pH-dependent water permeability switching and its memory in MoS 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. Two essential features of intelligent transport are the ability to (1) adapt to different external and internal conditions and (2) memorize the previous state. In biological systems, the most common form of such intelligence is expressed as hysteresis. 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. Here we demonstrate the memory effects and stimuli-regulated transport of molecules through an intelligent, phase-changing MoS membrane in response to external pH. We show that water and ion permeation through 1T' MoS 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, 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.