Experimental evidence has shown that graphene oxide (GO) can be impermeable to liquids, vapors and gases, while it allows a fast permeation of water molecules. Theoretical studies to understand the filtration mechanisms come mostly from water desalination, while very few works have been dedicated to alcohol dehydration. In this work, we have investigated the molecular level mechanism underlying the alcohol/water separation inside GO membranes. A series of Molecular Dynamics and Grand-Canonical Monte Carlo simulations were carried out to probe the ethanol/water and methanol/water separation through GO membranes composed of multiple layered graphene-based films with different interlayer distance values and number of oxygen-containing functional groups. Our results show that the size exclusion and membrane affinities are not sufficient to explain the selectivity. Besides that, the favorable water molecular arrangement inside GO 2D-channels forming a robust H-bond network and the fast water permeation are crucial for an effective separation mechanism. In other words, the separation phenomenon is not only governed by membrane affinities (enthalpic mechanisms) but mainly by the geometry and size factors (entropic mechanisms). Our findings are consistent with the available experimental data and contribute to clarify important aspects of the separation behavior of confined alcohol/water in GO membranes.

中文翻译：

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对多层氧化石墨烯膜中水-醇分离机制的见解：熵与焓因子

实验证据表明，氧化石墨烯 (GO) 可以不渗透液体、蒸汽和气体，同时它允许水分子快速渗透。了解过滤机制的理论研究主要来自水淡化，而很少有研究致力于酒精脱水。在这项工作中，我们研究了 GO 膜内醇/水分离的分子水平机制。进行了一系列分子动力学和正则蒙特卡罗模拟，通过由具有不同层间距离值和含氧官能团数量的多层石墨烯基薄膜组成的 GO 膜来探测乙醇/水和甲醇/水的分离. 我们的结果表明尺寸排阻和膜亲和力不足以解释选择性。除此之外，GO 2D 通道内有利的水分子排列形成强大的 H 键网络和快速的水渗透对于有效的分离机制至关重要。换句话说，分离现象不仅受膜亲和力（焓机制）的控制，而且主要受几何和尺寸因素（熵机制）的控制。我们的发现与可用的实验数据一致，有助于阐明 GO 膜中受限醇/水分离行为的重要方面。GO 2D 通道内有利的水分子排列形成强大的 H 键网络和快速的水渗透对于有效的分离机制至关重要。换句话说，分离现象不仅受膜亲和力（焓机制）的控制，而且主要受几何和尺寸因素（熵机制）的控制。我们的发现与可用的实验数据一致，有助于阐明 GO 膜中受限醇/水分离行为的重要方面。GO 2D 通道内有利的水分子排列形成强大的 H 键网络和快速的水渗透对于有效的分离机制至关重要。换句话说，分离现象不仅受膜亲和力（焓机制）的控制，而且主要受几何和尺寸因素（熵机制）的控制。我们的发现与可用的实验数据一致，有助于阐明 GO 膜中受限醇/水分离行为的重要方面。