Liquid-phase Photocatalytic Degradation of Formaldehyde via near-UV/TiO2

[[abstract]]摘要 本研究以二氧化鈦當觸媒，利用液相光催化反應進行甲醛之分解實驗，光催 化反應器採用泥漿式反應槽，以四支10W 螢光黑燈管作為紫外光光源。研究中 探討不同反應參數水溶液pH、觸媒劑量及光照強度等，對甲醛光催化分解反應 速率之影響，此外，本研究為了確定光催化降解效果，反應過程中分析甲醛濃度 及水溶液總有機碳含量，以確定甲醛之光催化反應分解速率與有機物礦化程度之 關係。甲醛濃度之檢測，則以DNPH 為衍生試劑，使HCHO 與DNPH 反應產生 HCHO-DNPH 之衍生物，並以HPLC/DAD 檢測。 根據實驗結果，甲醛最佳檢測條件為：HPLC 偵測器掃描波長370 nm，衍生 時間90 分鐘以上，衍生溶液pH 值在2 ~ 4 之間，使用pH= 3 的H3PO4-NaHPO4 緩衝溶液可將不同pH 值的衍生溶液控制在pH= 2 ~ 4 之間。pH 值對甲醛之光催 化降解速率有很大影響，反應速率隨著pH 值升高而升高，最快的降解速率出現 在pH= 11 的條件下，在120 分鐘的反應時間內去除率為84 %，這與在鹼性的條 件下氫氧離子會形成較多的氫氧自由基有關。不同TiO2 劑量對甲醛光催化降解 之影響實驗結果顯示，甲醛之去除率隨TiO2 濃度之增加而增加，而最佳的TiO2 劑量為1000 mg/L，去除率為73%，超過此依劑量會因遮蔽與凝聚效應使得甲醛 去除率降低。光照強度對甲醛光催化分解速率之影響方面，在低光照強度下，反 應速率隨著光照強度之增加而增加，且呈線性關係。甲醛光催化降解礦化程度， 隨pH 值由高至低依序為pH= 7 > pH= 3 > pH= 11，因受到中間產物甲酸之影響， 使得pH= 11 之礦化程度會低於pH= 7 之礦化程度。 III 本研究根據實驗結果，以擬一階反應動力模式，建立甲醛光催化分解速率常 數與pH、觸媒劑量及光照強度等實驗參數之經驗式。[[abstract]]Abstract This study investigated liquid-phase photocatalytic oxidation of formaldehyde by using TiO2 as the photocatalyst The experiments were conducted in a batch photocatalytic slurry reactor Four fluorescent black light lamps (365nm) were applied as the light source Formaldehyde concentration was determined by HPLC/DAD after its derivatization reaction with DNPH (2 4-Dinitrophenylhydrazine) to form the HCHO-DNPH hydrazones Several experimental parameters including solution pH the dosage of catalyst and the light intensity were investigated to discuss their effects on degradation rates and mineralization ratios of formaldehyde The experimental results indicated that solution pH level had a significant effect on the degradation of formaldehyde The degradation rate of formaldehyde increased with increasing solution pH level and illumination light intensity typically It was observed that the fastest degradation rate occurred as slution pH equal to 11 due to more formation of hydroxyl radicals More than 84% conversion ratio for formaldehyde was achieved after a 120-min reaction period Different TiO2 dosage tests showed that the formaldehyde degradation rates increas with photocatalyst concentrations as TiO2 concentration below 1000 mg/L The highest degradation V rate of formaldehyde was observed as TiO2 concentration equal to 1000 mg/L while 73% formaldehyde decomposes The mineralization ratio of formaldehyde was in the order of pH= 7 > pH= 3 > pH= 11 Some degradation intermediates might be formed at pH= 11 which caused low mineralization ratio in this condition This study also developed an empirical formula relationship for predicting the pseudo-first order degradation rate of formaldehyde as a function of formaldehyde concentration TiO2 concentration and irradiated light intensit