Titanium anatase, synthesis

Baldassari, S., Komarneni, S., Mariani, E. and Villa, C. (2005) Rapid microwave-hydrothermal synthesis of anatase form of titanium dioxide. Journal of the American Ceramic Society, 88, 3238—3240. 

Several preparation methods have been reported for the synthesis of TS-1. In this work, we have investigated the physicochemical properties of TS-1 samples synthesized by different preparation metiiods and tested these materials as catalysts for the oxidation of n-octane, 1-hexene and phenol using aqueous hydrogen peroxide (30 wt%) as oxidant at temperatures below 100 C. For comparison, Ti02 (anatase) and the octahedral titanium-containing silicate molecular sieve (ETS-10) (5) have been studied. The effect of the presence of aluminum and/or sodium on the catalytic activity of TS-1 is also discussed. 

Tomita K, Petrykin V, Kobayashi M, Shiro M, Yoshimura M, Kakihana MA (2006) Water-soluble titanium complex for the selective synthesis of nanocrystaUine brookite, rutile, and anatase by a hydrothermal method. Angew Chem Int Edit 118 2438-2441... 

Solvothermal decomposition of titanium tcrt-butoxide and titanium oxy-acetylacetonate (TiO(acac)2) in toluene at 300°C yields nanocrystalline anatase. It should be noted that the lowest temperature required for the formation of crystalline titania by CVD synthesis was reported to be 400 to 450°C. ° ° ... 

Besides alkoxides, acetylacetonates are also used as the starting materials for the synthesis of oxides. Titania (anatase) is obtained by decomposition of titanium oxyacetylacetonate (TiO(acac)2) in toluene at 300°C. Similarly solvothermal treatment of Fe(lll) acetylacetonate in toluene yields microcrystalline magnetite. One of the drawbacks of the use of acetylacetonate may be formation of various high boiling point organic by-products via aldol-type condensation of the acetylacetone. Actually more than 50 compounds are detected by gas chromatography-mass spectrometry (GC-MS) analysis of the supernatant of the reaction, some of which are phenolic compounds and are hardly removed from the oxide particles by washing with acetone. ... 

Because of its many applications, a few attempts are known in which ultrasonic waves have been applied for the synthesis of nanosized titania. Yu and coworkers [126] discovered a novel method for preparing highly photoactive nano-sized Ti02 photocatalysts with anatase and brookite phases. The method has been developed by hydrolysis of titanium tetraisopropoxide in pure water or a 1 1 Et0H H20 solution under ultrasonic irradiation the photocatalytic activity of Ti02 particles prepared by this method exceeded that of Degussa P25. 

The addition of increasing amount of NaOH to a solution of high purity tetrapropylammonium hydroxide, was showed to produce an increase of the amount of Ti detected in the solid recovered at the end of the synthesis and a decrease of the 960 cm UR band [21]. At the highest level of sodium, the presence of anatase beside the silicalite crystals, was revealed by X-ray diffraction analysis. The presence of sodium in the reaction mixture seems to favour the formation of insoluble titanium-silicate species which reduce the amount of titanium available for the formation of the TS-1 crystals. 

Titanium (IV) oxide crystallizes In three modifications of decreasing stability rutile, anatase and brookite. Whether the synthesis of brookite has been achieved is still in doubt. Anatase is formed via the hydrolysis of Ti halides at not too high a temperature (600°C) or via low-temperature calcining ( 700°C) of precipitated titanic acid. The lattice is stabilized by adsorbed anions, among which the most effective are sulfate and phosphate. Pure TiOg calcined at high temperature always yields the rutile lattice. 

T. Peng, D. Zhao, K.D.W. Shi, K. Hirao, Synthesis of titanium dioxide nanoparticles with mesoporous anatase wall and high photocatal3dic activity . Journal of Physical Chemistry B, 109 (11), 4947-4952, (2005). 

Unfortunately, Ti(IV) forms hydroxides of low solubility. In order to avoid precipitation during the synthesis of Ti-MFI the admixture of complexing agents like acetylacetone has been studied [73]. Due to the DR spectra acetylacetone admission resulted in a higher amount of framework titanium (212 nm), again in the absence of anatase, and in a distinct reduction of extraframework Ti species, e.g., like octahedrally coordinated titanium (274 nm). 

Titanium has also been incorporated into ordered mesoporous silicas of the SBA-15 type (126). The influence of synthesis parameters on the properties of titanium-substituted SB A-15 silicas prepared by a direct one-step synthesis (cocondensation) was systematically investigated (127) through characterizing the products by N2 physisorption, XRD, diffuse reflectance UV-vis spectroscopy, and elemental analysis. The results showed that when a low titanium precursor concentration (i.e., less than 0.05 mol/1) was used in the initial synthesis gel, incorporation of titanium into the solid was not completed. Under these conditions, titanium ions were well dispersed in the silica framework and present mainly in tetrahedral coordination in the product. When the isolated titanium species present in the gel reached a critical concentration, an increase in titanium incorporation into the sofid was observed as a consequence of the formation of anatase clusters on the material s surface. The titanium loading at which anatase formation was observed was found to he strongly influenced by the synthesis conditions. Moreover, when the formation of anatase takes place, the amorphous titanium species... 

A two-microemulsion method was employed by Chhabra et al. [266] for synthesis of titania particles. A surfactant, Triton X-100 and a co-surfactant, n-hexanol were mixed with cyclohexane, the oil phase, to obtain reverse micelles. In one of these, an aqueous solution of titanium tetrachloride (0.3M) formed the microemulsion core in the other, an ammonia solution was added. The two microemulsions thus obtained were mixed under vigorous stirring at room temperature to start a precipitation reaction leading to the formation of hydroxide precursor particles. The particles were collected by centrifugation and washed with chloroform and methanol. The anatase particles obtained at 700°C had a size... 

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