Photoreduction of Cr(VI) on magnetized TiO2 and polyoxometalates
| Autor: | Ya-Ting He, 何雅婷 |
|---|---|
| Rok vydání: | 2008 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 96 Environments, including atmosphere, lithosphere, hydrosphere and biosphere, influenced by toxic Cr(VI) have been widely studied. To decrease the toxicity and mobility of Cr(VI), the transformations of Cr(VI) to Cr(III) using reducing agents or catalysts are the most favorable processes due to their less impacts to the ecosystem. During the past decades, degradation of organic contaminants or transformation of inorganic contaminant to its solidic or less toxic forms induced by light energy through photosensitive materials, such as semiconductors, had received much scientific attentions. However, the photosensitive materials are either too small or dissoluble, which leads to the difficulty in recycling and reuse of the materials. Therefore, this study is aim to magnetize the photosensitive materials for enhancement of their applications in treating environmental pollutant, i.e., Cr(VI). TiO2 and polyoxometalates (POMs) are both photocatalysts, which are magnetized and employed in the study. Briefly, magnetite was first synthesized as a core material followed by precipitating TiO2 and POM on it. To avoid the possible photodissolution of the core material due to electron-transfer from photocatalysts during the photo-reactions, a silica layer was sit between the magnetite and photocatalysts. The magnetized TiO2 and POM were denoted as MSTi and MSPOM, respectively, and reduction of 0.0385 mM Cr(VI) on these two photocatalysts was conducted at acidic solutions. The optimal reaction parameters were investigated, and the used MSTi and MSPOM were separated from solutions by a magnet for further use. The results indicated that 1 g L-1 MSTi could remove 0.0292 mmol g-1 Cr(VI) after 6 h reaction at pH 3 under UV illumination. The removal involves adsorption and reduction of Cr(VI) on MSTi. On the other hand, added Cr(VI) (i.e., 0.0385 mM) disappeared completely within 6 h when 1g L-1 MSPOM was added into a solution exposed to UV light at pH 1. The disappearance was attributed to Cr(VI) reduction on MSPOM. Because MSPOM exhibited a low adsorption ability of Cr(III), the Cr(III) predominate in solution once it was produced. It was found that Cr(VI) removal on MSTi would decrease slightly with increasing the times of use. This may be due to the limited adsorption sites on MSTi. However, MSPOM reduced Cr(VI) efficiently, and it would not adsorption the reductive products (i.e., Cr(III)). Therefore, its ability for Cr(VI) removal would not decrease with increasing the times of use. Accordingly, it was found that MSTi and MSPOM can be readily recycled and reused without eliminating their efficiency for Cr(VI) removal. These two magnetized photocatalysts may be cost-effective and potential materials for treatment of Cr(VI) or other contaminants in wastewaters. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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