Nanoscale investigation into the water uptake and multivalent ion suppression on pristine and APTES grafted ZSM-5 membranes

Abstract

The remarkable properties of porous zeolites and their modified materials have found promising applications across various fields. This study leveraged molecular dynamics simulations to explore the wetting and permeation behaviors of salt solution droplets (i.e., NaCl, Na₂CO₃, and Na₂SO₄) on ZSM-5 and its 3-aminopropyltriethoxysilane functionalized (APTES-ZSM-5) surfaces. The larger ionic aggregates enhanced the internal cohesion of droplet, and slowed down the wetting process. However, the ionic effects were mitigated by surface modification. The increased hydrophobicity of the APTES-ZSM-5 surface effectively decelerated the wetting process and influenced the ensuing permeation dynamics. As the ions exhibited limited ability to permeate into the membrane, the frontier water molecules entering the zeolite membrane displayed similar permeation profiles. Nonetheless, the water adsorption capacity of the membrane decreased with increasing ionic aggregates. The ion rejection rate after surface modification has been strengthened at the expense of reduced water adsorption efficiency. This work elucidates the atomic-level interactions between salt solution droplets and zeolite membranes, highlighting the potential of functionalized zeolites to mitigate corrosion and shrinkage in cement-based materials.