Vacancy Functionalized MoS₂ Nanolaminated Membranes for Efficient Sieving in Forward Osmosis

2D transition-metal dichalcogenides (TMDs) based nanolaminates are promising candidates for water purification. However, fabricating nanochannels with tunable capillary widths remain a challenge. This study proposed a sulfur vacancy functionalization strategy for fabricating high performance nanolaminate membranes by grafting three kinds of thiol (S-H) containing molecules (Cysteine, 3-Mercapto-1,2-propanediol, 1-Propanethiol) on MoS₂ nanosheets, in which propanethiol functionalized MoS₂ membrane exhibited best salt rejection (99.3%) and water/salt selectivity (800 bar^-1) in forward osmosis (draw solution: sucrose solution). It is found the capillary width increased from 0.2 Å in pristine MoS₂ to ≈5 Å in propanethiol functionalized MoS₂ membranes. Numerical simulations suggest that nanofluidic properties of the functionalized membranes are governed by the fundamental interaction between water and the corresponding S-H functional group, and the interlayer distance. Importantly, since the S-H containing molecules can repair MoS₂ nanosheets by fitting into the sulfur vacancies, the stability of the membranes is also improved with minimal swelling, which is promising for their practical applications.