Key Laboratory of Hydraulic Machinery Transients of Ministry of Education, School of Power and Mechanical Engineering, Wuhan University , Wuhan, Hubei 430072, China.
ACS Appl Mater Interfaces. 2017 Jul 12;9(27):22826-22836. doi: 10.1021/acsami.7b05307. Epub 2017 Jun 30.
Transport of ionic solutions through graphene oxide (GO) membranes is a complicated issue because the complex and tortuous structure inside makes it very hard to clarify. Using molecular dynamics (MD) simulations, we investigated the mechanism of water transport and ion movement across multilayer GO. The significant flow rate is considerably influenced by the structural parameters of GO membranes. Because of the size effect on a shrunken real flow area, there is disagreement between the classical continuum model and nanoscaled flow. To eliminate the variance, we obtained modified geometrical parameters from density analysis and used them in the developed hydrodynamic model to give a precise depiction of water flow. Four kinds of solutions (i.e., NaCl, KCl, MgCl, and CaCl) and different configurational GO sheets were considered to clarify the influence on salt permeation. It is found that the abilities of permeation to ions are not totally up to the hydration radius. Even though the ionic hydration shell is greater than the opening space, the ions can also pass through the split because of the special double-deck hydration structure. In the structure of GO, a smaller layer separation with greater offsetting gaps could substantially enhance the membrane's ability to reject salt. This work establishes molecular insight into the effects of configurational structures and salt species on desalination performance, providing useful guidelines for the design of multilayer GO membranes.
离子溶液通过氧化石墨烯（GO）膜的传输是一个复杂的问题，因为其内部复杂而曲折的结构使得很难阐明。我们使用分子动力学（MD）模拟研究了多层 GO 中水分子传输和离子运动的机制。GO 膜的结构参数对显著的流速有很大的影响。由于实际流动面积缩小的尺寸效应，经典连续体模型与纳米尺度流动之间存在分歧。为了消除差异，我们从密度分析中获得了修正的几何参数，并将其用于开发的流体动力学模型中，以精确描述水流。考虑了四种溶液（即 NaCl、KCl、MgCl 和 CaCl）和不同构型的 GO 片，以阐明其对盐渗透的影响。结果发现，离子的渗透能力并不完全取决于水合半径。即使离子的水合壳层大于开口空间，由于特殊的双层水合结构，离子也可以穿过分裂。在 GO 的结构中，较小的层间距和更大的偏移间隙可以显著提高膜的抗盐能力。这项工作为理解构型结构和盐种类对脱盐性能的影响提供了分子层面的认识，为多层 GO 膜的设计提供了有用的指导。
