| 摘要: | 奈米零價金屬因具有反應迅速以及還原能力強的特性，能有效地去除水中污染物，已被廣泛應用在水污染之整治上。惟金屬在奈米尺寸下，容易造成團聚效應，降低奈米金屬在水中的去除效果。本研究主要目的，就是將奈米金屬分散附著在載體上，防止奈米金屬團聚，藉此提高處理效率。近年薄膜的技術持續突破，由於沒有二次污染的問題，且許多的應用也得到很好的處理效果。除了傳統的過濾外，許多研究也針對薄膜特性加以改質，以加強薄膜的處理效率。由於PVDF薄膜具有高化學抵抗力，在室溫下不被酸、鹼、強氧化劑和鹵素所腐蝕，且較高的耐壓性及極佳之機械強度且抗氯性也比PS膜更高，故常被廣泛的用來製造MF及UF膜。由於單一材質的膜無法滿足膜系統中應用在實場的需要，所以藉由膜表面進行改性使其具有某些需要的性能，以提高分離效率。膜表面接枝聚合物是膜表面改性的重要手段之一。膜表面改質有下列各種方法：化學氧化、有機化學反應、電漿改質、接枝、交聯。零價金屬廣泛應用於污染物的去除、土壤及地下水污染整治工作上具有相當的效果。尤其零價鐵是近年來研究重點，若金屬發展至奈米尺寸，則粒子與粒子間相互吸引、碰撞造成團聚現象，致使喪失原有奈米粒子表面效應之優勢。因此，減少團聚現象乃成為奈米金屬首要克服之難題。使用PVDF做為奈米金屬之載體，利用化學交聯方式配製聚丙烯酸合成溶液，經加熱後金屬離子則分散在PVDF表面，金屬離子以NaBH4還原成零價金屬，即為奈米金屬複合膜。聚丙烯酸溶液內含有乙二醇及金屬鹽類。其中乙二醇則扮演交聯之角色，交聯PVDF和聚丙烯酸，而聚丙烯酸做為金屬螯合劑主要連接金屬離子經離子交換形成奈米粒子。本研究乃結合微孔濾膜（MF）和奈米零價金屬（nZVM）之優點加以合成，以以聚偏二氟乙烯(PVDF)微孔濾膜作為奈米零價金屬之載體，藉由聚丙烯酸(PAA)溶液以交聯方式將奈米零價金屬合成在微孔濾膜上，成為奈米零價金屬之複合膜；再利用化學還原法讓鐵金屬還原為奈米零價金屬，並均勻分佈在微孔濾膜上。此外，並加入第二種奈米零價金屬（鎳），以批次實驗分別在不同pH值(4.0及7.0)及不同膜孔徑(0.1μm, 0.22μm, 0.45μm, 0.65 μm )，探討奈米零價鐵與奈米零價鐵鎳雙金屬之金屬複合膜對Cr(Ⅵ)的去除效果，並選擇出處理效果較佳之奈米零價金屬複合膜，同時對照比較金屬複合膜、微孔濾膜和奈米零價金屬對於Cr(Ⅵ)之處理效率的差異以及不同金屬複合膜製備方式及pH值變化對水中Cr(Ⅵ)去除效果之影響。最後將探討不同膜孔徑之複合膜對Cr(Ⅵ)去除之機制是還原或吸附作用。
The nanoscale zero-valent metal (nZVM) containing properties of quick reaction and high reduction ability could remove efficiently the contaminations in water environment, which is widely used in current wastewater treatment process. However, the metal size at nanoscale is easily to form cluster effect that decrease its removal efficiency in water. Therefore, the purpose of this study is to coat dispersedly the nanoscale metal onto the supporting layer to prevent its cluster effect, and finally enhance the treatment efficiency. In these three decades, the membrane technology increases dramatically. Many of their applications have resulted in excellent outcomes owing to problems free of second pollutions. Moreover, despite the traditional filtration process, many researchers have devoted their attentions to improve the material properties of membrane, as well as enhance the treatment efficiency. Because the PVDF membrane contains high resistance of chemical effect, free erosion under various conditions of acid, base, strong oxidant and halogen in room temperature, high pressure resistance and great mechanical strength, and higher chlorine resistance than PS membrane, it is used widely in producing MF and UF membranes. However, single material in making various types of membrane is not sufficient to fulfill the requirements of membrane process in field applications. The surface modification of membrane is necessary to acquire needed properties to enhance the treatment efficiency. The membrane grafted polymer brushes is considered as an essential technique to modify the membrane surface, which includes the process of chemical oxidation, organic chemistry reaction, plasma treatment, graft, and crosslinking process . In recent years, zero-valent metal has widely used in the areas of pollutants removal, and has illustrated excellent efficiency in soil and groundwater remediation. However, the cluster effect of metallic particles under nanoscale was considered as a serious drawback in losing its advantage on surface effect of nanoparticles, which is also a major obstacle to overcome. Therefore, Hydrophilized PVDF MF membrane was ever used as the supporting layer. An aqueous coating solution was prepared by polyacrylic acid (PAA) solutions with ethylene glycol as the crosslinking agent. After heating, M1 n+ (Fe2+) in the PAA layer was reduced by NaBH4 to form nanoscale M1 particles. Thus, the metallic nanoparticles were synthesized to form PAA/PVDF membrane matrix. This study combined the advantages of MF and nZVM. The membrane-based nZVM was synthesized by using polyvinylidene (PVDF) as the supporting layer to crosslink with the metallic nanoparticles (NPs) by polyacrylic acid (PAA). The metal on the membrane matrix was reduced by NaBH4 to form nZVM particles. Moreover, the second metal (Ni) was added to form Fe/Ni NPs membrane matrix. The bench scale experiments for Cr(VI) removal by two different metallic NPs membranes were conducted under different conditions of various pH values (4.0 and 7.0) and polar sizes (0.10μm, 0.22μm, 0.45μm, and 0.65 μm). The metallic NPs membrane that illustrated the best performance was carefully examined and confirmed. The differences of Cr(VI) removal by bimetallic Fe0/Ni0 NPs membrane, MF membrane and nZVM were executed and compared. Finally, the Cr(VI) removal under different process in making metallic NPs membrane, various pH values and mechanisms were executed and evaluated. |
