Evaluating the Performance of Novel Cyclodextrin Polymer Granules to Remove Perfluoroalkyl Acids (PFAAs) from Water

Abstract

Cyclodextrin polymers (CDPs) are promising adsorbents for the removal of per- and polyfluoroalkyl substances (PFASs) from water. For CDPs to be implemented in packed-bed filtration (PBF) systems, CDP powders must be processed to produce CDP granules of a defined size. In this study, we introduce CDP granules with average particle diameters (d p) of 84–718 μm produced from a CDP powder by means of high-shear spray granulation. We evaluated the performance of the CDP granules in batch studies to evaluate the adsorption kinetics, capacity, and affinity for six perfluoroalkyl acids (PFAAs). We also performed rapid small-scale column test (RSSCT) experiments for three of the CDP granules (d p = 84, 175, 359 μm) to test whether the assumptions of constant diffusivity (CD) or proportional diffusivity (PD) are appropriate for these CDP granules. We found that CDP granules exhibit slower adsorption kinetics than the CDP powder (rate constants ranging between 0.2 and 2.7 g mg–1 h–1 for all PFAAs and all CDP granules), but that CDP granules of varying sizes exhibit relatively consistent adsorption kinetics. Adsorption capacity (139–479 μmol g–1) and affinity (0.6–149 L mg–1) were relatively constant across CDP granules of varying particle diameters for all PFAAs but adsorption capacity decreased and adsorption affinity increased for longer-chain PFAAs. Data from the RSSCT experiments suggest that neither the assumption of CD nor PD are unequivocally appropriate for CDP granules and that an improved understanding of mass transfer limitations as a function of particle size is essential. Overall, our results demonstrate the potential for novel CDP granules to be implemented in PBF systems for the removal of PFAAs from water.

Trace Organic Contaminant Removal from Municipal Wastewater by Styrenic β-Cyclodextrin Polymers

“…The high affinity of Cationic StyDex toward the selected PFAS in wastewater is consistent with equilibrium adsorption and kinetics results, in which Cationic StyDex demonstrated nearly complete PFAS removal with the fastest adsorption kinetics out of the three adsorbents. The affinity trend of Cationic StyDex toward the selected PFAS, PFHxS (3.58 ± 0.27 L g –1 ) > PFOA (2.72 ± 0.33 L g –1 ) > PFHxA (1.82 ± 0.24 L g –1 ), is also consistent with our previous report that evaluated different sized β-CD polymer granules (prepared based on the previous generation of cross-linking chemistry) for PFAS removal in nanopure water …”

“…The authors demonstrated that RSSCT can be applied for the removal of the tested PFAS onto the IX resins . We previously applied RSSCT under both CD and PD designs to evaluate different sized β-CD polymer (CDP) granules based on the previous generation of cross-linking chemistry and found that neither the assumption of CD nor PD was unequivocally appropriate for CDP granules . Therefore, an improved understanding of mass transfer limitations of these novel adsorbents as a function of particle size will be desirable, as they are scaled to pilot-sized systems.…”

“…The affinity trend of Cationic StyDex toward the selected PFAS, PFHxS (3.58 ± 0.27 L g −1 ) > PFOA (2.72 ± 0.33 L g −1 ) > PFHxA (1.82 ± 0.24 L g −1 ), is also consistent with our previous report that evaluated different sized β-CD polymer granules (prepared based on the previous generation of cross-linking chemistry) for PFAS removal in nanopure water. 49 Cationic StyDex and F600 exhibited similar log K D values for BEZ and DCF, which suggest that the binding sites present in each adsorbent have similar affinities for BEZ and DCF (Figure 4). However, F600 experienced more reduced BEZ and DCF removal and slower kinetics than Cationic StyDex in wastewater, which further highlight the selectivity of Cationic StyDex toward the target TrOCs in complex matrices.…”

“…50 We previously applied RSSCT under both CD and PD designs to evaluate different sized β-CD polymer (CDP) granules based on the previous generation of cross-linking chemistry and found that neither the assumption of CD nor PD was unequivocally appropriate for CDP granules. 49 Therefore, an improved understanding of mass transfer limitations of these novel adsorbents as a function of particle size will be desirable, as they are scaled to pilot-sized systems. Nevertheless, RSSCT experiments can be a valid approach to demonstrate the potential of implementing β-CD polymers under continuous flow systems.…”

Data-Driven Discovery of Linear Molecular Probes with Optimal Selective Affinity for PFAS in Water

“…The relative paucity of highly performant linear probe molecules identified by our ML-enabled workflow militates for an expansion of the molecular search space to molecular libraries containing a richer chemical diversity of candidate molecules including branched and cyclic hydrocarbons, as well as more exotic molecules such as cyclodextrin-based probes that have garnered some attention and success in PFAS sequestration. ,− Further enlargements of the design space can make the computational screening platform established in this work even more valuable in performing an efficient filtration of the enlarged design space to identify the most promising molecular probes to be explored experimentally and also in excavating a molecular-level understanding of probe performance that can be coupled with experimental intuition to help inform rational molecular design. The performance of our active learning pipeline in achieving convergence after considering only 6% of the molecular space provides support for its capacity to efficiently navigate and traverse large search spaces and quickly focus on the most promising candidates.…”