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Research of Controllable Synthesis of Bismuth-based Nanostructures and Their Photocatalytic Activity

Author: CuiZhanKui
Tutor: ZengDaWen
School: Huazhong University of Science and Technology
Course: Materials Science
Keywords: Bismuth-based nanostructures BiOCl Bi2WO6 Controllable synthesis Oriented-Attachment mechanism Photocatalytic activity
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Type: PhD thesis
Year: 2012
Downloads: 209
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Abstract


With the improvement of living standard, more and more attention has been paid toenvironmental pollution issue. Photocatalysis is a newly developed technology whichutilizes semiconductor materials to degrade organic dyes in water and poisonous gases inair. The photocatalytic process is energetically driven by UV or visible light and the finalproducts are CO2and H2O, which endows the technology with green andenvironment-friendly characteristics. And thus a great application potential in thetreatment of pollution is expected. Bismuth-based nanostructures are a class of new highperformance photocatalysts and in this thesis, we systematically investigated the controlledsynthesis and photocatalytic activity of this kind of materials, typically indcluding BiOCland Bi2WO6.The mesoporous BiOCl nanostructures were synthesized by a facile non-template lowtemperature solvothermal method using ethylene glycol as solvent. The urea was used toaffect the crystal growth process and thus realize the controllable synthesis. With theincrease of the addition amount of urea into the recipe, the microstructure of the sampleschanged from non-porous to mesoporous and the mesoporous BiOCl sample exhibitedmuch higher photocatalytic activity. The synthesized sample was then modified with Ptnanoparticles through impregnation method. The photocatalytic activity of Pt/BiOClsample increased obviously and the photodegradation process of toluene was changed,leading to the inhibition of the formation of more poisonous formaldehyde. Furthermore,we also annealed the as-prepared sample to control the oxygen defects and thusinvestigated the effect of oxygen vacancy defects on the photocatalytic activity of BiOClsamples. It was found the photocatalytic efficiency could be strengthened obviously for theannealed sample and no formation of formaldehyde was monitored when using the sampleto photodegrade toluene, indicating the effect of annealing and the role of oxygenvacancies in the photocatalysis.The growth mechanism of mesoporous BiOCl nanostructures was also investigated. Itwas found the growth of BiOCl nanosheet units follows Oriented-Attachment mechanism but not the popular known Ostwald–Ripening crystallation theory. When tungsten sourcewas added into the solvothermal reaction system, BiOCl phase was formed first and thentransformed to Bi2WO6phase accompanied by the dissolution of BiOCl particles. Thegrowth of Bi2WO6nanosheets also follows Oriented-Attachment mechanism. Furthermore,it seems that in the EG solvothermal system, the bismuth-based inorganics tends to grow inaccordance with Oriented-Attachment mechanism.QDS modified Bi2WO6nanostructures were prepared by controlling the solvothermalreaction conditions and the product demonstrated high performance when used tophotodegrade RhB dye under visible light irradiation. Similarly, in the Bi-W-Cl-Osolvothermal system, with the variation of urea concentration, the phase of the productevoluted from BiOCl to Bi2WO6and the microstructure of Bi2WO6changed fromnon-porous spheres to porous nanowalls. When annealing the sample at400oC, theBi2WO6QDS disappeared and the photocatalytic activity decreased a lot. Moreover,according to the analysis of solvothermal reaction kinetics, we attempted to synthesizeBi2WO6/BiOCl composite materials and the result show that the photocatalyst ofheterojunction type displayed better photocatalytic performance.

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