| Summary: | 博士 === 國立交通大學 === 環境工程系所 === 97 === A novel TiO2/Fe0 composite as water treatment chemical:
Zerovalent iron (ZVI) and titanium dioxide (TiO2) have been considered potent reagents in the degradation of organic pollutants. However, the diminishing reactivity with time has obstructed their wide applications, due to the building-up of oxide layer on the surface of ZVI and the electron-hole recombination in TiO2. This study proposed to used the reduction potential of photocatalytic TiO2 (-0.2 to 3.0 eV) to retard the formation of the surface oxide layer and to retard the electron-hole recombination phenomena in TiO2. By this theory, a novel TiO2/Fe0 composite (NTFC) has been developed.
This study is comprised of the synthesis of the NTFC, the testing and optimization of NTFC reactivity efficiency by using Acid Black-24 (AB-24) as the target compound, the enhanced degradation of TOC by the compound UV/NTFC/H2O2 system, the choice of light source in the UV/VIS/NTFC system, and the mechanisms of NTFC.
The nanoscaled neutral TiO2 sol and nanoscaled zerovalent irons (nZVI) were prepared separately. Surface characterization confirmed that the NTFC is a composite of TiO2 and ZVI with partial core shell structure. The composite is with high specific surface area and microporous structure, with strong binding between TiO2 and ZVI. Moreover, The NTFC which has good strong binding structure strength can be recycled by magnets.
Results showed that NTFC was highly efficient in degrading AB-24. The NTFC of highest reactivity was obtained when the TiO2 and Fe0 ratio was 1 to 10. And the optimal pH for reaction was discovered between 3 and 7. Experimental result with color removal of AB-24 showed that the NTFC can be excited by visible lights with the possibility of combining cold cathode fluorescent light (CCFL) and light emitted diode (LED). Tests by the combined UV/NTFC/H2O2 system indicated that the color of the AB-24 containing wastewater was removed by the Fe0 in the beginning and the TOC was degraded by UV/H2O2.
The results from the analysis of Electron Paramagnetic Resonance (EPR) and Electrochemical impedance spectroscopy (EIS) confirmed that the NTFC can retard the formation of the oxide layers on the Fe0 and the recombination of electron-hole in TiO2. High concentration of ferrous ions can be maintained in the reaction, and the hydrogen peroxide and free radicals can be produced resulting in Fenton reaction. The TiO2-iron oxide/Fe0 core shell was formed, which resulted in the adsorption of pollutants and the Galvanic cell effect. The mechanism of NTFC reaction can be summarized as: (1) strong reduction in the first stage, (2) oxidation in the second stage, (3) adsorption on the core-shell and Galvanic cell effect in the final stage. The reaction of AB-24 in the NTFC began with the N=N bonds breaking which released the chromophores and auxochromic groups and resulted in decoloration. The moieties from AB-24 bond breaking containing functional groups such as sulfonic acid and N=N bonds were adsorbed on the surface of Fe0 ready for further treatment.
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