我們發表了一項使用海藻酸氣凝膠(alginate aerogel, AA)的研究，這是一種新穎的光活性材料，在可再生的太陽光驅動下，具有在30分鐘內將有毒的六價鉻還原成無毒的三價鉻並同時產生高活性氧化物質—氫氧自由基(∙OH)的能力。海藻酸氣凝膠是由天然的原料:海藻酸鹽 (alginate)所合成，海藻酸鹽是一種由藻類所萃取的多醣體生物性聚合物，非常容易與二價陽離子(如:鈣和鋇離子)產生交聯反應(cross-linking)並生成水凝膠(Hydrogel)。而水凝膠可進一步透過冷凍乾燥的程序，產生高孔洞性的材料，稱為“氣凝膠”。
本研究在光還原六價鉻的過程中探討多項參數，例如: pH 值、草酸(Oxalate)的添加、不同的光照波長、溶氧含量。我們發現在海藻酸氣凝膠的光催化反應下有添加草酸和低pH值的情況能讓六價鉻的還原效率以及氫氧自由基的生成有大幅的提升。當六價鉻存在時，過氧化氫(H2O2)以及氫氧自由基(∙OH)並不能有效的進行生產，直到六價鉻耗盡。不論是太陽光或是可見光都能驅動海藻酸氣凝膠的光活性。綜合上述所說，在海藻酸氣凝膠的光催化反應下能有效的產生氫氧自由基，因此它具有很大的潛能作為一種新型態的高級氧化程序（AOP）並由太陽光驅動，可用於處理難分解之有機污染物，以及光還原有毒的六價鉻。

We present a study using alginate aerogel (AA), a new photoactive material that was capable of mediating the reduction of toxic Cr (VI) to non-toxic Cr (III) in 30 min and generating highly reactive ∙OH oxidant under renewable solar irradiation. AA was synthesized from a natural feedstock, alginate, a polysaccharide biopolymer extracted from algae that can be readily cross-linked with divalent cations, e.g., Ca2+ and Ba2+, forming hydrogel. The hydrogel was subsequently processed by freeze-drying, resulting in a highly porous material called “aerogel”. We studied several parameters such as pH, the presence of oxalate, light wavelength, and dissolved O2 level. We found that the photoactivity of AA toward Cr (VI) reduction and ∙OH generation was greater in the presence of oxalate at lower pH. In the presence of Cr (VI), the generation of H2O2 and ∙OH did not proceed efficiently until the depletion of Cr (VI). Both sunlight and visible light can drive the photoactivity of AA. Considering that photoactivity of AA can generates ∙OH efficiently, it has a great potential as a new sunlight-driven advanced oxidation process (AOP) that can be used to treat recalcitrant organic pollutants, in addition to photoreduction of toxic Cr (VI).

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