U(VI)、Re(VII)在Fe(II)/a-Fe2O3界面吸附、还原反应的晶面效应与机制

a-Fe2O3能够通过界面反应控制放射性核素在环境中的分布和化学行为。吸附态Fe(II)在a-Fe2O3表面通过吸附与氧化还原反应可有效实现核素的固定。研究不同晶面的a-Fe2O3纳米晶的表面反应，能够阐明核素离子在Fe(II)/a-Fe2O3界面的吸附与还原机理。本项目拟通过静态法、电化学研究U(VI)、Re(VII)在不同晶面的Fe(II)/a-Fe2O3纳米晶表面的吸附与还原性能及其反应过程；利用X射线吸收光谱(XAFS)与穆斯堡尔谱(Mössbauer)研究Fe(II)/a-Fe2O3界面反应活性、吸附形态与微观结构，揭示界面吸附与还原反应的晶面效应；通过理论计算证实Fe(II)/a-Fe2O3不同暴露面的反应活性及深层还原反应机理。研究结果为放射性核素与a-Fe2O3矿物的相互作用机制提供依据，对评估核素在环境中的迁移转化行为有重要意义。

a-Fe2O3 surface play an important role in the transport and the remediation of the radionuclide in the environment through interfacial reaction. Fe(II) sorbed and/or precipitated on a-Fe2O3 have the highly reactive properties with respect to reduction of radionuclides. a-Fe2O3 nanocrystals exposed by specific planes directly influence the amount of accessible reactive surface area of a-Fe2O3 properties. The exploration of the interfacial configuration of U(VI) or Re(VII) species on well-defined Fe(II)/a-Fe2O3 architectures with different exposed facets is indispensable to clarify the radionuclides adsorption and reduction mechanism. In addition, these specific surfaces provide the opportunity to examine the influence of surface structure and chemical composition on reactivity. In this proposal, we intend to study the adsorption and reduction processes of U(VI) or Re(VII) on Fe(II)/a-Fe2O3 facets, and to clarify the facet-dependent of Fe(II)/a-Fe2O3 on U(VI) or Re(VII) adsorption and reduction phenomenon which is impossible to be achieved by traditional experiments in detail. The intrinsic differences of the affinities toward U(VI) or Re(VII) adsorption on a-Fe2O3 and/or the reduction properties of U(VI) or Re(VII) in Fe(II)/a-Fe2O3 system over a representative range of relevant conditions will be investigated by batch technique. The differences of U(VI) or Re(VII) binding site and the microstructure of the adsorbed U(VI) on a-Fe2O3 facets will be systematically investigated with X-ray absorption fine structure (XAFS) spectroscopy, density functional theory (DFT) calculation, and other methods. XAFS technique can be applied to study the structural information for the adsorption speciation at molecular level. Fe-Mössbauer spectroscopy were used to identify the various a-Fe2O3 sample for their isomer shift and quadrupole splitting, etc. And DFT can be used to study the reactive functional groups of Fe(II)/a-Fe2O3 surfaces and the adsorption and reduction of U(VI) or Re(VII) on the different sites of a-Fe2O3 surface. Combination of experimental and theoretical methods can elucidate the slight variations in the reactivity of a-Fe2O3 with exposed facets, as well as the deep reduction reaction mechanism of these facets. The results presented in this study help us to clarify the roles of a-Fe2O3 on the mobility and the bioavailability of radionuclides in the environment, also provide some insight on the guidance for the practical application of a-Fe2O3 for the remediation of uranium-contaminated wastewater.