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自从20世纪70年代末引入电化学高级氧化工艺(EAOPs)以来,EAOPs在处理水中的难生物降解和有毒有机污染物方面引起了世界各国科学团体的广泛关注[1-2]。EAOPs是一种基于原位生成羟基自由基(·OH)强氧化剂的技术,·OH可无选择性破坏废水中有机物成分。在各种水处理方法中,电化学氧化法在处理工业废水和目标污染物去除方面的应用越来越广泛,相对于其它高级氧化技术来说,具有1)与环境兼容;2)无需添加化学试剂;3)用途广泛;4)易于自动化;5)条件温和及设备简单;6)安全性高等优点,但也存在着能耗大,运行费用过高和电流效率低等缺点[3-4]。
抗生素作为一种广泛用于细菌感染的药物,替代品非常有限,但是抗生素在使用过程中只有20%—30%的抗生素在人和牲畜的身体系统中被代谢,其余以其原有的形态或中间产物的形式进入或排泄到水环境中。尽管此类新兴污染物带来的环境及健康威胁已逐步体现,但是由于人们对此类产品的依赖性和消费水平,此类化学物的消耗并不会随之下降[5]。根据相关研究报告称,地表水、地下水和污水处理厂的废水中抗生素的含量范围通常在几ng·L−1到100 mg·L−1,其中以制药厂及医院废水最为突出,尽管水体中浓度相对较低,但随着生物体的积累,抗生素浓度会随着时间的推移而越来越大,最终对生态系统产生深远和不可逆转的影响[6]。
由于其生物难降解特性和技术自身限制,污水处理厂中使用的传统物理化学和生物处理方法难以从废水中有效去除抗生素类污染物[7],电化学氧化法技术在应用于降解废水中新兴抗生素的应用研究成为一种适合的选择,而阳极材料是直接影响电催化效率的关键因素[8]。掺硼金刚石(boron-doped diamond, BDD)电极以其自身优异的物理及化学性质被认作为电催化氧化有机持久性污染物最为理想的电极材料[9-10],相对于传统的金属氧化物涂层阳极,BDD阳极在有机污染物的处理方面能够达到较高的去除率甚至可将有机物完全矿化为CO2和H2O,并同时保持较高的电流效率[11-13]。但是,如何实现高效去除水中存在的新兴抗生素类污染物,探讨电催化过程关键因素对降解动力学的影响机制是电催化氧化应用的重要前提。
本部分以当前环境中常见的一种抗生素药物,甲氧苄啶(trimethoprim,TMP)为研究对象,BDD电极为阳极,重点考察抗生素TMP在BDD电极上的电催化降解及动力学行为,分析降解过程中施加电流密度、溶液pH、TMP浓度、支持电解质浓度对抗生素污染物、化学需氧量去除率及降解过程动力学的影响规律,根据降解过程中的中间产物,提出TMP的可能降解路径,为电催化氧化技术和BDD阳极电催化降解水中新兴抗生素类污染物提供实验依据和技术支持。
掺硼金刚石阳极电催化降解甲氧苄啶抗生素及其动力学研究
Electrochemical degradation of antibiotic trimethoprim on boron doped diamond anode and kinetics
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摘要: 水中新兴抗生素类污染物是环境工作者关注的重要问题,如何高效去除抗生素及其去除动力学是需要重点探讨的研究内容。本文以掺硼金刚石为阳极,着重研究抗生素甲氧苄啶在BDD电极上的电催化降解及动力学行为,分析降解过程中施加电流密度、溶液pH、TMP浓度、支持电解质类型和浓度对降解动力学的影响规律,根据降解过程中的中间产物,提出TMP的可能降解路径。结果表明,高电流密度加快强氧化性活性物种的产生,可促进有机物的降解,但析氧副反应的加剧降低了过程的电流效率;低溶液pH有利于强氧化性活性物种的产生,加快有机物的降解动力学;由于电催化过程受传质控制,有机物的浓度的提高有利于促进降解动力学;由于活性氯的产生,电解质中氯离子的存在可加快有机物的去除,同时支持电解质Na2SO4浓度对有机物的矿化影响不大。TMP在BDD电极上的可能的降解路径主要包括羟基化反应、脱甲氧基化反应、裂解和开环反应,最终实现TMP完全矿化为CO2、NO3−和H2O.Abstract: Emerging antibiotic contaminants in water are considered as an important environmental issue. How to efficiently remove the antibiotics and kinetics are of great concern and need to be discussed. Electrochemical degradation of antibiotic trimethoprim (TMP) on boron doped diamond (BDD) anode was conducted in this paper, and operating parameters including applied current density, pH, pollutant concentration and supporting electrolyte concentration on the mineralization kinetics were discussed. Moreover, the possible degradation pathway of TMP during electrochemical oxidation was also proposed based on the degradation mechanism and intermediate products. The results reveal that high current density accelerates the generation of highly oxidizing active species and promotes the degradation of TMP. However, the occurrence of oxygen evolution side reaction under high current reduces the current efficiency of the process. Low pH is favorable for the generation of highly oxidizing active species and accelerates the degradation kinetics. Due to the fact that the electrocatalytic process is controlled by mass transfer process, the increase of TMP concentration is beneficial to promote the degradation kinetics. The presence of chloride ion accelerates the removal of TMP benefitting from the generation of active chlorine while the concentration of sodium sulfate exhibits little effect on the mineralization efficiency. Finally, the possible degradation pathway of TMP on BDD electrode was proposed, which mainly includes the hydroxylation, demethoxylation, cleavage and open ring reactions, realizing the mineralization into CO2, NO3- and H2O.
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表 1 TMP降解过程的中间产物信息
Table 1. Information of intermediate products during TMP degradation
化合物
Compound分子式
Formulam/z 保留时间/min Retention time 中间产物
Intermediate productTMP (A) C14H18N4O3 291.1 4.5 (B)/(C)/(D) C14H18N4O4 307.1 4.0/4.8/5.3 (E) C13H16N4O4 293.1 2.2/3.2 (F) C10H14O4/C4H6N4 199.1/110.1 6.5/1.2 -
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