Interfacial processes involving metal (oxyhydr)oxide phases are important for the mobility and bioavailability of nutrients and contaminants in soils, sediments, and water. Consequently, these processes influence ecosystem health and functioning, and have shaped the biological and environmental co-evolution of Earth over geologic time. Here we employ reactive molecular dynamics simulations, supported by synchrotron X-ray spectroscopy to study the molecular-scale interfacial processes that influence surface complexation in ferrihydrite-water systems containing aqueous $${\text {MoO}_4}^{2-}$$ . We validate the utility of this approach by calculating surface complexation models directly from simulations. The reactive force-field captures the realistic dynamics of surface restructuring, surface charge equilibration, and the evolution of the interfacial water hydrogen bond network in response to adsorption and proton transfer. We find that upon hydration and adsorption, ferrihydrite restructures into a more disordered phase through surface charge equilibration, as revealed by simulations and high-resolution X-ray diffraction. We observed how this restructuring leads to a different interfacial hydrogen bond network compared to bulk water by monitoring water dynamics. Using umbrella sampling, we constructed the free energy landscape of aqueous $${\text {MoO}_4}^{2-}$$ adsorption at various concentrations and the deprotonation of the ferrihydrite surface. The results demonstrate excellent agreement with the values reported by experimental surface complexation models. These findings are important as reactive molecular dynamics opens new avenues to study mineral-water interfaces, enriching and refining surface complexation models beyond their foundational assumptions.

中文翻译：

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利用反应分子动力学探测水铁矿-水界面的原子级过程


涉及金属（羟基）氧化物相的界面过程对于土壤、沉积物和水中营养物质和污染物的流动性和生物利用度非常重要。因此，这些过程影响生态系统的健康和功能，并塑造了地球在地质时期的生物和环境协同进化。在这里，我们采用反应分子动力学模拟，在同步加速器 X 射线光谱的支持下，研究影响含有 $${\text {MoO}_4}^{2-}$$ 的水铁矿-水系统中表面络合的分子尺度界面过程。我们通过直接从仿真中计算表面复合模型来验证这种方法的实用性。反作用力场捕捉了表面重组、表面电荷平衡以及界面水氢键网络响应吸附和质子转移而演变的现实动力学。我们发现，在水合和吸附后，水铁矿通过表面电荷平衡重组成更加无序的相，正如模拟和高分辨率 X 射线衍射所揭示的那样。我们通过监测水动力学，观察了这种重组如何导致与散装水相比不同的界面氢键网络。使用伞式采样，我们构建了不同浓度的 $${\text {MoO}_4}^{2-}$$ 吸附和水铁酸盐表面的去质子化的自由能景观。结果表明，与实验表面络合模型报告的值非常吻合。这些发现很重要，因为反应分子动力学为研究矿水界面开辟了新的途径，丰富和完善了超越其基本假设的表面络合模型。