β-Cyclodextrin Polymers on Microcrystalline Cellulose as a Granular Media for Organic Micropollutant Removal from Water

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.