pH-dependent water permeability switching and its memory in MoS 2 membranes.

Intelligent transport of molecular species across different barriers is critical for various biological functions and is achieved through the unique properties of biological membranes 1-4 . Two essential features of intelligent transport are the ability to (1) adapt to different external and internal conditions and (2) memorize the previous state 5 . In biological systems, the most common form of such intelligence is expressed as hysteresis 6 . Despite numerous advances made over previous decades on smart membranes, it remains a challenge to create a synthetic membrane with stable hysteretic behaviour for molecular transport 7-11 . Here we demonstrate the memory effects and stimuli-regulated transport of molecules through an intelligent, phase-changing MoS 2 membrane in response to external pH. We show that water and ion permeation through 1T' MoS 2 membranes follows a pH-dependent hysteresis with a permeation rate that switches by a few orders of magnitude. We establish that this phenomenon is unique to the 1T' phase of MoS 2 , due to the presence of surface charge and exchangeable ions on the surface. We further demonstrate the potential application of this phenomenon in autonomous wound infection monitoring and pH-dependent nanofiltration. Our work deepens understanding of the mechanism of water transport at the nanoscale and opens an avenue for the development of intelligent membranes.