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高级氧化技术因其在反应过程中可产生具有强氧化能力的活性氧物质(ROS),常用于处理难生物降解的有机污染物[1-2]。基于过氧化单硫酸盐(PMS)活化的高级氧化技术,与传统的芬顿技术相比,具有更宽的pH适应范围及更高的氧化电位,近年来受到研究者们的广泛关注[3-4]。
过渡金属可有效活化PMS,其中Co离子在活化PMS过程中展现出最佳的催化性能,然而具有一定的生物毒性,限制了实际应用[5-6]。与其它过渡金属相比,Fe离子及其氧化物具有环境友好,成本低等优点,相关研究最为广泛。在均相高级氧化过程中,溶液中存在大量的过渡金属离子,易造成二次污染,同时存在催化剂回收困难等问题[7]。
Fe3O4中存在Fe(Ⅱ),可以作为催化剂的活性中心活化PMS,而且通过外部磁力可以实现回收利用,降低了催化剂的回收成本[8]。然而,Fe3O4催化氧化过程中也存在表面Fe(Ⅱ)的再生问题,表面Fe(Ⅱ)被氧化成Fe(Ⅲ)后失去对PMS的活化能力,导致其催化活性有所下降,影响其对有机污染物的降解效果[9]。
二硫化钼(MoS2)是由S—Mo—S层通过范德华力堆积在一起的过渡金属二卤化物,作为一种非贵金属催化剂在析氢反应、光电传感器件及消毒灭菌中显示出巨大的应用前景[10]。MoS2中的Mo(Ⅳ)易失去电子,转化为更高价态的Mo(Ⅴ)或Mo(Ⅵ),因此MoS2具有还原性,可将高价态金属还原为低价态。Xing等[11-12]在将MoS2引入Fe(Ⅱ)活化H2O2的体系中,发现MoS2可以还原过程中生成的Fe(Ⅲ),使其转化为Fe(Ⅱ)从而加速了H2O2的活化。
目前,MoS2常用作均相高级氧化过程中的助催化剂,可显著提升催化效果,然而其用于非均相催化过程中的助催化研究仍十分有限。因此,设想采用MoS2作为载体,负载Fe3O4纳米颗粒,可有效增强对PMS的活化性能,具有较大的催化潜力。
2,4-二氯苯氧乙酸(2,4-D)作为常见的除草剂,多用于控制阔叶杂草。它具有较高的溶解度,土壤吸附系数低,容易通过地表径流和雨水渗透的作用,进入地表和地下水[13]。研究表明2,4-D对人和哺乳动物具有毒害作用,是可能的致癌物质和诱变剂[14],故本研究选择了2,4-D作为模型污染物,以MoS2为载体,采取水热法合成了纳米Fe3O4/MoS2复合物,并将其用于活化PMS降解2,4-D。研究了反应过程中的影响因素、催化性能和PMS的活化机理,此外,还考察了催化剂的稳定性。
Fe3O4/MoS2强化过氧化单硫酸盐活化去除2,4-二氯苯氧乙酸
Removal of 2,4-dichlorophenoxyacetic acid by Fe3O4/MoS2 enhanced PMS activation.
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摘要: 以MoS2为载体,通过水热法合成Fe3O4/MoS2催化剂,采用X射线衍射、透射电子显微镜和X射线光电子能谱分析对材料进行表征,研究了Fe3O4/MoS2/PMS体系中2,4-二氯苯氧基乙酸(2,4-D)的降解效率并探究了其反应机理。结果表明,以Fe3O4、MoS2和Fe3O4/MoS2为催化剂,30 min内2,4-D的去除率分别为31%、20%和89%。表征结果发现,在MoS2的存在下,Fe3O4表面的Fe(Ⅲ)还原为Fe(Ⅱ),Mo(Ⅳ)被氧化为Mo(Ⅵ),Fe3O4和MoS2间的协同作用加强了PMS分解,提高了2,4-D去除效率。自由基淬灭实验表明,·OH、
$ {\rm{SO}}_4^ - \cdot $ 、$ {\rm{O}}_2^ - \cdot $ 和1O2均参与了2,4-D的降解过程,且1O2的作用比其他活性物质更显著。低浓度Cl−和腐殖酸(HA)对2,4-D的降解没有明显的抑制效果,而$ {\rm{HCO}}_3^ - $ 对Fe3O4/MoS2/PMS体系有明显的抑制作用。此外,催化剂循环实验表明Fe3O4/MoS2在催化反应过程前后保持良好的稳定性。-
关键词:
- 过一硫酸盐 /
- 四氧化三铁 /
- 二硫化钼 /
- 2,4-二氯苯氧基乙酸
Abstract: Fe3O4/MoS2 catalyst was synthesized by hydrothermal method with MoS2 as support. The material was characterized by X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy analysis. The degradation efficiency and influencing factors of 2,4-dichlorophenoxyacetic acid(2,4-D) in Fe3O4/MoS2/PMS system were studied, and the reaction mechanism was explored. The results showed that when Fe3O4, MoS2 and Fe3O4/MoS2 were used as catalysts, the removal rates of 2,4-D within 30 min were 31%, 20% and 89%, respectively. Characterization results showed that in the presence of MoS2, Fe(Ⅲ) on the surface of Fe3O4 was reduced to Fe(Ⅱ) accompanied by the oxidation of Mo(Ⅳ) to Mo(Ⅵ), and the synergistic effect between Fe3O4 and MoS2 enhanced PMS decomposition and improved the removal efficiency of 2, 4-D. The experiment of radical quenching showed that ·OH,$ {\rm{SO}}_4^ - \cdot $ ,$ {\rm{O}}_2^ - \cdot $ and 1O2 were all involved in the degradation process of 2,4-D, and the effect of 1O2 was more significant than that of other active substances. Low concentrations of Cl− and humic acid (HA) had no obvious inhibitory effect on the degradation of 2,4-D, while$ {\rm{HCO}}_3^ - $ had obvious inhibitory effect on Fe3O4/MoS2/PMS system. In addition, XRD and catalyst cycling experiments show that Fe3O4/MoS2 maintains good stability before and after the catalytic reaction.-
Key words:
- permonosulfate(PMS) /
- Fe3O4 /
- MoS2 /
- 2, 4-D
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图 2 (a) Fe3O4/MoS2对2,4-D的吸附效果,(b) Fe3O4/MoS2活化PMS降解2,4-D,(c) Fe3O4/MoS2活化PMS的效果,(d) Fe3O4/MoS2催化剂活化PMS降解2,4-D过程中TOC的去除率。
Figure 2. (a)Adsorption effect of Fe3O4/MoS2 on 2,4-D, (b) The Fe3O4/MoS2 activation of Fenton-like of PMS for catalytic degradation of 2,4-D, (c) Effect of Fe3O4/MoS2 activation on PMS, (d) Fe3O4/MoS2 catalyst activates the removal of TOC in the process of PMS degradation 2,4-D.
图 4 (a) Fe3O4/MoS2催化剂循环催化降解2,4-D的效果及反应后材料的磁性,(b) 体系中Fe和Mo的浓度,(c) Fe3O4/MoS2反应前和反应后的XRD图,(d) Fe2+及Fe3+活化PMS降解2,4-D,反应条件:[Fe2+]0=[Fe3+]0=0.3 mg·L−1 ,PMS=0.3 g·L−1,2,4-D= 0.1 mmol·L−1
Figure 4. (a) Effect of Fe3O4/MoS2 catalyst on cyclic degradation of 2,4-D, (b) Fe and Mo concentrations in the system, (c) XRD patterns of Fe3O4/MoS2 before and after reaction, (d) Fe3O4/MoS2 catalyst activated PMS to degrade 2,4-D, and the material was magnetic after the reaction
图 5 (a)Tert-butanol,PBQ,Methanol,L-histidine和FFA对2,4-D的去除的抑制效果,Tert-butanol= 200 mmol·L−1,PBQ=0.06 g·L−1, Methanol= 200 mmol·L−1, L-histidine= 0.06 g·L−1,(b) 不同浓度FFA对2,4-D降解的抑制效果,(c) Fe3O4/MoS2/PMS在不同气氛下去除2,4-D,(d)(e)(f) Fe3O4/MoS2反应前和反应后Mo 3d、Fe 2p和S 2p的XPS谱图。
Figure 5. (a) Inhibition effect of Tert-Butanol, PBQ, Methanol, L-Histidine, FFA on removal of 2,4-D, (b) Inhibitory effect of FFA at different concentrations on removal of 2,4-D, (c)Fe3O4/MoS2/PMS divided by 2, 4-D at different atmospheres, The XPS pattern of Mo 3d (c) Fe 2p (d) S 2p (e) before and after reaction
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