奈米級二氧化鈦-零價鐵複合材料去除水中硝酸鹽之研究

Abstract

以零價鐵(nFe0)或二氧化鈦(TiO2)處理水中硝酸鹽之可行性在過去研究中已被證實。但礙於反應最終產物均以氨氮(NH4+)為主，且nFe0氧化快速，形成氧化鐵包覆於外，阻礙電子之傳遞及二價鐵(Fe2+)釋出；此外，TiO2經光激發躍遷之電子，會因能階不穩定而導致電子再回覆現象的發生。以上問題均會造成nFe0或TiO2於應用時，效能受到限制。因此，實驗室自行開發一新型奈米級二氧化鈦-零價鐵複合材料(Nano-TiO2-Fe0 composite；NTFC)，來改善此問題。本研究中將針對NTFC還原效能進行評估，並應用於水中硝酸鹽之處理與探討其初步之反應機制。 NTFC於酸性(pH 3)且有UV光激發之情況，能長時間下持續釋出Fe2+，維持水體處於還原態，相較於nFe0能具有較佳的還原能力，提升對污染物之處理效能。硝酸鹽之去除研究上，pH值、NTFC之合成比例及劑量均影響硝酸鹽之去除率及氮物質之轉換情形；反應之最佳條件為pH 3、NTFC (1:10)：0.25 g/30 mL，對硝酸鹽能有近95%的去除率，且反應最終能有37%的氮氣轉換率。由於NTFC於反應過程中能持續釋出高濃度之Fe2+，此外也產生大量H2，在TiO2觸媒的作用下更能促使H2與污染物反應。由實驗結果證實NTFC能有效應用於硝酸鹽之處理，且氮氣之轉換效率較nFe0佳。

Nano-zero-valent iron (nFe0) and titanium dioxide (TiO2) have been widely applied for the treatment of nitrate in water. However, the treatment produces ammonium (NH4+) as the end product of nitrate reduction, which is another pollutant in water. Moreover, the treatment efficiency is limited by the formation of the metal oxide layer on the nFe0 surface and the recombination phenomenon on the TiO2. Therefore, a nano-TiO2-Fe0 composite (NTFC) material was developed in our laboratory to overcome these problems. The reductive ability of NTFC was first investigated and the feasibility of NTFC treatment for nitrate removal was evaluated. The result showed that at pH 3 and under UV irradiation, the ferrous iron (Fe2+) concentration increased continuously in the NTFC system. Compared with the nFe0 system, the NTFC system performed more effectively in nitrate reduction. In NTFC system, it was found that the nitrate reduction was strongly affected by the pH, NTFC dosage and the ratio of TiO2 and nFe0 in NTFC. The system favored more acidic and higher NTFC dosage. At pH 3 and the NTFC (TiO2: nFe0 = 1:10) dosage of 0.25 g/30 mL, 58% of nitrate was reduced to NH4+ while 37% turned into N2. The higher nitrate removal and N2 conversion rate under this condition was most likely due to the high Fe2+ and H2 generations from the NTFC. In conclusion, the NTFC is feasible for nitrate removal from water with high N2 yield.