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近年来,大量的抗生素如四环素类和氟喹诺酮类等被广泛用作促进畜禽生长、预防和治疗感染的饲料添加剂[1-2]. 尤其是四环素类抗生素,它是一类广谱性抗生素,因杀菌效率高和成本低等已广泛应用于畜牧业的. 然而,30%—90%的四环素类污染物不能被畜禽所吸收消化[3],在畜禽体内未代谢的四环素类会通过尿液、粪便排泄进入水环境,未经处理的富含四环素类的废水会对环境和人体健康造成潜在的危害,还会引起一些致病菌产生抗药性基因的环境风险[2,4]. 因此,必须采取高效的治理措施对这些残留水体中的抗生素进行消减处理. 到目前为止,很多处理方法如吸附法、生物法和化学氧化法都被应用于抗生素废水的治理,其中高级氧化法因效率高和操作简单等优势受到了广泛的应用[5-7]. Fenton 法是高级氧化法的一种,是利用溶解性Fe2+与H2O2反应所生成的OH·的强氧化性把抗生素降解去除的一种均相Fenton法[8-9],但其pH适应范围窄,Fenton铁泥产量大成了最主要的直接限制因素. 而非均相Fenton法则克服了均相Fenton法的缺点,采用含铁的矿物或复合材料作为非均相Fenton法的溶解性Fe2+离子源,被广泛用于抗生素类物质的高效降解去除[5, 7]. 近年来,黄铁矿是一种有色金属矿山开采的尾矿渣,具有来源广泛和价格低廉的特点[10-12],常被用作为非均相Fenton的溶解性Fe2+离子源应用于多种有机污染物如染料和抗生素等的去除[7,13],如采用黄铁矿与过氧化氢或过硫酸盐联合高效降解水中的难降解的有机污染物如2,4,6-三硝基甲苯、罗丹明B、双氯芬酸和2,4-二氯苯酚[10-11,14-15]. 大量研究表明,黄铁矿除了提供Fenton所需的Fe2+离子源外,在反应过程中,黄铁矿经氧化释放出来的H+能较好地维持体系的酸性环境,而且,黄铁矿本身的还原性可促进Fe2+/Fe3+循环等,能实现黄铁矿Fenton对污染物的高效持续去除[13-15]. 另外,据研究表明,超声(US)不仅能通过声空化产生自由基,还能加速催化剂表面反应,实现声化学和催化化学的协同,能提升污染物的去除效果[16-18]. 而且,US也能激活H2O2分解产生OH· [17, 19],若在黄铁矿/H2O2体系引入超声或许能较大地提升抗生素的去除效率,加速黄铁矿物与抗生素的界面反应. 到目前为止,有关黄铁矿与超声联合激活H2O2降解去除水体中的抗生素的研究仍鲜见报道.
基于四环素类和氟喹诺酮类抗生素是目前应用广泛的抗生素两大主要类型,本研究以典型的四环素类抗生素金霉素(CTC)和氟喹诺酮类抗生素氧氟沙星(OFX)为主要目标污染物,采用天然黄铁矿与超声(US)联合激活H2O2降解去除水体中的抗生素CTC和OFX. 系统地考察了不同条件下金霉素的去除效果,鉴定了反应过程中的自由基组分和降解产物,评估了黄铁矿/H2O2/US体系对CTC和OFX的同步去除效果,探讨了CTC和OFX在黄铁矿/H2O2/US体系的降解反应机制,以期为利用黄铁矿Fenton体系去除水中的抗生素提供理论基础,实现尾矿渣黄铁矿“以废治废”的环境治理理念.
超声协同天然黄铁矿Fenton催化降解水中的金霉素和氧氟沙星
Ultrasound-assisted heterogeneous natural pyrite based Fenton-like catalytic degradation of chlortetracycline and ofloxacin in water
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摘要: Fenton 氧化常被广泛应用于环境水体中难降解有机污染物的高效去除. 本研究以天然黄铁矿为Fenton铁源,联合超声(US)激活H2O2高效降解去除水体中的抗生素金霉素(CTC)和氧氟沙星(OFX). 采用扫描电子显微镜(SEM)和X射线衍射(XRD)分析了黄铁矿物的形貌、元素组成和晶相结构,并考察了不同条件下黄铁矿/H2O2/US对CTC的去除影响,并结合淬灭实验和降解中间产物分析,探究了黄铁矿/H2O2/US体系同步去除CTC和OFX的反应机理. 结果表明,CTC的高效去除主要归因于黄铁矿与US在激活H2O2分解产生羟基自由基的协同效应. 在最佳反应条件下,CTC能在60 min内实现约96% 的去除,且CTC降解过程符合准一级动力学方程. 羟基自由基主导着CTC的降解去除过程,CTC能通过脱氯、开环、脱烷基化和羟基化等过程降解生成一些分子较小的中间产物而去除. 经5轮连续反应后,黄铁矿/H2O2/US体系对CTC的去除率均能保持在93%以上,具有良好的稳定性. 而且,黄铁矿/H2O2/US体系还能较好地同步去除CTC和OFX. 基于上述实验结果,推导出了黄铁矿/H2O2/US体系同步高效降解去除CTC和OFX的反应机理,溶液Fe2+与H2O2的均相Fenton反应和黄铁矿表面≡Fe2+与H2O2的非均相Fenton反应的协同高效降解这两种抗生素. 本研究较好地为受抗生素污染水体的治理提供理论和技术支撑.Abstract: In recent years, Fenton oxidation is often widely used for efficient removal of refractory organic pollutants from aquatic environment. In this study, the natural pyrite was used as Fenton iron source, and combined with ultrasound (US) to activate H2O2 for the efficient degradation of antibiotics chlortetracycline (CTC) and ofloxacin (OFX) in water. The morphology, element composition and crystal phase structure of pyrite were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The effects of different reaction conditions on CTC removal by pyrite/H2O2/US system were investigated, and quenching experiment and analysis of degradation intermediates were also carried out to explore the reaction mechanism for the simultaneous removal of CTC and OFX by pyrite/H2O2/US system. The experimental results show that the efficient removal of CTC was mainly attributed to a synergistic effect of pyrite and US in activating H2O2 decomposition for the formation of OH•. About 96% of CTC could be removed within 60 min under the optimal reaction conditions, and the CTC degradation process was well fit to the pseudo-first-order kinetic equation model. OH• dominated the removal process of CTC, CTC molecule could be degraded into intermediate products with smaller molecules through dechlorination, ring opening, dealkylation and hydroxylation. The reactivity of pyrite showed a nice stability, and above 93% of CTC removal could be maintained in pyrite/H2O2/US system within five runs. Moreover, the simultaneous removal of CTC and OFX could be achieved by pyrite/H2O2/US system. The reaction mechanism of the pyrite/H2O2/US system for the simultaneous removal of CTC and OFX was proposed based on the experimental results, which involved in synergistic effect of homogeneous Fenton reaction of solution Fe2+ with H2O2 and heterogeneous Fenton reaction of pyrite surfaces Fe2+ with H2O2. This study provided theoretical and technical support for the treatment of antibiotic-contaminated water.
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Key words:
- antibiotics /
- pyrite /
- Fenton /
- chlortetracycline(CTC) /
- ofloxacin(OFX)
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