表面改質之奈米零價鐵及其在處理含鉻污染地下水體之研究

Decontamination of Chromium by Surface-Modification Zero-Valent Iron Nanoparticles

劉宇杰(Yeu-Jye Liu)

指導教授 ： 林錕松

元智大學/工程學院/化學工程與材料科學學系/碩士(2006年)

https://doi.org/10.6838/YZU.2006.00240

摘要

近年來，國內受高污染重金屬污染之地下水體十分嚴重，來源包括電鍍、染整、紡織、皮革、染料工業及玻璃製造等工業，因而造成人體危害及環境之衝擊，因此本研究之主要目的是探討利用化學還原法製備奈米零價鐵粉，經由表面包覆有機分子使零價鐵粉懸浮於水相中並用以吸附鉻，其結果藉由場發掃描式電子顯微鏡(FE-SEM)、X光粉末繞射儀(XRPD)及穿透式電子顯微鏡(TEM)、X光光電子光譜儀(XPS)測試檢測奈米零價鐵粉吸附鉻後之變化與結構分析，以期望進深入了解利用零價鐵粉處理現址含鉻污染地下水體之可能性。
自行合成之奈米零價鐵粉於氬氣烘乾並惰化後XRD圖譜在2θ=44.59處有強訊號與資料文獻相同，並且自行合成之奈米零價鐵粉在FE-SEM圖中為粒徑10-50 nm之球形顆粒，經由BET量測其比表面積為42.557 m2/g總孔體積為0.232 cm3/g，利用XPS/ESCA分析表面Fe/O之比例為0.54，並且含有FeO, Fe3O4, α-Fe2O3, FeSO4 ,FeB ,B2O3等訊號在自行合成並惰化之零價鐵粉表面。
以不同種類有機分子包覆奈米零價鐵粉實驗：油酸包覆零價鐵粉在FE-SEM下為球形顆粒鏈狀連接在一起，在TEM下觀察包覆最完整外層為5-7 nm包覆膜，並由FTIR在2849 cm-1及2913 cm-1處測得CH2之訊號，XRD圖被油酸包覆後訊號不明顯，被油酸包覆的零價鐵粉比表面積為2.137 m2/g總孔體積為0.125 cm3/g，置於水相中仍會發生聚集無法分散；聚乙二醇(PEG)包覆零價鐵粉在FE-SEM下以直徑約200 nm外層為片狀的微球形式將零價鐵粉包在裡面，由TEM分析外層應為50 nm的PEG與氧化鐵混合層並且以FTIR分析在3383 cm-1處有寬的OH訊號但在XRD下幾乎完全沒訊號，被PEG包覆的零價鐵粉比表面積為54.261 m2/g總孔體積為0.362 cm3/g，置於水中1 h內幾乎完全沉澱；聚乙基亞胺(PEI)包覆零價鐵粉於FE-SEM下為球狀顆粒，於TEM下膜厚難分別但在FTIR顯示出在3380 cm-1處有一寛的NH訊號而在XRD下2θ=44.83處出現微弱訊號，被PEI包覆的零價鐵粉比表面積為29.469 m2/g總孔體積為0.235 cm3/g，置於水中可在水中懸浮時間達數天以上，由於在TEM不明顯因此用XPS/ESCA縱深分析其包覆層厚度結果約2 nm。
由於本實驗目的在製備能分散懸浮於水相之零價鐵粉，因此實驗後以PEI為主要包覆零價鐵粉藥品：PEI濃度以800 ppm為可控制零價鐵粉於水中懸浮粒徑達最小；利用AA量測批次實驗零價鐵吸附鉻含量，未包覆前的零價鐵粉吸附鉻至穩定時Cr/Fe為165 mg/g而以PEI包覆零價鐵粉吸附鉻至穩定時Cr/Fe為457 mg/g，比未包覆前的零價鐵粉高了約3倍；以XPS/ESCA分析表面相對原子百分比，未包覆前零價鐵粉吸附鉻後表面Cr/Fe為2.07以PEI包覆零價鐵粉吸附鉻後表面Cr/Fe為12.74；比未包覆前的零價鐵粉高了約6倍。對於零價鐵粉吸附鉻後特性變化，在FE-SEM下未包覆零價鐵粉吸附鉻後表面呈鏈形粗糙膨鬆狀，以PEI包覆的零價鐵粉吸附鉻後表面呈不規則大小顆粒團聚；XPS分析比較PEI包覆前後零價鐵吸附6價鉻後表面鉻化合物訊強度號變化，未包覆前零價鐵粉吸附6價鉻後CrOOH的訊號比Cr2O3強而以PEI包覆零價鐵吸附6價鉻後表面Cr2O3訊號強度增加比CrOOH強；延伸細微結構X光吸收光譜(EXAFS)及X光吸收邊緣結構光譜(XANES)分析結果顯示，未包覆零價鐵粉吸附鉻(批次實驗時間三天)後並未完全氧化仍含有零價鐵訊號並且反曲點介於FeO及Fe3O4之間，以PEI包覆零價鐵粉吸附鉻後反曲點最接近Fe3O4，零價鐵粉吸附鉻(管柱實驗時間三天)反曲點介於FeO及Fe3O4之間。藉由EXAFS分析Cr-O鍵距為1.98 ± 0.01 Å並幾乎沒變化，被零價鐵粉還原後鉻中心原子配位數為3.5，而以PEI包覆的零價鐵還原後鉻中心原子配位數接進4；Fe-O的鍵距約為1.99 ± 0.01 Å對於鐵而言其中心原子配位數都為4。
關鍵詞：奈米零價鐵粉、表面包覆、油酸、聚乙二醇、聚乙基亞胺、含鉻污染地下水體、XPS、延伸細微結構X光吸收光譜/X光吸收邊緣結構光譜。

關鍵字

奈米零價鐵粉 ； 表面包覆 ； 油酸 ； 聚乙二醇 ； 聚乙基亞胺 ； 含鉻污染地下水體 ； XPS ； 延伸細微結構X光吸收光譜/X光吸收邊緣結構光譜

並列摘要

In resent years, groundwater polluted by heavy metal was very serious in Taiwan. The contaminant produced by industry of electroplating, spinning or dyeing is known to be toxic and carcinogenic. Therefore, the main objectives of the present study were to investigate chemical reduction of chromium by nanoscale zero-valent iron (ZVI) in aqueous solution and related reaction kinetics or pathways. The characteristics and identifications of ZVI nanoparticle or nanofims were also conducted. Nanophase zero-valent iron powders encapsulated with polyethyleneimine (PEI) nanofilms could be enhanced the dispersion or transportation abilities and contamination removal efficiency in the chemical reductive treatment processes.
By FE-SEM analyses, spherical ZVI nanoparticles with a diameter of 10-50 nm are measured. ZVI nanoparticles having a strong main characteristic peak at 2θ = 44.59 were investigated by XRD patterns. The specific surface area and pore volume of ZVI nanoparticles measured by BET isotherms are 42.557 m2/g and 0.232 cm3/g, respectively. From XPS/ESCA spectra, the proportion of Fe/O is 0.54 on ZVI nanopaerticle surface including the main species of FeO, Fe3O4, α-Fe2O3, FeSO4, FeB, and B2O3.
By using the surface coating of oleic acid (OA), ZVI nanopartilces were in the chain form of spherical particle and linked together measured by FE-SEM analyses. The OA/ZVI nanoparticles with 5-7 nm outside nanofilms, surface area of 2.137 m2/g, and the pore volume of 0.125 cm3/g were measured by TEM and BET, respectively. Similarly, ZVI nanoparticles coated with polyethylene glycol (PEG) in the form of spheical particle with 200 nm, outside mixing layer of 50 nm for PEG and iron oxide nanofilms, surface area of 54.261 m2/g, and the pore volume of 0.362 cm3/g were analyzed by FE-SEM, TEM, and BET isotherms, respectively. In addition, ZVI nanoparticles coated polyethyleneimine (PEI) in the form of spheical particle were measured by FE-SEM microphotos. PEI/ZVI nanoparticles having weak main characteristic peak at 2θ = 44.83, surface area of 29.469 m2/g, the pore volume of 0.235 cm3/g, and the thickness of PEI nanofilm of 2 nm were identified by TEM, BET isotherms, and XPS/ESCA, respectively.
The surface properties of Cr(VI)-absorbed ZVI and PEI/ZVI nanoparticles were measured by XPS/ESCA technique. The relative atomic percentages of Cr/Fe on the surfaces of ZVI and PEI/ZVI nanoparticles were 2.07 and 12.74, respectively. By using FE-SEM analysis, the surface of Cr(VI)-adsorbed PEI/ZVI nanoparticles was incompact with abnormal size nanoparticles. The existence of Cr(III) species on the Cr(VI)-adsorbed PEI/ZVI nanoparticles was also confirmed by XPS measurement. It was also found that main CrOOH and Cr2O3 species were adsorbed on the surface of PEI/ZVI nanoparticles. In addition, the XANES spectra showed that the valency of Fe atoms for Cr(VI)-absorbed PEI/ZVI nanoparticles is 8/3. Similarly, the valency of Fe atoms for Cr(VI)-absorbed ZVI nanoparticles is between 2 and 3. It may be due to the positive charge of PEI coated on well-dispersed ZVI nanoparticles that can enhance the chemical reduction of Cr(VI) species on the ZVI nanoparticles.
Keywords: Zero-valent iron nanoparticle, Surface coating, Olceic acid, Polyethylene glycol, Polyethyleneimine, Chromium contaminants, XPS, XANES/EXAFS.

並列關鍵字

Zero-valent iron nanoparticle ； Surface coating ； Olceic acid ； Polyethylene glycol ； Polyethyleneimine ； Chromium contaminants ； XPS ； XANES/EXAFS

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