Güvensoy-Morkoyun Aysa, Baysal Tuğba, Tantekin-Ersolmaz Ş Birgül, Velioğlu Sadiye
Department of Chemical Engineering, Istanbul Technical University, Maslak, Istanbul 34469, Türkiye.
Institute of Nanotechnology, Gebze Technical University, Gebze, Kocaeli 41400, Türkiye.
J Chem Theory Comput. 2024 Nov 12;20(21):9642-9654. doi: 10.1021/acs.jctc.4c00693. Epub 2024 Nov 4.
Organic solvent nanofiltration (OSN) stands out as an energy-efficient and low-carbon footprint technology, currently reliant on polymeric membranes. With their exceptional chemical stability and tunable sieving properties, two-dimensional (2D) nanolaminate membranes present distinct advantages over conventional polymer-based membranes, attracting tremendous interest in the OSN community. Computational approaches for designing innovative 2D nanolaminates exhibit significant potential for the future of OSN technology. Imitating the pressure gradient in filtration processes by applying an external force to atoms within a predefined slab, boundary-driven nonequilibrium molecular dynamics ((BD)-NEMD) is a state-of-the-art simulation method with a proven track record in investigating the water transport in nanopores. Nevertheless, implementation of (BD)-NEMD for a broad range of solvents poses a challenge in estimating the OSN performance of theoretical membranes. In this work, we developed a (BD)-NEMD protocol that elucidates the effects of several computational details often overlooked in water simulations but are crucial for bulky solvent systems. We employed a MXene (TiCO) nanochannel as a model membrane and examined the transport of nine solvents (methanol, ethanol, acetone, -hexane, -heptane, toluene, ethyl acetate, dichloromethane, and water) having different properties. First, the impact of ensemble type, thermostatting, channel wall model, and restraining force constant was elaborated. After optimizing the thermostatting approach, we demonstrated that the location of the force slab particularly affects the flux of bulky solvents by changing the density distribution in the feed and permeate sides. Similarly, the uniformity of intramolecular force distribution in bulky solvents and resulting flux are shown to be prone to manipulation by slab boundaries. Next, the magnitudes of the external force generating a linear relation between the pressure gradient and solvent flux were identified for each solvent to ensure that calculated fluxes could be extrapolated to experimentally related pressures. This linear relation was also validated for a mixture system containing 50% ethanol and 50% water. We then correlated the calculated solvent permeances with various solvent properties, such as viscosity, Hansen solubility parameters, kinetic diameter, and interaction energy. Remarkably, we observed a linear correlation with an value of 0.96 between permeance and the combined parameter of viscosity and interaction energy. Finally, the solvent permeances calculated with our proposed methodology closely align with the experimentally reported data. Overall, our work aims to serve as a practical guide and bridge the gap in established simulation methods that are suited for a broad range of solvents and membrane materials.
有机溶剂纳滤（OSN）作为一种节能且碳足迹低的技术脱颖而出，目前依赖于聚合物膜。二维（2D）纳米层压膜具有出色的化学稳定性和可调的筛分性能，与传统的聚合物基膜相比具有明显优势，在OSN领域引起了极大关注。设计创新2D纳米层压膜的计算方法对OSN技术的未来具有巨大潜力。通过对预定义平板内的原子施加外力来模拟过滤过程中的压力梯度，边界驱动非平衡分子动力学（(BD)-NEMD）是一种先进的模拟方法，在研究纳米孔中的水传输方面有着可靠的记录。然而，将(BD)-NEMD应用于多种溶剂时，在估计理论膜的OSN性能方面面临挑战。在这项工作中，我们开发了一种(BD)-NEMD方案，该方案阐明了一些在水模拟中经常被忽视但对大体积溶剂系统至关重要的计算细节的影响。我们采用MXene（TiCO）纳米通道作为模型膜，研究了九种具有不同性质的溶剂（甲醇、乙醇、丙酮、己烷、庚烷、甲苯、乙酸乙酯、二氯甲烷和水）的传输。首先，阐述了系综类型、恒温方法、通道壁模型和约束力常数的影响。在优化恒温方法后，我们证明了力平板的位置通过改变进料侧和渗透侧的密度分布特别影响大体积溶剂的通量。同样，大体积溶剂中分子内力分布的均匀性以及由此产生的通量容易受到平板边界的影响。接下来，确定了每种溶剂产生压力梯度与溶剂通量之间线性关系的外力大小，以确保计算出的通量可以外推到与实验相关的压力。这种线性关系也在含有50%乙醇和50%水的混合体系中得到了验证。然后，我们将计算出的溶剂渗透率与各种溶剂性质相关联，如粘度、汉森溶解度参数、动力学直径和相互作用能。值得注意的是，我们观察到渗透率与粘度和相互作用能的组合参数之间存在线性相关性，相关系数为0.96。最后，用我们提出的方法计算出的溶剂渗透率与实验报道的数据非常吻合。总的来说，我们的工作旨在作为一份实用指南，弥合适用于多种溶剂和膜材料的既定模拟方法之间的差距。
