RCEES OpenIR  > 环境水质学国家重点实验室
基于活性位结构调控的铁锰复合材料制备及其吸附与催化性能研究
Alternative TitleFe,Mn-Based Heterostructures: Active Site Tailoring for Rational Preparation and Their Adsorptive and Catalytic Applications
余力
Subtype博士
Thesis Advisor刘会娟
2018-06
Degree Grantor中国科学院生态环境研究中心
Place of Conferral北京
Degree Name工学博士
Degree Discipline环境工程
Keyword铁,锰,活性位,吸附,催化 Iron, Manganese, Active Site, Adsorption, Catalysis
Abstract

      铁、锰基复合材料是常见的吸附载体与氧化还原主体之一,在吸附、催化与电化学领域发挥着重要作用。充分利用其化学活性,拓展其应用范围具有重要的理论与现实意义,而表界面活性位的识别、调控与稳定是结构与性能优化的关键。本论文结合纳米合成技术,在铁锰基材料的制备中,通过复合结构的可控调控(包括二维片层结构、微纳多级结构、单原子分散态的构建)提升活性位点的均匀分散与利用率;通过界面化学键联结构、缺陷态构建以实现活性位的稳定与调控,丰富并拓展了铁锰复合材料在吸附与催化领域的应用,在材料分离回收、重金属离子吸附与选择性吸附、有机污染物催化氧化降解以及氧的电催化还原方面体现出明显的结构优势。

      实现了磁性复合铁锰氧化物(FMBO)片层材料的可控制备。中空多孔Fe3O4磁核表面丰富的亲水性羧酸基团首先促进了铁锰金属离子的结合,同时聚乙烯吡咯烷酮(PVP)作为结构导向剂,以及由六亚甲基四胺(HMTA)持续缓慢提供的碱性环境,能够确保铁锰离子的可控水解,控制FMBO团聚与晶体的过快生长,实现了FMBO片层在Fe3O4表面的可控组装。由此形成了Fe2O3、FeOOH、Fe3O4与Mn(II)、Mn(III)复合组分共存的介孔吸附材料,吸附位点具有较高的利用率。在氧化与吸附效应协同的作用下,复合吸附剂对As(III)表现出较好的去除效果(饱和吸附量56.1 mg g–1),同时亚铁磁性的性质赋予吸附剂以良好的磁响应与可回收性。

     通过乙酸辅助下KMnO4与Fe3O4表面碳的氧化还原反应得到了磁性锰基复合材料。研究发现,乙酸配体在水溶液中能稳定锰的不饱和配位态,促进锰氧八面体上羟基化边面位点的选择性暴露进而特异性结合Pb(II),同时降低了对金属离子吸附具有无选择性的八面体空位的比例。该结构能够进一步在Fe3O4磁核表面形成均匀的片层锰氧化物,有效地避免了表面吸附位点间的团聚。相对于其他二价金属阳离子,复合材料因此对Pb(II)的吸附表现出更为理想的特异性(选择性系数31.2–172.0)。即使在竞争性离子处于较高浓度(摩尔浓度10–50倍于Pb(II))的情况下,稳定的特异性吸附仍能得以保持,同时吸附剂能通过溶液pH的调节在酸性环境下解吸再生。

      利用两相组分间的键合作用研制了界面稳定的不饱和配位铁(UCI)/锰基复合材料,促进了对反应物过硫酸氢盐(PMS)的吸附与催化氧化还原效应的协同,在包括酚类、染料等在内的多种有机污染物的去除方面表现出优越的效果。多种物化表征以及原位测试结果表明UCI邻近的阴离子氧缺陷表面的富电子区利于从水溶液中结合PMS(HSO5?);同时UCI作为路易斯酸中心可以与锰氧化物结合形成稳定的界面键联结构,并促进电子效应的耦合。铁锰复合的多功能活性位点因此实现了从PMS结合、界面电子转移调控到最后的活化整个催化循环的一体化的优化。PMS首先能诱导高氧化性(Fe, Mn)─氧中间体的形成,该中间体不稳定,并能直接氧化有机底物,或是从另一分子PMS处夺取电子歧化生成活性单线态氧1O2与(HSO4?)2阴离子二聚体。夺取的电子能够还原之前被氧化的Fe–Mn中心,使得表面结构得以恢复并保持一定的抗氧化性和较为持久的催化活性。

     以苯胺、吡咯为单体,以曲拉通X-100为软模板,通过共聚合反应发展了一种通用的单原子铁、锰活性中心限域在空心碳球的方法。合成过程中冰水浴的环境能很好地抑制铁、锰金属离子的水解,使其定向地与苯胺、吡咯单体上丰富的含氮基团结合形成单分散态的活性Fe (Mn)–N中心。曲拉通X-100作为软模板促进了中空碳结构的形成,这种结构即使在高温煅烧的过程中仍能保持其稳定均一的形貌。据此得到的FeNxC结构同时具有高含量的铁氮活性中心与较高的电化学活性面积(3.13 mF cm–2),表现出较好的电催化氧还原的能力,在0.1 M KOH的碱性溶液中,反应起始电位与半波电位分别为0.99 V与0.85 V vs RHE。相比于Pt/C,FeNxC复合催化剂具有更高的电流密度、更低的Tafel斜率与更好的稳定性。

Other Abstract

      Earth-abundant Fe and Mn based materials have been widely exploitable as versatile platforms and tools for sorptive, heterogeneous catalytic and electrochemical investigations. Further extending their applications relies largely on the identification and tailoring of surface/interface functional sites for performance enhancement. We introduced the developing synthetic nanotechnology into preparation of Fe, Mn-based materials, with special emphases on site exposure and stabilization. Well-defined structures could be obtained via rational construction of two-dimensional (2D) nanosheets, micro/nano hierarchical structures and single-atom sites, as well as by virtue of interfacial chemical bonds or defect engineering. Such heterostructures showed great potential and structural superiority in sorbent separation, metal ion sorption/selective sorption, organic pollutant removal and oxygen reduction.

     Fe-Mn binary oxide (FMBO) nanoplatelet encapsulated magnetic nanoparticles were first prepared by controlled engineering of the interparticle coupling of Fe3O4 and FMBO. The porous magnetic supports and carboxyl-ligand-modified surface enabled well-assembled 2D FMBO nanoplatelets and highly dispersed sites. Polyvinylpyrrolidone (PVP) and hexamethylenetetramine (HMTA) were introduced to stabilize the aggregation and overgrowth of FMBO and to control the hydrolysis of metal precursors via a slightly alkaline medium. The synthesized composites retained highly porous structure and good magnetic response, with main components of Fe2O3, FeOOH, Fe3O4, as well as Mn(II) and Mn(III). A quite high capacity for As(III) capture (56.1 mg g–1) was finally realized, whereby As(III) oxidation coupled with synchronous sorption contributed to the improved performance.

     We then showed an increased selectivity of manganese oxides for lead (Pb) ions via a facile acetic acid (HAc)-assisted KMnO4-engaged redox procedure. Acetate ligands herein facilitated the evolution of undercoordinated Mn structures, which not only benefited the formation of hydroxylated lateral edge sites for preferential complexation of lead Pb(II) but also favored a decrease in the proportions of metal-ion-nonspecific octahedral vacancy sites. On the basis of this strategy, magnetic supports were used to ensure a selective exposure of hydroxylated lateral edge sites, achieving high selectivity coefficients (31.2–172.0) of Pb(II) against various metal cations. Even these metal cations coexisted at higher concentrations, the general specificity was still maintained with pH-enabled switchable sorption-desorption.

     We further stabilized naturally prevalent undercoordinated iron (UCI) centers on manganese oxides via the interface confinement effect between transition metal oxides. The created heterostructure showed efficient activation of peroxymonosulfate (PMS) molecules, with aqueous organic contaminant oxidation efficacy several times that of reference metal oxides. The combined spectroscopic, electrochemical, and in-situ measurement results revealed that these interfacial oxygen-deficient UCI sites not only benefited thermodynamically favored PMS accumulation, but also facilitated surface-to-surface electronic communication across atomic interface-bonding channels, thus providing a feasible platform to give rise to highly oxidizing (Fe, Mn)-oxo intermediates. Such PMS-activating metal centers in transitional states were sequentially reduced via either direct oxidation of organic substrates or electrophilic attack of other PMS molecules, with generation of singlet oxygen and (HSO4?)2 dimers. This reaction pattern guaranteed preservation of the catalyst structure after the reversible redox cycle, enabling a stable, kinetics-enhanced catalytic process.

     To maximize the utilization efficiency of atomic metal sites, a general copolymerization derivative strategy was further developed toward single Fe/Mn sites embedded hollow carbon nanospheres. The synthesis conditions suppressed aqueous hydrolysis of Fe/Mn ions, which were instead preferentially anchored by N-containing functional groups in isolated states. Well-defined hollow spherical morphology could be maintained during the sequential calcination process. Owing to the high density of active sites and high electrochemical active surface area (3.13 mF cm–2), the therefore formed atomic FeNxC sites showed superior oxygen electroreduction activity─an onset potential of 0.99 V and a half-wave potential of 0.85 V vs RHE in 0.1 M KOH alkaline media. The recorded performance and stability were even better than that of Pt/C with a higher current density and a lower Tafel slope.

Pages141
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/41573
Collection环境水质学国家重点实验室
Recommended Citation
GB/T 7714
余力. 基于活性位结构调控的铁锰复合材料制备及其吸附与催化性能研究[D]. 北京. 中国科学院生态环境研究中心,2018.
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