Challenges associated with water separation technologies for per- and polyfluoroalkyl substances (PFASs) require efficient and sustainable processes supported by a proper understanding of the separation mechanisms. The solute rejections by nanofiltration (NF) at pH values near the membrane isoelectric point were compared to the size- and mass-transfer-dependent modeled rejection rates of these compounds in an ionized state. We find that the low pKa value of perfluorooctanoic acid (PFOA) relates to enhanced solute exclusions by minimizing the presence and partitioning of the protonated organic compound into the membrane domain. The effects of Donnan exclusion are moderate, and co-ion transport also contributes to the PFAS rejection rates. An additional support barrier with thermo-responsive (quantified by water permeance variation) adsorption/desorption properties allows for enhanced separations of PFAS. This was possible by successfully synthesizing an NF layer on top of a poly-N-isopropylacrylamide (PNIPAm) pore-functionalized microfiltration support structure. The support layer adsorbs organics (178 mg PFOA adsorbed/m2 membrane at an equilibrium concentration of 70 mg/L), and the simultaneous exclusion from the NF layer allows separations of PFOA and the smaller sized heptafluorobutyric acid from solutions containing 70 μg/L of these compounds at a high water flux of 100 L/m2-h at 7 bar.
|Journal||ACS Environmental Science and Technology Water|
|State||Accepted/In press - 2022|
Bibliographical noteFunding Information:
Research reported in this publication was supported by the National Institute of Environmental Health Sciences of the National Institutes of Health under Award Number P42ES007380. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. Partial support was also provided by Honeywell UOP. The authors would like to thank Dr. Andrew Morris, Dr. Abigail Burrows, Dr. Scott Stanley, and Michael Hedge for the time, assistance, and analytical support on LC-MS/MS analysis. Additionally, thanks to Benjamin Weaver and Solecta for providing technical expertise and the PVDF400 membranes. Also, thanks to Dr. Nicolas Briot for SEM assistance and Nicholas Cprek for helping to create the crossflow membrane testing unit.
© 2022 American Chemical Society.
- organic anions
- responsive materials
- water treatment
ASJC Scopus subject areas
- Chemical Engineering (miscellaneous)
- Chemistry (miscellaneous)
- Environmental Chemistry
- Water Science and Technology