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Title: | 自由餘氯存在下之4-甲基亞芐樟腦光降解 Free Chlorine Photolysis of 4-Methylbenzylidene Camphor |
Authors: | Kuen-Lin Chen 陳坤霖 |
Advisor: | 林郁真(Yu-Chen Lin) |
Keyword: | 自由餘氯光降解,防曬劑,4-甲基亞芐樟腦, free chlorine photolysis,UV filters,4-methylbenzylidene camphor, |
Publication Year : | 2018 |
Degree: | 碩士 |
Abstract: | 自由餘氯(Free Chlorine, FC)常作為游泳池和污水處理廠之消毒劑,此外,還能夠透過陽光照射激發產生自由基,促進水中耐氯和光穩定化學物質之降解。而近年來新興污染物之一4-甲基亞芐基樟腦(4-MBC)常見於環境水體,其為廣泛使用的防曬劑;由於其具有環境持久性且對水中生物之危害性資訊有限,本研究探討4-甲基亞芐基樟腦在自由餘氯存在下之太陽光降解(自由餘氯光降解)。4-甲基亞芐基樟腦之自由餘氯光降解相較於光解或氯化降解研究顯示,自由餘氯光降解顯著提升4-甲基亞芐基樟腦之降解速率且其動力學符合擬一階反應。水體中pH為自由餘氯光降解關鍵因子之一;在pH 7時其反應速率常數為0.146±0.022 min-1。進一步研究顯示,在pH 3 – 9之環境中,其降解速率在pH 3時最高(0.591±0.047 min-1),在pH 9時最低(0.063±0.007 min-1)。此外,自由餘氯濃度亦為影響4-甲基亞芐基樟腦降解速率的重要因素。自由餘氯濃度5 - 40 mg/L之範圍內,自由餘氯濃度與降解速率呈正線性關係。而反應機制之探討指出水體中氧氣、氯自由基(Cl·)和氫氧根自由基(·OH)在4-甲基亞芐基樟腦之自由餘氯光降解中亦扮演重要角色。其中氫氧根自由基為pH 7和9時的主要活性物質;而在pH 3時,除了·OH和Cl·之外,仍有其他未知的重要活性物質如活性氯衍生物(reactive chlorine species, RCS)參與反應。反應產物分析結果顯示共有21種降解產物形成。其中發現降解途徑包含脫氫,氫化、去甲基化、還原、氯化和氧化,因此大部分降解產物的分子量比4-MBC還要大,也更進一步的印證Cl·和·OH參與反應。除此之外,在pH 3發現的降解產物種類多於pH 7和pH 9,並且在pH 7和9發現的降解產物幾乎相同,此結果更進一步地證實pH 3有不同於pH 7和pH 9之降解機制如RCS參與反應。經由費氏弧菌毒性試驗顯示在pH 3、7和9時4-甲基亞芐基樟腦經由自由餘氯光降解後水體毒性顯著增加(反應三小時後,在pH 3毒性增加至173.82 TU),且毒性隨著4-甲基亞芐基樟腦的降解率提升而增加。降解產物P1、P2、P4-1、P4-2、P5, 291、293.13、293.15-1、293.15-2、305、307和327-2很可能是毒性來源,且大部分不容易光降解。 Free chlorine (FC) can be photoactivated by sunlight, which can promote the degradation of chlorine-resistant and photostable chemicals. This study investigated the degradation of an ultraviolet (UV) filter, 4-methylbenzylidene camphor (4-MBC), under sunlight photolysis in the presence of free chlorine (sunlight/FC). Compared with the degradation rate of 4-MBC under photolysis or chlorination alone, the rate under sunlight/FC was significantly enhanced and followed pseudo-first-order kinetics with a rate constant of 0.146 ± 0.022 min-1 at pH 7. Further experiments indicated that within a pH range from 3 to 9, the degradation rate was highest at pH 3 and lowest at pH 9. Free chlorine concentration is also an important factor that affects the degradation rate of 4-MBC. In the range of 5 to 40 mg/L, free chlorine concentration has a linear relationship with degradation rate. A mechanistic study indicated that O2, Cl· and ·OH play important roles in the degradation of 4-MBC under sunlight/FC. ·OH is the major reactive species at pH 7 and 9. However, in addition to ·OH and Cl·, there are other unknown important reactive species such as reactive chlorine species (RCS) at pH 3. Reaction product analysis showed that 21 degradation products were found; majority of them consist of Cl and additional numbers of O, resulting in a higher molecular weight than 4-MBC. The identified degradation pathways including dehydrogenation, hydrogenation, demethylation, reduction, chlorination and oxidation, which further supports ·OH and Cl· participate in the reaction. More degradation byproducts were found at pH 3 compared to pH 7 and 9, and the types of degradation byproducts found at pH 7 and 9 were nearly identical. This result suggests that a different reaction mechanism occurred at pH 3. Toxicity assays using Vibrio fischeri showed that the toxicity significantly increased after reaction under sunlight/FC at all three pH values, and the toxicity continued to increase as more 4-MBC was transformed (Toxicity Unit reached 173.82 at end of 3 hrs reaction at pH 3). The degradation products P1, P2, P4-1, P4-2, P5, 291, 293.13, 293.15-1, 293.15-2, 305 ,307 and 327-2 were proposed to the sources of toxicity, and most of them were photostable. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/79108 |
DOI: | 10.6342/NTU201802836 |
Fulltext Rights: | 有償授權 |
metadata.dc.date.embargo-lift: | 2023-08-23 |
Appears in Collections: | 環境工程學研究所 |
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ntu-107-R05541206-1.pdf Restricted Access | 1.8 MB | Adobe PDF |
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