline metal oxides in sensor devices is now well-established, and should produce benefits in terms of improved sensitivity and speed of response. On a similar note, nanomaterials have become increasingly important in battery technology, particularly in the development of lithium solid-state batteries [106, 303, 304]. Nanocrystalline oxides offer many advantages in SOFCs, primarily by increasing the surface area of the materials and hence the catalytic activity [305, 306], and this is especially important for lowering the cell s operating temperature. Overall, however, it remains clear that further research into the... 

K. Kalyanasundaram and M. Gratzel (1999) in Optoelectronic Properties of Inorganic Compounds, ed. D.M. RoundhiU and J.P. Fackler, Plenum Press, New York, p. 169 - Efficient photovoltaic solar cells based on dye sensitization of nanocrystalline oxide films . 

As can be seen, the heart of the device is the semiconducting mesoporous or nanocrystalline oxide, composed of a network of nanoparticles that have been sintered together to establish electronic conduction, which is characterized by the total depletion of the semiconductor due to the small size of the nanoparticles and porous structure [65]. The Fermi level in the dark is therefore near the bandgap center, allowing for the generation of high photovoltages upon illumination [71]. 

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