Nanocrystalline surfaces preparation

Nanocrystalline Ti02 surfaces are prepared by coating conducting glass with a paste containing colloidal semiconductor particles, followed by a sintering process. For the solar cell type applications of nanocrystalline surfaces under discussion here,... 

Until a few years back, the crystal shape of solid materials was of academic curiosity only and shape was not considered to have an effect on the chemical properties and reactivities of a material. However, recent studies clearly indicate that the shape of nanocrystals does indeed affect the chemistry. For example, it has been shown that 4 nm nanocrystalline MgO particles adsorb six molecules of S02 per nm2 at room temperature and 20 Torr pressure.30 However microcrystalline MgO adsorbs only 2 molecules of S02 per nm2 under similar conditions. Similarly, the nanocrystalline aerogel prepared, AP-MgO material adsorbs four times as much C02 as the microcrystals. There are not only differences in the amounts of gaseous molecules adsorbed on these surfaces, but also the mode of surface binding can also be different. S02 binds more predominantly as a monodentate species on the AP-MgO crystal but favors a bidentate geometry on conventionally prepared, CP-MgO microcrystals. Clearly, these results indicate that the shape and size of the crystals affect the adsorptive properties of the MgO surfaces. The high reactivities of the... 

Since the enhanced reducibility of nanocrystalline ceria is primarily due to facilitated oxide ion vacancy formation at the surface, one would expect the condition of the surface (segregation of impurities and dopants at the surface, surface structure, etc.) to strongly affect the reduction properties of nanocrystalline ceria. Indeed, thermogravimetric measurements by Kim et aV on nanocrystalline ceria prepared by two different synthesis routes demonstrate substantially different reduction behavior. They measured pOg exponents varying from 0 to -1/2 for differently prepared nanocrystalline ceria powders, and explained these results on the basis of oxide ion vacancies at different ionization states in addition to charged impurities segregated onto the surface. °... 

According to the characterizations by TEM and XRD, the sample prepared from a CH4/H2 plasma was composed of nanocrystalline diamond and disordered microcrystalline graphite. Then nondiamond carbon was effectively removed with an increase in [CO]. It is therefore concluded that the VDOS of the nanocrystalline diamond and DEC films extracted from the HREELS data is in qualitative agreement with the characterizations of TEM and XRD. Although the HREELS probes only the region near the surface, the agreement suggests that the surface dynamics do not differ dramatically from those of the bulk. 

Elbaum R, Vega S, Hodes G (2001) Preparation and surface structure of nanocrystalline cadmium sulfide (sulfoselenide) precipitated from dimethyl sulfoxide solutions. Chem Mater 13(7) 2272-2280... 

Menzies, D. B. Dai, Q. Bourgeois, L. Caruso, R. A. Cheng, Y. B. Simon, G. P. Spiccia, L. 2007. Modification of mesoporous Ti02 electrodes by surface treatment with titanium(IV), indium(III) and zirconium(IV) oxide precursors Preparation, characterization and photovoltaic performance in dye-sensitized nanocrystalline solar cells. Nanotechnology 18 125608. 

Oxidative catalysis over metal oxides yields mainly HC1 and C02. Catalysts such as V203 and Cr203 have been used with some success.49 50 In recent years, nanoscale MgO and CaO prepared by a modified aerogel/hypercritical drying procedure (abbreviated as AP-CaO) and AP-MgO, were found to be superior to conventionally prepared (henceforth denoted as CP) CP-CaO, CP-MgO, and commercial CaO/MgO catalysts for the dehydrochlorination of several toxic chlorinated substances.51 52 The interaction of 1-chlorobutane with nanocrystalline MgO at 200 to 350°C results in both stoichiometric and catalytic dehydrochlorination of 1-chlorobutane to isomers of butene and simultaneous topochemical conversion of MgO to MgCl2.53-55 The crystallite sizes in these nanoscale materials are of the order of nanometers ( 4 nm). These oxides are efficient due to the presence of high concentration of low coordinated sites, structural defects on their surface, and high-specific-surface area. 

In addition to C onions, C atoms condense into various kinds of chemically bonded forms, and they are known to have excellent physical properties depending on the bonding nature. This means that research and applications not only in the materials science but also in other scientific fields are expected. At JAERI, the optimum growth conditions have been successfully obtained for the preparation of high-quality Cgo, diamondlike carbon, and nanocrystalline diamond by means of ion-beam-assisted deposition [80-82]. The susceptibility of Ni/Cgo thin films to thermal treatment, the formation of nanocrystalline diamond and nanotubes due to codeposition of Co and Ceo, and the surface modification of glassy... 

After preparation of the porous nanocrystalline Ti02 film, the N3 dye is adsorbed onto the 2 film surface. The film is immersed into the dye solution (0.2-0.3 mmol in ethanol or mrt-butanol/acetonitrile, 1 1 mixed solution) followed by... 

The effect of surface modification of the 2 photoelectrode by other oxide materials has been also investigated by several research groups. For example, Zaban et al. prepared a nanocrystalline 2 photoelectrode coated with a... 

Preparation and Structural Features of Nanocrystalline Ti02 Surfaces... 

Kivelson and Niemann [301] showed that both An and gn correlate well with the type of ligand atoms bound to Cu2+ and with the polyhedron structure [301-303]. Therefore, changes in the EPR spectrum shape and parameters have to reflect rearrangements in the coordination sphere. Fig. 8.22 presents typical EPR spectra of Cu(II) complexes adsorbed onto nanocrystalline Ti02 particles from solutions containing Cu(N03)2 and edta at the ratio [Cu] [edta] = 1 1 at different pH values. The line-shape analysis showed that at pH 2.9 and 8.0 the EPR spectra are a superposition of the spectra of at least two different species, while the spectrum, recorded for the sample prepared at pH 6.9 with a short (1 h) time of adsorption, indicates the formation of only one Cu2+ species at the surface (type A ). 

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