(487g) Material Properties and Water Transport of Nanofiltration Membranes at Different pH Using Molecular Dynamics

Polyamide nanofiltration (NF) membranes are widely implemented for water purification and treatment. Most NF membranes have different charge concentrations depending on pH levels, which can influence flux and solute selectivity. However, previous atomistic models assume membrane neutrality, so the effect of membrane charge on membrane material properties and water transport on a molecular level is unclear. In this work, we use molecular dynamics to virtually polymerize piperazine and trimesoyl-chloride monomers at a specific ratio to achieve realistic NF membrane models. We then prescribe the deprotonation of carboxylate end-groups in the membrane to match a given feed pH, ranging from 6.3 to 10.2. Non-equilibrium molecular dynamics simulations are used to examine membrane properties such as density and free volume, as well as transport properties including water flux and diffusivity as a function of membrane net charge. Finally, ion interaction with the charged carboxylate end-groups is investigated to determine the impact of charged solutes on the membrane flux and physical properties. This work begins to uncover the factors that determine the performance of charged NF membranes using realistic atomistic models. Funded by NSF Grant CBET-1840816.