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.