- 期刊
炭化稻草對於2-氯酚之吸附
Carbonized Rice Straw on the Sorption of 2-Chlorophenol
摘要
氯酚廣泛的應用於工業中，但由於儲存與處理不當，常造成氯酚遍佈於環境。又因其對人體健康造成極大危害，USEPA早已將氯酚類化合物列為優先處理的污染物。農業生產過程常造成大量的廢棄物質，若能將其轉變為吸附劑，則可達減廢及再利用之雙重目的。由於黑炭並沒有經過活化處理過程，可能導致黑炭具有與活性碳不同的吸附特性。因此，本試驗以不同溫度炭化之稻草作為吸附劑，探討製備條件對於黑炭表面結構的影響，並比較不同製備條件下之黑炭對於2-氯酚吸附。結果指出，黑炭於pH 4時對於2-氯酚的吸附量高於pH 10，主要原因在於pH 10時，2-氯酚為陰離子型態(pKa=8.3)，溶液中的氫氧根會與其競爭黑炭表面的吸附位置。而700℃下炭化之黑炭對於2-氯酚之吸附量高於400℃的結果，可能與高溫時芳香族碳比例的增加有關，此可由13C-NMR圖譜中芳香族碳的含量隨著炭化溫度的增加而遞增證實。而通空氣製備的黑炭對於2-氯酚的吸附量高於通氮氣的黑炭，其原因為空氣中含有20%的氧氣，炭化時氧氣會與碳基質形成富含氧的官能基，此可藉由XPS的半定量及元素分析的極性指標(N+O)/C獲得證實。由於2-氯酚屬於極性的有機污染物，因此，通空氣所製備具較高極性的黑炭，對於2-氯酚的吸附量較高。
並列摘要
Chlorophenols are commonly used in various industries. Due to inappropriate storage or mishandling of the materials, these chemicals have been found in surface water, ground water, atmospheric air, and soils. Chlorophenols are harmful to both ecosystems and human beings. Therefore, USEPA had classified cholorophenols as hazardous chemicals, which need to be treated or cleaned with top priority. A huge amount of agricultural wastes (e.g. crop residues) are produced each year in Taiwan. Disposal of these wastes have become problematic. Thus, conversion of these wastes into organic adsorbents (e.g. black carbon, a carbonized material), the previously mentioned problems may be simultaneously solved. In this study, rice straws, the precursor of adsorbents, were first carbonized at 400 and 700oC under aeration conditions (i.e. sparging with limited air or nitrogen gas) without being chemically or physically activated. The surface structures of carbonized rice straws (CRS) were then characterized using spectroscopic techniques, and were correlated to sorptive properties and capacities of CRS for 2-chlorophenol (2-CP) as influenced by pH. The results showed that sorption of 2-CP on CRS was higher at pH 4 than at pH 10. The dissociation of 2-CP (pKa=8.3) associated with OH ions competition may explain the low 2-CP sorption on CRS at pH 10. Rice straws carbonized at 700℃ exhibited a higher sorption capacity of 2-CP as compared with those carbonized at 400℃. The result may attribute to a significant increase in aromatic C (110-160ppm) with increasing carbonization temperature as evidenced by 13C-NMR spectra. In addition, rice straws carbonized with a limited air exhibited a higher sorption level for 2-CP than that with nitrogen gas. The result was probably due to the incorporation of O2 into the surfaces of CRS, creating a more polar surface, which was evidenced by using an X-ray Photoelectron Spectroscopy (XPS) analysis. In addition, an increase in polarity index [atomic ratio of (N+O)/C], which was calculated by elemental analysis of carbonized samples, was also observed with air sparging. The increase in polarity of CRS may lead to an efficient interaction between polar 2-CP and the polar surfaces of CRS.