- 期刊
具磁性polyoxometalates對Cr（VI）之光還原研究
Photoreduction of Cr(VI) on Magnetized Polyoxometalates
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架鉻，對生態環境較有利，常見的六價鉻還原方法，主要有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，已有許多的研究成果指出，可利用光催化劑的光敏感特性，利用光能降解品境中之有機污染物或轉變無機污染物，以降低其毒性。然而催化劑之分離回收部份，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。POMs（polyoxometalates）為具有半導體性質之光催化物質，將此光敏感物質分別包覆於磁鐵礦外圍，可藉由磁鐵礦之磁性增加材料回收的便利性。材料合成過程中於POMs和磁鐵礦間插入一矽酸層，以避免外圍POMs對核心磁鐵礦造成光溶解反應，而能有放隔絕電子的傳遞。本實驗將所合成之具磁性polyoxometalates（MSPOM）對0.0385 mM Cr（VI）進行光還原反應，評估最佳反應條件；並利用其磁性回收材料，選擇最佳回收條件，並測試材料的再利用效果。研究結果顯示，MSPOM於UV光下以固液比1 g L^-1，pH1之0.01 M KCl背景液為環境，反應6小時後可完全移除懸浮液中的Cr（VI）。其反應主要以還原方式將Cr（VI）還原成Cr（III），且MSPOM僅具少量吸附量，因此還原後的Cr（III）存在於水體中。由反應過後之MSPOM的再利用評估結果可知，其對Cr（VI）移除量隨使用次數增加並無明顯差異，此乃MSPOM主要是以還原方式移除Cr（VI），因此在重覆使用過程中，材料不會因吸附位置的減少而減少其對Cr（VI）的移除量。另外MSPOM之磁性末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，材料可回收再利用，使成本降低並減少環境二次汙染的機會。
並列摘要
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, 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).Polyoxometalates (POMs) are photocatalysts, which are magnetized and employed in the study. Briefly, magnetite was first synthesized as a core material followed by polyoxometalates 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 POM, denoted MSPOM, was used to reduce 0.0385 mM Cr(VI) at acidic solutions. The optimal reaction parameters were investigated, and the used MSPOM was separated from solutions by a magnet for further use. The results indicated that Cr(VI) (i.e.,0.0385 mM) disappeared completely within 6 h when lg 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) was released to the in solution once it was produced. It was found that MSPOM reduced Cr(VI) efficiently, and it would not adsorb the reductive products (i.e., Cr(III) ). Therefore, its ability for Cr(VI) removal would not decrease with increasing the time of use .Accordingly, MSPOM can be readily recycled and reused without eliminating its efficiency in Cr(VI) removal. The photocatalyst may be cost-effective and potential material for treatment of Cr(V I) or other contaminants in wastewaters.