非晶零价铁微球的形成机理及其典型环境污染物去除性能研究

Zero-valent iron (ZVI), characterized by its advantages in low-cost and environmental friendliness, has been extensively applied for the remediation of groundwater contaminated with environmental pollutants. However, this ZVI technology is encountered by some difficulties such as the limited efficiency for the treatment of pollutants. To solve this problem, most of the previous studies were focused on the utilization of nanoscaled ZVI or modification of reaction environment, whereas the influence of ZVI crystallinity was overlooked. Recently, the amorphous structure was found to significantly enhance the performance of ZVI in the removal of pollutants, whereas the synthesis conditions of amorphous ZVI are harsh. In addition, efficient experimental characterization and theoretical investigation are still lacking to discuss the effect of amorphous structure of ZVI on the transformation of pollutants. In this project, stable amorphous ZVI microparticles will be synthesized firstly through a NaBH4 reduction route mediated by small organic ligand at room-temperature. And the formation mechanism of amorphous ZVI will be uncovered by various characterizations such as the synchrotron radiation X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectra. Secondly, the adsorption, redox and electron transfer processes of typical environmental pollutants (including hexavalent chromium Cr(VI), nitrobenzene, pentachlorophenol and thiamphenicol) on amorphous ZVI will be studied to clarify the relationship between amorphous structure and the special adsorption and transformation behaviors of contaminants on the ZVI. Finally, we hope to reveal the intrinsic mechanism for the effect of amorphous structure on the performance of ZVI at atomic level. The related results of this project will enrich theoretical knowledge on the pollution-control by ZVI, and could provide support for the development of green and efficient pollution-control technology based on amorphous ZVI.

零价铁以其廉价和环境友好等优点被广泛用于环境污染治理，但面临着效率低等难题。前人大多采用纳米零价铁或改变反应环境来解决这一难题，却忽略了零价铁结晶度的影响。近期研究表明非晶结构可以显著增强零价铁去除污染物的效率，但非晶零价铁的合成条件较为苛刻，且缺少合适实验表征手段深入探讨非晶结构影响污染物转化的作用途径。本项目提出利用有机小分子配体调控硼氢化钠室温化学还原途径制备具有稳定非晶结构的零价铁微球，利用同步辐射XRD和EXAFS光谱等系统分析非晶零价铁微球的结构，探讨其形成机理；研究六价铬Cr(VI)、硝基苯、五氯酚和甲砜霉素等典型环境污染物在非晶零价铁微球上的吸附、还原以及电子转移过程，阐明零价铁非晶结构依赖的环境污染物吸附和转化特性，在原子水平上揭示非晶结构影响零价铁去除污染物性能的内在机制，丰富零价铁污染控制化学的理论知识，为发展基于非晶零价铁的绿色高效污染控制技术奠定基础。

本项目利用有机小分子配体介导的室温化学还原法可控合成出非晶零价铁微球，系统探讨了主要反应条件对零价铁晶态结构及形貌的影响，分析非晶零价铁微球的原子结构及局部微环境，探讨零价铁非晶结构与有机配体空间分布规律之间的联系，研究有机小分子配体调控非晶结构的形成机制，发现液相还原过程中引入乙二胺延缓铁原子的成核生长，降低了零价铁的生长驱动力而形成非晶结构。在此基础上，我们以非晶和晶态零价铁为研究对象，探讨了零价铁非晶结构依赖的环境典型污染物去除特性。内容包括：一、研究了零价铁还原去除六价铬和硝基苯的反应动力学及机理，利用原位光谱等技术手段研究了六价铬和硝基苯的吸附及还原过程，结合零价铁表面及溶液相中各铁物种的价态及组成变化规律，阐明六价铬及硝基苯在非晶及晶态零价铁上的还原机理和转化途径。二、研究了零价铁活化分子氧去除五氯酚和甲砜霉素的降解过程，解析非晶零价铁活化分子氧的分子机制，阐明分子氧活化降解污染物的具体途径。三、探讨了溶液共存离子和有机小分子等环境因素对非晶零价铁去除典型污染物性能的影响。项目的完成厘清了非晶结构在零价铁去除典型环境污染物过程中的贡献，为发展高效非晶零价铁污染控制技术提供了理论支持。