Photocatalytic Decomposition of Water

The detailed mechanism of forming O2 from water involves a number of elementary reaction steps, so that photoinduced interfacial coordination reactions are needed that may induce water species to form metal complexes, which are gradually oxidized and may, thereby, liberate oxygen. This may be done by introducing 

In any case, no electrode material or approach fulfills the requirements for a successful photoelectrochemical process in all respects, i.e., for routine practical use hence novel materials and approaches are constantly pursued. Note that beside the robust performance needed, the most important figure of merit for a semiconductor photoelectrode used for water splitting is the photoconversion efficiency, which is 

Suspensions of semiconductors with heterojunctions formed by CdS or solid solution ZnyCdi-yS and Cu , S have been prepared and tested as photocatalysts for photochemical hydrogen production [278]. With platinized powders of Zno.nCdo.ssS/CujS in solution containing both S and SOj ions, hydrogen was generated concomitantly with thiosulfate ions with quantum yield of about 0.5. 

Studies performed on CdS [282, 283] have revealed the importance of the microstructure, i.e., crystal structure, crystallite size, and geometrical surface area, in both the control of band structure and the concentration and mobility of charges, in relation to the photocatalytic performance of the photocatalyst. It has been shown also that the solubility product of CdS colloids prepared from acetate buffer aqueous solutions of suitable precursors increases from 7.2x 10 for large particles to about 10 for small ( 2.5 nm) particle colloids, this increase invoking a positive shift on the cathodic corrosion potential [284]. 

In situ metallization has been claimed to provide a convenient method for the preparation of metal-deposited and metal sulfide deposited CdS during photocatalytic decomposition of aqueous sulfide. As-prepared MS/CdS and M/CdS bifunctional photocatalysts (MS = Pt or Ir sulfide M = Pt or Ir) were reported to be more active photocatalysts than CdS and ex-situ metallized CdS [285]. 

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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. 

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). 

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. 

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

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

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... 

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... 

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... 

Photocatalytic decomposition of water on semiconductors is usually conducted under reduced pressure. There are arguments that 02 production is much less than stoichiometric when water photolysis is carried out under atmospheric pressure.20-34,353 Such nonstoichiometric 02 evolution is often ascribed to the photoadsorption of 02 onto semiconductor particles20,34,353 or the formation of peroxides.363 On the other hand, the electrochemical potential of H2 evolution shifts to the positive direction with increasing ambient pressure according to the Nemst equation. Therefore, pressure effect may be negatively significant for water photolysis by Ti02 photocatalysts, since tne flat band potentials of TiO are close to the potential of NHE.23,243... 

Photocatalytic decomposition of water over various metal oxides to H2 and O2 is of current interest, representing an approach to the utilization of solar energy. This catalytic system catalyzes C—C bond fission and, to a lesser extent, the hydrogenation of multiple bonds. Titania220,221 and its binary oxides222 have been studied most in the hydrogenation of simple alkenes (ethylene, propylene and butenes). This photohydrogenation activity is,... 

Photocatalytic Decomposition of Water Principles of water-splitting reviewed including a section on semiconductor-based approaches. 72... 

Photocatalytic Decomposition of Water Vapour on an NiO-SrTiCh Catalyst. A series of studies begun with this particular study which uses powdered photocatalyst. See Entries below. 392... 

Study of the Photocatalytic Decomposition of Water Vapour over a NiO-SrTiCh Catalyst. Mechanistic aspects probed by using a closed gas circulation system and IR spectroscopy (see Entries 7 and 15). 401... 

Photocatalytic Decomposition of Water into H2 and O2 over NiO-SrTiCh Powder. 1. Structure of the Catalyst. Nickel metal also found at the interface of NiO and SrTiCh. See also Entries 7,15 and 16. 404... 

Combinatorial synthesis has recently been applied to photocatalytic decomposition of water. If a formula of MiM2M30y, for example Fe203 Cr203 CS2O or Fe2Cr2Cs207, was being considered where 60 different metals were possible for Ml, M2, and M3, how many combinations are possible ... 

Maruska H. P. and Ghosh K. A. (1978), Photocatalytic decomposition of water at semiconductor electrodes . Solar Energy 20, 443 58. 

Takata, T., Shinohara, K., Tanaka, A., Kara, M., Kondo, J., Domen, K. Photocatalytic decomposition of water on spontaneously hydrated layered perovskites. J. Photochem. Photobiol. 106, 45 (1997)... 

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