Investigation of the photocatalytic properties of polyoxometalates
Başlık çevirisi mevcut değil.
- Tez No: 400863
- Danışmanlar: DR. JOHN L. FERRY
- Tez Türü: Doktora
- Konular: Kimya, Chemistry
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2002
- Dil: İngilizce
- Üniversite: University of South Caroline
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 200
Özet
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Özet (Çeviri)
In this dissertation the thermal and photocatalytic properties of different photoactive heteropolyoxometalates ([PWi2O40]3\ [SiW^o]4“, [PM012O40]3”. [W,o03;]4“ . and [NaP5W30Oiio]14') are investigated in several model systems. The photodegradation kinetics of a probe compound, 1.2-dichlorobenzene. are used as a probe of the reactivity of these oxidation catalysts in solution and supported on Ti02 or Y-zeolite surfaces. In all cases. POM-mediated photocatalytic oxidation of DCB is first order in [DCB]. Competition experiments employing OH radical scavengers (including a comparison of the effectiveness of protonated vs deuterated probes) revealed that the degradation reaction is initiated by electron transfer rather than OH radicals. Combination of POMs with Ti02 resulted in eight-fold rate enhancement on the photooxidation of DCB upon illumination at 350 nm in aqueous medium. In this system. POMs act as electron transfer catalysts for removing electrons from the conduction band of excited Ti02 to molecular oxygen. Y-zeolites were also used as solid support for POM photocatalysis and it was found adsorption onto Y-zeolites increased the photocatalytic activity of POMs by a factor of 4-10 times. A new type of photocatalytic system was developed based on Y-zeolite-supported [NaPsWsoOuo]14' which functions at environmentally relevant pHs (5-10). We explored the relationship between the oxidation rate of 1,2-DCB and a variety of zeolites, varying the Si/Al ratio, pore sizes and surface areas. Maximum rates were attainted with the Y-zeolite with highest Si/Al (80). We hypothesize that adsorption of POMs on the surface of Y-zeolites plays the primary role in the observed rate enhancement of Y-zeolite/POM systems. This system is also less likely to be affected by the presence of common ion scavengers like bicarbonate and natural organic matter. The increased quantum efficiency of zeolite-supported [NaPsW^oOno]14”in the presence of these scavengers is attributed to the electrostatic repulsion between scavengers and the negatively charged photocatalyst.
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