اميرعباس نظري

Desalination of water an‎d the development of membrane technologies for freshwater production remain global challenges. While nanofluidic membranes have demonstrated significant potential in energy conversion, their application in desalination processes has been relatively underexplored. This study investigates the performance of cylindrical nanofluidic membranes in removing monovalent salts likes LiCl, NaCl, an‎d KCl that focusing on the effect of soft layer charge configuration on desalination efficiency. Three distinct charge patterns are examined: unipolar (negative), bipolar (negative–positive), an‎d tripolar (negative–positive–negative). The coupled Poisson–Nernst–Planck an‎d Navier–Stokes equations are numerically solved under steady-state conditions to analyze the combined effects of electrostatic interactions, convective transport, an‎d applied external fields on desalination performance. The results indicate that bipolar nanochannels exhibit the highest desalination efficiency due to ion rectification (diode-like behavior) an‎d the formation of strong ion-depletion zones. At an applied pressure of 30 bar, the bipolar nanochannel achieves 81%–95% salt rejection with voltage an‎d 47%–86% without voltage, outperforming the unipolar an‎d tripolar configurations. Additionally, the bipolar nanochannel exhibits superior current rectification behavior, with ionic currents reaching 1.08 nA for LiCl, 1.25 nA for NaCl, an‎d 1.60 nA for KCl at 1 V, confirming enhanced selec‎tivity. Further analysis of the Peclet number (Pe) an‎d electrolyte concentration reveals that bipolar nanochannels maintain NaCl rejection above 95% at Pe ≈ 0.05, whereas unipolar an‎d tripolar configurations experience a sharper decline in selec‎tivity, with rejection dro‎pping below 50% at Pe ‎> 0.2 an‎d TMP ‎> 80 bar. Furthermore, the bipolar nanochannel is capable of delivering a water flux of 19 L^(-1).m^(-2) 〖.h〗^(-1) while simultaneously achieving 90% salt rejection for NaCl .These findings underscore the significant impact of charge modulation in nanofluidic membranes an‎d highlight that bipolar nanochannels provide the most effective balance between ion rejection an‎d water permeability. This study establishes a novel framework for charge-engineered nanofluidic membranes, demonstrating that hybrid electrohydrodynamic strategies, integrating charge inversion with external field-assisted ion transport, could enable next-generation high-efficiency desalination systems.

كلمات كليدي: غشاهاي نانوسيال، نانوكانال‌هاي هوشمند، نمك‌زدايي، لايه‌هاي پلي‌الكتروليت چند قطبي.

Keywords: Nanofluidic Membranes; Smart Nanochannels; Water Desalination; Multipolar Polyelectrolyte Layers;

Amir Abbas Nazari

Seyed Nezameddin Ashrafizadeh