改質光電觸媒應用於甲苯去除之研究

Abstract

本研究利用金屬及非金屬共摻雜光觸媒於可見光照射之下，對氣相甲苯進行光催化反應去除之研究。經由研究證實，利用化學沉澱法(precipitation method)製作製備非金屬改質光觸媒，採用初溼含浸法(impregnation)分別添加不同金屬材料於非金屬改質光觸媒之上，合成金屬及非金屬共摻雜光觸媒。並將所合成之觸媒進行特性分析，包含高解析掃描式電子顯微鏡(HRSEM)、穿透式電子顯微鏡(TEM)、元素分析(EA)、能量散射光譜儀(EDS)、表面積及孔隙度測定分(BET)、X光粉末繞射儀(XRD)、X光繞射分析儀(XPS)、紫外可見光光譜儀(UV-Vis)、傅立葉轉換紅外線光譜儀 (FTIR)、螢光光譜儀 (PL)、感應耦合電漿原子發射光譜儀（ICP-OES)、電化學特性分析(Photovoltaic characteristics)等。 經由EA分析，不同濃度銅金屬之摻雜對其元素之含量變化亦有不同之影響，其中5Cu/TNST、10Cu/TNST及12 Cu/TNST之H、S及O含量隨Cu濃度之增加而增加，其中H含量分別為0.13、0.72及0.84 wt.%，S含量分別為0.13、1.16及1.48 wt.% 。由EDS分析結果可以看出金屬元素的成功添加，BET分析結果可以明顯觀察出不同金屬摻雜之觸媒其比表面積皆有下降之趨勢，而摻雜濃度越高其比表面積下降愈多，且TNST隨銅濃度的增加其比表面積從120.71降至88.55 m2 g-1。 由XRD圖譜可以判斷出5Cu/TNST的晶體分布幾乎是銳鈦礦組成。而XPS顯示Cu 摻雜可能為Cu+ 轉變為Cu2+，呈現在2p3/2 及2p1/2 軌域。藉由紫外可見光譜儀分析，5Cu/TNST可換算能階為3.10 eV。經由金屬添加之觸媒於FTIR下之分析結果，主要組成為CH3的伸縮帶、吸收帶及分裂帶。 探討利用金屬及非金屬改質光觸媒10Ag/TNST、10Ce/TNST及10Cu/TNST的光催化效益，其甲苯去除效果依序為10Cu/TNST＞10Ag/TNST＞10Ce/TNST，去除率皆高於80%，其擬一階速率常數 (kobs)分別為0.0158、0.0142及0.0137 min-1。於不同光源(VLL、WLED及RLED)下測試10Cu/TNST於初始甲苯濃度12.60∼16.71 ppmv，其去除效率分別為95.42、85.14及18.13%，其擬一階反應常數 (kobs) 分別為0.0246、0.0158及0.0015 min-1。能量效益分別為0.0623、0.0686及0.0427 mg kWh-1，因此使用LED作為光源於長時間使用下可以有效達到省能之效果。利用濃度分別為2、5、10 及12 wt. %酸銅水溶液對氮硫觸媒進行摻雜，甲苯初始濃度15.17~38.18 ppmv下，反應3小時後去除率分別為5Cu/TNST (100%) >10Cu/TNST (99.06%) > 2Cu/TNST (95.55%) > 12Cu/TNST (77.64%)，可以明顯看出在以VLL為光源，於5Cu/TNST反應下有最佳之降解效果。且於不同初始濃度下，進行Langmuir-Hinshelwood模式(L-H model)估算，可獲得反應速率常數(k)及吸附平衡常數(KL)分別為0.7307 ppmv min-1 及 0.0474 ppmv-1。利用L-H模式模擬的結果與實驗值進行迴歸r2比較，結果顯示低濃度模擬結果良好，因此此模式可適用低濃度污染情況。 連續式反應器測試中，使用UVC為光源，並以二氧化鈦進行催化，對甲苯初始濃度分別從3632.81降至358.06 ppmv，其去除效率從21.26增加到72.38%。同時比較TiO2及TNST在連續式反應器中反應，在TiO2光催化反應下，UVC＞VLL＞5050WLED＞UVLED，其去除率分別為97.75、61.9、32.01及 15.16%，平均為51.71%。在TNST光催化反應下，UVC＞5050WLED＞VLL＞UVLED，其去除率分別為96.99、86.88、61.73及44.93%，平均為72.63%。可見紫外光仍是最有效之光催化反應光源，而日光燈管於TiO2及TNST兩種觸媒反應下無顯著之差異，而在高強度WLED作為光源下，含氮硫之觸媒TNST去除效率為純二氧化鈦之2.7倍。 此外，利用Cu/TNST對甲苯進行光催化，主要是因為金屬在TiO2表面上，使電子有效轉移，增加電子-電洞對分開的週期且提升光催化能階，進而提升甲苯降解率。本研究相關觸媒合成製作、反應器裝置及光催化測試效益，未來可以作為室內或排氣管道VOCs污染物控制反應系統設計參考使用。

This study investigated the photocatalytic activity of metal (copper, silver and cerium) and non-metal (nitrogen and sulfur) co-doped photocatalysts (TNST) and their applications on photodegradation of volatile organic compounds (VOCs), taking toluene as a model compound, at the irradiation of different light sources. The syntheses of metal and non-metal co-doped catalysts were successfully made by incipient wet impregnation method. The operation parameters of decomposition efficiency, such as the temperature and reaction time of autoclave reactor, types of doped metals (Cu, Ag, Ce), light sources (visible light lamp (VLL), light emitting-diode (LED), ultra violet (UV)), intensity of light radiation, fabrication method of photocatalysts, initial concentration (10.96-90.01 ppmv for batch reactor and 3632.81 ppmv for continuous flow reactor), and coating mass percentages of catalysts (0.5-12 wt.%) etc. were evaluated as well as the characteristics and photovoltaic characteristics analysis (EDS, HRSEM, HRTEM, BET surface area, UV-visible, XPS, PL, EA, FT-IR, GC/MS, ICP-OES, I-V curve etc.). Furthermore, the related kinetic models were established to simulate the system behavior and the relationship between degradation efficiency and simulated results. The decomposition efficiencies of toluene for batch reaction with different metal co-doped TNST under VLL irradiation were 10Cu/TNST＞10Ag/TNST＞10Ce/TNST, and their efficiencies reached to 85.14、83.13, and 82.59, respectively. The comparisons with different percentages (2, 5, 10 and 12%) of copper were tested; the maximum degradation efficiency achieved almost 100% at 5Cu/TNST with the removal mass of 731.77 mg g-1 after 50 min reaction. Moreover, the order of other percentages was 10Cu/TNST (99.06%)> 2Cu/TNST(95.55%)> 12Cu/TNST (77.64%) after 3 hr, while the unit removal mass was 745.45, 719.10 and 584.32 mg g-1, respectively. The pseudo first-order rate constant (kobs) of 2, 5, 10, 12 Cu/TNST were 0.0172, 0.0726, 0.0264 and 0.0076 min-1, respectively. Langmuir-Hinshelwood model (L-H model) was then evaluated and simulated for the different initial concentration (10, 25 and 90 ppmv) with the highest efficiency catalyst of 5Cu/TNST. The pseudo first-order rate constant (kobs) of 10, 25 and 90 ppmv were 0.0220, 0.0189 and 0.0056 min-1, respectively. The reaction rate constant (k) and adsorption equilibrium constant (KL) at 5Cu/TNST under VLL irradation were 0.7307 ppmv min-1 and 0.0474 ppmv-1, respectively. In the deactived test, the reused times after consecutive run was more than four times. Furthermore, in the test of continuous flow reaction with UVC (λ=254 nm) irradiation and TiO2 (P25), while the initial concentration of toluene was decreased from 3632.81 to 358.06 ppmv, the photodegradation efficiency increased from 21.26 to 72.38%. The unit removal mass of toluene increased from 44.45 to 151.31 mg/ g-TiO2 as the initial concentration decreased from 3632.81 to 358.06 ppmv. The photocatalytic degradation efficiency increased with the initial concentration decreased significantly. The different light sources and photocatalysts also used in the continuous flow reaction. In the TiO2 reaction , the order of different light source was UVC (97.75%)＞VLL (61.90%)＞5050WLED (32.01%)＞UVLED (15.16%) with the average value of 51.71%. In the catalyst of TNST, the order was UVC (96.99%)＞5050WLED (86.88%)＞VLL (61.73%)＞UVLED (44.93%) with the average value of 72.63%. The efficiency of TNST was higher than that of TiO2 obviously. All the results obtained from this study can provide the useful information and design specifications to the industrial, domestic and scientific researchers. Finally, effectively energy saving and environmentally novel technologies for the removals of VOCs will be elucidated by this study.