Photocatalyst Rutile

Titania photocatalyst is used for air and water purification, photo-splitting of water to produce hydrogen, odor control and disinfectant. Crystal structure and crystallite size of titania particles are one of the most important factors that affect on the photoactivity. Photoactivity of anatase is higher than that of rutile, and increases with crystallite size [1]. Therefore, to increase photoactivity, it is desirable to find a route for the synthrais of the pure anatase titania with large crystallite size. 

In the past few years, a large number of experimental and theoretical studies have focused on metal oxide surfaces with the aim of gaining insight into their catalytic, photocatalytic, and gas-sensing activity [68]. Owing to its thermodynamic stability and relatively easy preparation, the rutile Ti02(l 10) surface has evolved into one of the key models for metal oxide surfaces. For example, it has been extensively used in the research of biocompatible materials, gas sensors, and photocatalysts [69]. 

Figure 4.12 Schematic representation of the proposed reaction mechanism for overall photocatalytic water splitting using 03 - redox mediator and a mixture of Pt-Ti02-anatase and Ti02-rutile photocatalysts. Adapted from [161] (2001) with permission from Elsevier.

Solar light photocatalytic hydrogen production from water over Pt and Au/Ti02 (anatase/rutile) photocatalysts influence of noble metal and porogen promotion. Journal of Catalysis, 269 (1), 179—190. 

Abe, R., Sayama, K., Domen, K., and Arakawa, H. (2001) A new type of water splitting system composed of two different Ti02 photocatalysts (anatase, rutile) and a IOj"/r shuttle redox mediator. Chemical Physics Letters, 344 (3-4), 339-344. 

Various pairs of inorganic ions such as lOsVr, Fe /Fe, and Ce /Ce have been used as redox mediators to facilitate electron-hole separation in metal loaded oxide semiconductor photocatalysts [105-107], Two different photocatalysts, Pt-Ti02 (anatase) and Ti02 (rutile), suspended in an aqueous solution of Nal were employed to produce H2 and O2 under, respectively, the mediation of 1 (electron donor) and IOs (electron acceptor) [105]. The following steps are involved in a one-cell reaction in the presence of UV light. 

Liu H, Gao L (2004) (Sulfur, Nitrogen)-codoped rutile-titanium oxide as a visible-light-activated photocatalyst. J Am Ceram Soc 87 1582-1584... 

Liu HY, Gao L (2004) Codoped rutile Ti02 as a new photocatalyst for visible light irradiation. Chem Lett 33 730-731... 

In passing, we note that reaction 17.39 is also used in the conversion of natural rutile ore, which is usually red-brown because of its iron(III) content, to pure Ti02, which is used as a filler for paper, as a white pigment in paints, and as a photocatalyst (Sections 10.4 and 14.4.2). The high optical refractive index gives Ti02 the best available covering power in... 

Chemoselecti vity could potentially be achieved if the oxidation potential of a desired donor adsorbate lies between the valence band edges of two possible semiconductor photocatalysts. Since TiOj has a more positive valence band edge than does CdS, it should be the more active photocatalyst. Consistent with this idea, decarboxylation of organic acids, Eq. (5), is much more efficient on irradiated suspensions of rutile than of CdS... 

The photocatalytic properties of Ti02 strongly depend on the preparation conditions. It has been reported that the activity of photocatalysts is affected by the conditions of heat treatment and by the crystal structure, which changes from anatase to rutile by the heat treatment.16) To obtain more useful Ti02 powders, it is necessary to clarity the factors which cause the differences in photocatalytic activity. 

Heterogeneous photocatalytic reaction products and their production rates depend on the kind of photocatalysts. As noted above, each photocatalyst powder has different properties. In the case of the sonophotocatalytic reaction, products or their yields also depend on the kind of photocatalysts. The effect of surface area on product ratio was discussed in section (12.2.1C). The influence of surface area on product ratio was noted, but factors other than surface area must be introduced to explain the difference in product ratios. It is known that there are several crystal structures of Ti02. The major structures are anatase and rutile. 2... 

Fig. 12.2 Time dependencies of sonophotocatalytic reaction products from pure water. As powdered photocatalyst, Ti02-A (200mg, Soekawa, Commercial Reagent, rutile-rich type and specific surface area 1.9 m2/g) was used without further treatment. Liquid water (150 cm3, Wake, Distilled water for HPLC was used as reactant and was purged with argon, a Pyrex glass bulb (250-300 cm3) was used as a reactor and was placed m a temperature-controlled bath (EYELA NTT-1200 and ECS-0) all time. After the glass bulb was sealed, the irradiation was carried out under argon atmosphere at 35°C. Photo and ultrasonic irradiations were performed from one side with a 500 W xenon lamp (Ushio, UXL500D-O) and from the bottom with an ultrasonic generator (Kaijo. TA-4021-4611, 20C kHz 200 W), respectively.

Titanium dioxides The most common forms of titanium dioxide (TiCL) are rutile, anatase, and brookite. Brookite is orthorhombic, whereas rutile and anatase are tetragonal (PAflmnm and lAfamd space groups, respectively) (Klein, 2002, 383-384). Titanium dioxides may sorb both As(III) and As(V) from water. The compounds are also important photocatalysts in the oxidation of As(III), MMA(V), and DMA(V) to inorganic As(V) in water (Nakajima et al., 2005 Xu, Cai and O Shea, 2007). 

Niobium-doped Ti02 has been used both as a appropriate material for rutile masers [224, 225], and as a photocatalyst for water cleavage processes [46]. Nb4+, Ta4+ and Ce4+ substituted the Ti4+ ions in the lattice, and Nb4+, Ta4+ at helium temperatures had short 7) times suitable for maser applications [224]. 

This material is often regarded as a standard T1O2 photocatalyst [57,71], Nevertheless T1O2 in the form of rutile, as well as an amorphous material, shows a certain activity. Recently the third T1O2 phase, brookite, has also attracted some interest [72],... 

The observed phase selectivity phenomenon vividly shows that the crystalline phase of titania nanoparticles has a major effect on their reactivity. A similar phenomenon had been recently described for dissolution of a similar Ti02 sample in HF.16 This reaction can be used for the preparation of a pure nanoscale rutile phase for use as a photocatalyst. 

Ohno, T., T. Tsubota, M. Toyofuku and R. Inaba (2004b). Photocatalytic activity of a Ti02 photocatalyst doped with C4+ and S4+ ions having a rutile phase under visible light. Catalysis Letters, 98(4), 255-258. 

Upon stirring a suspension of titania powders in an aqueous solution of H2[PtCl6] in the dark, different maximum amounts were adsorbed. For the anatase hydrate and anatase/rutile samples TH (Kronos) and P25 (Degussa), there were taken up 4.0% and 1.1%, respectively, whereas only traces were adsorbed onto the rutile material Aid. The almost four times larger amount adsorbed by TH corresponds with the about four times larger surface area as compared to P25 (vide infra). Subsequent heat treatment at 200 °C afforded the desired photocatalyst (21). Surface modification may be performed also by simple grinding with PtCU, but the resulting powders are of lower photocatalytic activity and less stability (18,20). 

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