Ardalan Hayatifar, Simon Gravelle, Beatriz D. Moreno, Valerie A. Schoepfer, Matthew B. J. Lindsay
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引用次数: 0
Abstract
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.
涉及金属(氧氢)氧化物相的界面过程对于营养物质和污染物在土壤、沉积物和水中的流动性和生物利用率非常重要。因此,这些过程影响着生态系统的健康和功能,并决定了地球在地质年代中生物和环境的共同演化。在此,我们采用反应分子动力学模拟,并辅以同步辐射 X 射线光谱法,研究影响含水 $$\{text {MoO}_4}^{2-}$$ 的铁水系统表面复合的分子尺度界面过程。我们通过直接模拟计算表面复合模型,验证了这种方法的实用性。反应力场捕捉了表面重组、表面电荷平衡以及界面水氢键网络随吸附和质子转移而演变的真实动态。我们发现,正如模拟和高分辨率 X 射线衍射所揭示的那样,在水合和吸附作用下,无水铁通过表面电荷平衡重组为更无序的相。我们通过监测水的动态变化,观察了这种重组如何导致与大体积水不同的界面氢键网络。利用伞状取样,我们构建了水$${\text {MoO}_4}^{2-}$ 在不同浓度下的吸附自由能景观以及铁水盐表面的去质子化。这些结果与实验性表面复合模型所报告的数值非常吻合。这些发现非常重要,因为反应分子动力学开辟了研究矿物-水界面的新途径,丰富和完善了表面复合模型,使其超越了其基础假设。
期刊介绍:
Geochemical Transactions publishes high-quality research in all areas of chemistry as it relates to materials and processes occurring in terrestrial and extraterrestrial systems.