Dipole Alignment and Layered Flow Structure in Pressure-Driven Water Transport through MoS$_{2}$ Membranes

TL;DR

This study addresses how pore size and edge chemistry control water transport through MoS2 nanopores. Using atomistic molecular dynamics simulations of water flowing under pressure through MoS2 pores of three diameters, the work reveals that larger pores yield higher flux due to reduced hydrodynamic resistance and the formation of layered water near the pore edges, while narrow pores exhibit dipole alignment driven by asymmetric Mo/S edge chemistry that directs transport. Edge regions emerge as active zones that concentrate flow and accelerate water, with dipole orientation reinforcing directional, high-speed transport. The findings provide design principles for MoS2-based nanofluidic membranes with potential applications in desalination and filtration, highlighting the importance of pore geometry and edge chemistry on permeation performance.

Abstract

Efficient water transport through nanostructure membranes is essential for advancing filtration and desalination technologies. In this study, we investigate the flow of water through molybdenum disulfide (MoS$_{2}$) nanopores of varying diameters using molecular dynamics simulations. The results demonstrate that both pore size and atomic edge composition play crucial roles in regulating water flux, molecular organization, and dipole orientation. Larger pores facilitate the formation of layered water structures and promote edge-accelerated flow, driven by strong electrostatic interactions between water molecules and exposed molybdenum atoms. In narrower pores, confinement and asymmetric edge chemistry induce the ordered alignment of dipoles, thereby enhancing directional transport. Velocity and density maps reveal that pore edges act as active zones, concentrating flow and reducing resistance. These findings highlight the significance of pore geometry, surface chemistry, and molecular dynamics in influencing water behavior within MoS$_{2}$ membranes, providing valuable insights for the design of advanced nanofluidic and water purification systems.

Figures (7)

• Figure 1: Side view of the simulation box. The y-axis is out-of-plane, towards the reader.
• Figure 2: Nanoporous membranes structures with different pores diameters.(a)-(c) represents the represents the MoS$_{2}$ membrane.
• Figure 3: Water flow rates through molybdenum disulfide nanopores at various diameters: 0.95 nm (red), 1.22 nm (blue), and 1.63 nm (green).
• Figure 4: Oxygen density maps for membrane under a pressure difference of $\Delta P = 100\; \mathrm{MPa}$. Red regions indicate a high probability of water molecule presence, blue regions indicate low probability, and black regions correspond to areas where no water molecules were detected.
• Figure 5: Dipole angle distribution of water molecules along the x-direction for MoS$_{2}$ nanopores with diameters of 0.95 nm (red), 1.22 nm (blue), and 1.63 nm (green) under a pressure gradient of $\Delta P = 100\; \mathrm{MPa}$