Alkali Metal Ion-Modified Vanadium Mononuclear Complex for Photocatalytic Mineralization of Organic Compounds
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Alkali Metal Ion-Modified Vanadium Mononuclear Complex for Photocatalytic Mineralization of Organic Compounds Fumiaki Amano • Masako Tanaka Bunsho Ohtani
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Received: 13 June 2010 / Accepted: 11 August 2010 / Published online: 24 August 2010 Ó Springer Science+Business Media, LLC 2010
Abstract Modification of silica-supported vanadium oxide (VS) photocatalysts with alkali metal ions enhanced the photocatalytic activity of the vanadium(V) mononuclear complex for oxidative decomposition of gaseous organic compounds into carbon dioxide. Action spectrum analysis revealed that the onset wavelength for cesium-ionmodified VS was 420 nm, which was ca. 20 nm longer than that with a titania photocatalyst, P25. Keywords Highly dispersed metal oxides Cesium ion V2O5/SiO2 Single-site photocatalyst Charge-transfer excited state
1 Introduction Photocatalytic oxidative decomposition of gaseous organic pollutants into carbon dioxide (CO2) is a useful technique for purification of indoor air. Recently, titanium–oxygen– cerium complexes supported on mesoporous silica have been reported to induce oxidation of gaseous 2-propanol under visible light irradiation [1]. Such all-inorganic complex photocatalysts could be further tuned and manipulated at a molecular level to be highly active photocatalysts. Mononuclear complexes supported on metal-oxide supports such as silica and zeolite have been shown to induce photocatalytic reactions such as partial F. Amano (&) B. Ohtani Catalysis Research Center, Hokkaido University, Sapporo 001-0021, Japan e-mail: [email protected] F. Amano M. Tanaka B. Ohtani Graduate School of Environmental Science, Hokkaido University, Sapporo 060-0810, Japan
oxidation of organic compounds and reduction of nitrogen oxides with hydrocarbons [2–5]. However, these supported complexes seem less active for complete oxidative decomposition, i.e., mineralization, of organic pollutants because of the localized nature of the photoexcited state to induce one-electron transfer. Thus, the principle is different from that of a semiconductor photocatalyst, which could induce multi-electron transfer reactions. Indeed, a tetrahedrally coordinated vanadium mononuclear complex supported on silica, which is produced by dehydration of silica-supported vanadium oxide (VS), was effective for selective partial oxidation of alkanes and alkenes rather than for complete oxidation into CO2 [6–8]. This is the reason why the application of mononuclear-complex photocatalysts has not been possible for oxidative decomposition of gaseous organic pollutants. In the present study, we investigated the photocatalytic activity of vanadium(V) mononuclear-complex on silica for oxidative decomposition of acetaldehyde in air. Although an isolated bare complex was unstable in the presence of polar molecules and the photocatalytic activity was not high, modification by an alkali metal ion enhanced the stability of the mononuclear-complex structure and the photocatalytic activity for complete decomposition of acetaldehyde into CO2. The p
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