以二氧化鈦固定在活性碳纖維分解氣相丙酮及二甲基甲醯胺

Abstract

二氧化鈦光催化技術近來普遍應用於揮發性有機物之處理，此技術具有光穩定性、操作簡單及觸媒便宜等優點。光催化反應速率受到反應濃度及水蒸氣影響，而觸媒低吸附能力意味著與反應物碰撞機會小且慢；而當遇到毒化物種處理時，觸媒活性的衰退造成具危害性的反應物及中間物釋放出。本研究以TO2固定在活性碳纖維(ACF)進行批次循環反應來分解氣相丙酮及毒化物種二甲基甲醯胺(DMF)，另以TiO2固定在玻璃纖維(GFC)作為比較，探討以活性碳纖維之高吸附能力來提升丙酮降解速率並減緩觸媒活性之衰退。 活性碳纖維具有開放性之孔洞，每個吸附孔洞並非都與TiO2有直接性接觸，因此低丙酮初始注入濃度時，吸附之丙酮無法供給TiO2反應，直到活性碳纖維吸附丙酮之表面覆蓋率達到40％後，孔洞皆有吸附丙酮分子而使TiO2反應速率逐漸提升，最佳速率常數比值可達2.1。水蒸氣的存在使得TiO2吸附丙酮能力降低，由於活性碳纖維之高吸附能力能減緩其影響；此外水蒸氣能與電洞產生自由基且降低電子-電洞再結合機會，有助於提升光催化反應效率。 由碳質量平衡及二氧化碳生成顯示ACF吸附之丙酮皆有被TiO2利用而礦化。ACF開放性孔洞吸附迅速且脫附容易，以TiO2光催化氧化再生ACF能確保TiO2-ACF能連續使用而不損失反應能力。 TiO2固定在活性碳纖維及玻璃纖維上皆會受到二甲基甲醯胺觸媒毒化影響，尤以TiO2-GFC嚴重。以FT-IR分析觸媒表面吸附物種之官能基，光催化反應前，DMF中的C=O鍵最為明顯；反應過後，殘留著未分解之DMF及中間產物甲醛，觸媒活性的衰退主要是甲醛造成的，未分解的DMF影響到觸媒之吸附能力。其中TiO2-ACF具有提升DMF降解及礦化速率之作用，甲醛生成量因而提高。

Recently, it is universal to apply TiO2 photocatalytic technology for the decomposition of volatile organic compounds. This technology is photo-stability, easy operation and low cost. The photocatalytic reaction rate depends on reaction concentration and water vapor but low adsorption capacity of catalyst with respect to organic molecule has lower and slower opportunity for reaction. Besides, when oxidation of organic compounds poison the catalyst, the activity of the catalyst was gradually reduce and many harmful organic compounds and intermediates were released. The photocatalytic oxidation of gaseous acetone and DMF by TiO2 immobilized on activated carbon fiber (ACF) and glass fiber cloth (GFC) was investigated and compared in this study. The object of this study was to investigate the use of ACF with high adsorption capacity to enhance the rate of reaction and reduce the deactivation of catalyst. The ACF has opening pores, but not every pore contacted with the catalyst. At low initial concentration, the rate of photocatalytic reaction was not improved. Because the adsorbed acetone cannot be utilize by catalyst until the surface coverage of acetone on TiO2-ACF was 40%. The best of rate constant ratio was 2.1. Although water vapor competed with acetone molecule for the sites of adsorption, it could form hydroxyl radicals and increased the degradation rate of acetone. The strong adsorption capacity of TiO2-ACF was not influenced by water vapor. With the evidence of carbon mass balance and CO2 involved, the adsorbed acetone on ACF can be utilized. TiO2 photocatalyst was used to regenerate ACF adsorbent, and the abilities of adsorption and reaction on TiO2-ACF were not reduce because the desorption of adsorbed acetone was easy and fast. The oxidation of DMF photodegraded was inhibited on both TiO2-ACF and TiO2-GFC. Before the photocatalytic reaction, the C=O bond was detected on the surface of catalyst adsorbed by DMF FT-IR. After the photocatalytic reaction, the DMF was not photodegraded completely and with an intermediate of Formaldehyde were then detected. The deactivation was mainly affected by formaldehyde and the adsorption capacity was affected by DMF which was not photodegraded completely. Because the rate of photodegradation and mineralization were enhanced by TiO2-ACF, the amount of formaldehyde was larger on TiO2-ACF than that on TiO2-GFC