Titania single crystals

Table 1.S Physical properties of various polymorphs of titania single crystals.

Some physical properties of the three polymorphs of Ti02 are hsted in Table 1.5. Systematic data on titania single crystals are relatively scarce, and this applies especially to brookite, most likely due to difficulties with its preparation. The presence of impurities also results in a significant scatter of the property values. 

Iwabuchi A, Choo CK, Tanaka K Titania Nanoparticles Prepared with Pulsed Laser Ablation of Rutile Single Crystals in Water J Phys Chem B 108 10863-10871... 

Figure 5.13. In situ atomic-resolution ETEM image of Pt/titania catalyst (a) finely dispersed Pt particles (b) in situ real-time dynamic activation in hydrogen imaged at 300 C. The 0.23 nm (111) atomic lattice spacings are clearly resolved in the Pt metal particle, P and (c) the same particle imaged at 450 C, also in H2. SMSI deactivation with a growth of a Ti-oxide overlayer (C), and the development of nanoscale single-crystal clusters of Pt, with atomic resolution (arrowed). (After Gai 1998.)...

Figure 5.27. Nanocatalysts of Ru/Ti02 (a) HR LVSEM image iUustrating the uniform distribution of Ru (arrowed) on the support surface (b) atomic structure of Ru/Ti02 in atomic-resolution ETEM at room temperature. The Ru is in single-crystal clusters in (001) (Ru is hexagonal a = 0.27 nm, c = 0.428 nm) and titania exhibits primarily (010) and (110). (After Gai et al 2000.)...

The absorption of light by semiconductors cremes electron-hole pairs e h+) which can be separated because their components diffuse in different directions. The energies of these moieties can be stored by several mechanisms or used in photocatalysis or photosynthesis for nitrogen fixation, formation of amino acids, methanol, etc. The efficiencies of such conversions depend almost entirely upon the semiconductor material, and as yet these efficiencies are too low for significant application. Currently the most promise is demonstrated by the use of titania on a platinum substrate or single crystals of strontium titanate. See also Photoelectric Effect. 

The samples prepared have a good surface area after calcination at 500°C, as can be seen in table 1. Alumina-titania mixed oxide supported samples have surface areas larger than those of the alumina and titania single oxides. As expected x-ray diffraction results show that the mixed oxide catalysts are amorphous, but alumina shows a y phase structure, and Ti02 is a well crystallized anatase phase. No nickel metal or nickel oxide was detected in any of the samples, including Ti02 sample, suggesting the metal was well dispersed, and present as small crystallites (< 50A). 

The structure and composition of titania deposited on the surface of a Rh foil or single crystal were investigated using ISS, AES, and XPS. 

Methanol decomposes on titanium dioxide surfaces by mechanisms that are similar to those by which formic acid decomposes. Methanol can reversibly adsorb on single crystal surfaces of titania (reaction 16) in a molecular state, or it may dissociatively adsorb by interaction with surface lattice oxygen anions, forming a surface methoxide (reaction 17). Reaction (18) represents the disproportionation reaction of hydroxyl groups on the surface of the metal oxide. 

The small domain size of nanofacet supported stractures and multiple overlapping LEED patterns obtained from extended encapsulated metal films on the TiO surface significantly complicates quantitative structural interpretation. Several groups have developed techniques to grow TiO overlayers on Pt single-crystal surfaces to obtain large, well-defined titania films. Koel has performed detailed work on the Pt(lOO)... 

Figure 15. Aggregated nanoparticles of titania forming a single-crystal chain, an example of oriented aggregation. From Penn and Barrfield (1999) with permission from Elsevier, pubhshers of...

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