| Summary: | 碩士 === 國立成功大學 === 環境工程學系碩博士班 === 97 === TiO2 and ZnO being environmental friendly and high chemical and mechanical stability are very effective in photocatalysis degradation processes. Nanosize ZnO and TiO2 have attracted great research interests and applications such as optoelectronics, sensing, field emission and piezoelectrics. Chlorinated volatile organic compounds (Cl-VOCs) are carcinogenic and extremely persistent in the environment. Of which, TCE and CHCl3 is chosen as the probe molecules because their emissions are associated to a wide range of industrial processes and are of great environmental concern. Thus, the main objectives of this work were (1) Synthesis of ZnO nanorods thin films, (2) Determination of sensitivity and photocatalysis of the ZnO thin films with Cl-VOCs (such as TCE and CHCl3), (3) Synthesis of novel reticular TiO2 nanowires, (4) Determination of photocatalysis of the reticular TiO2 nanowires with TCE, (5) Speciation studies of Zn, Ti and Fe in the ZnO nanorods thin films and reticular TiO2 nanowires.
Experimentally, well aligned ZnO nanorod arrays with a diameter of about 150 nm and a length of 2500 nm have been formed on the glass substrate. The sensitivities of the ZnO nanorod thin films in the presence of 1000 ppm CHCl3 are measured at 300-573 K. Note that the sensitivity of the ZnO nanorods is increased as the reaction temperature increases. For instance, at 573 K, the sensitivity of ZnO nanorods thin films is 13 approximately. The EXAFS data also shows that as CHCl3 is introduced onto the ZnO nanorods thin film, the bond distance of Zn-O is decreased slightly from 1.962 to 1.961 Å. During photocatalysis, by in situ FT-IR spectroscopy, splitting of CH bonding of trichloroethylene (TCE) has been observed. Prolong the UV irradiation to 300 min, about 40% of TCE can be photocatalytically degraded. The intermediate dichloroacetyl chloride yielded during photocatalytic degradation of TCE has also been observed and eventually is oxidized to CO2 and HCl.
Scanning electron microscopy (SEM) and superconducting quantum interference device vibrating sample magnetometer (SQUID VSM) show that Fe and Ti are well dispersed. With typical ferrimagnetic properties, the catalyst well suspended and assembled in solution under an external magnetic field. During photocatalysis, in the presence of TiO2/Fe3O4@C and TiO2/Fe2O3, about 57% and 55% of TCE can be photocatalytically degraded without an external magnetic field. Under 250 Gauss magnetic field, the TiO2/Fe3O4@C has a greater efficiency (about 70%) for photocatalytic degradation of TCE.
The Ti K-edge least-square fitted XANES spectra of the TiO2/Fe3O4@C photocatalyst show that the main titanium species are nanosize TiO2 (9 nm) (77%) and bulky TiO2 (23%). Speciation of titanium in the TiO2/Fe3O4@C during photocatalytic degradation of 100 ppm trichloroethylene (TCE) has also been studied by in situ X-ray absorption near-edge structural (XANES) spectroscopy. TiO2 is not perturbed during the course of photocatalysis. Nevertheless, about 33% of FeO and 67% of Fe3O4 are observed under photocatalytic degradation of TCE for 120 min, suggesting that the carbon layer on the TiO2/Fe3O4@C photocatalysts can reduce the process of photoexcited electron-hole recombination as usually found on the relatively narrow bandgap of ferric oxide during photocatalysis.
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