Molecular Insight into Water Transport through Heterogeneous GO-based Two-Dimensional Nanocapillary.

Nanofluidics in two-dimensional (2-D) heterogeneous layered materials with hybrid overlapping structures exhibit promising potential in filtration and separation applications. However, molecular transport across the heterogeneous interlayer galleries remains largely unexplored, in particular, there exists disputation in the function and performance of hybrid graphene oxide (GO)-based laminate membrane for the water transport. Herein, heterogeneous 2-D GO-based nanochannels were employed as a typical platform to investigate the water flow by nonequilibrium molecular dynamics (MD) simulation. It is demonstrated that both heterogeneous and homogeneous GO nanochannels exhibit similar reduced water flow behavior, even if one surface of the 2-D channel is the pristine graphene. In particular, the flow rate in the hybrid GO/pristine graphene nanochannels does not lie between those of the oxidized and the pristine regions, and the high-friction GO surface suppresses the water transport and controls the entire flow performance. This result is qualitatively consistent with the recent experimental observation. By comparing with the MD simulation, a hydrodynamic model was developed to describe the flow rate for 2-D heterogeneous nanochannels. The reduced water transport has been revealed as the distinct vertical dragging effect, arising from the synergistic effect between the interfacial affinity from GO surfaces and the interlayer molecular interaction. Our results provide novel physical pictures for the molecular transport inside heterogeneous 2-D nanochannels.