Multilayer Separation Effects on MoS2 Membranes in Water Desalination

Abstract

Climate change and its related effects are imposing severe stress on the current freshwater supplies. This has been exacerbated due to the growth in population, rapid industrialization, and increased energy demand. Increased water requirement is a global challenge. Although more than 70% of the Earth is covered by water, much of it is unusable for human use. Freshwater reservoirs, ponds, and subterranean aquifers account for just 2.5% of the world’s overall freshwater availability. Unfortunately, these water supplies are not very unevenly spread. Therefore, the need to augment these supplies through the desalination of seawater or brackish water. Reverse osmosis (RO) is currently the most widespread method of desalination. However, the unit cost of water is still high partly due to the thin-film composite (TFC) polymer membranes used in the current desalination system. Thus the need for low-cost nanomaterials for Water Desalination and Purification. A promising way to meet this demand is to use two-dimensional (2D) nanoporous materials such as graphene and MoS2 to minimize energy consumption during the desalination process. New nanotechnology methodologies that apply reverse osmosis have been developed. Among some of these technologies is using 2D materials such as graphene and MoS2, which have been studied extensively for water desalination. Single-layer nanoporous 2D materials such as graphene and MoS2 promises better filtrations in the water channel. Although single-layer MoS2 (SL_MoS2) membrane have much promise in the RO desalination membrane, multilayer MoS2 are simpler to make and more cost-efficient. Building on the SL_MoS2 membrane knowledge, we have used the molecular dynamics method (MD) to explore the effects of multilayer MoS2 in water desalination. This comparison is made as a function of the pore size, water flow rate and salt rejection. In addition, we also looked at the effect of the increased interlayer spacing between layers of the nanoporous 2D membrane and then made the comparison. The ions rejection follows the trend trilayer> bilayer> monolayer from results obtained, averaging over all three membrane types studied for the MoS2, the ions rejection follows the trend trilayer > bilayer > monolayer. We find that the thin, narrow layer separation plays a vital role in the successful rejection of salt ions in bilayers and trilayers membranes. These findings will help build and proliferate tunable nanodevices for filtration and other applications.