Semiconductor photocatalysts have recently attracted much interest because of their possible applicability to detoxification of environmental pollutants [1] and solar-energy conversion. [2] Among the photocatalysts, TiO 2 is believed to be the most promising presently known material because of its superior photoreactivity, nontoxicity, long-term stability, and low price. The photocatalytic activity of TiO 2 depends on various parameters, including crystallinity, impurities, surface area, and density of surface hydroxy groups; however, the most significant factor is its crystal form. [3] TiO 2 is usually used as a photocatalyst in two crystal structures: rutile and anatase. Anatase generally has much higher activity than rutile. [4] More interesting is the fact that the activity of P-25 (Degussa), which consists of anatase and rutile (4/1 w/w), exceeds that of pure anatase in several reaction systems. [3b, 5] Indeed, P-25 has frequently been used as a benchmark for photocatalysts.However, the origin of the high photocatalytic activity of P-25 remains unclear. Here we report on the fundamental mechanism and present a highly active photocatalyst film designed on the basis thereof. Thin films of photocatalysts not only serve as models of particulate systems but also aid in the development of their applications. [1b] Addition of 1-phenyl-1,3-butanedione (BzCH 2 Ac) to a solution of Ti(OC 4 H 9 ) 4 in methanol led to a red shift of the absorption peak for the p ± p* transition of BzCH 2 Ac from 310 to 360 nm, owing to chelation of Ti 4 . After hydrolysis, the resultant sol was used to form a gel film in which the chelate bonds were kept intact. Significant lower solubility of the gel film in alcohol was induced by photoexcitation of the p ± p* absorption band. [6] Patterned (pat-) TiO 2 films were prepared by utilizing this phenomenon. The dimensions of the patterning are expressed by the width w of the stripes of the TiO 2 film and their spacing s. Figure 1 shows a 3D surface-structure photograph of a sample formed on quartz by using a photomask with slits of 0.2 mm in width. Regularly spaced, Figure 1. Three-dimensional surface-structure photograph of pat-TiO 2 (A)/ quartz (w s 0.2 mm). 0.2 mm wide stripes of TiO 2 film with a thickness of about 65 nm are present on the substrate with a spacing of 0.2 mm (TiO 2 /quartz; w s 0.2 mm).X-ray diffraction (XRD) patterns are shown in Figure 2 A for a sputter-deposited TiO 2 (sp-TiO 2 ) film (a) and a sol ± gel TiO 2 (sg-TiO 2 ) film overlaid on the sp-TiO 2 film (b). In pattern (a), the diffraction peaks from the (110) and (211) Figure 2. A) X-ray diffraction patterns of the sp-TiO 2 film (a) and the sg-TiO 2 /sp-TiO 2 film (b). B) Plots of (ahn) 1/2 vs photon energy for the sg-TiO 2 (a) and sp-TiO 2 (b) films. planes of rutile are observed at 2 q 27.4 and 54.38, respectively. The peak intensity ratio I(211)/I(110) is much smaller than that of randomly oriented rutile powder (ca. 0.6) [7] and suggests that the sp-TiO 2 film has a preferred orientation towards the [001]...

Semiconductor photocatalysts have recently attracted much interest because of their possible applicability to detoxification of environmental pollutants [1] and solar-energy conversion. [2] Among the photocatalysts, TiO 2 is believed to be the most promising presently known material because of its superior photoreactivity, nontoxicity, long-term stability, and low price. The photocatalytic activity of TiO 2 depends on various parameters, including crystallinity, impurities, surface area, and density of surface hydroxy groups; however, the most significant factor is its crystal form. [3] TiO 2 is usually used as a photocatalyst in two crystal structures: rutile and anatase. Anatase generally has much higher activity than rutile. [4] More interesting is the fact that the activity of P-25 (Degussa), which consists of anatase and rutile (4/1 w/w), exceeds that of pure anatase in several reaction systems. [3b, 5] Indeed, P-25 has frequently been used as a benchmark for photocatalysts.However, the origin of the high photocatalytic activity of P-25 remains unclear. Here we report on the fundamental mechanism and present a highly active photocatalyst film designed on the basis thereof. Thin films of photocatalysts not only serve as models of particulate systems but also aid in the development of their applications. [1b] Addition of 1-phenyl-1,3-butanedione (BzCH 2 Ac) to a solution of Ti(OC 4 H 9 ) 4 in methanol led to a red shift of the absorption peak for the p ± p* transition of BzCH 2 Ac from 310 to 360 nm, owing to chelation of Ti 4 . After hydrolysis, the resultant sol was used to form a gel film in which the chelate bonds were kept intact. Significant lower solubility of the gel film in alcohol was induced by photoexcitation of the p ± p* absorption band. [6] Patterned (pat-) TiO 2 films were prepared by utilizing this phenomenon. The dimensions of the patterning are expressed by the width w of the stripes of the TiO 2 film and their spacing s. Figure 1 shows a 3D surface-structure photograph of a sample formed on quartz by using a photomask with slits of 0.2 mm in width. Regularly spaced, Figure 1. Three-dimensional surface-structure photograph of pat-TiO 2 (A)/ quartz (w s 0.2 mm). 0.2 mm wide stripes of TiO 2 film with a thickness of about 65 nm are present on the substrate with a spacing of 0.2 mm (TiO 2 /quartz; w s 0.2 mm).X-ray diffraction (XRD) patterns are shown in Figure 2 A for a sputter-deposited TiO 2 (sp-TiO 2 ) film (a) and a sol ± gel TiO 2 (sg-TiO 2 ) film overlaid on the sp-TiO 2 film (b). In pattern (a), the diffraction peaks from the (110) and (211) Figure 2. A) X-ray diffraction patterns of the sp-TiO 2 film (a) and the sgTiO 2 /sp-TiO 2 film (b). B) Plots of (ahn) 1/2 vs photon energy for the sg-TiO 2 (a) and sp-TiO 2 (b) films. planes of rutile are observed at 2 q 27.4 and 54.38, respectively. The peak intensity ratio I(211)/I(110) is much smaller than that of randomly oriented rutile powder (ca. 0.6) [7] and suggests that the sp-TiO 2 film has a preferred orientation towards the [001] ...

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Ultrafine spherical titanium, silicon, and aluminium oxide particles were prepared by the thermal decomposition of their alkoxide vapors, produced by evaporation and subsequent heating. High-concentration ultrafine particles having geometric mean diameters ranging between 0.01 and 0.06 pm and a geometric standard deviation of about 1.4 were obtained by varying the temperatures of the evaporator containing the liquid alkoxides and the reactor furnace, and the flow rate of carrier gas. For furnace temperatures lower than 400°C for TiO, and 1000°C for SiO, and AI,O,, the particles obtained were found to be amorphous. The observed changes in the particle size distributions due to changes in operating conditions were compared with those predicted theoretically by solving the discrete-continuous aerosol general dynamic equation accounting for coagulation and generation of monomer by thermal decomposition. The effect of monomer number concentration on the size distribution of generated particles was found to be qualitatively explained.

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