- 期刊
具磁性二氧化鈦對Cr（VI）之光還原研究
Photoreduction of Cr(VI) on Magnetized TiO2
摘要
將環境中的六價鉻還原轉變為毒性和移動性較低的三價鉻，是對生態環境較有利的過程。常見的六價鉻還原方法中，添加化學還原劑之化學還原法及利用光能促進反應的光催化還原法常被提出討論。近20年來，利用光催化劑的光敏感特性，吸收光能降解環境中之有機污染物或轉變為無機污染物，降低其毒性，已有相當多的成果，然而催化劑分離回收的部份，常因催化劑粒徑細小或是其為水溶性物質而在應用上有困難，因此尚具有發展的空間。TiO2是具半導體性質之光催化物質，將此光敏感物質包覆於磁鐵礦外圍，藉由磁鐵礦之磁性以增加材料回收的便利性，為避免外圍之TiO2與核心磁鐵礦產生光溶解反應，可於兩者間插入一矽酸層，有效隔絕電子的傳遞，因此本實驗為利用所合成之MSTiH對0.0385 mM Cr（VI）進行光還原反應，評估MSTiH最佳反應條件並利用其磁性回收MSTiH，且於最佳反應條件下測試MSTiH的再利用效果。研究結果顯示，MSTiH在UV光照下以固液比1g L^(-1)背景液為pH3 0.01M KCl環境中，反應6小時後可有效移除0.0292 mmol g^(-1)的Cr（VI），移除方式為吸附和還原反應。MSTiH再利用評估結果可知，MSTiH之Cr（VI）移除量隨使用次數的增加而減少，還原量無顯著差異，移除量降低的原因主要為材料表面吸附位置隨使用次數增加而減少所致，且MSTiH之磁性並未隨使用次數增加而減弱，連續使用後結果顯示，對Cr（VI）的移除量無明顯下降，且由於材料可回收再利用，在應用上可使成本降低並減少環境二次污染的機會。
並列摘要
The impacts of toxic Cr (VI) on the environment 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, received much scientific attentions. However, the photosensitive materials are either too small or dissoluble, which leads to the difficulty in recycling and reusing the materials. Therefore, this study aims to magnetize the photosensitive materials for enhancement of their applications in treating environmental pollutant, i.e., Cr (VI). TiO2 is photocatalyst, which is magnetized and employed in the study. Briefly, magnetite was first synthesized as a core material followed by precipitating TiO2 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 optimal reaction parameters were investigated, and the used MSTiH was separated from solutions by a magnet for regeneration. The results indicated that 1 g L^(-1) MSTiH 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 MSTiH. It was found that Cr (VI) removal on MSTiH would decrease slightly with increasing the times of use. This may be due to the limited adsorption sites on MSTiH. Accordingly, it was found that MSTiH can be readily recycled and reused without eliminating their efficiency for Cr (VI) removal. This magnetized photocatalysts may be costeffective and potential materials for treatment of Cr (VI).