Carboxylated Covalent Organic Frameworks with Size Adjustment for the Identification of Polychlorinated Biphenyls

Polychlorinated biphenyls (PCBs) are persistent organic pollutants that pose a severe threat to the environment and organisms, even at trace levels. In this study, we used carboxylated covalent organic frameworks (COFs) as molecular probes for the extraction of trace PCBs using solid-phase microextraction (SPME). Benefiting from the flexible and adjustable features of the COFs, a series of carboxylated COFs with different pore sizes were tailored and fabricated as SPME fibers. The carboxylated COFs presented significant extraction sensitivity and specificity compared to the pristine COFs, which were attributed to the interplay of twisted nanochannels and formed secondary nanopores, as well as the intermolecular hydrogen bonding between COFs and PCBs. The limits of detection (LODs) were calculated to be 0.02–0.2 ng L^–1, which were much lower than the maximum content of PCBs in drinking water recommended by the United States Environmental Protection Agency (USEPA) (0.5 μg L^–1). Furthermore, SPME probes were successfully performed for PCB detection in real water samples with satisfactory results. This study demonstrated the potential of carboxylated COF-based SPME fibers for the selective extraction of PCBs and could contribute to the development of new and effective SPME coatings for the efficient detection of pollutants in environmental samples efficiently.