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標題: 摻氮比例及鍛燒溫度對於氮摻雜二氧化鈦之特性分析及其光催化反應動力模式探討
The Effect of N/Ti Molar Ratio and Calcination Temperature on the Characteristics of N-Doped TiO2 Catalyst and Kinetics of Heterogeneous Photocatalytic Oxidation of Ethylene
作者: 許惠然
Hsu, Hui-Jan
關鍵字: 摻氮二氧化鈦;N-doped TiO2;溶膠凝膠;摻氮比例;鍛燒溫度;乙烯可見光光催化;sol-gel method;doped nitrogen molar ratios;calcinations temperature;visible light photocatalytic of ethylene
出版社: 土壤環境科學系所
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研究結果顯示,批次可見光光催化反應降解乙烯,發現本研究最理想之氮摻雜二氧化鈦光觸媒材料為鍛燒溫度400℃,摻氮比例2.0莫耳比。因此,材料特性影響之實驗結果顯示,針對最佳鍛燒溫度為400℃,摻氮比例2.0莫耳比進行探討。熱量重量損失之結果發現二氧化鈦銳鈦礦相轉變成金紅石相溫度有遲緩之現象,符合晶相結構分析之結果。晶相結構得知最佳摻氮光觸媒材料有較小之結晶尺寸約為28 nm,其尺寸相近高解析穿透式電子顯微鏡之最小奈米結晶尺寸約為11 ± 1 nm。比表面積及孔徑分佈方面顯示等溫吸脫附曲線在400℃為類型IV,而遲滯環為類型H3,此顯示於摻氮條件可形成良好之介孔洞結構;觸媒也顯示有較大之比表面積與孔洞體積,分別為98m2/g與0.26 cm3/g,而相對孔洞尺寸分佈曲線與孔洞尺寸可得知有較小之孔洞尺寸約為65 nm。粒徑尺寸呈現稍不規則之變化,但大致趨勢可發現較低溫度與較高摻氮比例有較小之粒徑尺寸。選區繞射 (SAED) 發現鍛燒溫度於400℃時,有良好之銳鈦礦相之繞射環,其平面晶相d-sapcing 約為0.35 nm,符合晶相結構鍛燒低溫結果。紫外光-可見光吸收光譜之波長範圍於400 – 550 nm,有較佳可見光吸收值之現象。X射線光電子能譜之N 1s可發現於399 - 400 eV範圍內有波峰鍵結能,皆屬於間位氮 (Interstitial N) (Ti-O-N) 鍵結之範圍,此為氮原子鍵結於氧原子所產生之化學鍵結。表面官能基看到於光催化反應前只有O-H團吸附於觸媒表面,而經過光催化反應後,其觸媒表面有更多之O-H團及水分子吸附於觸媒表面。元素分析因受限於儀器分析背景訊號,而有較不規則之變化,但大致趨勢以較低溫度與較高摻氮比例有較多之氮含量摻雜進入二氧化鈦。
可見光光催化降解乙烯試驗中,影響光催化環境控制因子可分為氣體流速、乙烯初始濃度、水氣濃度、氧氣濃度、光強度及反應溫度等六大影響因子。氣體流速方面,氣體流速 < 1000 mL/min,受限於質傳控制;氣體流速 > 1000 mL/min,受限於表面反應控制。乙烯初始濃度方面,乙烯初始濃度 < 500 ppmv,活性位置尚未佔滿,乙烯初始濃度 > 500 ppmv,活性位置則已填滿,未能再增加乙烯降解速率。水氣濃度方面,水氣濃度 < 1561 ppmv,有更多氫氧自由基進行光催化反應;水氣濃度 > 1561 ppmv且 < 6239 ppmv,水分子與乙烯分子競爭而減少活性位置,歸因同類型於光觸媒表面;當水氣濃度 > 6239 ppmv,活性位置則已填滿,不會再降低乙烯降解速率。氧氣濃度方面,氧氣濃度 < 50000 ppmv,有更多超氧自由基進行光催化反應;氧氣濃度 > 50000 ppmv,其光催化所需氧氣分子含量已足夠,更多氧分子含量未能進一步增加降解速率,與乙烯分子屬於不同類型於光觸媒表面,因此也不會抑制光催化乙烯降解速率。可見光強度方面,隨光強度增加有更多之光源能量使電子電洞對受光能量激發而分離,且減少電子電洞對再結合作用,達到增加光催化降解乙烯速率,本實驗之可見光源效能約為0.49。反應溫度方面,較低反應溫度能使水氣置換TiO2表面吸附的乙烯分子,因此水氣會抑制乙烯的反應效率;較高反應溫度則使水分子親和性降低,致水分子蒸發或熱脫附,表面釋出大量活性位址,促進乙烯催化之反應速率。

The conservation deadline of vegetables and fruits are limiting with plants hormone ethylene which always are promoting them ripe. Therefore, we use the photocatalyst of N-doped TiO2 degrade ethylene pollutant under visible light response. It aims that we can remove of ethylene for vegetables and fruits, improving the conservation deadline of vegetables and fruits. In our studies, the titanium tetraisopropoxide and aqua ammonia are titanium and nitrogen precursor, respectively. We had focused on the sol gel synthesis of N-doped TiO2 at calcination temperatures and various Aqua ammonia/TTIP molar ratios for photocatalyst of N-doped TiO2 characterized effect, in order to establish optimum synthesis parameter. Eventually, N-doped TiO2 were evaluated photocatalytic activity for the decomposition of the ethylene target pollutant under the visible light irradiation.
The research result indicates that the optimum synthesis condition is calcinations temperature 400℃ and ammonia/TTIP 2.0 molar ratio for photocatalyst of N-doped TiO2. Hence, we focused on calcinations temperature 400℃ and ammonia/TTIP 2.0 molar ratio to discuss. On the part of caloricity and gravity loss, it retards the phase of titanium dioxide transformation from anatase to rutile, consistency with crystal structure results. Respecting crystal structure, we can find that the optimium N-doped TiO2 photocatalyst possesses the smaller crystalline sizes about 28 nm, to approach with the nanocrystalline size about 11 ± 1 nm for crystal morphology results. In the way of BET, the adsorption-desorption isotherm curve of photocatalysts of N-doped TiO2 calcination at 400℃ belong to type IV, and the hysteresis loops displays H3, that is formation the good mesopores structure with the nitrogen doped into lattice of titanium dioxide. It exhibits the large specific surface areas and pore volumes for 98 m2/g and 0.26 cm3/g, respectively. It also presents the smaller pore sizes about 65 nm. Particle sizes reveal that the irregular change, but it discovers the smaller particle sizes with the lower temperature and higher nitrogen doped molar ratios. For selection area election diffraction, it’s the good phase of anantase of titanium dioxide diffusion rings calcinations at 400℃, and the interplaner d-spacing is about 0.35 nm for phase of anatase, consistent with the crystal structure results. The absorption wavelength between 400 - 550 nm for UV-visible displays excellent visible light range absorption. The x-ray photoelectron spectroscopy of N 1s bind energy range between 399 – 400 eV exhibit the peak which belong the interstitial N, namely the nitrogen atoms bond after the oxygen atoms. On the part of surface fundation analysis, the N-doped TiO2 photocatalyst presents the O-H groups adsorption on the photocatalyst surface before the photocatalytic reaction, however the more ones after the photocatalytic reaction. For element analysis, the N-doped TiO2 photocatalyst reveals irregular change due to the bad instrument analysis signal, notwithstanding it discovers the smaller particle sizes with the lower temperature and higher nitrogen doped molar ratios.
There are six environmental effect factors inclunding flow rate, ethylene initial concentration, water concentration, oxygen concentration, light intensity and reaction temperature for photocatalytic reaction test decomposes ethylene under the visible light irradiation. Respecting of flow rate smaller than 1000 mL/min, it exposes limiting due to the mass flow control; the flow rate larger than 1000 mL/min, it shows limiting owing to the surface reaction control. On the part of ethylene initial concentration smaller than 500 ppmv, the activity sites of photocatalyst is unoccupied fully; the ethylene initial concentration larger than 500 ppmv, the activity sites of photocatalyst is occupied fully, cannot increasing the ethylene degrade rate. In the way of water concentration smaller than 1561 ppmv, it processes photocatalytic reaction with the much hydroxyl radical; the water concentration larger than 1561 ppmv and smaller than 6239 ppmv, it reduces the activity sites of photocatalyst because of water molecular competition with ethylene molecular owing to the same type of photocatalyst surface activity sites; the water concentration larger than 6239 ppmv, the activity sites of photocatalyst has been occupied fully, did not decreasing the ethylene degrade rate. Respecting of oxygen concentration smaller than 50000 ppmv, it operates photocatalytic reaction with the much superoxide radical; the oxygen concentration larger than 50000 ppmv, the oxygen molecular is much enough and can not improve the ethylene decomposition rate with increasing the oxygen concentration. Moreover, oxygen molecular cannot competition with ethylene molecular due to the different type of photocatalyst surface activity sites. On the part of light intensity, there are much light source energy can let the electron-hole pairs dispersion with increasing the light source intensity, and reducing the recombination of electron-hole pairs, promoting the ethylene decomposition rate. In our research, the light intensity efficient is about 0.49. In the way of reaction temperature, water molecular can substitute the ethylene molecular on titanium dioxide surface with low reaction temperature. Hence, the water concentration inhibited ethylene degrade rate; water molecular reduces the hydrophilic ability with high reaction temperature, leading water vapor or desorption and releasing a large number of activity sites of photocatalyst. Therefore, It can improve ethylene degrade rate.
其他識別: U0005-0108201211565600
Appears in Collections:土壤環境科學系

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