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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 39968 (04)
- University: Sharif University of Technology
- Department: Physics
- Advisor(s): Moshfegh, Ali Reza; Akhavan, Omid
- Abstract:
- In photocatalitic activity of titana an effective approach to achieve high charge separation efficiency and high level of sensitivity under visible light is coupling it with another semiconductor with smaller band gap and appropriate banding energy structure. achieving all mentioned above, we used bilayer structure and coupled TiO2 with hematite which its small band gap(Eg ~ 2.1 ev) is sensitive to visible light. Bilayer systems of TiO2/Fe2O3 , Fe2O3/TiO2 were fabricated by sol-gel process and variable parameter was upper layer thickness. The layers were deposited on glass substrate via sol-gel process. The upper layers were prepared in different thicknesses in two ways. First, they prepared by variation of raising rate of the sample from solution and second, variation of coating steps in constant raising rate. At last, all the samples were annealed in a furnace at 500ºc in air for 1h. stochiometery of bilayers, surface was determined by X-Ray photoelectron spectroscopy(XPS) which emphasizes stochiometery of Fe2O3 for chemical composition of upper layer of Fe2O3/TiO2 system and TiO2 for upper layer of TiO2/Fe2O3 . AFM results indicated increasing thickness of the layers caused increasing paticle sizes and this results were confirmed by optical measurement. The crystal phase of TiO2 layer was determined anatase and the crystal phase of Fe2O3(hematite) layer was alpha. In order to determining the exact thickness of TiO2 layer in TiO2/Fe2O3 system we used Ratherford back scattering spectrometry(RBS) due to optical results. The absorption edge of bilayer systems is the same with hematite absorption edge which has smaller band gap (Eg ~ 1.98 ev). at last , photocatalytic results revealed increasing photocatalytic activity by increasing the upper layer thickness for TiO2/ Fe2O3 system surface and decreasing the upper layer thickness for Fe2O3/ TiO2 system surface. In addition to photocatalitic experiment, hydrophilic properties of TiO2/ Fe2O3 system was measured and was compared to the hydrophilic results of TiO2 and Fe2O3 monolayers. These results indicated decreasing of water contact angle in bilayer systems in contrast of monolayers.
- Keywords:
- Photocatalyst ; Hydrofilicity ; Sol-Gel Method ; Dipping ; Bilayer System
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