Effect of divalent versus monovalent cations on the MS2 retention capacity of amino-functionalized ceramic filters

Abstract

Ceramic capillary membranes conditioned for virus filtration via functionalization with n-(3-trimethoxysilylpropyl)diethylenetriamine (TPDA) are analyzed with respect to their virus retention capacity when using feed solutions based on monovalent and divalent salts (NaCl, MgCl₂). The log reduction value (LRV) by operating in dead-end mode using the model bacteriophage MS2 with a diameter of 25 nm and an IEP of 3.9 is as high as 9.6 when using feeds containing MgCl₂. In contrast, a lesser LRV of 6.4 is observed for feed solutions based on NaCl. The TPDA functionalized surface is simulated at the atomistic scale using explicit-solvent molecular dynamics in the presence of either Na⁺ or Mg²⁺ ions. Computational prediction of the binding free energy reveals that the Mg²⁺ ions remain preferentially adsorbed at the surface, whereas Na⁺ ions form a weakly bound dissolved ionic layer. The charge shielding between surface and amino groups by the adsorbed Mg²⁺ ions leads to an upright orientation of the TPDA molecules as opposed to a more tilted orientation in the presence of Na⁺ ions. The resulting better accessibility of the TPDA molecules is very likely responsible for the enhanced virus retention capacity using a feed solution with Mg²⁺ ions.