Why is Single-Layer MoS₂ a More Energy Efficient Membrane for Water Desalination?

Abstract

Water desalination technologies are extensively utilized to solve water scarcity problems in many regions of the world. Discovery and application of two-dimensional (2D) nanoporous materials provide engineers a viable solution for reducing to a large extent energy consumption during the water desalination process. In this work, we conducted a thorough comparison of the water permeability and ion rejection rate between various 2D materials, including MoS2, graphene, phosphorene, boron nitride, and MoSe2. Through molecular dynamics simulation, we demonstrated that among all 2D materials with the same pore size, single-layer MoS2 consistently performs 27% better than graphene, 38% than phosphorene, 35% than BN, and 20% than MoSe2 in terms of water permeability while maintaining a greater than 99% ion rejection rate. We further investigated how the fundamental physics behind the outstanding performance of MoS2 is a combination of water structure and dynamics near the membrane surface, energy barrier, and water packing and velocity inside the nanopore.