- 學位論文
二氧化鈦包覆奈米零價鐵之製備及其處理硝酸鹽及亞硝酸鹽廢水之研究
Synthesis of Photocatalytic Titania/Zero-valent Iron Nanocomposites for Remediation of Nitrate and Nitrite in Wastewater
摘要
本研究主要目的為探討表面改質之奈米零價鐵之製備及其處理硝酸鹽及亞硝酸鹽廢水之效率，實驗部分是將polyethyleneimine (PEI)及TiO2包覆於奈米零價鐵表面進行改質。PEI包覆實驗部份利用化學還原法製備奈米零價鐵顆粒，經由表面包覆有機高分子使零價鐵粉懸浮於水相中得到PEI包覆之奈米零價鐵；TiO2包覆實驗部份，分別以Titanium isopropoxide (TTIP)及Tetrabutyl orthotitanate (TBOT)為前驅物合成TiO2包覆奈米零價鐵，並以貴重儀器鑑定其表面形貌與化學結構，比較不同表面改質特性對處理硝酸鹽及亞硝酸鹽廢水的效率及可能的反應機制。 由FE-SEM分析可知，奈米零價鐵之粒徑大小在80-100 nm左右，經PEI包覆後的奈米零價鐵，粒徑分布在20-30 nm左右，顯示團聚現象已明顯改善。比較水相中的懸浮效果，改質後之奈米零價鐵可懸浮數月而不沉降，明顯優於未改質之奈米零價鐵。經TEM分析結果顯示，以PEI改質之奈米零價鐵可分為中心未氧化的鐵、外層氧化鐵層及最外層有機分子包覆層三部分，由XRD分析結果可知，奈米零價鐵在2θ = 44.59o及64.62o出現特徵峰，符合鐵標準品之圖譜，並經ESCA分析可知，以PEI改質之奈米零價鐵，表面以Fe3O4及α-FeOOH為主，且以α-FeOOH含量較多，PEI包覆前後之奈米零價鐵比表面積分別為40.1及53.4 m2/g，可知奈米零價鐵包覆後比表面積增加。 以TTIP為TiO2的前驅物，製備TiO2包覆奈米零價鐵，經過煅燒可得到anatase之TiO2包覆奈米零價鐵。另以TEM觀察可知，TiO2包覆奈米零價鐵中心為球狀之奈米零價鐵，外層包覆氧化鐵及amorphous之TiO2；煅燒溫度達500oC時，TiO2成雲狀而包覆在奈米零價鐵的外層。並由FE-SEM分析結果可知，零價鐵表面包覆TiO2後表面粗糙，形狀呈塊狀，無法觀察到內部之核心粒子；以500oC絕氧煅燒後之TiO2包覆奈米零價鐵呈顆粒狀結構、粒徑分佈約20-30 nm。利用XRD分析煅燒前後的變化可知，以瞭解奈米零價鐵被TiO2包覆後之晶形，除鐵的特徵峰並無其他明顯波峰。煅燒溫度達500oC時，除了零價鐵的晶形，於2θ = 25.7o處增加anatase TiO2的特徵峰。包覆TiO2之奈米零價鐵其比表面積亦增加為84.8 m2/g。由XANES分析結果可知，實驗所製備的TiO2包覆奈米零價鐵與Ti4+的吸收峰相疊，TiO2包覆奈米零價鐵反曲點在4984.8 eV，而銳鈦礦反曲點在4984.9 eV的位置，因此可以證明TiO2包覆奈米零價鐵結構為Ti(IV)，另由EXAFS結構參數分析結果可知，合成之TiO2包覆奈米零價鐵，第一層Ti-O的配位數為3.40，鍵長為1.94 Å，結果與TiO2鈦銳鈦礦相近。以TBOT為TiO2的前驅物，製備TiO2包覆奈米零價鐵，由TEM分析可知，核心的奈米零價鐵外層包覆了雲狀具孔洞的TiO2，核心粒徑大小約50 nm，並未出現明顯鍊狀團聚的現象，且包覆亦較均勻。以FE-SEM分析可知，包覆TiO2之奈米零價鐵外觀十分粗糙且有團聚成大小不一的塊狀結構，且無法觀察到內部粒子，與未包覆前的顆粒狀圓球明顯不同。以XRD分析可知，在2θ = 43.14°及2θ = 63.41°為零價鐵的特徵峰，於2θ = 25.42°、37.82°及48.04°則為TiO2銳鈦礦的特徵峰。由XRD分析可知以TBOT為前驅物合成之TiO2其銳鈦礦的晶型較以TTIP為前驅物所合成之TiO2明顯。 以表面改質之奈米零價鐵處理60 ppm之硝酸鹽及亞硝酸鹽廢水，反應時間達30 min，硝酸鹽及亞硝酸鹽廢水的去除率分別約50及70%，反應時間達3 h，硝酸鹽及亞硝酸鹽廢水去除率均可達到100%。而在紫外光環境下，以TiO2/Fe(0)處理60 ppm之硝酸鹽及亞硝酸鹽廢水，當反應時間達3 h，硝酸鹽氮的去除率約為23%，而亞硝酸鹽的去除率約為40%，反應速率緩慢應與TiO2包覆層過厚，使零價鐵能直接與亞硝酸鹽廢水接觸的表面積減少有關。由奈米零價鐵處理硝酸鹽及亞硝酸鹽廢水之氮質量平衡計算可知，隨著硝酸鹽及亞硝酸鹽廢水濃度遞減，氨氮濃度有遞增的趨勢。實驗結果亦顯示硝酸鹽及亞硝酸鹽廢水的氨氮轉化率約為70%，故推測本實驗中奈米零價鐵處理硝酸鹽及亞硝酸鹽廢水的產物以氨氮為主，而副產物應為少量的氮氣。
並列摘要
The main objectives of the present study were to prepare surface-modified zero-valent iron nanoparticles for the remediation of nitrate and nitrite in wastewater. The experimental part contains the synthesis of the material, identification and application to treat with nitrate and nitrite wastewater. Prepare surface-modified zero-valent iron nanoparticles by coating polyethyleneimine (PEI) and titania nanofilms. Coating titania part, Titanium isopropoxide (TTIP) and Tetrabutyl orthotitanate (TBOT) were used as the precursors to synthesize titania/zero-valent iron nanocomposites. Characterization of PEI/Fe(0) and TiO2/Fe(0) reacted with nitrate and nitrite wastewater were also investigated by precision instrument. In addition, this study was also carried out to provide information concerning the removal efficiencies and mechanism in the chemical reductive treatment processes for nitrate and nitrite wastewaters. By FE-SEM and TEM analyses, spherical zero-valent iron nanoparticles have a diameter around 80~100 nm. In addition, zero-valent iron nanoparticles coated with PEI in the form of spherical particles with diameter around 20-30 nm were also measured by FE-SEM and TEM microphotos. PEI/Fe(0) has a characteristic peak of Fe(0) at 2θ = 44.59o and 64.62o identified by XRD patterns and surface area of 53.4 m2/g measured by BET isotherms was also investigated. From ESCA spectra, the main species on PEI/Fe(0) surface were Fe3O4 and α-FeOOH. Using TTIP as the precursor to synthesize TiO2/Fe(0) nanocomposites, after calcined at 500oC for 2 h, the single phase of TiO2/Fe(0) nanocomposites became armophous to anatase. By TEM and FE-SEM analyses, TiO2 coating was enwrapped on the zero-valent iron nanoparticles, forming core-shell structure of TiO2/Fe(0) nanocomposites, after calcined at 500oC for 2 h, the TiO2 shell becomes relatively loose and possesses aperture structure with diameter around 20-30 nm. TiO2/Fe(0) nanocomposites has a characteristic peak of anatase TiO2 at 2θ = 25.7o identified by XRD patterns and surface area of 84.8 m2/g was measured by BET isotherms. By using X-ray absorption near edge structure (XANES), the valence and framework of TiO2/Fe(0) are similar with Ti(IV) structures. The EXAFS data revealed that TiO2/Fe(0) had a first shell of Ti-O bonding with bond distances of 1.94 Å and coordination numbers was 3.40. Using TBOT as the precursor to synthesize anatase TiO2/Fe(0) nanocomposites and without heat treatment. By TEM and SEM analyses, the core Fe(0) with diameter around 50 nm and the anatase TiO2 shell relatively loose and possesses aperture structure. TiO2/Fe(0) nanocomposites has characteristic peak of anatase TiO2 and Fe(0) at 2θ = 25.24o、37.82°、48.04° and 2θ = 25.42°、37.82°、48.04° identified by XRD patterns, respectively. Surface-modified zero-valent iron nanoparticles reaction with nitrate and nitrite solution of 60 mg/L as N. The concentrations of the nitrate and nitrite solution were decreased obviously. After 30 min, the nitrate and nitrite removal efficiency were 50 and 70%, respectively. After 3 h, the nitrate and nitrite removal efficiency reached 100%. TiO2/Fe(0) nanocomposites reaction with nitrate and nitrite solution of 60 mg/L as N. After 3 h, the nitrate and nitrite removal efficiency were only 40 and 23%, respectively. According to the mass balance of nitrogenous species during the reactions for the surface-modified zero-valent iron nanoparticles, around 70% nitrate and nitrite were converted to ammonia. It appeared that some of the nitrate and nitrite was converted to nitrogen gas.