Magnetite nanoparticles (MNPs) play an important role in geological and environmental systems because of their redox reactivity and ability to sequester a wide range of metals and metalloids. X-ray absorption spectroscopy conducted at metal and metalloid edges has suggested that the magnetite {111} faces of octahedrally shaped nanoparticles play a dominant role in the redox and sorption processes of these elements. However, studies directly probing the magnetite surfaces, especially in their fully solvated state, are scarce. Therefore, we investigated the speciation and stability over a wide Eh/pH range of octahedrally shaped MNPs of 2 nm size by means of Kohn–Sham density functional theory with Hubbard correction (DFT+U). By altering the protonation state of the crystals, a redox-sensitive response of the octahedrally coordinated Fe could be achieved. Furthermore, the preferential H distribution could be identified, highlighting the difference between the edges, vertices, and facets of the nanocrystals. Subsequently, the interactions of the MNPs with a solvent of pure water or a 0.5 M NaCl solution were studied by classical molecular dynamics (MD) simulations. Finally, a comparison of the corresponding macroscopic magnetite (111) surface to the investigated MNPs was conducted.

中文翻译：

---

磁铁矿纳米颗粒八面体表面及其溶剂相互作用的计算研究


磁铁矿纳米颗粒 （MNP） 在地质和环境系统中发挥着重要作用，因为它们具有氧化还原反应性以及隔离多种金属和准金属的能力。在金属和准金属边缘进行的 X 射线吸收光谱表明，八面体形状的纳米颗粒的磁铁矿{111}面在这些元素的氧化还原和吸附过程中起主导作用。然而，直接探测磁铁矿表面的研究，尤其是在其完全溶剂化状态下的研究很少。因此，我们通过带有哈伯德校正 （DFT+U） 的 Kohn-Sham 密度泛函理论研究了 2 nm 大小的八面体形状 MNP 在宽 Eh/pH 范围内的形态和稳定性。通过改变晶体的质子化状态，可以实现八面体配位 Fe 的氧化还原敏感响应。此外，可以识别优先 H 分布，突出纳米晶体的边缘、顶点和刻面之间的差异。随后，通过经典分子动力学 （MD） 模拟研究了 MNP 与纯水溶剂或 0.5 M NaCl 溶液的相互作用。最后，将相应的宏观磁铁矿 （111） 表面与研究的 MNP 进行了比较。