TUNING HOST-GUEST CHEMISTRY IN THE DEVELOPMENT OF ADSORBENTS FOR REMEDIATION OF ORGANIC POLLUTANTS

Abstract

Perfluoroalkyl substances (PFASs) are a group of anthropogenic chemicals that generate concerns globally due to its worldwide occurrence in aquatic systems, persistence and resistance to biological degradation. Unfortunately, conventional remediation methods are not efficient to sequester PFASs from water, including activated carbons, membrane filtration and other destructive technologies. This motivates effort to develop new adsorbents for PFASs remediation. β-Cyclodextrin (β-CD), which is capable of forming stable host-guest complex with a number of PFASs, has been incorporated into adsorbents to treat PFASs-contaminated water, whereas, the removal of PFASs by β-CD-based adsorbents at environmentally relevant concentrations (few ng/ L to μg/ L) is barely explored. Moreover, the relationship between the structure of β-CD-based adsorbents and their affinity for PFASs is poorly understood due to the insoluble nature of β-CD-based adsorbents (Chapter 1). We have focused on the development of β-CD-crosslinked polymers for PFASs remediation. We first demonstrated that the synthesis of β-CD with a perfluorinated arene decafluorobiphenyl (DFB) generates cross-linked polymer DFB-CDP that reduces PFOA from environmentally relevant concentration to below the 2016 U.S. EPA advisory level. The polymer was not fouled by humic acids, which are major constituents of NOM, and was regenerated and reused multiple times by washing with methanol (Chapter 2). We further studied the chemical structure of DFB-CDP intensively and determined important factors that affect the uptake potential of PFASs by β-cyclodextrin polymers (Chapter 3). We have applied host-guest chemistry to other systems and developed a high-surface-area calix[4]arene-based polymer which exhibited high capacities for benzene and other aromatic hydrocarbons (Chapter 4). This work shows that host-guest chemistry can be tuned to develop new adsorbents for the remediation of organic pollutants from water and air.