Photocatalysts semiconductors

Sabate J, Cervera-March S, Simarro R, Gimenez J (1990) A comparative study of semiconductor photocatalysts for hydrogen production by visible light using different sacrificial substrates in aqueous media. Int J Hydrogen Energy 15 115-124... 

BorreU L, Cervera-March S, Gimenez J, Simarro R, Andujar JM (1992) A comparative study of CdS-based semiconductor photocatalysts for solar hydrogen production from sulphide + sulphite substrates. Sol Energy Mater Sol Cells 25 25-39... 

Semiconductor photocatalysts in a form of colloids, powders, porous granules, thin films or bulk solids including single crystals (used in model studies) provide both liquid phase and gas phase transformations. Comprehensive reviews in this field can be found in monographs [4] (Chapters by N.S.Lewis and M.L.Rosenbluth M.Gratzel M.Schiavello and A.Sclafani P.Pichat and J.-M.Herrmann G.A.Somorjai T.Sakata H.Tributsch M.A.Fox H.Al-Ekabi and N.Serpone D.F.Ollis, E.Pelizzetti and N.Serpone) [8] (Chapter by Yu.A.Gruzdkov, E.N.Savinov and V.N.Parmon) and [3]. 

Recently was estimated an expected impact on the global chemistry of the atmosphere of the indirect heterogeneous photocatalytic reactions under the much more abundant near ultraviolet, visible and near infrared solar light [2]. As photocatalysts may serve atmospheric aerosols, i.e. ultrasmall solid particles that sometimes are embedded into liquid droplets. Aerosols are known to contain Ti02, Fc203, ZnO and other natural oxides, as well as metal sulfides of volcanic or antropogenic origin, that may serve as semiconductor photocatalysts (see Fig.5). Aerosols are known to be concentrated mainly in the air layers near the surface of the Earth, i.e. in the troposphere, rather than stratosphere. 

Investigation of direct conversion of methane to transportation fiiels has been an ongoing effort at PETC for over 10 years. One of our current areas of research is the conversion of methane to methanol, under mild conditions, using li t, water, and a semiconductor photocatalyst. Research in our laboratory is directed toward ad ting the chemistry developed for photolysis of water to that of methane conversion. The reaction sequence of interest uses visible light, a doped tungsten oxide photocatalyst and an electron transfer molecule to produce a hydroxyl i cal. Hydroxyl t cal can then react with a methane molecule to produce a methyl radical. In the preferred reaction pathway, the methyl radical then reacts with an additional wata- molecule to produce methanol and hydrogen. 

A long-term goal of our research group is to explore and evaluate novel pathways for the direct conversion of methane to liquid fiiels, chemicals, and intermediates. One of our current areas of research is the conversion of methane to methanol, under mild conditions, using li t, water, and a semiconductor photocatalyst. The use of three relatively abundant... 

Drew, K., Girishkumar, G., Vinodgopal, K., and Kamat, P.V. (2005) Boosting fuel cell performance with a semiconductor photocatalyst Ti02/Pt-Ru hybrid catalyst for methanol oxidation. Journal of Physical Chemistry B, 109 (24), 11851-11857. 

Polyoxometalates (POMs) have been the object of growing interest as photocatalysts for the oxidation or reduction of organic or inorganic compounds [225-230], Many of these POM systems share the same general photochemical characteristics as semiconductor photocatalysts. For example,... 

Y. Nosaka, K. Norimatsu, H. Miyama, The function of metals in metal-compounded semiconductor photocatalysts, Chem. Phys. Lett. 106 (1984) 128-131. 

Xiang, Q., J. Yu, and M. Jaroniec, Graphene-based semiconductor photocatalysts. Chemical Society Reviews, 2012. 41(2) p. 782-796. 

Arakawa, H., Sayama, K. 2000. Solar hydrogen production significant effect of Na CO, addition on water splitting using simple oxide semiconductor photocatalysts. Catal Surv Jpn 4 75-80. 

Zou, Z.G., Ye, J.H., Sayama, K., Arakawa, H. 2001. Direct splitting of water under visible light irradiation with an oxide semiconductor photocatalyst. Nature 424 624-627. 

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. 

Zou Z, Ye J, Sayama K, Arakawa H (2001) Direct splitting of water under visible light irradiation with an oxide semiconductor photocatalyst. Nature 414 625-627 Konta R, Ishii T, Kato H, Kudo A (2004) Photocatalytic activities of noble metal ion doped SrTiOs under visible light irradiation. J Phys Chem 108 8992-8995 Kato H, Kudo A (2002) Photocatalytic activities of noble metal ion doped SrTiOs under visible light irradiation. J Phys Chem B 106 5029-5034... 

Design and Development of New Titanium Dioxide Semiconductor Photocatalysts... 

Even without deposition of a metal island, such powders often maintain photoactivity. The requirement for effective photoelectrochemical conversion on untreated surfaces is that either the oxidation or reduction half reaction occur readily on the dark material upon application of an appropriate potential, so that one of the photogenerated charge carries can be efficiently scavenged. Thus, for some photoinduced redox reactions, metallization of the semiconductor photocatalyst will be essential, whereas for others platinization will have nearly no effect. 

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... 

Gas-phase oxidation of methane could be enhanced by the addition of a small amount of NO or N02 in the feed gas.1077 Addition of methanol to the CH4-02-N02 mixture results in a further increase in methane reactivity.1078 Photocatalytic conversion of methane to methanol is accomplished in the presence of water and a semiconductor photocatalyst (doped W03) at 94°C and atmospheric pressure.1079 The yield of methanol significantly increased by the addition of H202 consistent with the postulated mechanism that invokes hydroxyl radical as an intermediate in the reaction. 

NiO is known to work as a good co-catalyst for water photocleavage by semiconductor photocatalysts in an aqueous suspension.18) The catalytic activity of NiOx is very low for the reaction of H2 with 02, while it appears to produce efficiently H2 from protons. NiO/ri02 was used for water photolysis in NaOH solution under the same conditions as shown in Fig. 13.6. H2 and 02 are produced in a stoichiometric ratio even when the amount of NaOH solution is relatively large.15) The yield increases with decreasing amount of NaOH solution and maximized at ca. 0.12 ml quite similarly to the case of Pt/Ti02.15 Since the reverse reaction is very slow on NiOx/Ti02, this result indicates that some factors other than the reverse reaction suppress the yield of the water photolysis in suspension. 

After the finding of photocatalytic water decomposition by Pt Ti02, many new semiconductor photocatalysts which are able to photolyze watei ir. ar. aqueous suspension have been reported.383 These photocatalysts are characterized... 

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