(520d) Mixed Solute Feed Interactions for Charged Polyamide Membranes Using Molecular Dynamics Simulations

Nanofiltration (NF) membranes are widely implemented for water treatment and contaminant removal. When in use, the water flux and solute rejection are affected by the charged functional group concentration in the membrane, which depends on the feed pH. While size exclusion plays an important role in solute rejection, membrane charge interactions with mixed solutes can also affect the selectivity of mono-/divalent ions for polyamide membranes. To better understand solute-membrane charge interactions, molecular dynamics simulations are used to model the filtration processes. Previous atomistic models assume a neutral membrane and focus on single solute type in the feed. In this study, we account for the effect of feed pH on membrane charge and show how the amount and location of charge in the membrane affects ion selectivity and rejection. We also consider mixed ionic solutes with different valencies to uncover solute-solute and solute-membrane charge interactions. This work sheds light on the influence of membrane charge and membrane structure on solute selectivity. Funded by NSF Grant CBET-1840816.