疏水性材料包覆海藻酸鈉固定奈米鈀鐵雙金屬選擇性降解四氯乙烯之研究

Selective degradation of tetrachloroethylene by nPd/Fe bimetals immobilized in alginate beads coated with hydrophobic materials

陳建廷(Chen Chien-Ting)

指導教授 ： 黃益助

國立屏東科技大學/工學院/環境工程與科學系所/碩士(2019年)

https://doi.org/10.6346/NPUST201900087

摘要

工業製程中大量使用含氯有機溶劑(Chlorinated organic compounds, COCs)，這些COCs由於工廠不當放置、工廠隨意排放或意外洩漏等行為，對土壤及地下水造成污染。本研究主要目的為合成nZVI、nPd/Fe、nPd/Fe-B和nPd/Fe-B-OA，探討顆粒特性(粒徑、元素等)及影響PCE降解之操作參數如溫度、污染物濃度、還原劑使用量、表面修飾改質、干擾鹽等，並監測實驗過程中之pH、ORP、EC、硝酸鹽、污染物濃度等之變化。結果顯示，EDS的元素分析圖像、SEM和TEM的表面分析圖像及XRD分析圖譜顯示，nZVI、nPd/Fe為典型的晶形金屬，利用海藻酸鹽生物聚合物性質，可將nPd/Fe改質成非晶形金屬，金屬顆粒也較不會從海藻酸晶球上脫落。1 g nZVI的kobs為0.0169 hr-1，去除率為55.7%，當nZVI改質為nPd/Fe，只需0.5 g nPd/Fe，其降解效果就比5 g nZVI佳，再將添加量提升至1 g nPd/Fe，其去除率更提升至>99.9%，證明了雙金屬對於PCE的降解效率是有明顯地提升。nZVI及nPd/Fe還原硝酸鹽(10、100 mg/L)效果都可達到98%以上，兩著皆適合還原地下水中之硝酸鹽，但nPd/Fe-B還原低濃度硝酸鹽(10 mg/L)，其還原效果略低於90%，而其對高濃度硝酸鹽(100 mg/L)的還原效果略低於60%，顯示nPd/Fe-B較不適用於直接還原硝酸鹽。利用兩種不同製備方法所製成之nPd/Fe-B，非晶形nPd/Fe比晶形nPd/Fe對PCE降解具有較佳的反應活性。nZVI之Ea約32.0 kJ，nPd/Fe之Ea約24.2 kJ，nZVI改質成nPd/Fe，其活化能約下降7.8 kJ，表示奈米鐵改質為nPd/Fe雙金屬有利於PCE的降解。在同時含PCE及NO3-溶液與只含單一PCE溶液之降解效率作比較，其kobs和去除率均略微下降，顯示NO3-會干擾nPd/Fe-B降解PCE之反應，系統中之NO3-會和PCE競爭nPd/Fe有限的還原能力，降低PCE之kobs和去除率。nPd/Fe-B在有無塗覆油酸條件下，去除含PCE及NO3-溶液之效能，結果顯示nPd/Fe-B塗覆油酸可提升PCE去除率至96.9%，而NO3-去除率則下降至28.2%，表示nPd/Fe-B塗覆油酸可優先選擇性去除水中的PCE，降低水中NO3-之干擾。nPd/Fe-B在有無塗覆油酸條件下，還原含高濃度NO3-(100 mg/L)之效能，結果顯示未塗覆油酸的最終去除率為57.4%，塗覆油酸最終去除率為7.3%，顯示油酸可有效阻隔NO3-進入nPd/Fe-B。

關鍵字

含氯有機溶劑 ； 海藻酸鹽 ； 非晶形 ； 油酸 ； 硝酸鹽

並列摘要

Large amount of chlorinated organic compound (COCs) is used in the industrial process. As COCs are improperly handled and deliberately or accidentally discharged, it may cause serious soil and groundwater pollution. The main objective of this study is to synthesize the nZVI (nano zero valent iron), nPd/Fe (nano palladized iron), nPd/Fe-B (nano palladized iron bead) and nPd/Fe-B-OA (nano palladized iron bead coated with oileic acid) particles and to study their characteristics such as particle size and contents as well as the operation parameters affecting the PCE degradation such as the reaction temperature, pollutant concentration, reductant dosage, surface modification, interference salt. From the images of elemental mapping of energy dispersive spectrometer (EDS), environmental scanning electron microscope (ESEM), X-ray diffractometer (XRD) and transmission electron microscope (TEM), nZVI and nPd/Fe particles were typical crystalline metals. Sodium alginate, as the biopolymer matrix of the composites, could successfully inhibit the crystallization of Pd/Fe nanoparticles and controlled their formation. Amorphous Fe and Pd were tightly integrated into the alginate matrix, which cannot be solely exfoliated from the whole composites. The observed reaction rate constants (kobs) and removal efficiency (r) of 1 g nZVI was 0.0169 hr-1 and 55.7%, respectively. As the nZVI was modified to nPd/Fe, the degradation effects of 0.5 g nPd/Fe were better than those of 5 g nZVI. As the addition amount was increased to 1 g nPd/Fe, the r was further increased to >99.9%, which proved that the r of bimetal for PCE was significantly improved. The r of nZVI and nPd/Fe to reduce nitrate (10, 100 mg/L) could achieve more than 98%, both were suitable for reducing nitrate in aquifer. But the reduction of nPd/Fe-B for low concentration (10 mg/L) or high concentration (100 mg/L) of nitrate, its r was slightly lower than 90% and slightly less than 60%, respectively, indicating that the nPd/Fe-B might not suitable for direct reduction of nitrate. The nPd/Fe-B synthesized by two preparation methods, the nPd/Fe-B containing amorphous iron had a better reactivity with respect to PCE degradation than that containing crystalline one. The activation energy (Ea) of nZVI and nPd/Fe was about 32.0 kJ and 24.2 kJ, respectively. The Ea decreased about 7.8 kJ as the nZVI was modified to nPd/Fe, indicating that the modification of nZVI to nPd/Fe bimetal was beneficial to the degradation of PCE. The kobs and r of solution containing both PCE and NO3- decreased compared with individual PCE solution, indicating that NO3- would interfere with the degradation of PCE by nPd/Fe-B. NO3- might compete with PCE for the limited reduction capacity of nPd/Fe, reducing the kobs and r of PCE. The effect of nPd/Fe-B on the removal of solution containing both PCE and NO3- in the presence or absence of oleic acid showed that nPd/Fe-B coated with oleic acid increased the r of PCE to 96.9%, while the r of NO3- decreased to 28.2%, indicating that nPd/Fe-B coated with oleic acid could preferentially and selectively remove PCE from water and reduced the interference of NO3- in water. The effect of nPd/Fe-B on the reduction of individual high concentration of NO3- (100 mg/L) in the presence or absence of oleic acid showed that the final r of uncoated oleic acid and application of oleic acid was 57.4% and 7.3%, respectively, indicating that oleic acid can effectively block NO3- into nPd/Fe-B.

並列關鍵字

COCs ； alginate ； amorphous ； oileic acid ； nitrate

參考文獻

行政院環境保護署網站 https://www.epa.gov.tw/

行政院環境保護署土壤及地下水污染整治網 https://sgw.epa.gov.tw/ContaminatedSitesMap/Default.aspx

行政院環境保護署毒理資料庫https://erdb.epa.gov.tw/Subjects/MetaSubject.aspx?topic1=%E5%9C%B0&topic2=%E6%B1%A1%E6%9F%93%E9%98%B2%E6%B2%BB&subject=%E6%AF%92%E5%8C%96%E7%89%A9%E8%B3%AA

行政院環境保護署環境檢驗所https://www.epa.gov.tw/niea/A048BA729D1F7D58

行政院環境保護署網站法規資料庫https://www.epa.gov.tw/Page/1C0ABB5077B6B496