Anatase-rutile mixtures

We have studied nanorutile samples with surface area ranging from 1758-5833 m/mol. The transformation enthalpies versus the surface area gives surface enthalpy of 2.2 J/m (see Fig. 6). A nanoanatase sample (-12000 m /mol) and a nanobrookite sample (-6400 rn/mol) have enthalpies of 7.02 0.96 kJ/mol and 7.75 1.12 kJ/mol, respectively, relative to bulk rutile (see Table 4). Efforts to deconvolute surface energy and transformation enthalpy of anatase and brookite from the energetics of these samples and of nanophase anatase-rutile mixtures and anatase-brookite mixtures are in progress. 

Properties XRD pattern available, anatase-rutile mixture [2112]. 

Hydrothermal Phase Transformation from Anatase to Rutile the phase transformation from anatase to rutile was investigated under various hydrothermal conditions by using as-hydrothermally-synthesized nanocrystals of pure anatase or mixture of anatase and rutile as starting materials. 

Very recently, mesoporous Ti02 with anatase, rutile, bicrystalline mixture (anatase and rutile) with controlled phase composition, and tricrystalline mixture (anatase, rutile, and brookite) were reported by using triblock copolymer as template and TiCLi as precursor. The resulting crystalline titanias are thermally stable and have high surface area and large pore size up to 16 run. 

S. Bakardjieva, J. Subrt, V. Stengl, M. Dianez, M. Sayagues, Photoactivity of anatase-rutile Ti02 nanocrystalline mixtures obtained by heat treatment of homogeneously precipitated anatase . Applied Catalysis B Environmental, 58, 193-202, (2005). 

Under UV light, all forms of titania oxidize propane to carbon dioxide. The conversion was followed by periodical illumination with dark periods of 5 min during which propane was found to be the only weakly adsorbed in the dark. Analysis of the carbon mass balance (Figure 4.2) obtained by online MS indicates the formation and accumulation of intermediate reaction products at the catalyst surface whose concentration increases with reaction time in the order anatase > rutile >= mixed anatase/rutile > P25. Taking into account the specific surface areas, the turn over number (TON) increases in the order anatase (9) rutile (15) P25 (112). The activity of titania P25 is higher by a factor of 10 compared to rutile, anatase, or their physical mixture. 

The anatase-rutile transition is not observed in supported samples. This transition is generally catalyzed by oxide mixture we conclude that y-alumina support hinders the crystallization of the TiOj anatase structure, in agreement with DRX data. 

The first studies on porous powders [22-27] proposed the preparation of crystalline powders in the form of anatase, rutile, or a mixture of the two and studied the best conditions for obtaining high specific surfaces and pore size in the range of mesopores, confirming the increase in the efficiency of the photocatalytic process. 

A simple approach to prepare doped Ti02 powders relies on mixing a titanium alkoxide with a solution of the dopant precursor (namely, vanadium oxychloride) in dichloromethane. Then the solvent is evaporated, and either Ti isopropoxide or Ti tetrachloride is added. After reacting the final mixture with water and acetone, the powders are dried and calcined. Thick film sensors are fabricated by screen printing a paste of annealed powders surprisingly, the vanadium doping facilitates the anatase-rutile transition, in contrast to what has... 

The physical properties of the solids obtained by thermohydrolysis of TiCU in aqueous solutions are strongly influenced by the synthetic variables. In particular, acidity, presence (and nature) of anions, and titanivun concentration govern the composition and the photoreactivity of the Ti02 photocatalysts (Cheng et al., 1995 Koelsch et al., 2004). Depending on the e>q)erimental conditions, ratile or anatase, binary mixtures of anatase and rutile or anatase and brookite, or temaiy mixtures of anatase, brookite and ratile, can be obtained. Table 1 shows the crystal phase composition of some selected samples prepared under different experimental conditions. 

McEvoy JG, Cui W, Zhang Z (2013) Degradative and disinfective properties of carbon-doped anatase-rutile Xi02 mixtures under visible light irradiation. Catal Xoday 207 191-199... 

Figure 4.12 Schematic representation of the proposed reaction mechanism for overall photocatalytic water splitting using 03 - redox mediator and a mixture of Pt-Ti02-anatase and Ti02-rutile photocatalysts. Adapted from [161] (2001) with permission from Elsevier.

X-ray diffraction conducted on the codeposited powder revealed that the deposit obtained from a suspension of gamma alumina, which had been partially converted to the alpha phase, contained both phases of alumina. Whereas, the powder codeposited from a suspension having a 50 50 mixture of alpha to gamma alumina powder, consisted only of the alpha phase. Using a parallel plate electrode configuration, Chen et al. [31] concluded that only alpha alumina can be codeposited. Chen also observed a difference in codeposition with copper when using two different phases of the titanium oxide particle system rutile readily codeposited but anatase titania did not... 

This chapter has been concerned mainly with the chemistry of making pigments but has also stressed the importance of preparing them in the correct physical form. In the case of those pigments which can be made in more than one crystal form, such as the anatase and rutile forms of titanium dioxide, this may mean that all the pigment should be in one form only. In others, a mixture of polymorphic forms may be required, and it is then necessary to ensure that the desired ratio of these forms is present. 

Infrared spectra suggested that a sulfate ion coordinates to two titanium atoms as a bidentate in particles. The maximum particle size was found at Aerosol OT mole fraction of 0.35 in the mixtures. The particle size increased linearly with increasing the concentration of sulfuric acid at any Wo, but with increasing Wo the effect was the opposite at any sulfuric acid concentration. These effects on the particle size can be explained qualitatively in relation with the extent of number of sulfate ions per micelle droplet. These precursor particles yield amorphous and nanosized TiO particles, reduced by 15% in volume by washing of ammonia water. The Ti02 particles transformed from amorphous to anatase form at 400°C and from anatase form to rutile form about at 800°C. In Triton X-100-n-hexanol-cyclohexane systems, however, spherical and amorphous titanium hydroxide precursor were precipitated by hydrolysis of TiCl4 (30). When the precursor particles were calcinated,... 

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