Collaborative Research: NSF-BSF: Elucidating the role of ion dehydration in regulating transport and selectivity of monovalent ions in polyamide nanofiltration membranes

Arizona State University, Scottsdale AZ

Investigators

Abstract

Rapid population growth and rising living standards have caused the depletion of global water sources and other valuable resources. Separation technologies that can purify saline or contaminated water and recover valuable components are urgently needed. Separation using nanofiltration (NF) has been widely used for water purification and desalination, but emerging challenges such as the extraction of lithium from brines to satisfy the booming lithium-ion battery market go beyond the capabilities of current NF membrane technology. Thus, the overarching goal of this collaborative project is to explore a novel mechanism known as ion dehydration that can be applied using modified NF membranes to carry out challenging separations. This project leverages expertise in computational simulation, laboratory experimentation, and NF membrane fabrication in an international collaboration with researchers at the Technion - Israel Institute of Technology. Successful completion of this project will advance our understanding of NF separation to address pressing societal needs. Beyond the technical focus, the project will benefit society by educating the public through outreach activities to increase scientific literacy and awareness of water and resource sustainability. NF membranes have been used for water purification and desalination processes for many years. Recently, there has been increasing demand for high membrane selectivity between solutes to enable energy-efficient separation for water purification and resource recovery. However, achieving precise separation between similarly sized and charged ions using current polyamide NF membranes remains a significant challenge. Addressing this challenge requires leveraging mechanisms beyond those prevailing in current water-solute separation. Accordingly, the project will pursue three primary thrusts to regulate the transport and selectivity of monovalent ions in polyamide NF membranes: 1) investigate the role of ion dehydration on the transport and selectivity of ions in state-of-the-art NF membranes; 2) delineate the effect of membrane surface hydrophobicity and charge on ion dehydration using self-fabricated membranes with tunable surface properties; and 3) use molecular dynamics (MD) simulations to support the results of ion dehydration and membrane selectivity experiments. Thrust 1 will utilize a custom-made diffusion cell to probe the ion-ion selectivity for a series of ions with distinct hydration properties at different temperatures, pressures, and solvent types. Thrust 2 will focus on fabrication of thin-film composite polyamide (TFC-PA) NF membranes with systematically altered surface hydrophobicity and surface charge. Thrust 3 will apply MD simulations of water and solute ion transport through a TFC-PA NF membrane, which can be used to understand the relationship between the membrane structure and ion transport/rejection. Beyond the direct technical thrusts, the project will include outreach and educational activities that broaden its impacts by providing research training opportunities to graduate and undergraduate students, especially those from underrepresented groups. The team will also perform outreach activities for K-12 students from local communities of Colorado and Wisconsin to increase scientific literacy and support the Nation’s STEM workforce. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.