Formation Of Anatase Nanocrystals Research Articles

Structure and Properties of Sol-Gel Derived TiO<sub>2</sub>/SiO<sub>2</sub> Films by Hot Water Treatment

TiO2/SiO2composite films were prepared by treating the sol-gel derived films with hot water. Amorphous silica was used as a binder with the aim of producing Si-O-Ti bonds. This process was done at 90°C under atmospheric pressure, and thus anatase nanocrystals-dispersed films can be formed on various kinds of substrates including organic polymers with poor heat resistance. The formation of anatase nanocrystals was found to proceed to hydrolysis of Si-O-Ti bonds. The crystalline phase, structure, morphology and photocatalytic performance of the films have been investigated.

Transformation of layered titanate nanosheets into nanostructured porous titanium dioxide in polycation solution

Nanostructured porous TiO 2 particles constructed from nanorod-like crystals were prepared from a layered titanate nanosheet precursor. The synthesis process includes two steps: construction of a porous nanostructure by assembling the nanosheets with poly (diallyldimethylammonium) (PDDA) polycations, and topotactic transformation of the nanostructured titanate nanosheets into anatase-type TiO 2 nanocrystals by hydrothermal reaction. The reaction process and nanostructured porous particles were characterized by XRD, DTA-TG, SEM, TEM analyses, and measurements of specific surface area, pore size distribution, ruthenium dye (N719) adsorption, and photocatalytic activity. The morphology of the porous particles is dependent on the PDDA concentration in the reaction system. Spherical particles constructed from nanorod-like anatase crystals can be prepared under the high PDDA concentration conditions. The topotactic transformation reaction from the titanate nanosheet to anatase resulted in the formation of anatase nanocrystals which preferentially expose the (0 1 0) plane of anatase on the surface. The surface of the nanostructured porous anatase particles shows high N719 dye adsorption ability and high photocatalytic activity, which have potential application in dye-sensitized solar cells.

Characterization of Anatase Nanocrystal-Precipitated Coatings From (100 − x)SiO2·xTiO2 Gel Films Via The Sol-Gel Process with Boiling Hot Water Treatment

Considerable amounts of anatase nanocrystals were formed on the (100 − x)SiO2·xTiO2 coatings with x of 16.5 and 25 mol% with boiling water treatment, whereas the formation of anatase nanocrystals was not clearly observed for the coatings with x of 50 and 75 mol%. Despite the lower TiO2 content, the coatings with x of 16.5 and 25 mol% showed higher concentration of Si–O–Ti bonds among the coatings. Thus, the hydrolysis of Si–O–Ti bonds and resultant sites should facilitate the nucleation and growth of anatase nanocrystals. High transparency, high photocatalytic activity, and superhydrophilicity were demonstrated for the anatase nanocrystals-precipitated coatings.

Effects of Addition of Poly(ethylene glycol) on the Formation of Anatase Nanocrystals in SiO2−TiO2 Gel Films with Hot Water Treatment

Effects of the addition of poly(ethylene glycol) (PEG) in SiO2−TiO2 gel films on the formation of anatase nanocrystals with hot water treatment were investigated. Anatase nanocrystals were formed in the whole SiO2−TiO2 gel films with the addition of PEG by the treatment, whereas in the films without PEG the nanocrystals were formed mainly on the surface of the films. PEG in the SiO2−TiO2 films was completely leached out with the hot water treatment in about 1 min. The pores produced by the leaching of PEG probably allow anatase nanocrystals to be formed inside the films. Hydrolysis of Si−O−Ti bonds was presumed to play an important role in the nucleation of anatase nanocrystals in the hot water treatment.

Photocatalytic Decomposition of Acetaldehyde with Anatase Nanocrystals-Dispersed Silica Films Prepared by the Sol-Gel Process with Hot Water Treatment

Anatase nanocrystals of 5 to 10 nm in diameter were formed in the silica-titania films by treatment with hot water. The formation of nanocrystals with hot water treatment was a unique phenomenon to the silica-titania system and the addition of organic polymers such as PEG was indispensable for the high dispersion of anatase nanocrystals in the films. The hydrolysis of Si—O—Ti bonds with hot water was considered to play an important role for the formation of anatase nanocrystals. The resultant films were transparent even after the formation of anatase nanocrystals. Acetaldehyde was photocatalytically decomposed into CO2 on the films which were subjected to a hot water treatment. The amounts of generated CO2 were twice of that of introduced acetaldehyde, indicating that the total acetaldehyde was completely decomposed to CO2. Anatase nanocrystals-dispersed films can be formed on various kinds of substrates including those with poor heat resistance such as organic polymers and organisms by this process, so that the substrates coated with the films are expected to be widely used for photocatalytic applications.

Formation of Anatase Nanocrystals in Sol-Gel Derived TiO2-SiO2 Thin Films with Hot Water Treatment

We have successfully prepared transparent and porous anatase nanocrystals-dispersed films by treating the sol-gel derived TiO2-SiO2 films containing poly(ethylene glycol), PEG, with hot water. This process was done at temperatures lower than 100°C under atmospheric pressure, and thus anatase nanocrystals-dispersed films can be formed on various kinds of substrates including organic polymers with poor heat resistance. The changes in structure and composition of the TiO2-SiO2 gel films with hot water treatment were related to the formation process of anatase nanocrystals in the TiO2-SiO2 gel films with hot water treatment. The formation of anatase nanocrystals was found to proceed to hydrolysis of Si–O–Ti bonds and dissolution of SiO2 component. In addition, porous film structure formed by leaching of PEG with hot water treatment led to homogenous dispersion of anatase nonocrystals in the films.