利用紫外光及可見光應答型TiO2降解水中抗癌藥物之研究

Abstract

全世界罹患癌症的人數在近十年有明顯的增加趨勢。相對的，抗癌藥物的使 用量也是逐年成長。而抗癌藥物經藥理學研究發現它本身具有致畸性、基因毒性 以及致癌性。研究亦發現，傳統家庭廢水處理廠及醫院廢水處理廠對於抗癌藥物 並無法有效地去除。5-氟尿嘧啶(5-fluorouracil)以及環磷醯胺(cyclophosphamide)為全世界兩種使用最廣泛的抗癌藥物，故本研究選用此兩種抗癌藥物當作主要的研究對象。 經初步光催化材料的篩選發現，Dagussa P25 TiO2為降解兩種抗癌藥物效果 較好的光催化材料，故作為後續的光催化反應研究中所使用的材料。5-氟尿嘧啶最佳處理的操作條件下(20 mg L-1的P25 TiO2以及溶液的pH=5.8)，初始濃度為200 μg L-1的5-氟尿嘧啶可以在兩小時內被完全去除(k=0.0375 min-1)。在降解機制的研究結果中發現，5-氟尿嘧啶是經由靠近觸媒表面，經電洞(h_vb^+)所產生的氫氧自由基(˙OHfree)所氧化。而5-氟尿嘧啶在有較高初始濃度(27.6 mg L-1)且觸媒量為300 mg L-1時，去除效率可在4小時後達到99.9%以上，並在24小時後達完全礦化及96.7%的理論氟離子回收率。另一方面，環磷醯胺在初始濃度為27.6 mg L-1且觸媒量為300 mg L-1時，去除效率亦可在4小時後達到99.9%以上，但在16小時僅達51.1%的礦化及79.9%的理論氯離子回收率。在MicrotoxR毒性測試方面發現，環磷醯胺在反應後毒性有上升趨勢，經由研判應該是所產生的副產物所造成;而5-氟尿嘧啶在反應前後皆無任何毒性反應。 為了增加紫外光光觸媒的應用性，並使其可以在可見光的光源下進行反應， 近幾年相關的研究正在陸續進行中。而其中可見光應答型的N-doped TiO2則更 受重視，主要是因為它較其他元素改質後有較高的可見光催化效果，以及較為簡 易的合成方法。微波在近幾年被視為一種較為「綠色」的合成及處理的方法，因 為它擁有處理時間短的優勢，在合成步驟上可以大為降低能源的消耗。研究結果 發現，將微波應用在合成N-doped TiO2上，並用在可見光下進行5-氟尿嘧啶光 催化反應。其降解效果明顯比利用傳統氨氣鍛燒合成法所合成的N-doped TiO2 要來的好。而最佳化後的合成步驟是先經由濃度為1M的氨水浸潤一小時，接著 放入微波消化器中，在180˚C下反應三小時後取出，再進行550˚C氨氣鍛燒6 小時後得之最佳可見光應答行光觸媒(N6)。拿N6以及未改質的Dagussa P25 TiO2在可見光下進行光催化實驗，再20小時後N6可以去除88.8%的5-氟尿嘧啶，而Dagussa P25 TiO2則僅能去除61.5%。在環磷醯胺的可見光催化實驗中，亦N6有較高的去除效果。另外，在物性鑑定方面，合成後的N-doped TiO2顆粒尺寸變大、孔隙容量增加、比表面積減少、表面鹼量跟鹼度都減少，但表面的等電位點卻無太大的改變。 本研究顯示，利用光催化降解水中難分解之抗癌藥物有不錯的效果。若往後 能應用在醫院廢水處理廠進行高級氧化處理，應能有不錯的處理潛力。但處理廠 中，水質複雜性高，不同的水質參數皆會影響處理效果。另外，毒性的變化以及 副產物間的關係也是需要加以深入研究;而總有機物的去除結果也提供未來在廢 水處理廠設計時一個重要的參考依據。

Cytostatic drugs are a class of pharmaceuticals that are increasingly used in cancer therapies. However, they have genotoxic, mutagenic, carcinogenic or teratogenic effects in non target organism. They have been detected in the both effluent of the municipal and hospital wastewater treatment plants due to their stability and persistency. 5-fluorouracil and cyclophosphamide are two of the most commonly used cytostatic (antineoplastic) drugs in the world. This study applied photocatalytic oxidation to remove 5-fluorouracil and cyclophosphamide. Degussa P25 showed a higher photocatalytic degradation efficiency for 5-fluorouracil removal than Aldrich TiO2 and ZnO. Under optimal conditions (20 mg L-1 TiO2 at pH 5.8), 200 μg L-1 5-fluorouracil can be removed within 2 h (k = 0.0375 min-1). 5-fluorouracil was found to be decomposed by near-surface ˙OHfree radicals produced from valence holes (h_vb^+). At a relatively high concentration, 5-fluorouracil (27.6 mg L-1) is >99.9% removed within 4 h by 300 mg L-1 Degussa P25, while 24 h is required to reach complete mineralization with 96.7% fluoride recovery. On the other hand. cyclophosphamide (27.6 mg L-1) was also >99.9% eliminated within 4 h, but dechlorination and mineralization reached only 79.9% and 55.1%, respectively, after 16 h of irradiation. Together with the results for MicrotoxR, it is suggested that the oxidation products of cyclophosphamide are even more recalcitrant and toxic. In order to apply photocatalytic oxidation system under visible light, visible light responsive TiO¬¬¬2 has been widely studied for several years. Among visible light responsive TiO2, N-doped TiO2 has been received much more attention because of its higher photoactivity and relatively simple manufacture process. Microwave has been considered as a promising and energy saving process as synthesis in the recent years. The microwave-treated N-doped TiO2 removed 5-fluorouracil with a higher degradation efficiency than N-doped TiO2 synthesized with the traditional thermal treatments. The most efficient N-doped TiO2 (N6) was synthesized using 1 M NH4OH pre-immersion and a 3 h 180°C microwave treatment, followed by 550°C calcination for 6 h. The photocatalytic degradation of 5-fluorouracil achieved 88.8% removal within 20 h of treatment by N6 under visible light, which is higher than that obtained by Degussa P25 TiO2 (61.5%). Higher concentrations of NH4OH and longer calcination times resulted in decreased 5-fluorouracil degradation; the particle size of the synthesized N-doped TiO2 increased after calcination. The surface area decreased while the pore volume and pore size increased after synthesis. Furthermore, the basicity of the sites on the synthesized N-doped TiO2 decreased after calcination. Photocatalytic oxidation was shown to be effective in decomposing 5-fluorouracil and cyclophosphamide, therefore, it has potential to apply to hospital wastewater treatment plants. However, the effects of water matrix, the relationship between toxicity changes and by-products, mineralization must be the important considerations and necessarily investigated before real application.