Liquid phase photocatalytic reaction for measurement hydroxyl radical-used dimethyl sulfoxide as a radical capture

[[abstract]]摘要 本研究以二甲基亞碸(DMSO)做為氫氧自由基捕捉劑，利用DMSO與氫氧自由基反應生成甲醛(HCHO)之特性，藉以間接量測液相光催化反應系統所生成之氫氧自由基濃度。本實驗中以P-25二氧化鈦粉末為光觸媒，採用Pyrex玻璃材質之泥漿式光催化反應器，以四支10 W螢光黑燈管為紫外光來源。分別針對不同反應參數如：自由基捕捉劑濃度、水溶液pH值、光觸媒劑量及光照強度等，探討各反應參數對氫氧自由基產量所產生之影響。 實驗中針對甲醛的分析，係以高效能液相層析儀結合二極體矩陣偵檢器(DA detector)，分析反應過程所生成的甲醛，為減少實驗誤差，除了確認甲醛分析方法之穩定性之外，也對分析儀器之精確性做測試。實驗結果顯示，甲醛以DNPH為衍生試劑，以及pH值為3之H3PO4-NaHPO4緩衝溶液，衍生90分鐘後，於波長370 nm，移動相比例Methanol/H2O= 70/30 (v/v)，以C-18 column分析HCHO-DNPH衍生物，可得最佳之分析條件。 實驗結果成它a證明，以DMSO為自由基捕捉劑，可量測氫氧自由基的生成濃度，且為一簡便之方法。研究結果發現，DMSO之濃度為40 mM時可捕捉大部分之氫氧自由基，濃度過低的DMSO會高估氫氧自由基之產量，而濃度過高之DMSO則因過多中間產物佔據TiO2的表面，使氫氧自由基濃度會有低估的現象；此外，就所估算獲得之二氧化鈦光觸媒表面所生成氫氧自由基濃度，此濃度隨水溶液酸鹼值之增加而增加；理論上較多的二氧化鈦濃度，可提供較多的氫氧自由基，但在泥漿式光催化反應系統中，過多的二氧化鈦懸浮物，反而會因為光照強度之干擾，導致單位重量二氧化鈦表面生成之自由基濃度略微降低，也導致有機物分解速率之降低。對於本研究之反應系統，以TiO2濃度為0.5 g/L，光照強度為8640 μW/cm2時，可獲致較大的氫氧基產率。 根據實驗結果，本研究以一階反應動力模式，建立光催化系統下，氫氧自由基濃度推估之經驗式。[[abstract]]Abstract The main objective of this study is to apply dimethyl sulfoxide (DMSO) as the radical capture to determine formation concentrations of hydroxyl radicals (⣶97;OH) on TiO2 surfaces in liquid-phase photocatalytic reactions In the study a commercial semiconductor material P-25 TiO2 was used as the photocatalyst DMSO reacts with hydroxyl radicals to form formaldehyde and can be applied as an indicator to quantify the concentrations of hydroxyl radicals The experiments are conducted in the slurry photocatalytic reactor that is made of Pyrex glass surround by four 10-W fluorescent black lamp as the light source Several experimental parameters including DMSO concentration solution pH level catalyst dosage and light intensities are investigated to understand their effects on the formation of hydroxyl radicals Formaldehyde which the major reaction intermediates is quantified by HPLC after being derived with DNPH in pH= 3 H3PO4-NaHPO4 buffer solution for 90 minutes The operation conditions for the HPLC are methanol/H2O= 70/30 (v/v) separation column is C18 column and is detected at 370nm The experimental results successfully demonstrate a convenient procedure for determining radical formation concentrations with DMSO as the radical capture The experiments also indicate that the 40-mM DMSO can capture most of the yielded hydroxyl radicals on TiO2 surfaces while the TiO2 concentration can be as high 0 5 g/L However it is observed that too low DMSO may overestimate the radical concentrations due to the competitive reactions of both the radical capture and its reaction intermediates for the radicals on TiO2 surfaces The results show high formation concentration of hydroxyl radicals in high pH environment and irradiated light intensity Nevertheless too density TiO2 can scatter the illumination intensity and results in less formation of hydroxyl radicals on per gram of TiO2 surfaces even though most experimental cases show high reaction ration in high concentration TiO2 Base upon our observation it is found that the maximal overall concentrations of hydroxyl radicals is achieved as TiO2 concentration equals to 0 5 g/L by being provided with irradiated light intensity of 8640 μW/cm2 According to the experiment results an empirical relationship is provided in this investigation for estimating the hydroxyl radical formations as a function of proton (H+) concentration TiO2 concentration and irradiated light intensit