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  • 學位論文

光老化聚苯乙烯塑膠微粒促進水中希每得定光降解機制探討

Enhanced cimetidine photolysis in the presence of photoaged polystyrene microplastics in an aqueous environment

指導教授 : 林郁真
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摘要


塑膠微粒目前已廣泛存在於環境水體中,其對於生態環境的影響及衝擊為國際間高度重視的議題之一。環境中的塑膠微粒在陽光照射下會逐漸老化,導致表面物化特性改變,間接影響環境水體中其他汙染物的宿命。然而,老化塑膠微粒的光化學反應及對環境水體中共存之新興汙染物的影響至今卻很少被提及與研究。因此,本研究選用環境中分布廣泛的聚苯乙烯塑膠微粒,利用紫外光加速老化,探討不同老化時間 (0-7 天) 聚苯乙烯塑膠微粒對水中新興汙染藥物──希每得定 (cimetidine) 光降解的影響與機制。研究結果顯示,在模擬陽光 (強度 700 W/m2) 照射兩小時下,99%以上cimetidine 能被老化五天的聚苯乙烯塑膠微粒加速降解,而未經老化的聚苯乙烯塑膠微粒僅造成 8%的 cimetidine 降解。老化後聚苯乙烯塑膠微粒能促進 cimetidine 的光降解與老化過程中含氧官能基 (C=O, C-O) 增加及吸收峰紅移有關,使其光反應性上升,進而產生環境持久性自由基 (environmental persistent free radicals)、氫氧自由基、單氧自由基和激發三重態聚苯乙烯等活性物種。然而,進一步研究發現系統中僅有單氧自由基和激發三重態聚苯乙烯能促進cimetidine光降解,其中又以單氧自由基的貢獻較多。本研究同時發現易受間接光解影響的新興汙染藥物──嗎啡和可待因與老化五天聚苯乙烯塑膠微粒共存時可分別在 4 和 5 小時的陽光照射下被完全降解 (>99%)。因此本研究結果顯示,老化聚苯乙烯塑膠微粒在環境中能扮演光敏劑角色,進而提升水中共存新興汙染藥物的光降解行為。

並列摘要


Microplastics (MPs) have received much attention in recent years since they undergo a continuous photoaging process in aquatic environments. However, little research has been conducted on the photochemistry of aged MPs and the associated effects on coexisting pharmaceuticals. This study investigated the photodegradation of cimetidine under simulated sunlight irradiation (700 W/m 2 ) via polystyrene microplastics (PS-MPs) aged by different times of UV exposure (0-7 d). PS-MPs with 5 d of aging time resulted in much faster cimetidine degradation (>99%) after 2 h of irradiation than pristine PS-MPs (8%). The enhanced photodegradation of cimetidine by aged PS-MPs was related to the increase in chromophoric oxygenated groups (C=O, C-O) followed by redshifted absorbance through the aging process, thus inducing more production of environmentally persistent free radicals (EPFRs), •OH, 1 O 2 and 3 PS * . However, only 1 O 2 and 3 PS * contributed to cimetidine photodegradation, with 1 O 2 playing more important role. Additionally, we also found that morphine and codeine, which are susceptible to indirect photolysis, are highly degraded (>99%) in the presence of 5-d aged PS-MPs at 4 and 5 h illumination, respectively. Thus, this study provides important insights into the role of aged PS-MPs as photosensitizers to enhance coexisting pharmaceutical photodegradation in aquatic environments.

參考文獻


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