芬顿试剂

芬顿试剂(英語:Fenton’s reagent)是一种含有过氧化氢H2O2亚铁离子 Fe2+(作催化剂,通常是硫酸亚铁)的溶液。芬顿试剂被用于氧化有机污染物或废水,是高级氧化技术英语Advanced oxidation process(AOPs)中常用的方法,其对有机废水中的三氯乙烯(TCE)和四氯乙烯(PCE)等有机物的降解效果明显。芬顿试剂是由H. J. H. Fenton英语Henry John Horstman Fenton在1894年发现的。[1][2][3]

机理

芬顿试剂的氧化性来源于过氧化氢在Fe2+ 催化下产生的羟基自由基 ·OH [4],首先亚铁离子被过氧化氢氧化为铁离子,在此过程中产生羟基自由基和氢氧根离子,而后铁离子被另一个过氧化氢分子还原为亚铁离子,产生过氧化氢自由基和氢离子,反应总和为亚铁离子催化过氧化氢歧化为两种自由基。

Fe2+ + H2O2 → Fe3+ + HO + OH 1
Fe3+ + H2O2 → Fe2+ + HO2 + H+ 2
2 H2O2 → HO + HO2 + H2O 1+2

此过程产生的自由基有着较高的氧化还原电位,是一种非选择性强氧化剂[5],芬顿试剂与有机物的氧化反应迅速且放出大量热,主要氧化产物为二氧化碳。反应(1)的机理由哈伯与韦斯在1932年提出,并囊括于哈伯 - 韦斯反应之中[6]

硫酸亚铁是最常用的铁催化剂,对于亚铁离子氧化后还原重新切入催化循环的机制尚未有共识。Yamazaki等人报道利用顺磁共振(ESR)方法以5,5-二甲基吡咯啉-1-氯氧化物(DMPO)作为自由基捕获剂分析芬顿反应的机理[7],据称反应是亚铁离子被过氧化氢氧化成三价铁后,由Fe2+和Fe3+共同催化产生羟基自由基的过程,且有部分铁被氧化为Fe(IV)价态。也有研究认为芬顿反应中除了产生羟基自由基外,也有高价铁中间体产生,并且在有机物的氧化过程中是Fe=O2+起主导作用[8]

影响因素

对于芬顿反应的速率(尤其是对光芬顿反应而言),pH是关键因素之一。在低pH值时,Fe2+水合物会与HO发生络合,降低氧化效率[9],且较低pH值时体系中的多余质子也会与产生的HO发生反应[10]。而pH值偏高时,铁离子会形成沉淀,使铁逐渐从催化体系中被去除,从而降低反应速率[11],并且在碱性条件时H2O2也会自发地分解[12]。较高的pH值也会降低HO的氧化还原电位,从而降低其氧化效果[13][14]

pH对反应速率的影响
低pH 形成[Fe(H2O)6]2+水合物
OH被过量的H+消耗
高pH 降低OH的氧化还原电位
H2O2在碱性条件下会自发分解
产生Fe(OH)3沉淀

应用

芬顿试剂被用作污水处理试剂[11][15],芬顿试剂在化学反应中可用作羟基供体或氧化剂,如[16]

芬顿反应在生物化学中有着不同的应用方法,通过在体内细胞中铁的反应产生或消除自由基,虽然临床上的用途和重要性尚不明确,但也是活动性感染时避免补铁的可行方法之一,或是其他任何由铁介导的感染[19]

拓展阅读

外部链接

参考文献

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  7. ^ Isao Yamazaki; Lawrence H Piette. ESR Spin-trapping Studies on the Reaction of Fe2+ Ions with H2O2-reactive Species in Oxygen Toxicity in Biology. The journal of Biological Chemistry. 1990, 265 (23): 13589–13594. 
  8. ^ Hage John P; Llobet Antoni; Sawyer Donald T. Aromatic Hydroxylation by Fenton Reagents {Reactive Intermediate [Lx+Fe][OOH(BH+)], not Free Hydroxyl Radical (HO•)}. Bioorganic & Medicinal Chemistry. 1995, (3): 1383–1388. 
  9. ^ Xu, Xiang-Rong; Li, Xiao-Yan; Li, Xiang-Zhong; Li, Hua-Bin. Degradation of melatonin by UV, UV/H2O2, Fe2+/H2O2 and UV/Fe2+/H2O2 processes. Separation and Purification Technology. 5 August 2009, 68 (2): 261–266. doi:10.1016/j.seppur.2009.05.013. 
  10. ^ Tang, W. Z.; Huang, C. P. 2,4-Dichlorophenol Oxidation Kinetics by Fenton's Reagent. Environmental Technology. 1 December 1996, 17 (12): 1371–1378. doi:10.1080/09593330.1996.9618465. 
  11. ^ 11.0 11.1 Cai, Q. Q.; Lee, B. C. Y.; Ong, S. L.; Hu, J. Y. Fluidized-bed Fenton technologies for recalcitrant industrial wastewater treatment–Recent advances, challenges and perspective. Water Research. 15 February 2021, 190: 116692. PMID 33279748. S2CID 227523802. doi:10.1016/j.watres.2020.116692. 
  12. ^ Szpyrkowicz, Lidia; Juzzolino, Claudia; Kaul, Santosh N. A Comparative study on oxidation of disperse dyes by electrochemical process, ozone, hypochlorite and fenton reagent. Water Research. 1 June 2001, 35 (9): 2129–2136. PMID 11358291. doi:10.1016/s0043-1354(00)00487-5. 
  13. ^ Velichkova, Filipa; Delmas, Henri; Julcour, Carine; Koumanova, Bogdana. Heterogeneous fenton and photo-fenton oxidation for paracetamol removal using iron containing ZSM-5 zeolite as catalyst (PDF). AIChE Journal. 2017, 63 (2): 669–679 [2022-08-26]. doi:10.1002/aic.15369. (原始内容存档 (PDF)于2022-02-27). 
  14. ^ Cai, Qinqing; Lee, Brandon Chuan Yee; Ong, Say Leong; Hu, Jiangyong. Application of a Multiobjective Artificial Neural Network (ANN) in Industrial Reverse Osmosis Concentrate Treatment with a Fluidized Bed Fenton Process: Performance Prediction and Process Optimization. ACS ES&T Water. 9 April 2021, 1 (4): 847–858. S2CID 234110033. doi:10.1021/acsestwater.0c00192. 
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