Enhancing the Dynamics of Water Confined between Graphene Oxide Surfaces with Janus Interfaces: A Molecular Dynamics Study.
Enhancing the Dynamics of Water Confined between Graphene Oxide Surfaces with Janus Interfaces: A Molecular Dynamics Study.
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DOI：
10.1021/acs.jpcb.8b12341
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发表时间：
2019-03
期刊：
影响因子：
--
通讯作者：
Raja Manokaran;K. Ayappa
中科院分区：
文献类型：
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作者：
Raja Manokaran;K. Ayappa
氧化石墨烯膜因其在海水淡化应用中的潜在应用而被广泛研究。为了了解宏观膜中形成的相反表面对表面氧化的影响和固有的非均质性，对由不同表面类型组成的纳米孔(8-15？)中的水进行了分子动力学模拟。在离子分子筛分的最佳分离距离8？时，观察到最大的差异。在完全氧化(OO)表面之间，承压水的偶极-偶极驰豫和HH旋转弛豫最慢，而由氧化表面与石墨烯表面相邻的Janus约束所观察到的偶极-偶极驰豫时间减少了2个数量级。在较小的间隔下，平移和转动态密度分别表现出明显的蓝移和红移，移动的程度取决于表面类型。自中间散射函数显示，OO表面在8？处有一个明显的平台区，这暗示了类玻璃动力学，而在其他表面观察到了扩展的α弛豫。虽然在较小的表面间隔下，水的扩散系数比整体扩散系数小一个数量级，但Janus表面之间的水总是具有最高的扩散系数。在所研究的不同体系中，亲水基团数目最少的JANUS表面的水分子转移自由能最小(∼为4kJ/m ol)。因此，Janus界面似乎为水传输提供了最佳环境，在组装用于净水的基于石墨烯氧化物的膜堆时提供了一种设计策略。
Graphene oxide membranes have been widely studied for their potential applications in water desalination applications. To understand the influence of surface oxidation and the inherent heterogeneity imposed by opposing surfaces formed in macroscopic membranes, molecular dynamics simulations of water confined in nanopores (8-15 Å) made up of different surface types are carried out. The greatest differences are observed at 8 Å, which is the optimal separation distance for molecular sieving of ions. The dipole-dipole relaxation and HH rotational relaxation of confined water are the slowest between fully oxidized (OO) surfaces with a 2 order decrease in the dipole-dipole relaxation time observed for the Janus confinement consisting of an oxidized surface adjacent to a graphene surface. The translational and rotational density of states show distinct blue shifts and red shifts, respectively, at the smaller separations, with the extent of the shifts dependent on the surface type. Self-intermediate scattering functions show a pronounced plateau region for the OO surfaces at 8 Å, suggestive of glasslike dynamics, and extended α-relaxations were observed for the other surfaces. Although water diffusivity is an order of magnitude smaller than bulk diffusivities at the smaller surface separations, water between the Janus surfaces always had the highest diffusivities. The free energy to transfer a water molecule from bulk water was found to be the smallest (∼4 kJ/mol) for the Janus surfaces, which have the lowest number of hydrophilic groups among the different systems studied. Thus, the Janus interface appears to provide the optimal environment for water transport, providing a design strategy while assembling graphene oxide-based membrane stacks for water purification.