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Design & Synthesis of ZnO-based Composite Nanofiber Photocatalysts with Z-Scheme Structure for Degradation of Organic Pollutants

Naseri, Amene | 2018

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 51528 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Moshfegh, Alireza; Pourjavadi, Ali; Mahmoodi, Niaz Mohammad
  7. Abstract:
  8. The aim of conducting this research is to study, fabrication and photocatalytic application of electrospun ZnO-based composite nanofibers. One of the most important challenges is to apply photocatalyst under solar irradiation and improve its activity for pollutant degradation. ZnO is a wide band gap semiconductor, hence, it is not active under the visible light. In Iran, we have at least 300 sunny days in a year. Therefore, fabrication and application of photocatalytic material with activity under the sunlight which contains 47% of visible light is so vital in our country. Since CuO is a visible light active photocatalyst and its interface with ZnO forms a type I heterojunction, this heterostructurewhich results in retardation of electron-hole recombination. ZnO/CuO nanofibers with the average diameter of 120 nm, with different concentrations of CuO have been used in this research. On the basis of our obtained data analysis, photocatalytic activity of the ZnO/(0.5 wt%)CuO as optimized sample, exhibited a 3 times higher rate constant as compared with pure ZnO sample, for methylene blue degradation, under similar sunlight irradiation. In another study, g-C3N4 nanosheets, with the thickness of 2-4 layers, have been prepared from the bulk g-C3N4 material, by means of acid treatment and ultrasonication. These nanosheets have shown enhanced photocatalytic activity in comparison with the bulk counterpart. Then, the composite of prepared nanosheets with ZnO have been used. For preparation and synthesis of a visible light active photocatalyst, the effect of oxygen vacancy defects and carbonaceous species in ZnO structure have been investigated. Therefore, ZnO/carbon/(x wt%) g-C3N4 nanofibers with average diameter of 70 nm, were fabricated. The optimized sample, ZnO/carbon/(0.25 wt%)g-C3N4, has shown higher photocatalytic activity for methylene blue degradation (k=2.06×10-2 min-1) than pure ZnO/Carbon (k=0.82×10-2 min-1) and g-C3N4 nanosheets sample (k=0.50×10-2 min-1), under similar sunlight irradiation. For further understanding the enhanced photodegradation rate, three different methods have been applied namely photoluminescence spectra (PL), determination of the valence band position of the g-C3N4 nanosheets and use of scavengers. According to our data analysis, a Z-scheme mechanism for charge carriers transfer at the interface of ZnO/carbon/(0.25 wt%) g-C3N4 structure, was proposed
  9. Keywords:
  10. Organic Pollutant ; Zinc Oxide Based Composite Nanofiber ; Electrospinning ; Sunlight Irradiation ; Photocatalytic Activity ; Zinc Oxide/Cupric Oxide ; Z-scheme Mechanism ; Degradation Pollutants

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