【作者】 王晶；

【导师】 全燮；

【作者基本信息】 大连理工大学 ， 环境工程， 2019， 博士

【摘要】 水中难降解有机污染物毒性高且易于在生物体内富集,危害生态安全和人类健康。非均相催化臭氧氧化技术是一种去除水中难降解有机污染物的有效方法。催化剂是非均相催化臭氧氧化技术的核心,催化活性高且稳定性好的臭氧催化剂是决定该技术能否进一步推广的关键因素。然而,现有非均相臭氧催化剂存在催化活性有待进一步提高、稳定性不足且催化机理不明确等问题。针对这些问题,本论文设计并制备了铈、锰负载碳纳米管及氟掺杂碳纳米管催化剂,研究了它们催化臭氧氧化有机污染物性能,探索了催化剂结构与其催化性能之间的构效关系,并揭示了催化机理。主要研究内容和结论如下:(1)采用水热法制备了二氧化铈负载碳纳米管(CeO2-CNT)催化剂,考察其催化臭氧氧化有机污染物性能。随着CeO2负载量的增加,CeO2-CNT的催化活性先升高后降低,当CeO2负载量为9.0 wt%时催化活性最高,相同条件下其催化臭氧氧化苯酚在60 min反应时间内的TOC去除率为96%,分别是单独CNT(33%)及CeO2(47%)的2.9倍与2.0倍。CeO2-CNT具有良好的稳定性和重复利用性,且在pH=4.1-9.3范围内均表现出良好的催化性能。利用CeO2-CNT/O3体系处理某焦化废水二级出水,反应60 min后CODcr值由104.0 mg L-1降低至40.1 mg L-1,优于国家污水排放标准(GB 18918-2002,50 mg L-1)。电子顺磁共振(EPR)结果表明CeO2-CNT催化臭氧氧化降解有机污染物的活性氧自由基(ROS)为羟基自由基(OH)。CeO2-CNT催化臭氧氧化过程中,Ce4+得到电子被还原为Ce3+,Ce3+催化臭氧生成·OH并转化为Ce4+,维持催化反应的进行。X射线电子能谱(XPS)结果显示反应后的Ce02-CNT中Ce3+/Ce4+比例是单独CeO2中Ce3+/Ce4+比例的1.2倍,说明CNT可以促进Ce4+还原生成Ce3+,有利于催化臭氧生成·OH,提高催化效率。(2)以铈-锰复合金属氧化物为活性组分,磁性碳纳米管包覆碳化铁(CNT@Fe3C)为载体,制备了铈-锰复合金属氧化物负载CNT@Fe3C催化剂(Ce-Mn-O/CNT@Fe3C)。考察Ce-Mn-O/CNT@Fe3C催化臭氧氧化性能,相同条件下Ce-Mn-O/CNT@Fe3C催化臭氧氧化苯酚在45 min反应时间内的TOC去除率为98%,分别是Ce02/CNT@Fe3C(65%)和MnxOy/CNT@Fe3C(54%)的 1.5 倍和 1.8 倍,是臭氧催化剂 CeO2-CNT 的 1.3 倍。Ce-Mn-O/CNT@Fe3C具有良好的稳定性和重复利用性,且在pH=4.2-8.3范围内均表现出良好的催化性能。EPR结果表明Ce-Mn-O/CNT@Fe3C催化臭氧氧化降解有机污染物的ROS为·OH。此外,Ce-Mn-O/CNT@Fe3C是一种磁性材料,容易收集,便于回收再利用。(3)采用离子交换法制备了二价锰离子键合氧化碳纳米管复合材料(Mn2+-OCNT),利用有机污染物降解过程中小分子酸中间产物的生成和降解导致的溶液pH先降低后升高的自发变化,引发Mn2+在OCNT表面可逆的脱附和吸附过程,实现了Mn2+均相催化臭氧氧化有机污染物过程,并且反应后以Mn2+-OCNT非均相形式的回收。考察Mn2+-OCNT催化臭氧氧化有机污染物性能,发现相同条件下Mn2+-OCNT催化臭氧氧化苯酚效率相较于单独CNT和商业MnO2明显增强,甚至与均相Mn2+的催化效率相当。苯酚降解过程中,溶液pH由6.2降低至3.5,引发92%的Mn2+脱附进入溶液中,溶液中的Mn2+催化臭氧生成·OH降解有机污染物;随后溶液pH由3.5升高至4.5,引发溶液中88%的Mn2+重新吸附到OCNT表面;利用NaOH将溶液pH由4.5提高至5.0(NaOH投加量为0.86 g m-3),增强Mn2+在OCNT表面的吸附,实现了 100%的Mn2+回收,催化活性恢复至初始水平。(4)通过表面改性制备了氟掺杂碳纳米管(F-CNT),考察其催化臭氧氧化有机污染物性能。随着氟掺杂量的增加,F-CNT的催化性能先升高后降低,当氟掺杂量为2.17 at%时催化活性最高,相同条件下其催化臭氧氧化草酸在90 min内的TOC去除率为99%,是单独CNT(45%)的2.2倍,且催化性能优于几种典型金属氧化物臭氧催化剂(ZnO、Al2O3、Fe203及MnO2)。F-CNT在催化臭氧氧化有机污染物过程中表现出良好的稳定性和重复利用性。EPR结果表明F-CNT催化臭氧氧化降解有机污染物的ROS为超氧自由基阴离子(O2·-)和单线态氧(1O2),它们的氧化能力低于·OH，但F-CNT是一种非金属催化剂,能够彻底克服含有金属催化剂存在的金属离子溶出问题。更多还原

【Abstract】 Refractory organic pollutants in water are usually highly toxic and easy to be enriched in organisms,which endanger ecological safety and human health.Heterogeneous catalytic ozonation is an efficient technology for the treatment of wastewaters containing refractory organic pollutants.The catalysts play a key role in heterogeneous catalytic ozonation,which determine the feasibility and efficiency of this technology.However,the heterogeneous catalysts generally show low activity and poor stability.To address these issues,cerium or/and manganese-loaded carbon nanotubes and heteroatom-doped carbon nanotubes were designed and prepared for catalytic ozonation of organic pollutants.The relationship between the structure of catalysts and their catalytic performance was studied.And the catalytic mechanism was also explored.The main research contents and results are shown as follows:(1)Cerium dioxide loaded carbon nanotubes(CeO2-CNT)was prepared by a hydrothermal method.The catalytic performance of CeO2-CNT towards catalytic ozonation was evaluated.The results showed that with the increase of CeO2 loading content,the catalytic performance of CeO2-CNT illustrated a volcano-shaped variation.The CeO2-CNT exhibited best performance when the loading content of CeO2 was 9.0 wt%.After 60 min of reaction,the TOC removal efficiency of phenol on CeO2-OCNT was 96%,which was 2.9 and 2.0 times as much as that of pure CNT(33%)and CeO2(47%)respectively.The CeO2-CNT showed good stability and reusability.And the CeO2-CNT illustrated efficient mineralization of phenol under a wide range of pH 4.1-9.3.The CeO2-CNT/O3 system was highly effective for the treatment of a secondary effluent from coking wastewater.After 60 min of treatment,the CODcr value was decreased from 104.0 mg L-1 to 40.1 mg L-1,which was below the emission limit of Chinese National Standard for the Wastewater Discharge(GB 18918-2002,50 mg L-1).The results of EPR experiments revealed that hydroxyl radicals(·OH)was the reactive oxygen species(ROS)for organic pollutants degradation during CeO2-CNT/O3 system.During the CeO2-CNT/O3 system,the Ce4+ could be reduced to Ce3+ by electrons.The Ce3+catalyzed ozone decomposition to generate· OH and Ce4+.The results of XPS analysis showed that the Ce3+/Ce4+ratio for used CeO2-CNT was 1.2 times as much as that for CeO2.This indicated that CNT could favor the redox cycling of Ce4+/Ce3+,which benefited the conversion of ozone into ·OH and thereafter enhanced the removal of organic pollutants.(2)The cerium-manganese oxides complex loaded CNT@Fe3C(Ce-Mn-O/CNT@Fe3C)was synthesized with magnetic CNT@Fe3C as a supporter and manganese-cerium oxides complex as an active component.The Ce-Mn-O/CNT@Fe3C was employed as a catalyst for catalytic ozonation.After 45 min of reaction,the TOC removal efficiency of phenol on Ce-Mn-O/CNTs@Fe3C was 98%,which was 1.5 and 1.8 times as much as that of CeO2/CNT@Fe3C(65%)and MnxOy/CNT@Fe3C(54%)respectively,and was 1.3 times as much as that of CeO2-CNT.The Ce-Mn-O/CNT@Fe3C displayed good stability and reusability.And the Ce-Mn-O/CNT@Fe3C illustrated effcient mineralization of phenol under a wide range of pH 4.2-8.3.The results of EPR experiments revealed that ·OH was the ROS for organic pollutants degradation during Ce-Mn-O/CNT@Fe3C/O3 system.Additionally,the magnetic Ce-Mn-O/CNT@Fe3C is easy to be recovered and reused.(3)Heterogeneous Mn2+-bonded oxidized carbon nanotubes(Mn2+-OCNT)was synthesized by an ion-exchange method.Homogeneous catalytic ozonation has been achieved over heterogeneous Mn2+-OCNT through the reversible de-/ad-sorption of Mn2+on OCNT surfaces.The de-/ad-sorption reversibility of Mn2+was induced by the spontaneous variations of solution pH that caused by the formation and degradation of organic acid intermediates.The results showed that the Mn2+-OCNT displayed remarkably enhanced catalytic performance for phenol mineralization compared with that of pure OCNT and commercial Mn02,and was even comparable to that of hoUogeneous Mn2+/O3 system.Benefiting from the dropped solution pH(from 6.2 to 3.5)during phenol degradation,around 92%of Mn2+was rapidly desorbed from OCNT surfaces and accumulated in solution.The desorbed Mn2+in the solution catalyzed ozone decomposition to generate·OH for organic pollutants degradation.The solution pH was then increased from 3.5 to 4.5,which caused the re-sorption of 88%Mn2+.By increasing the solution pH from 4.5 to 5.0 with the treatment of NaOH(0.86 g m-3),100%of Mn2+recovery was achieved and the catalytic performance could be recoverd to its original level.(4)Fluorine-doped carbon nanotubes(F-CNT)were prepared and its catalytic performance towards catalytic ozonation was evaluated.The results showed that the catalytic performance of F-CNT illustrated a volcano-shaped variation with the increase of fluorine doping content.The F-CNT exhibited best performance when the doping content of fluorine was 2.17 at%.After 90 min of reaction,the TOC removal efficiency of oxalic acid on F-CNT was 99%,which was 2.2 times as much as that of pure CNT(45%),and was even superior to several typical metal oxides for catalytic ozonation(such as ZnO,Al2O3,Fe2O3 and MnO2).The prepared F-CNT showed good stability and reusability.The results of EPR experiments revealed that F-CNT could catalyze ozone decomposition to generate superoxide radicals(O2·-)and singlet oxygen(1O2)for organic pollutants degradation.Although the oxidation ability of O2·-and 1O2 is lower than that of ·OH,the metal-free F-CNT is extremely desirable in heterogeneous catalytic ozonation process because it can completely avoid metal leaching.更多还原