Titania particle

The crystallite size of the particles prepared at different HNO3 and TENOH concentration can be determined by the Scheirers equation [5] and is listed in Table 1. The titania particles prepared using... 

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. 

Titania photocatalyst is used for air and water purification, photo-splitting of water to produce hydrogen, odor control and disinfectant. Crystal structure and crystallite size of titania particles are one of the most important factors that affect on the photoactivity. Photoactivity of anatase is higher than that of rutile, and increases with crystallite size [1]. Therefore, to increase photoactivity, it is desirable to find a route for the synthrais of the pure anatase titania with large crystallite size. 

Various methods are applied to the synthesis of titania particles including sol-gel method, hydrothermal method [2], citrate gel method, flame processing and spray pyrolysis [1]. To utilize titania as a photocatalyst, the formation of ultrafme anatase titania particles with large crystallite size and large surface area by various ways has been studied [4]. 

In this work, flame spray pyrolysis was applied to the synthesis of titania particles to control the crystal structure and crystallite size and compared with the particle prepared by the conventional spray pyrolysis... 

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. 

Fig. 1. XRD patterns of titania particles by conventional spray pyrolysis wife various preparation tempaatures.

The reason for the formation of anatase phase at such a high temperature might be explained as following. The as-prqiared ultrafine titania particles are liquefied at sufficimtly high temperature because melting point of nanoparticlra are lower than that of bulk titania (1850 C). The liquid titania particles are supercooled and became metastable states. The residence time in the flame is only in the order of miU-second so that the metastable phase has no time to become thermodynamically stable phase, rutile. 

Another distinguishing feature of titania prepared by flame spray pyrolysis is the draar e of anatase crystallite size with the increase of flame temperature. Generally, the increase of preparation temperature increases the crystallite size in other processes such as sol-gel method, hydrothermal method [2, 3], flame processing and conventional spray pyrolysis. The decrease of crystallite size was directly related to the decrease of particle size. Fig. 5 shows SEM and TEM images of titania particles prepared by flame spray pyrolysis. 

At low temperature flame, as-prepared titania particles had bimodal particle size. However,... 

Fig. 5. SEM images of titania particles prepared by flame spray pyrol is with various flame ten jeratures (a) 900TC (b) llOOt (c) 1400r (d) 1600t (e) IQOOTC (f) TEM image of titania particles at 160013...

Compared with the conventional spray pyrolysis, flame spray pyrolysis produces titania particles that are strikingly different in crystd phase and surfece arra. The fraction of anatase phase increases with the increase of flame tempCTature while it decreases with the increase of preparation temperature in the conventional spray pyrolysis. The sur e area and... 

Rajeshwar and co-workers performed photocatalytic underpotential deposition of Cd and Pb onto the surface of Se-modified Ti02 particles to prepare CdSe/Ti02 and PbSe/Ti02 composites [97, 98]. The Se-modified Ti02 particles were prepared themselves by UV illumination of titania particles in a Se(fV)-containing aqueous solution. The photocatalytic UPD of Cd and Pb on the bare Ti02 surface was found... 

First, the selective deposition method was developed. It is the novel preparation technique, where the maximum loading around 20 wt% with keeping the particle size below 2nm [14]. Figure 6 shows Pt metal particles supported on monodispersed spindle titania particles. 

Figure 4.11 Schematic representation of a photocatalytic reaction occurring on a titania particle on which Pt nanoparticles have been deposited. Adapted from [160] with permission from Springer Science and Business Media.

The presence of titania particles in sunscreens was the main reason for the investigation of its dermal penetration properties, and a study suggested that fine particles (10-50 nm) can penetrate the skin, although the sample size was too small to... 

Li, Y. and Kim, S.J. (2005) Synthesis and characterization of nano titania particles embedded in mesoporous silica with both high photocatalytic activity and adsorption capability. Journal of Physical Chemistry B, 109, 12309-12315. 

We also include in this class of quasi-2D nanostructured materials Titania deposited inside ordered mesoporous silica (because an inner coating of mesoporous silica may be realized), or nano-dot type Titania particles well dispersed in the ordered porous matrix. We do not consider here solids which contain linear or zig-zag type TiOTiO-nanowires in a microcrystalline porous framework, such as ETS-4 and ETS-10, notwithstanding the interest of these materials also as photocatalysts,146-151 because these nanowires are located inside the host matrix, and not fully accessible from the gas reactants (the reactivity is essentially at pore mouth). 

Figure 12.1 Generation of photocatalytic active species at the surface of titania particles (NHE = normal hydrogen electrode).

Ti02 nanotubes were used to support M0O3 observing a spontaneous dispersion of molybdenum-oxide on the surface of nanotubes, which was different from that observed on titania particles.Supporting tungsten oxides a preferential orientation of the (002) planes was observed. Vanadium-oxide in the form of nanorods could be prepared using the titania nanotube as structure-directing template under hydrothermal... 

Finally the aerosol process could be used to coat particles, as exemplified in the system of titania cores and polyurea shells (39). In this case the titania particles were generated from Ti(IV) ethoxidc as described earlier, then contacted with dried... 

The opposed-flow situation has been used very successfully to study the structure of flames as a function of fluid mechanical strain rates. Figure 6.20 illustrates one such flame experiment. Here flow issues from two porous plates in an opposed-flow configuration. The velocity leaving each plate is uniform across the plate surface and the temperature and composition is also uniform. One flow stream is air and the other contains methane, and both streams are seeded with small titania particles. By illuminating the flow with a sheet of laser light, we see streak lines that are formed by the particles as they follow the flow. In the... 

Fig. 6.20 Experimental particle paths in an opposed stagnation flow. A mixture of 25% methane and 75% nitrogen issues upward from the bottom porous-plate manifold and a mixture of 50% oxygen and 50% nitrogen issues downward from the top porous-plate manifold. The inlet velocity of both streams is 5.4 cm/s. Both streams are seeded with small titania particles that are illuminated to visualize the flow patterns. The upper panel shows cold nonreacting flow that is, the flame is not burning. In the lower panel, a nonpremixed flame is established between the two streams. Thermal phoresis forces the particles away from the flame zone. The fact that the flame region is flat (i.e., independent of radius) illustrates the similarity of the flow. Photographs courtesy of Prof. Tadao Takeno, Meijo University, Nagoya, Japan, and Prof. Makihito Nishioka, Tsukuba University, Tsukuba, Japan.

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