放射性核素U在针铁矿(010)表面吸附的第一性原理研究

采用基于密度泛函理论的第一性原理研究了有水与无水环境下放射性核素U在针铁矿(010)表面的吸附。结果表明,由于水分子与(010)表面的初始构型不同,其吸附能为-0.56~-0.85eV。同时发现在缺水的情况下,U原子可吸附在针铁矿(010)表面的替代位(T)、八面体间隙位(O)及两个O原子的桥位(B)上。其吸附能为负,大小按吸附T、B、O的顺序依次增大。水对U原子吸附能的影响较明显。当U原子占据替代位和八面体间隙位时,在其附近的水分子可增强U原子在针铁矿(010)表面的吸附,可使U原子在针铁矿(010)表面的吸附能降低1~2eV;当U原子在桥位时,水分子既可增强也可减弱U原子在针铁矿(010)表面的吸附能力,这依赖于U原子与水分子作用后其价态的变化。所有这些吸附均为放热反应。计算结果显示,由于水分子与U原子的吸附引起的表面晶格畸变较小,所有涉及的表面键长变化均不大于0.055nm。所有涉及到的反应过程中均有H、U、Fe原子上的部分电子转移到O原子上。

Study on Adsorption of Uranium on (010) Surface of Goethite by First Principle

In the absence and presence of water, the absorption properties of uranium on the (010) surface of goethite (α-FeOOH) were studied by first principle. It is found that the adsorption energy of a water molecular on the (010) surface is at the range from -0.56 eV to -0.85 eV, depending on their initial configurations on the surface. It is also found that in the absence of water, uranium atom might be adsorbed into an octahedral site, or a substitution site, or a bonding bridge site between two oxygen atoms of the (010) surface of goethite. In the presence of water, the water molecular might enhance the absorption ability of uranium atom on the (010) surface of goethite when uranium atom occupies the substitution site and octahedral site. In this case, the adsorption energy of uranium atom on the surface may be reduced by 1.2 eV by water molecular. When uranium atom occupies the bridge site between two oxygen atoms on the surface, the water molecular may either enhance or weaken the adsorption ability of an uranium atom on the (010) surface, and it depends on the initial configuration of water molecular on the surface. But, no matter how, these adsorption processes of water and uranium on the (010) surface of goethite all belong to exothermic reaction. The lattice distortion induced by a uranium atom adsorption on substitution site, octahedral site, and bridge site between two oxygen atoms of the (010) surface of goethite or by a water molecular adsorption on the surface is found to be small, and all the bonding length changes concerned on the surface are less than 0.055 nm. All these cases result from the interaction between U, O, Fe, and H atoms, where partial electrons of the U, Fe, and H atoms transfer into the O atoms.