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氧氟沙星(OFX)作为第3代氟喹诺酮类抗生素因其良好的抑菌性能和较少的不良反应被广泛用作人畜抑菌药[1-2]。近年来,由于OFX的广泛生产和过度滥用,大量含有OFX的废水未经处置排放到水环境中,对生态环境和人类健康构成严重威胁[3]。因此,开发高效先进的处理技术以将其从水环境中去除至关重要。迄今为止,处理含有OFX废水的主要方法包括生物降解法[4],膜分离法[5],吸附法[6]和高级氧化技术(AOPs)。生物降解法处理效果不显著且耗时慢,膜分离和吸附技术不仅无法彻底矿化污染物还会造成二次污染,限制了其实际应用。AOPs在反应过程中可以产生高效活性氧物种,能将大部分有机污染物矿化成CO2和H2O[7],被认为是降解水中OFX类抗生素的最有效方法之一。
Fenton技术作为AOPs中最有效的方法之一,可以通过Fe2+活化H2O2产生高活性·OH而迅速破坏难降解有机污染物的分子结构,从而使其得以高效去除[8]。然而传统均相Fenton技术存在pH适用范围窄、水中的铁离子难以回收和易产生铁泥的缺点[9]。近年来,异相类Fenton技术以固相铁基催化剂代替可溶性Fe2+离子,可以克服均相Fenton反应的弊端,被认为是一种更有效的处理技术。目前应用于异相类Fenton技术的铁基催化剂主要是单金属含铁化合物,比如零价铁(Fe0)[ 10-11]、赤铁矿(α-Fe2O3)[12]、磁赤铁矿(γ-Fe2O3)[13]、磁铁矿(Fe3O4)[14]、针铁矿(α-FeOOH)[15]、黄铁矿(FeS2)[16]和氧基氯化铁(FeOCl)[17]。单金属铁基化合物的催化活性低和稳定性差,不利于其大规模应用。而多金属固体催化剂因不同金属间的协同作用可以有效提高催化活性。常见的多金属固相催化剂可以分为以下4类:尖晶石型铁氧体(AB2O4),如铁酸铜(CuFe2O4) [18]、铁酸锰(MnFe2O4)[19]和钴酸锰(MnCo2O4)[20]等;铜铁矿型氧化物(ABO2),如CuFeO2[9]、CuMnO2[21]等;新型多金属材料如多金属氧酸盐(POMs)[22]和多金属有机框架材料(MOFs)[23]等;多金属复合催化剂,如双金属复合催化剂[24]、金属/金属氧化物复合催化剂[25]、非金属/金属氧化物材料[26]等。已有研究表明,CuFeO2结构中的Cu+活化H2O2产生·OH的氧化速率常数(1.0×104 mol−1·s−1)比Fe2+活化H2O2产生·OH的速率常数更快(63~76 mol−1·s−1),同时Fe3+被H2O2还原成Fe2+(4.6×102 mol−1·s−1)比Cu2+被H2O2还原为Cu+(0.001~0.01 mol−1·s−1)具有更快的反应速率[27]。此外,CuFeO2结构中的Fe3+可与Cu+金属之间产生协同作用,有助于加快Fe2+的生成,使催化剂呈现出较高的催化活性。上述分析可知,CuFeO2作为一种成本低、毒性小的双金属异相类Fenton催化剂在难降解有机污染物处理方面显示出良好的潜力。然而,采用溶胶-凝胶法制备CuFeO2过程中需使用大量有机溶剂,增加了制备成本。固相烧结法制备CuFeO2时所需温度一般为1 100~1 200 °C 及以上,能耗高且反应过程中会产生大量的杂质。
为了降低CuFeO2的制备能耗和减少杂质,本文采用低温水热法,以三水合硝酸铜和九水合硝酸铁分别作为铜源和铁源,成功制备了高纯度3R型CuFeO2催化剂,利用各种表征手段对其形貌及晶型结构进行分析。以所制3R型CuFeO2为异相催化剂,考察了其活化H2O2降解OFX的效能和机制。深入探讨了催化剂投加量、H2O2浓度、溶液pH、共存阴离子等参数对OFX降解效果的影响;研究了所制3R型CuFeO2异相催化剂活化H2O2降解OFX的循环稳定性;通过自由基捕获实验和电子自旋共振(ESR)光谱鉴定了CuFeO2/H2O2类Fenton体系降解OFX的主要活性物质,通过分析反应前后CuFeO2的X射线光电子能谱进一步揭示CuFeO2活化H2O2的机理,根据质谱法鉴定的降解中间物质,提出了可能的OFX降解路径。
异相类Fenton催化剂CuFeO2的制备及其对水中氧氟沙星的降解性能
Preparation of CuFeO2 as heterogeneous Fenton-like catalyst and its degradation performance on ofloxacin in the water
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摘要: 以三水合硝酸铜、九水合硝酸铁分别作为铜源和铁源,通过简单的一步水热法合成纯3R相结构CuFeO2催化剂。通过X射线衍射仪、扫描电镜、透射电镜和高分辨透射电镜对其晶格结构和形貌进行了表征,构建了CuFeO2/H2O2体系对目标污染物氧氟沙星(OFX)进行降解,考察了不同催化剂投加量、H2O2浓度、溶液pH等参数对OFX降解效果的影响。结果表明,在催化剂投加量为1.1 g ·L−1、H2O2浓度为15 moL·L−1以及pH=3.65的条件下,反应300 min后,CuFeO2/H2O2体系对10 mg·L−1 OFX的降解率高达93.8%;此外,CuFeO2催化剂在活化H2O2降解OFX过程中具有良好的稳定性,经5次降解后的降解率仅降低了8.1%;自由基捕获实验和电子自旋共振波谱测试结果表明CuFeO2/H2O2体系中·OH是主要的活性自由基;降解反应前后CuFeO2的X射线光电子能谱表征结果表明,Cu+和Fe3+的相对含量均有不同程度的降低,表明CuFeO2中的Fe和Cu双活性位点在异相类Fenton反应中均起着重要的作用。最后,通过质谱鉴定了OFX的降解产物,并在此基础上提出了可能的降解路径。Abstract: The CuFeO2 catalyst with pure 3R phase structure was synthesized via a simple one-step hydrothermal method using copper nitrate trihydrate and iron nitrate as copper and iron sources, respectively. The lattice structure and morphology were characterized by X-ray diffractometer, scanning electron microscopy, transmission electron microscopy and high-resolution transmission electron microscopy. The CuFeO2/H2O2 system was constructed for the degradation of ofloxacin (OFX) as the target pollutant. To explore the optimum operating parameters, the effects of catalyst dosage, H2O2 concentrations, solution pH values and coexistence ion on OFX degradation were discussed. The results showed that the degradation efficiency of OFX (10 mg·L−1) by CuFeO2/H2O2 system was 93.8% after 300 min at catalyst dosage of 1.1 g·L−1, H2O2 concentration of 15 moL·L−1 and pH=3.65. In addition, the prepared CuFeO2 catalyst exhibited good stability, and the degradation efficiency after five successive degradation cycles only decreased by 8.1%. Based on the free radical scavenging experiments and electron spin resonance spectrometer results, ·OH was the major active free radicals in CuFeO2/H2O2 system for OFX degradation. The X-ray Photoelectron Spectrometer spectra of CuFeO2 before and after the degradation reaction revealed that the relative contents of Cu+ and Fe3+ decreased in varying degrees, indicating that the Fe and Cu as the double catalytic active sites in CuFeO2 played an important role in the heterogeneous Fenton-like reaction. A possible degradation pathway of OFX was proposed based on the intermediates identified by HPLC-MS spectra.
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Key words:
- heterogeneous catalyst /
- CuFeO2 /
- Fenton-like reaction /
- ofloxacin /
- degradation performance
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