Per- and poly fluorinated alkyl substances (PFASs), notably perfluorooctanoic acid (PFOA), contaminate many ground and surface waters and are environmentally persistent. The performance limitations of existing remediation methods motivate efforts to develop effective adsorbents. Here we report a β-cyclodextrin (β-CD)-based polymer network with higher affinity for PFOA compared to powdered activated carbon, along with comparable capacity and kinetics. The β-CD polymer reduces PFOA concentrations from 1 μg L to <10 ng L, at least 7 times lower than the 2016 U.S. EPA advisory level (70 ng L), and was regenerated and reused multiple times by washing with MeOH. The performance of the polymer is unaffected by humic acid, a component of natural organic matter that fouls activated carbons. These results are promising for treating PFOA-contaminated water and demonstrate the versatility of β-CD-based adsorbents.
Organic contaminants at low concentrations,
known as micropollutants,
are a growing threat to water resources. Implementing novel adsorbents
capable of removing micropollutants during packed-bed adsorption is
desirable for rapid water purification and other efficient separations.
We previously developed porous polymers based on cyclodextrins that
demonstrated rapid uptake and high affinity for dozens of micropollutants
(MPs) in batch experiments. However, these polymers are typically
produced as powders with irregular particle size distributions in
the range of tens of micrometers. In this powdered form, cyclodextrin
polymers cannot be implemented in packed-bed adsorption processes
because the variable particle sizes yield insufficient porosity packing
and consequently generate high back-pressure. Here we demonstrate
a facile approach to remove micropollutants from water in a continuous
manner by polymerizing cyclodextrin polymer networks onto cellulose
microcrystals to provide a core/shell structure. Batch adsorption
experiments demonstrate rapid pollutant uptake and high accessibility
of the cyclodextrins on the adsorbent. Similarly, column experiments
demonstrate rapid uptake of a model pollutant with minimal back-pressure,
demonstrating potential for use in packed-bed adsorption processes.
Furthermore, the pollutant-saturated columns were regenerated using
methanol and reused three times with almost no change in performance.
Column experiments conducted with a mixture of 15 micropollutants
at environmentally relevant concentrations demonstrated that removal
was determined by the affinity of each micropollutant for cyclodextrin
polymers. The cyclodextrin polymer grafted onto cellulose microcrystals
is more resistant to both anaerobic and aerobic biodegradation as
compared to cyclodextrins and unmodified cellulose crystals, presumably
due to the aromatic cross-linkers, demonstrating persistence. Collectively,
the findings from this study demonstrate a general strategy to incorporate
novel cyclodextrin adsorbents onto cellulose substrates to enable
rapid and efficient removal of micropollutants during packed-bed adsorption
as well as their promising long-term stability and regeneration capabilities.
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