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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