Water photocatalytic decomposition

Kinetic analysis based on the Langmuir-Hinshelwood model was performed on the assumption that ethylene and water vapor molecules were adsorbed on the same active site competitively [2]. We assumed then that overall photocatalytic decomposition rate was controlled by the surface reaction of adsorbed ethylene. Under the water vapor concentration from 10,200 to 28,300ppm, and the ethylene concentration from 30 to 100 ppm, the reaction rate equation can be represented by Eq.(l), based on the fitting procedure of 1/r vs. 1/ Ccm ... 

The oxidative degradation of organic pollutants in water and air streams is considered as one of the so-called advanced oxidation processes. Photocatalytic decomposition of organics found widespread industrial interest for air purification (e.g., decomposition of aldehydes, removal of NO , ), deodorization, sterilization, and disinfection. Domestic applications based on Ti02 photocatalysts such as window self-cleaning, bathroom paints that work under illumination with room light, or filters for air conditioners operating under UV lamp illumination have already been commercialized. Literature-based information on the multidisciplinary field of photocatalytic anti-pollutant systems can be found in a number of publications, such as Bahnemann s [237, 238] (and references therein). 

The photocatalytic decomposition of water was carried out in a closed gas circulation system connected to a high-vacuum line. About 200 mg of a powdered catalyst was dispersed in pure distilled water and irradiated through a water filter with an Xe lamp operated at 400 W. Hydrogen and oxygen evolved in the gas phase were analyzed by a gas chromatograph which was directly connected to the reaction system. 

Domen, K., Kudo, A., Onishi, T., Kosugi, N., and Kuroda, H., Photocatalytic decomposition of water into hydrogen and oxygen over nickel (II) oxide-strontium titanate (SrTiOj) powder. 1. Structure of the catalysts, ]. Phys. Chem., 90, 292,1986. 

Sayama, K. and Arakawa, H., Effect of carbonate salt addition on the photocatalytic decomposition of liquid water over PtTiOz catalyst, /. Chem. Soc., Faraday Trans., 93,1647,1997. 

Wu et al. (1999b) reported that the intercalated Fe Oj showed photocatalytic activity of evolution from a CH OH-HjO solution by transfer of the photoelectron from Fe Oj to the host layered compound, which decreased the recombination of electrons and holes under visible light irradiation. However, it was found in this work that hydrogen evolution under visible light was not due to photocatalytic decomposition of water (Wu et al., 1999b). 

Domen, K., Naito, S., Onishi, T., Tamaru, K. 1982. Photocatalytic decomposition of liquid water on a NiO-SrTiO, catalyst. Chem Phys Lett 92 433 34. 

Hwang, D.W., Kim, H.G., Jang, J.S., Bae, S.W., Ji, S.M., Lee, J.S. 2004. Photocatalytic decomposition of water-methanol solution over metal-doped layered perovskites under visible light irradiation. Catal Today 93-5 845-850. 

Kato, H., Kudo, A. 1999a. Photocatalytic decomposition of pure water into Hj and Oj overStTajO, prepared by a flux method. Chem Lett 11 1207-1208. 

Sayama, K., Arakawa, H. 1993. Photocatalytic decomposition of water and photocatalytic reduction of carbon-dioxide over ZrOj catalyst. J Phys Chem 97 531-533. 

With reference to Fig. 6.7, note there is no photocatalytic activity without Ft loading [99] the rate of gas evolution increases with increasing Ft content reaching a maximum at 0.3 wt%. Other metals have shown similar trends in photocatalytic activity. Therefore, it is suggested that metal loading is one of the essential requirements for photocatalytic decomposition of liquid water. However the back reaction of evolved gas on the Ft particles increases with Ft loading. To suppress the backward reaction of H2... 

Table fi.4 Photocatalytic decomposition of water over various semiconductor catalysts in NajCOi solution or pure water. 

Kawai T, Sakata T (1980) Photocatalytic decomposition of gaseous water. Chem Phys Lett 72 87-89... 

Domen K, Naito S, Soma M, Onishi T, Tamaru K (1980) Photocatalytic decomposition of water vapor on a NiO-SrTiOs catalyst. Chem Commun 543-544... 

Domen K, Kudo A, Onishi T (1986) Mechanism of photocatalytic decomposition of water into H2 and O2 over NiO-SrTiOs. J Catal 102 92-98... 

Kudo A, Domen K, Mauiya K, Aika K, Onishi T (1988) Photocatalytic decomposition of water over Ni0-K4Nb60i7 catalysts. J Catal 111 67-76... 

Sayama K, Arakawa H (1994) Effect of Na2C03 addition on photocatalytic decomposition of liquid water over various semiconductor catalysts. J Photochem Photobiol A Chem... 

Ikeda S, Kara M, Kondo JN, Domen K (1998) Preparation of K2La2Tl30io by polymerized complex method and photocatalytic decomposition of water. Chem Mater 10 ... 

A number of studies related to the spectroscopic properties of zinc and cadmium phthalocyanines in the context of the photocatalytic decomposition of water have been... 

Reaction scheme of photocatalytic decomposition of acetic acid under deaerated condition is analyzed based on the flow-rate dependence of the radical fomiation30) combined with the reported mechanism. In this scheme, CH3 radicals are formed via two reaction pathways. One is indirect oxidation via OH radicals which are formed by the oxidation of water with photoinduced holes (h+) at the valence band. Another is direct oxidation of adsorbed molecules by the hole. On the other hand, 011200011 radicals are not formed by direct oxidation but only by indirect oxidation via 0H radicals. The reaction scheme is proposed as illustrated in Fig. 5.7. 

Ti02 has three crystal forms, anatase, brookite, and rutile. Rutile is a stable form, and the others are a low-temperature form. The band gap energy of rutile is ca. 3.0 eV, while those of the other two are ca. 3.2 eV. Since an external bias was required for the photoelectrolysis of water in a Ti02(rutile)-Pt PEC cell,1 one may assume that rutile powder shows no activity for the photocatalytic decomposition of water. Yamaguti and Sato,3) found that platinized rutile Ti02 powder is active... 

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