Multifunctional intercalants create stable subnanochannels in MoS₂ membranes for wastewater treatment

MoS₂ nanosheets, featuring high chemical and mechanical stability, offer immense promise as building blocks for high-performance two-dimensional (2D) membranes. However, engineering these membranes to achieve tailored channel dimensions and chemistry while maintaining sufficient stability remains a significant challenge, impeding their real-world applications. Herein, we demonstrate the multifunctionality of polymeric quaternary ammoniums as intercalants in MoS₂ membranes, enabling the creation of selective, stable 2D subnanochannels in MoS₂ membranes. These intercalants fulfil three key roles: they define and secure the channel width at ~5 Å without disrupting the channel order, impart substantial positive charges to regulate the microenvironment within the channel, and establish strong non-covalent interactions with the electron-rich MoS₂ planes to stabilize the channels. Consequently, the resulting membranes exhibit superior stability across various aqueous environments, particularly showing excellent tolerance under highly acidic (1 M H₂SO₄) conditions. During harsh pressure-driven crossflow operations, the membranes demonstrate fast water permeation while maintaining high rejection (> 90%) and selectivity for heavy metal ions in acidic wastewater. This strategy of leveraging multifunctional intercalants offers critical insights for the design of task-specific 2D membranes for demanding applications.