Loading...

Fabrication and Characterization of ZnO Composites Nanofibers by Electrospinning Method for Photocatalytic Application

Samadi Amin, Morasae | 2013

623 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 44567 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Moshfegh, Ali Reza; Pourjavadi, Ali
  7. Abstract:
  8. In this research we focus on study and fabrication of ZnO composite nanofibers by electrospinning method for photocatalytic application. The most important challenges in the field of photocatalyst are photocatalytic activity under the visible light and efficiency enhancement. ZnO is a wide band gap semiconductor and it is not active under the visible light. In Iran, we have more than 300 sunny days in a year. Therefore fabrication and application of photocatalytic material with activity under the sun light that contained 40% of visible light is so vital in our country. In the first part of this project, ZnO-CNT nanofibers were fabricated and carbon doped in the crystal lattice of the ZnO. The doped carbon created new energy state in the band gap of the ZnO and caused the band gap reduction. CNT is a conductive material and caused that the photo-electrons transfer to it and subsequently retard the electron-hole recombination and increase the photocatalytic activity. CNT is a photosensitizer and under the visible light excitesand transfer the electrons to the ZnO and causes photocatalytic activity under the visible light in ZnO-CNT nanofibers. In the second part, ZnO-carbon nanofibers were fabricated by annealing the ZnO precursor fibers in the nitrogen atmosphere. Various characterization techniques showed the presence of oxygen vacancies in the nanofibers. Oxygen vacancy induces new band state under the conduction band of the ZnO and caused the band gap narrowing. In photocatalytic process the photo-electrons were trapped by this energy level and decrease the electron-hole recombination and increase the photocatalytic efficiency. More over the synergy between carbon and ZnO causes the retardation in the electron-hole recombination. Carbon species in the ZnO-carbon nanofibers act as a photosensitizer and excites by visible light. The photo-generated electron by the carbon transfer to the ZnO and the methylene blue degradation occurred on the surface of the photocatalyst.The photocatalytic activity in the presence of hydroxyl radical and hole scavengers in the ZnO-carbon nanofibers showed photo-electrons are the main pathway of the photocatalytic process. In the third part, CdO as narrow band gap semiconductor were used for the ZnO activation under the visible light and ZnO-CdO nanofibers with different amount of CdO were fabricated. In addition the effect of annealing rate on the photocatalytic activity was determined. The nanofibers were annealed in the higher heating rate have a better crystallinity with lower amount of defects. Defects cause the electron hole recombination and reduce the photocatalytic activity. Therefore higher crystallinity leads to better photocatalytic activity. The conduction and valance band of the CdO sandwich between the band gap of the ZnO, therefore CdO act as a sink of both electrons and holes, therefore the recombination of the electron-hole increase and the photocatalytic activity decrease under the UV light. Due to the narrow band gap of CdO, increase the amount of CdO in the ZnO-CdO nanofibers results in the increase of photocatalytic activity under the visible light
  9. Keywords:
  10. Electrospinning ; Composite ; Zinc Oxide ; Photocatalytic Property ; Photosensitive Material ; Radical Scavenger ; Hole Scavenger

 Digital Object List

 Bookmark

No TOC