Photoinduced reactivity of titanium dioxide

High purity, spherical anatase nanocrystals were prepared by a modified sol−gel method. Mixing of anhydrous TiCl4 with ethanol at about 0 °C yielded a yellowish sol that was transformed into phase-pure anatase of 7.7 nm in size after baking at 87 °C for 3 days. This synthesis route eliminates the presence of fine seeds of the nanoscale brookite phase that frequently occurs in low-temperature formation reactions and also significantly retards the phase transformation to rutile at high temperatures. Heating the as-is 7.7 nm anatase for 2 h at temperatures up to 600 °C leads to an increase in grain size of the anatase nanoparticles to 32 nm. By varying the calcination time from 2 to 48 h at 300 °C, the particle size could be controlled between 12 and 15.3 nm. The grain growth kinetics of anatase nanoparticles was found to follow the equation, D2 − D02 = k0tme(-Ea/RT) with a time exponent m = 0.286(±9) and an activation energy of Ea = 32 ± 2 kJ·mol-1. Thermogravimetric analysis in combination with infrared an...

High Purity Anatase TiO2 Nanocrystals: Near Room-Temperature Synthesis, Grain Growth Kinetics, and Surface Hydration Chemistry

Ru doped anatase supported on silica was prepared by solid-state dispersion method and examined for the photocatalytic reduction of carbon dioxide in aqueous medium at ambient conditions. To assist in interpreting the photocatalytic behaviour of Ru-TiO2/SiO2, reference systems consisting of Ru doped TiO2 and TiO2 supported on SiO2 were also analyzed and the conditions were optimized. Ru/TiO2 photocatalysts with metal loadings of 0.1, 0.3, 0.5 and 1.0 wt% were prepared by impregnation method and a series of TiO2/SiO2 catalysts with low TiO2 (1, 3, 5 and 10 wt%) contents were prepared by solid-state dispersion method. The photocatalysts were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), UV–vis DRS, FT-IR and Raman spectroscopy. The results showed that TiO2 particles with Ru ions have higher photocatalytic activity than undoped TiO2 and the optimum Ru loading was found to be 0.5 wt%. Nevertheless, the yield increased notably when TiO2 was supported on SiO2. This strong enhancement suggests that in 10 wt% TiO2/SiO2 the efficiency of charge separation is strongly influenced through the presence of Ti O Si bridging bonds. On the contrary, Ru-TiO2/SiO2 has no significant improvement in activity over TiO2/SiO2 except that it shows nearly quadruple times higher activity for the formation of methanol than Ru/TiO2. The difference in the photocatalytic activity is related to its physico-chemical properties.

Photocatalytic performance of Ru doped anatase mounted on silica for reduction of carbon dioxide

Iron(III)-doped titanium dioxide photocatalysts were prepared from aqueous titanium(III) chloride solution in the presence of dissolved FeCl3 (0–10.0 at.% relative to TiCl3) by co-precipitation method. The precipitate was completely oxidized in the aerated suspension, hydrothermally treated, washed and calcinated. The structure of the powders was characterized by thermoanalysis (TG-DTA), diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), nitrogen adsorption and transmission electron microscopy (TEM). The light absorption of the iron-containing powders is red shifted relative to the bare sample. The particle size and anatase content were found to significantly decrease at iron contents ≥6.0 at.% which is accompanied with the increase of their specific surface area. XANES measurements showed that the local structure of iron systematically changes with the variation of the dopant concentrations: at higher Fe-contents, hematite- or goethite-like environments were observed, consistent with the formation of separate X-ray amorphous Fe(III)-containing phases. The local structure of iron gradually transformed with decreasing dopant concentrations, possibly due to substitution of Fe(III) in the titania (TiO2) crystal lattice. Energy dispersive X-ray analysis (EDX) and chemical analysis was used to characterize the iron content of the samples in the bulk and X-ray photoelectron spectroscopy (XPS) in the surface layer of the particles. The photocatalytic performance of the prepared photocatalysts was compared with the activity of Aldrich anatase under UV–vis and VIS irradiation in two different photoreactors. Maximum photocatalytic performance was found at 3.0 at.% iron concentration for UV–vis and at 1.2 at.% for VIS irradiation. Doping with iron(III) ions increased the photodegradation rate of phenol by a factor of three for UV–vis irradiation and by a factor of two for VIS irradiation, relative to the bare photocatalyst.

Synthesis, structure and photocatalytic properties of Fe(III)-doped TiO2 prepared from TiCl3

The subject of this report is chemistry and engineering for the application of heterogeneous photocatalysts. The state of the art in catalysts are forms of titanium dioxide or modifications thereof, but work on other heterogeneous catalysts is included.

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Bibliography of Work on the Heterogeneous Photocatalytic Removal of Hazardous Compounds from Water and Air

Titania-coated silica microspheres containing 0.5-3.0 theoretical layers of TiOZ have been prepared by homogeneous precipitation of Tit&. All these x Ti02-SiOz materials were characterized by X-ray diffraction and FT-Raman spectroscopy. TiOz species are distributed on the surface as small anatase crystals and possess a titania-like behavior with a performance equivalent to that of bulk TiOz for the photodegradation of phenol. The fraction of used titania is higher than that on bulk catalysts and the absorption of the irradiation by excess titania is prevented. The crystal size of titania particles is critical for optimum performance of the catalyst, since it determines the appropriate surface exposure of titanium sites. A minimum size appears to be required to efficiently mineralize phenol. 0 1997 Elsevier Science B.V.

http://www.biblioteca.uma.es/bbldoc/articulos/16719128.pdf

Photodegradation of phenol in water using silica-supported titania catalysts

http://atarazanas.sci.uma.es/docs/articulos/16670498.pdf

Morphological and structural characterization of a titanium dioxide system

http://www.biblioteca.uma.es/bbldoc/articulos/16723338.pdf

E Pardo

Papers

Photodegradation of phenol in water using silica-supported titania catalysts

Morphological and structural characterization of a titanium dioxide system

Laser induced breakdown spectrometry of vanadium in titania supported silica catalysts.