Coupled Transport of Water and Ions through Graphene Nanochannels
Yunzhen Zhao, Decai Huang, Jiaye Su, Shiwu Gao
Abstract
Water and ion transport through graphene nanochannels has attracted considerable attention thanks to the possibility of dimensional control of the channel sizes down to a single atomic layer. Using molecular dynamics simulations, we systematically analyzed the coupled transport of water and ions in the solutions of LiCl, NaCl, and KCl salts as a function of channel sizes, applied electric fields, and salt concentrations. A universal order of ion flux is found with K+ > Cl– > Na+ ≈ Li+, and the K+ flux is twice as large as those of Na+ and Li+, indicating the ion selectivity with such graphene channels. The local structures and transport dynamics within the channels show sensitive dependence on the channel height, forming two-dimensional hydration shells in the low-height limit. The hydration shells of the ions undergo transformation from three- to two-dimensional structures upon entering the narrow channel. A power law relationship between the ion translocation time and electric field is also found and can be well described by the one-dimensional Langevin equation. In addition, the linear relation between the ion flux and concentration agrees well with the one-dimensional Poisson–Nernst–Planck equation. Our results provide insights into the ionic transport through graphene channels and have implications for the design of novel nanofluidic devices for selective ion transport in future applications.