Electrohydrodynamic ion regulation in soft-coated nanochannels: A comparative assessment of geometry effects on desalination performance

Overview & Synopsis

Meeting the growing demand for high-quality freshwater requires membrane systems that can provide strong ion discrimination while sustaining adequate water transport. This work presents a comprehensive, systematic numerical investigation comparing three distinct integrated nanochannel arrays—a uniform array of cylindrical channel (Type 1), an array of forward-tapered cone (Type 2), and an array of reverse-tapered cone (Type 3)—specifically within soft-coated nanochannels featuring a negatively charged polyelectrolyte layer. Our approach uniquely analyzes the electrohydrodynamic ion regulation by evaluating these architectures using a fully coupled Poisson–Nernst–Planck and Navier–Stokes framework for three monovalent electrolytes (NaCl, KCl, and KNO3) under a wide range of operating conditions. The simulations show that geometric confinement substantially alters electrohydrodynamic interactions inside the channels. The reverse-tapered design demonstrates the strongest ion-exclusion capability, reducing NaCl concentration by more than 99 %, whereas the cylindrical and forward-tapered structures achieve approximately 87 % and 95 % rejection, respectively. The same geometry also produces a favorable balance between ion blocking and hydraulic throughput, delivering a pure-water flux of 41.8 L·m⁻²·h⁻¹ compared to 38.0 L·m⁻²·h⁻¹ for the forward-tapered channel under identical conditions. Analysis of ionic conductance and selectivity further reveals that the reverse-tapered configuration enhances electrostatic focusing, suppresses co-ion leakage, and yields higher selectivity (S) and lower conductance (G) than the other two geometries. These findings demonstrate that optimizing both the shape of the nanochannel and the charge characteristics of the soft layer provides a robust pathway for designing next-generation nanofluidic membranes with high desalination efficiency and competitive water permeability.