Effects of zero-valent iron surface modification on aqueous nitrate reduction
| Autor: | Ya-Hsuan Liou, 劉雅瑄 |
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| Rok vydání: | 2006 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 94 Extensive studies over the past 15 years have demonstrated that chemical reduction of many substances in the environment, such as halogenated organic compounds, heavy metals and oxo-anions can be coupled to Fe0 oxidation. Early investigations have gained insight concerning the mechanism and kinetics of the electron transfer process through batch and column experiments. However, production and accumulation of intermediates and by-products, which are more toxic than the parent compounds, have been observed. Thus, not only reaction rate but also benign products yields attracts interesting. Both surface treatments, H2-reducing pretreatment at 400℃ and reducing particle size into nanoscale, were attempted to enhance the removal of nitrate (40 mg-N L-1) using zerovalent iron in a HEPES buffered solution at a pH of between 6.5 and 7.5. After the iron surface was pretreated, the deposition of noble metal onto freshly pretreated iron promoted nitrate degradation. The aims of this work are to develop an effective reductive material for removing nitrate at neutral pH and an effective surface treatment to activate and restore the reactivity of this material. Additionally, attention was also given to the reaction mechanisms through both the investigation of kinetic control and the identification of the reaction products and intermediates. After H2-reducing pretreatment, the removal of the passive oxide layers that covered the iron was indicated by the decline in the oxygen fraction (energy dispersive X-ray analysis) and the overlap of the cyclic polarization curves. The reaction rate was doubled, and the lag of the early period disappeared. Then, the deposition of copper onto freshly pretreated iron promoted nitrate degradation more effectively than that onto a nonpretreated iron surface, because of the high dispersion and small size of the copper particles. An optimum of 0.25-0.5% (w/w) Cu/Fe accelerated the rate by more than 7 times that of the nonpretreated iron. The aged 0.5% (w/w) Cu/Fe with continual dipping in nitrate solution for 20 days completely restored its reactivity by regeneration process with H2 reduction. Both high surface area materials, Fe0 and Cu/Fe nanoparticles, were employed for the denitrification in unbuffered 40 mg-N L-1 nitrate solutions at initial neutral pH. As compared with microscale Fe0 |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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