(338d) The Fabrication of ?-Cyclodextrin(BCD)-Crosslinked Homopolymer Membranes

Nearly one-quarter of the world population lives in a water scarce region, and this number is expected to continue to grow with the increase in population. Moreover, human activities have led to the introduction of a wide range of micropollutants into groundwater, including pharmaceuticals, personal care products, industrial chemicals, cleaning detergents, pesticides, etc. These pollutants are difficult to remove due to their small sizes and low concentrations. Porous membrane sorbents with high affinity ligands serve as a promising platform to absorb trace level pollutants in an energy-efficient manner. β-Cyclodextrin(BCD) is a promising ligand that can remove a wide range of micropollutants by host-guest interactions. The abundant hydroxyl (OH) groups on its exterior surface makes it possible to react with other moieties and be immobilized on substrates. Incorporating BCD into porous materials can rapidly remove pollutants and enhance membrane performance, because the porosity in the matrix provides efficient mass transfer pathways for pollutant molecules to diffuse to BCD binding sites.

In this study, an amphiphilic homopolymer was chosen to functionalize as the membrane matrix and further provided reactive sides to incorporate BCD on the pore walls. The hydrophobic backbone formed porous structures and the pendant carboxylic acid (COOH) moieties segregated to the surface of the pore walls during the phase separation. Notably, the homopolymer has one pendant COOH group in each monomeric unit, which provides high density of crosslinking sites for BCD. Casting solutions were prepared by dissolving homopolymer and BCD, separately, in 2-pyrrolidone and then mixing the solutions in different ratios after cooling down to room temperature. Over the course of 20 minutes at 95% relative humidity, humid air intrusion led to the phase separation process and created a thin film. The film was immersed in a water bath to fully solidify into a rigid porous membrane. Subsequently, the incorporated BCD was covalently linked to polymer chains through a heat-induced esterification between the pendant COOH groups and the BCD hydroxyl groups. Gel contents were measured to confirm that BCD crosslinked between the polymer chains and SEM images showed the membrane remained porous after the thermal crosslinking procedure. Two dyes, methylene blue (positively charged) and congo red (neutral molecule), and a common plastic pollutant, Bisphenol A, were chosen as model compounds to test the capacity of the BCD-incorporated adsorptive membranes. In conclusion, a BCD-crosslinked porous polymer membrane was successfully fabricated in this work, which can be used as a promising sorbent towards micropollutants to offer more sustainable and secure water supply for future generations.