(116d) Grad Student Paper Award, 2nd Place: "A New Avenue for Separating Contaminants from Water using Nanofiltration and Adsorptive Materials"

Challenges associated with water separation technologies for per- and polyfluoroalkyl substances (PFAS) require efficient and sustainable processes supported by proper understanding of the separation mechanisms. In this study, we investigate the separation mechanism of PFASs using nanofiltration (NF) membranes and then we propose a new separation technology that aims to leverage two separation mechanisms: exclusion and adsorption. First, monovalent organic anions with similarly effective diameters (0.55-0.6 nm) were filtrated using nanofiltration (NF) membranes. The solute rejections at pH values near the membrane isoelectric point were compared to the size and mass transfer-dependent modeled rejections of these compounds in an ionized state. We find that the low pKa value of perfluorooctanoic acid (PFOA) relates to higher solute exclusions by preventing the presence of the protonated organic compound that would preferably partition into the membrane domain. The effects of Donnan exclusion are moderate and co-ion transport also contributes to the PFAS rejection rates. The contribution of an additional barrier, however, is responsible for the high PFAS rejection rates when using NF membranes. Then, we successfully synthesized a NF layer on top of a poly-N-isopropylacrylamide (PNIPAm) pore functionalized support structure. This membrane adsorbs 178 mg/m² membrane of PFOA at an equilibrium concentration of 70 mg/L, and rejects 70% PFOA and 50% of the smaller size heptafluorobutyric acid from solutions containing 70 µg/L of these compounds. The temperature-responsive behavior of the PNIPAm is reflected on the water permeance of the thin-film composite membranes, which varies from 7 to 24 (L m^-2 h^-1).

Publication:

Dual-Functional Nanofiltration and Adsorptive Membranes for PFAS and Organics Separation from Water, Francisco Léniz-Pizarro, Ronald J. Vogler, Phillip Sandman, Natalie Harris, Lindell E. Ormsbee, Chunqing Liu, and Dibakar Bhattacharyya

ACS ES&T Water 2022 2 (5), 863-872

DOI: 10.1021/acsestwater.2c00043