Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/5281
標題: 以CVD法製備二氧化鈦光觸媒去除甲苯之研究
Photocatalytic oxidation of gasous toluene on TiO2 preparing by CVD method
作者: 林蔡毓
Lin, Tsai-Yu
關鍵字: photocatalysis;光催化;TiO2;toluene;CVD;FTIR;二氧化鈦;甲苯;化學氣相沈積法;傅立葉紅外線分析儀
出版社: 環境工程學系
摘要: 
中文摘要
本研究係以化學氣相沈積法(CVD)披覆二氧化鈦光觸媒於環管狀反應器上,藉由SEM及XRD的觀察,了解在不同氧化溫度及鍛燒溫度下,觸媒的粒徑分布及晶型變化,並採用365nm波長之UV燈管置於反應器中央作為激發光源,以連續流方式在,初始濃度、反應氣體流量、光照強度、溼度、氧氣含量等控制因子下,進行甲苯之異相光催化分解反應的探討。此外,並利用傅立葉紅外線光譜儀(FTIR)觀察中間產物及TiO2表面吸附物種的變化,推估其可能的反應機制與途徑,並了解其吸附機制。最後,對反應後的最終產物作分析,以瞭解甲苯在各種參數下之礦化情形。
實驗結果顯示,在觸媒製備方面:二氧化鈦粒徑約介於1µm-5µm之間,呈圓球或米粒型均勻分布,在未經鍛燒的情況下,只有氧化溫度200oC時沒有結晶,其餘皆有anatase晶型產生;在經過不同溫度鍛燒後,只有在850oC下,發現少部份的rutile晶型,但大部分皆以anatase為主,經過通以甲苯氣體照UV光測試,以氧化溫度350oC、550oC鍛燒下的轉換率最高。
在各種異相光催化的參數探討方面:甲苯的分解速率、轉換率及礦化率分別介於0.01-0.21µ mole/s-m2、0.05-0.95和0-0.15之間,觸媒在通反應氣體8分鐘後開始有活性衰退的現象發生,並有淡黃色物質覆蓋於觸媒表面,經停止進流並光照30分鐘後可將觸媒活化,但在無水氣存在下照光,則無法活化觸媒。流量的增加使得反應速率呈現下降的趨勢。就溼度的影響效應而言,水分子的存在對甲苯的分解有明顯的抑制作用,反應速率隨著濕度的增加而有降低的情形。氧氣在反應中扮演著電子捕捉者的角色,而降低了電子-電洞對重組的速率,因此反應速率隨著氧氣的增加而上升,但當氧含量達20 %後,反應速率則沒有顯著的影響。而初始濃度的增加使得反應速率增加,轉換率維持穩定,但當濃度大於4.7µM後,反應速率及轉換率皆快速減小。隨著光照強度的增加則增加了光子數目,則使得反應速率上升。
反應過程中,由FTIR偵測到的官能基推測,氣相中的二氧化碳及水分子會隨反應時間增加而增加,並有類似苯甲醛、苯及酚的波峰出現。在二氧化鈦表面,甲苯分子與其形成弱鍵結,會因真空抽氣而脫附。在水氣及氧氣存在下,施以UV光照,則觸媒表面有大量-COOH基的相關波峰生成,可能是苯甲酸的累積,且可能與觸媒活性衰退有關。將累積物種在負壓下持續光照,則發現反應在1分鐘內即不再變化,觸媒表面-OH基及-COOH基減少,但苯基及二氧化碳則大量增加,推測可能為苯甲酸利用觸媒表面-OH基所生成之氫氧自由基,氧化成苯及二氧化碳之故。

Abstract
This investigation used a tube reactor deposited TiO2 thin film inside by chemical vapor deposition (CVD) method and installed a UV lamp with 365 nm wavelength to study the heterogeneous photocatalytic reaction of gasous toluene. SEM and XRD were used to analyse the size and crystal structure of catalyst under different reactive temperature and annealing temperature. The influence of the parameters controlled in the photocatalytic reaction including concentration of reactant, flowrate, humidity, oxygen contain and light intensity was investigated in this research. The intermediates of reacton in gas phase and on the surface of catalyst were monitored by FTIR in order to propose the possible reaction mechanisms and pathways.
The X-ray analyses revealed that TiO2 film was amorphous when deposited at 200oC and had anatase polycrystalline structures when deposited at higher temperatures. We only found the rutile structure when the annealing temperature at 850oC. The best effect of conversion with toluene was reactive temperature at 350oC and annealing temperature at 550oC.
Catalyst deactivation was observed when air containing toluene and water was irradiated by UV lamp for 8 minutes. After irradiating without feeding mixture gas for 30 minutes, the catalyst was regenerated. According to the experimental results, the reaction rate decreased with increasing flowrate. The reaction rate decreased with increasing humidity, indicating moisture inhibited the decomposition of toluene. The reaction rate increased with the increasing oxygen contain. However, when the oxygen contain was higher than 20%(v/v), the reaction was not affected. The reaction rate increased with increasing concentration of toluene due to the increasing concentration gradient between bulk phase and TiO2 surface, but when it was more than 4.7μm, the reaction rate decreased, indicating that the result of catalyst deactivation. Increasing of the light intensity increased the number of photon and reaction rate.
Using FTIR to analyze the gas phase, the CO2 and H2O molecules increased as time went by, and observed the peaks which proposed to be benzaldehyde, benzene and phenol. The molecules of toluene was adsorbed on TiO2 surface with the weak physical bond and could be desorbed by outgassing at —756 torr. After illuminating with UV lamp, we found amount of —COOH groups, indicating the accumulation of benzoic acid which had relationship with the catalyst deactivation. When illumination at —756 torr was remained, the spaces of accumulation on the surface of TiO2 film didn't change anymore within one minute. We observed that —OH group and —COOH group decreased and the —C6H5 group and the CO2 increased, indicating that benzoic acid was photocatalyzed to become C6H6 and CO2.
URI: http://hdl.handle.net/11455/5281
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