Correlations in charged multi-pore systems: Implications for enhancing selectivity and permeability in nanoporous membranes

Nanoporous membranes have emerged as powerful tools for diverse applications, including gas separation and water desalination. Achieving high permeability for desired molecules alongside exceptional rejection of other species presents a significant design challenge. One potential strategy involves optimizing the chemistry and geometry of isolated nanopores to enhance permeability and selectivity, while maximizing their density within a membrane. However, the impact of pore proximity on membrane performance remains an open question. Through path sampling simulations of model graphitic membranes with multiple sub-nanometer pores, we reveal that nanoscale proximity between pores detrimentally affects water permeability and salt rejection. Specifically, counter-ion transport is decelerated, while co-ion transport is accelerated, due to direct interactions between water molecules, salt ions, and the dipoles within neighboring pores. Notably, the observed ionic transport timescales significantly deviate from established theories such as the access resistance model, but are well explained using the simple phenomenological model that we develop in this work. We use this model to pre-screen and optimize pore arrangements that elicit minimal correlations at a target pore density. These findings deepen our understanding of multi-pore systems, informing the rational design of nanoporous membranes for enhanced separation processes such as water desalination. They also shed light onto the physiology of biological cells that employ ion channel proteins to modulate ion transport and reversal potentials.