Structure of Titania

In anatase, the TiO octahedra share four edges to form a pseudo-tetragonal framework structure, and in brookite the octahedra share three edges. Each 

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Effect of the calcine condition on surface structure of titania nanocrystal photocatalyst... 

Nanocrystals titania was prepared by sol-gel method. X-ray diffraction result is shown in Figure 1, all samples were anatase phase. Based on Sherrer s equation, these samples had crystallite sizes about 7 nm. From XRD results, it indicated that titania samples showed the similar of crystallinity because the same ordering in the structure of titania particles make the same intensity of XRD peaks. 

Sakai N, Ebina Y, Takada K, Sasaki T (2004) Electronic band structure of titania semiconductor nanosheets revealed by electrochemical and photoelectrochemical studies. J Am Chem Soc 126 5851-5858... 

The preparation of Titania nanocoils has been yet not investigated in literature. However, quite recent results258 show that the effective structure of Titania nanotube likely produced by controlled anodization process is that of a helical (compressed) nanocoil. Fig. 11 shows this concept. It was also demonstrated that the formation of these helical nanocoils improves the photo-generated current compared to samples after short anodization where only a Titania layer is formed. 

The presence of sulfate ions markedly affects the nanopore structure of titania-sulfate aerogels. In Ti02-S042 materials, unlike in zirconia-sulfate aerogels, the larger sulfate load stimulates formation of a more consolidated structure. The XRD analysis shows that even a crystalline phase (anatase) may be present in fresh, dry aerogels, which, perhaps, is the first observation of this phase in sol-gel titania obtained from the low temperature drying process. 

The results obtained clearly demonstrate that sulfate ions promote the consolidation of titania morphology in nanometer scales and the formation of a crystalline, anatase phase in aerogels dried using supercritical carbon dioxide. This trend is consistently demonstrated by adsorption experiments as well as SAXS and XRD studies. The presence of platinum promotes the formation of a fine polymeric structure of titania in nanometric scales. After calcination all samples exhibit a similar morphology, yet with a notable difference in texture parameters. 

Parameters of the porous structure of titania samples (pores volume Vs, specific surface area Ssp) were calculated using BET theory [34] from the adsorption isotherms of methanol. The average pore diameter (Dp) values were estimated from the differential curves of pore size distribution. 

Control of pore structures of titanias and titania/aluminas using complexing agents... 

The surface hydration-hydroxylation structure of titania, proved previously mainly by IR studies using dry titania powders, also seems to hold when these powders are dispersed in water. An interesting approach, therefore, is to probe directly the uptake of water from the gas phase by DS-coated rutile surfaces (42). Water adsorption isotherms are presented in Figure 14. The dual nature of titania surface sites, a property not seen... 

The surface hydration-hydroxylation structure of titania, proved previously mainly by IR studies using dry titania powders, also seems to hold when these powders are dispersed in water. An interesting approach, therefore, is to probe directly the uptake of water from the gas phase by DS-coated rutile surfaces [42]. Water adsorption isotherms are presented in Figure 52.14. The dual nature of titania surface sites, a property not seen with other common oxides such as silica and alumina, leads to an unusual type of water adsorption isotherm for titania. The isotherm shows two distinct knees (Figure 52.14) connected by a region where adsorption increases linearly with the partial vapor pressure of water. The explanation for this adsorption behavior is rather complex [42] and beyond the scope of this chapter. This behavior is believed to be due to the presence of hydrated surface cation sites. 

Other possible reasons for the high experimental capacity values are the high surface area and highly organized ID structure of titania nanotube layers. When a rate of 100 pA cm (2.5C) is used, the reversible and irreversible capacities are lower than at a rate of 5 pA cm, but the capacity retention for crystalline is around 96% (close and star-shaped symbols in Fig. 5.13c Table 5.1). 

Kucheyev SO, van Buuren T, Baumarm TF, Satcher JH, Willey TM, Meulenberg RW, Feller TE, Poco JF, Gammon SA, TermineUo U (2004) Electronic structure of titania aerogels from soft x-ray abstnption... 

The fact that the solid-state reaction model applicable to the reaction between strontium carbonate and titania is dependent on the structure of titania was explained using considerations based on the process of epitaxial growth. 

Figure 11.14 Proposed structures of titania-chemisorbed siloxane chains derived from Si/ H CP-NMS ejqjeriments in Milanesi et al. [81]. It was observed that the various stmctures (di-functionalized chains) were the dominant reaction product. Reproduced with permission from [81] Copyright (2010) American Chemical Society.

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