A Patterned TiO ₂ (Anatase)/TiO ₂ (Rutile) Bilayer‐Type Photocatalyst: Effect of the Anatase/Rutile Junction on the Photocatalytic Activity

Abstract

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] ...

Brookite versus anatase TiO2 photocatalysts: phase transformations and photocatalytic activities

“…An analogous synergistic effect is also commonly observed between anatase and rutile phases [32][33][34][35] and is moreover experimentally supported by photodeposition experiments of Ag. 36 However, in the case of brookite-rich nanoparticles, this synergistic effect has not been observed before, as pure brookite showed higher photocatalytic activity than the brookite-rich nanoparticles (see Fig. 5(c) and (d)).…”

Design and Application of Magnetic Photocatalysts for Water Treatment. The Effect of Particle Charge on Surface Functionality

“…Recent studies have shown that photoactivity of P25 exceeds that of anatase in several reaction systems [41,42]. Previously, we have also reported that TiO 2 P25, which is a mixture of anatase and rutile phases exhibited higher efficiency of phenol, pyridine and 4-heptanone degradation compared to commercial anatase particles TiO 2 ST-01 and anatase obtained from titanium isopropoxide (TIP) and titanium butoxide (TBT) hydrolysis in aqueous phase [43,44].…”

Understanding the Reaction Mechanism of Photocatalytic Reduction of CO2 with H2O on TiO2-Based Photocatalysts: A Review

“…3 shows the two typical models of charge transfer between anatase and rutile. Some literature results (Bickley et al, 1991;Kawahara et al, 2002;Wang, Bai et al, 2012) suggested that photogenerated electrons tend to transfer from anatase to rutile, because the conduction band (CB) of anatase is more negative than that of rutile ( Fig. 3(A)).…”