Titania nanoparticles rutile

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... 

The observed phase selectivity phenomenon vividly shows that the crystalline phase of titania nanoparticles has a major effect on their reactivity. A similar phenomenon had been recently described for dissolution of a similar Ti02 sample in HF.16 This reaction can be used for the preparation of a pure nanoscale rutile phase for use as a photocatalyst. 

The microemulsion system water/Triton X-lOO/n-hexanol/cyclohexane has been used recently to cause reaction between TiOCl2 and NH4OH, and obtain amorphous titania nanoparticles [267]. The particles crystallized to anatase at 460°C and to rutile at 850°C. The crystallite size was 10-36 nm (500°-900°C), but the particles agglomerated easily during heating. 

AG values are nonlinear functions of the titania content because of several effects caused by textural changes of the materials and the formation of new phases (amorphous titania, anatase, and rutile) with particles of different sizes formed in pores and at the outer surface of the silica gel particles. Water becomes more strongly bound with increasing titania content (Figure 2.73). However, the AG(C J curves for all the SGT samples are above the curve for silica gel. The secondary porosity of silica gel decreases due to grafting of titania, and the peak intensity at / =40 nm of textural pores decreases (Figure 2.74), but a peak at / = 30 nm appears because of partial filling of these broad pores by titania nanoparticles. 

Cole and coworkers have also synthesized titania nanoparticles by incorporating spermidine and spermine as the condensation templates [89]. A SEM analysis of the resultant nanopartides revealed that the structures were composed of irregular polyhedra, ranging from 100 to 800 run in diameter for spermidine and from 50 to 300 nm for spermine. A powder analysis showed that both the spermidine- and spermine-templated titania nanopartides were X-ray amorphous at room temperature. Crystallization was induced at higher temperatures (800 °C). For the spermidine titania, crystalline patterns were evident at 600 °C and 800 °C (Figure 1.30), which corresponded to an anatase phase with trace amounts of rutile. 

Anatase and rutile titania nanoparticles and pigmentary titania particles were used for photooxidation studies on a metaUocene PE [4] and proved to be more photochemically active than the pigment particles. On the other hand, titania nanoparticles with enhanced photocatalytic activity (anatase) may be used in nanocomposites coatings having self-cleaning properties. 

Pressure-induced phase transformations for anatase-Ti02 were monitored by Raman spectroscopy.40 Raman spectroscopy was used to characterise rutile titania nanocrystalline particles with high specific surface areas.41 Micro-Raman spectra were used to follow surface transformations induced by excimer laser irradiation of Ti02.42 There was Raman spectroscopic evidence for modification of a titania surface by attached gold nanoparticles.43... 

Titania hollow fibrous structures can be formed as well by the use of organogel templates through either electrostatic or hydrogen bonding interactions between the template and the titanium compound [51,52]. Calcination at 450°C removes the organogel giving hollow anatase or anatase/rutile titania fibers with lengths of up to 200 pm and outer diameters between 150 and 1200 nm. The titania materials consist of crystalline nanoparticles (diameter 15-30 nm) compared with the siHca structures, which remain amorphous. 

The sample crystallinity depends mainly on the crystallinity of titania if alumina is not the main phase (Table 2.10) since silica is always amorphous (Figure 2.51). Individual titania includes both anatase and rutile (Figure 2.51b and d). For other titania-containing samples, the titania phase is composed mainly of anatase. This is of importance because the crystallinity and the type of titania phases can influence the adsorption, catalytic, and other important characteristics of the materials. Additionally, an increase in the Aw values (Table 2.10), i.e., enhancement of the surface roughness of nanoparticles and deviation of their shape from spherical, corresponds to increasing 5bet,x/ bet,n2 ratio for, e.g., X=acetonitrile. This correlation for acetonitrile is clear for 10 oxide samples from 14 ones studied. In other words, it is not strong because many structural and other effects overlap here. 

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