Properties of Titania

Ti02 is 21 markedly ionic dioxide formed by and 0 ions. It exists in several natural allotropic forms (anatase, rutile, brookite, and Ti02-B) and artificial forms [7]. From a structural standpoint, all the phases consist of slightly elongated octahedrites (TiOe) sharing vertices or edges. 

Rutile and anatase are thermodynamically stable at temperatures of over 600 °C and below 600 °C, respectively. In general, anatase is the most active phase (3.2 eV) and presents greater photocatalytic efficiency, even though rutile has a narrower bandwidth (3.0 eV). Different explanations have been put forward [8] the greater stability of hydroxyl groups (OH ) adsorbed by rutile, which make the formation of hydroxyl radicals (OH ) more difficult [9], or the 

As regards electronic structure, Ti02 is an n-type semiconductor and has a small amount of oxygen vacancies compensated by the presence of Ti centers. 

The atom network has as many electronic levels as the atoms in the network and the overlapping of atomic orbitals extends throughout it. These bands are essential for explaining many physical-chemical properties and photocatalytic behavior. 

One of the most important characteristics for using a semiconductor as a photocatalyst is its stability in highly humid atmospheres and even in contact with aqueous solutions, as is the case of Ti02. 

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Fig. 3. Effect of using either liquid or supercritical carbon dioxide on the textural properties of titania aerogels calcined at the temperatures shown. (—), dried with Hquid carbon dioxide at 6 MPa and 283 K (-------), dried with supercritical carbon dioxide at 30 MPa and 323 K. Reproduced from Ref. 36.

The properties of titania particles were investigated using X-ray diffraction (XRD, Model D/MAX-RB, Rigaku Ltd.), scanning electron microscopy (SEM, Model 535M, Philips Ltd.), transmission electron microscopy (TEM, Model 2000EX, JEOL Ltd.). The crystallite sizes were estimated by Scherrer s equation and the composition of rutile phase in titania were estimated from the respective integrated XRD peak intensities. 

Morales F., de Smit E., de Groot F.M.F., Visser T., and Weckhuysen B.M. 2007. Effects of manganese oxide promoter on the CO and H2 adsorption properties of titania-supported cobalt Fischer-Tropsch catalysts. J. Catal. 246 91-99. 

Acidic ion-exchange resins, 10 485 Acidic oxides, 12 190-191 Acidic papers, preservation of, 11 414 Acidic properties, of titania-silica, 1 764 Acidic silicate solutions, 22 458 Acidic zeolites, 16 825 Acid industrial refractories, 21 515 Acidity, biofiltration system, 10 76-77 Acidity analysis, of water, 26 36-37... 

Paulose M, Mor GK, Varghese OK, Shankar K, Grimes CA (2006) Visible light photoelectrochemical and water-photoelectrolysis properties of titania nanotube arrays. J Photochem Photobiol A 178 8-15... 

Mor GK, Shankar K, Varghese OK, Grimes GA (2004) Photoelectrochemical properties of titania nanotubes. J Mater Res 19 2989-2996... 

Fig. 5.28 Dielectric properties of titania ceramic as a function of frequency and temperature.

Kolen ko Y.V., Churagulov B.R., Kunst M. et al. (2004) Photocatalytic properties of titania powders prepared by hydrothermal method, Appl. Catal. B, 54(1), 51-58. 

Evaluation of the suitability was carried out by investigating the catalysts and catalytic performances, putting emphasis on the deactivation behavior. The present paper reports on the properties of titania supported iron oxide catalysts. This system was chosen to extend the concept to other supports, since a priori titania appeared to be a suitable material. Although textural properties were satisfactory, the strong interaction of titania with the applied components resulted in a rapid deactivation. However, the mechanism of deactivation was completely different from systems investigated earlier. 

Burgeth G, Kisch H. Photocatalytic and photoelectrochemical properties of titania-chloroplatinate(IV). Coord Chem Rev 2002 230 40-7. 

Wilke, K. and H.D. Breuer (1999). The influence of transition metal doping on the physical and photocatalytic properties of titania. Journal of Photochemistry and Photobiology A-Chemistry, 121(1), 49-53. 

Nadaud N., Nanot M., Boch P. Sintering and electrical properties of titania- and zirconia-containing In203-Sn02 (fTO) ceramics. J. Am. Ceram Soc. 1994 77 843-46. 

In the following, we discuss our results on the characterization and photocatalytic properties of titania-halogenometal complexes of Pt(IV) and Rh(III). Considering that the surface of titania contains about 3-6 OH groups per nm and imder-coordi-nated titanium atoms it may act both as a mono- and bidentate ligand (Fig. la-c) and as a coordination centre (Fig. Id-f). Research on the latter topic was recently summarized 14). 

Mariscal R., Lopez-Granados M., Fierro J. L. G., Sotelo J. L., Martos C. and Van Grieken R., Morphology and surface properties of titania-silica hydrophobic xerogels, Langmuir 16 (2()00) 9460-9467. 

The photochemical properties of titania surfaces are of interest for several reasons. They determine the stability of pigmented paint systems [76], the rate at which pollutants can be degraded in systems designed to purify air and water [77], and are the root cause of poorly understood phenomena such as water photolysis [78] and super hydrophilicity [79]. Using thin rutile epilayers with five low index orientations, it has been shown that the relative rates of photochemical reactions catalyzed by titania depend on the surface orientation [80]. In this chapter, experiments used to map the complete orientation dependence of the relative photochemical reactivity of TiO are described [81-83]. In this case, the relevant reactions are carried out at room temperature and this gives us the opportunity to fix both the surface morphological structure and stoichiometry. For the reactions described here, all of the surfaces were... 

Fig. 3. Effect of using either Hquid or supercritical carbon dioxide on the textural properties of titania aerogels calcined at the temperatures shown. ( ),...

S. Zheng, L.A. Gao, Q.H. Zhang, and J.K. Guo, Synthesis, Characterization and Photo-catalytic Properties of Titania-modified Mesoporous Silicate MCM-41, J. Mater. Chem., 2000, 10, 723-727. 

Bonsack, J.P., Ion-exchange and surface properties of titania gels from Ti(IV) sulfate solutions, J. Colloid Interf. Sci., 44, 430, 1973. 

We have reported that properties of titania/silicas depend on their preparation methods and a complexing-agent assisted sol-gel method gives the most homogeneous titania/silicas [4]. In the sol-gel titania/silicas, Ti-O-Si bonds are more effectively formed and Si and Ti components are higher dispersed than those in conventional titania/silicas [4]. Therefore, it is expected that the sol-gel titania/silicas are also effective catalysts for oxidation reactions. 

Rutile is the thermodynamically most stable Ti02 crystal structure, and the transformation from anatase to rutile takes place at about 1300 K. This temperature can be much lower in the presence of foreign atoms, which can catalyze the transformation. In a series of studies of the properties of titania, Shanon and Pask (45) postulated that the transformation to rutile... 

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