| AVS 56th International Symposium & Exhibition | |
| Advanced Surface Engineering | Monday Sessions |
| Session SE1-MoM |
| Session: | Photocatalytic Coatings |
| Presenter: | Y. Chen, National Dong Hwa University, Taiwan |
| Authors: | Y. Chen, National Dong Hwa University, Taiwan G. Jhan, National Dong Hwa University, Taiwan G. Cai, National Dong Hwa University, Taiwan T. Lin, National Dong Hwa University, Taiwan M.S. Wong, National Dong Hwa University, Taiwan C. Cheng, National Dong Hwa University, Taiwan |
| Correspondent: | Click to Email |
Titania nanopowders synthesized by low-pressure flat-flame metalorganic chemical vapor condensation method are known to possess visible light photocatalytic ability even they are produced without intentional doping. While the visible-light absorption of the powder is convincing, the cause of visible light absorption is still inconclusive. There are 3 main possible causes for visible light absorption discussed earlier. First is the anatase/rutile interface that generates defect levels for visible light absorption. Second is the nitrogen doping that forms the absorption center. Third is the carbon doping that forms the absorption center. In order to confirm that carbon doping is the major cause for the visible light absorption of the powder, we modify the process using helium in place of nitrogen to eliminate the nitrogen doping possibility. Helium in place of nitrogen is used as the titanium precursor carrier gas, where the precursor is titanium isopropoxide. Using acetylene and oxygen as fuel and oxidizer for the flame, the titanium isopropoxide was decomposed and oxidized, and the nanoparticles of titania were formed. From the methylene blue decomposition study we found that the powder synthesized under low precursor feed rate possesses high photocatalytic efficiency under illumination of visible light. Since nitrogen is avoided in the process, the visible light absorption cannot be due to nitrogen doping. We also found that the nanopowder formed has a single phase of anatase. Thus the nanopowder does not have anatase/rutile interface, and we can eliminate the possibility of visible light absorption by the anatase/rutile interface. The visible light absorption should thus be resort to the carbon doping. XPS studies show the presence of several carbon related bonds except Ti-C bond. This suggests that the carbon does not incorporate into the TiO2 crystal and should locate on the surface of the nanopowder. Thus the carbon species act as a visible light sensitizer for the titania as a photocatalyst. Among all carbon bonds the C-C bond is believed to be responsible for the light absorption, since all other carbon related bonds are not chromophores. The carbon should be in the cluster form to become colored. The visible light TiO2 photocatalysis induced by carbon doping is confirmed and explained.