新型纳米介孔铁锰双金属氧化物除砷效能及其对砷形态转化机制研究

Arsenic is a typical environmental pollutant, and the study for its redox transformation, migration and efficient removal is now becoming the research hot point and difficult point in environmental field. Due to the limits of micro-structural properties of traditional iron-based materials，as well as lacking of the systematically research between the redox transformation and removal mechanism in both solid and liquid phases, the arsenic removal efficiency is always low. In order to improve the uptake of arsenic from water, this project intends to use soft template to synthesize novel nanoscale mesoporous iron manganese bimetal oxides, which combines the superiority of bimetal oxides and nanoscale mesoporous materials. Meanwhile, this study systematically investigates the effect of synthesis condition such as the initial concentration of iron/manganese and calcination temperature on the morphology, crystal structure and arsenic removal in water, explores the influence of redox transformation of arsenic by crystal structure and valence of bimetal oxides, and deeply analyzes the arsenic speciation, distribution and combination mode on solid phase interface. According to the relationships between iron manganese bimetal oxides materials characteristics and the redox transformation of arsenic and its combination mode, the arsenic removal mechanism will be revealed. This project can not only enrich the research of arsenic abiotic transformation, migration and combination mode, but also guide to the development of novel iron-based bimetal materials for the excellent performances of arsenic removal.

砷是一种重要的环境污染物，研究其在水体中的转化、迁移以及高效去除成为当今环境领域的研究热点与难点。传统铁基材料由于微观结构特性的限制，以及对固液两相中砷形态转化和去除机制之间的关联研究不够系统，导致砷去除效能普遍较低。本项目结合双金属协同除砷效应和纳米介孔材料的优点，拟采用软模板法制备新型纳米介孔铁锰双金属氧化物，以提高水体中砷的去除效能。系统研究铁/锰比例、煅烧温度等合成条件对材料形貌、晶型和砷去除效能的影响，探讨双金属物相、结构特性和价态对水相中砷形态转化的规律，深入剖析双金属固相界面上砷的价态、分布和结合方式。通过建立铁锰双金属材料特性与砷形态转化、结合方式之间的内在联系，进一步揭示砷去除机制。本项目不仅丰富了无机砷非生物形态转化、迁移固化和结合方式的研究，而且对开发具有高效除砷性能的新型铁基双金属材料具有重要的指导意义。

水体砷污染已成为关系到人类健康和生命安全的重大环境问题。因此，迫切需要发展高效的砷污染控制与修复技术。结合铁基双金属协同除砷效应和纳米介孔材料的优点，本课题开展了以下三方面的研究工作：（1）明确了铁锰双金属氧化物对无机砷形态转化过程与规律的影响。通过反胶束法制备了有序Fe-Mn双金属氧化物，其组成、纳米结构和界面化学性能与煅烧温度紧密相关。除砷的最佳Fe/Mn比和煅烧温度分别为3/1和350 ℃。同步分析水相和固相界面砷氧化还原转化机制，表明双金属材料中的锰氧化物主要为砷的氧化剂，而铁氧化物主要起到吸附剂的作用。（2）建立了双金属材料特性与无机砷去除效能之间的构-效关联。基于溶胶-凝胶的反胶束法成功制备了磁性有序介孔铁铈双金属氧化物。煅烧能显著降低材料比表面积，同时扩大孔径和晶粒尺寸，形成高度有序的内部连接结构，进而改变材料结构性质和吸附性能。As(III)和As(V)的吸附均遵循伪二级动力学，离子强度和共存离子（硅酸根和磷酸根除外）对砷去除没有明显影响，而腐殖酸即使在较低浓度时也对除砷有显著影响。吸附机理研究表明，材料表面电荷和羟基基团是水体砷高效去除的关键因素。（3）探讨了铁锰双金属材料界面结合态亚铁[≡Fe(II)]对As(III)催化氧化的作用机制。研究发现锰元素的复合能有效提高Fe3O4表面结合态≡Fe(II)的含量，能加快铁锰双金属氧化物界面电子传递速度，进而促进≡Fe(II)对H2O2的分解作用而产生更多的活性物种。通过自由基猝灭实验和EPR测试，证实水中As(III)氧化主要来自于材料界面•OHads和而水相中•OHfree。研究结果对于砷污染的修复具有重要的指导意义。