Enhanced sieving from exfoliated MoS₂ membranes via covalent functionalization

Nanolaminate membranes made of two-dimensional materials such as graphene oxide are promising candidates for molecular sieving via size-limited diffusion in the two-dimensional capillaries, but high hydrophilicity makes these membranes unstable in water. Here, we report a nanolaminate membrane based on covalently functionalized molybdenum disulfide (MoS₂) nanosheets. The functionalized MoS₂ membranes demonstrate >90% and ~87% rejection for micropollutants and NaCl, respectively, when operating under reverse osmotic conditions. The sieving performance and water flux of the functionalized MoS₂ membranes are attributed both to control of the capillary widths of the nanolaminates and to control of the surface chemistry of the nanosheets. We identify small hydrophobic functional groups, such as the methyl group, as the most promising for water purification. Methyl- functionalized nanosheets show high water permeation rates as confirmed by our molecular dynamic simulations, while maintaining high NaCl rejection. Control of the surface chemistry and the interlayer spacing therefore offers opportunities to tune the selectivity of the membranes while enhancing their stability.