Ionic Selectivity of Nanopores: Comparison among Cases under the Hydrostatic Pressure, Electric Field, and Concentration Gradient

TL;DR

This study uses finite element simulations to compare ionic selectivity in nanopores under electric, pressure, and concentration fields, revealing how different parameters influence ion transport for energy applications.

Contribution

It systematically analyzes the effects of three common driving fields on nanopore ionic selectivity, providing insights for optimizing nanoporous membrane devices.

Findings

Cation selectivity order: electric > concentration > pressure.

Selectivity increases with pore length and surface charge density.

Selectivity decreases with pore diameter and salt concentration.

Abstract

The ionic selectivity of nanopores is crucial for the energy conversion based on nanoporous membranes. It can be significantly affected by various parameters of nanopores and the applied fields driving ions through porous membranes. Here, with finite element simulations, the selective transport of ions through nanopores is systematically investigated under three common fields, i.e. the electric field (V), hydrostatic pressure (p), and concentration gradient (C). For negatively charged nanopores, through the quantitative comparison of the cation selectivity (t+) under the three fields, the cation selectivity of nanopores follows the order of t+V > t+c > t+p. This is due to the transport characteristics of cations and anions through the nanopores. Because of the strong transport of counterions in electric double layers under electric fields and concentration gradients, the nanopore exhibits a relatively higher selectivity to counterions. We also explored the modulation of t+ on the properties of nanopores and solutions. Under all three fields, t+ is directly proportional to the pore length and surface charge density, and inversely correlated to the pore diameter and salt concentration. Under both the electric field and hydrostatic pressure, t+ has almost no dependence on the applied field strength or ion species, which can affect t+ in the case of the concentration gradient. Our results provide detailed insights into the comparison and regulation of ionic selectivity of nanopores under three fields which can be useful for the design of high-performance devices for energy conversion based on nanoporous membranes.