Molecular dynamics simulations of water flow enhancement in carbon nanochannels

Abstract

Fluidic flow in carbon nanochannels or nanopores has shown great application prospects in nanofiltration. Therefore, enhancing water flux while maintaining their filtration property is crucial to further extend their applications. In this work, inspired by the hourglass-shaped aquaporin water channel, we proposed a method to optimize water flux in carbon nanochannels using conical carbon nanochannels. Adopting nonequilibrium molecular dynamics simulations, water flow in a series of conical carbon nanochannels was simulated. The results showed that the conical channel with apex angle of 19.2° (38.9°) had the optimum water flux when water flowed from the base (tip) side to the tip (base) side of the conical channel, and the water flux was nearly twice as the recently developed MoS2 desalination membrane. Then, the physical mechanism for the conical channel optimizing water permeation was revealed through detailed analyses of potential of mean forces, average number of hydrogen bonds and pressure distributions of the simulation systems. Finally, the microscopic water structures in these channels were also analyzed to further rationalize the optimizing mechanism. This work indicates that other than decreasing the membrane thickness, regulating the channel configuration is a more effective method to enhance water permeation rate in channels with limited channel sizes.