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近年来,随着工业化进程不断向前,有机染料被广泛应用,我国是染料应用大国[1],其年产量约占全球7成以上[2]. 然而,高色度染料废水的大量排放会干扰自然水体的透光率,降低水生生物的光合作用强度,降低水体的复氧能力[3]. 其中,亚甲基蓝(methylene blue,MB)是使用普遍的染料之一,在水环境中高度稳定,能与多数无机盐生成复盐,具有抗生物降解特性[4 − 5]. 在生态系统中积累,会对人类及其他生物体产生有害影响. 因此,为避免生态环境健康遭到威胁,低能耗、高去除率的染料废水处理技术的研究具有重要意义.
在各种高级氧化技术(advanced oxidation process,AOPs)中电化学氧化由于环境友好、氧化效率高、易于控制等优点,已成为处理含生物难降解有机污染物废水的最有前途的技术[6]. 其中,阳极材料是影响电化学氧化效率的关键因素,与Pt、Ir等贵金属相比,B掺杂金刚石(boron-doped diamond,BDD)阳极由于具有极宽的电位窗口、腐蚀稳定性、强氧化能力等特性在众多材料中脱颖而出[7 − 9],已被广泛用于处理各种有机废水处理. 此外,基于Fenton反应的电化学氧化可利用碳毡(carbon felt ,CF)、生物炭[10]等碳质材料作为阴极,原位生成H2O2和Fe2+反应产生的·OH,以提高体系的氧化能力. 同时,避免了传统Fenton反应中必须外加H2O2带来的高昂成本以及高浓度爆炸性H2O2的处理、运输和储存相关的安全风险[11]. 因此,以BDD为阳极和CF为阴极的电Fenton体系(electro-Fenton,EF)已经成功地应用于有机污染物的降解[12 − 13]. 然而,Fe2+的再生是促进·OH生成的重要因素,但常规的铁基催化材料中Fe3+/Fe2+循环缓慢,成为电Fenton体系反应速率的限速条件. 目前,金属硫化物(FeS2、MoS2、WS2、Cr2S3、CoS2或PbS)已被证明是提高有机污染物降解效率和显著降低H2O2和Fe2+所需量的优良催化剂[14 − 15]. 其中,Cr2S3、CoS2、PbS都存在毒性,环境风险大的问题,相比之下,FeS2毒性较低,对环境危害小,且已有研究表明S2−作为电子供体,可促进Fe3+的连续还原和Fe2+的再生[16],便于在催化过程中反复利用,可作为一种含铁材料替代品,但单一金属硫化物由于活性中心和电子转移能力有限,S物种对Fe3+/Fe2+的循环不足以支持反应的进行. 而纳米花状MoS2具有比表面积高,反应位点丰富[17],电荷阻力较低,有利于反应过程中电子的转移[18]的优点,可作为助催化剂,Xing等[19]的研究表明,MoS2表面的不饱和硫原子可俘获溶液中的质子从而暴露出Mo4+,从而促进Fe3+/Fe2+循环,并将H2O2分解效率显著提高47.2%,降低AOPs中H2O2(0.4 mmol·L−1)和Fe2+(0.07 mmol·L−1)的消耗.
本研究将FeS2负载到MoS2上,成功合成双金属硫化物MoS2@FeS2,并将其引入BDD-CF电化学系统,对催化剂剂量、pH值、支持电解质等反应参数进行系统地探究,以确定最佳实验条件. 此外,对反应过程中Fe2+与·OH含量进行测定,以探究其在降解过程中的作用机理.
MoS2@FeS2催化电Fenton降解染料废水
Dye wastewater degradation in electro-Fenton system catalyzed by MoS2@FeS2
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摘要: 本研究以掺硼金刚石(boron-doped diamond,BDD)电极为阳极,碳毡(carbon felt,CF)为阴极,并采用简单的一步溶剂热法合成Fe、Mo双金属复合材料,构建电Fenton系统,处理亚甲基蓝(methylene blue,MB)污染物. 扫描电子显微(scanning electron microscopy,SEM)和X射线衍射(X-ray diffraction,XRD)表征结果表明MoS2@FeS2双金属硫化物成功合成. 实验结果表明MoS2@FeS2表现出优异的催化性能,在电流密度为5 mA·cm−2,投加量为0.3 g·L−1时, MB降解效率达94.7%,反应速率常数为0.019 min−1,是未投加催化剂的BDD-CF体系(0.008 min−1)的2.38倍. 此外,该催化剂在pH为3—9的范围内对MB均具有较高的去除率,在实际应用中不需要调节pH. 其机理分析表明在整个反应体系中Fe2+的浓度基本上维持在一个稳定的范围,表明该催化剂可通过Mo4+氧化为Mo6+促进Fe3+与Fe2+之间的氧化还原循环,从而可确保体系中有足够多的Fe2+用于有效活化,最大化H2O2的分解效率以促进·OH的产生,20 min时·OH的浓度达到1.43×10−5 mol·L−1.
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关键词:
- 电Fenton /
- BDD /
- CF /
- 亚甲基蓝 /
- MoS2@FeS2.
Abstract: In the present study, Fe and Mo bimetallic composite was prepared by one-step solvothermal method and applied in electro-Fenton system with boron-doped diamond (BDD) anode and carbon felt (CF) cathode for methylene blue (MB) degradation. The characterization results by scanning electron microscopy (SEM) and X-ray diffraction (XRD) indicated that bimetallic sulfide MoS2@FeS2 had been synthesized successfully. MoS2@FeS2 exhibited excellent catalytic performance, with 94.7% MB removed when the current density was 5 mA·cm−2 and the dosage is 0.3 g·L−1. Degradation rate constant of kobs (0.019 min−1) was about 2.38 times compared with BDD-CF system without catalyst (0.008 min−1). Moreover, MB removal rate kept high in the pH range of 3—9, which demonstrated that MoS2@FeS2 could be used in practical without the requirement of pH adjustment. The concentration of Fe2+ in the whole reaction system was maintained in a stable range. This result was mainly due to the redox cycle between Fe3+ and Fe2+ through the oxidation of Mo4+ to Mo6+, which ensured enough Fe2+ existing for effective Fenton reaction in the system. Concentration of ·OH reached 1.43×10−5 mol·L−1 at 20 min in the system coming form the efficient decomposition of H2O2 produced at cathode.-
Key words:
- electro-Fenton /
- BDD /
- CF /
- MB /
- MoS2@FeS2.
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