Covalent organic framework-based DGT sampler for in situ monitoring of per- and polyfluoroalkyl substances in aquatic environments.

Diffusive gradients in thin-films (DGT) is an important alternative to grab sampling for in situ monitoring of emerging contaminants such as per- and polyfluoroalkyl substances (PFAS) in aquatic environments. In this study, a covalent organic framework (COF) was developed as a high-capacity binding material for DGT. The synthesized COF exhibited high crystallinity, large surface area, and good hydrolytic stability, enabling rapid adsorption kinetics and high adsorption capacities toward PFAS, with a maximum uptake >1000 mg g-1 for perfluorooctanoic acid (PFOA). Adsorption kinetics and isotherm studies indicated strong interactions between PFAS and the COF, involving van der Waals interactions, hydrophobic interactions, hydrogen bonding, and pore confinement effects. The COF-based DGT sampler showed stable performance across a wide range of pH (5.2-9.1), ionic strength (0.0001-0.5 M), and dissolved organic matter concentrations (0-20 mg L-1), with CDGT/Csoln remaining within the acceptable range (0.9-1.1) for most of the compounds. Field deployment in a municipal wastewater treatment plant further demonstrated that the DGT technique produced comparable PFAS profiles to grab sampling while enabling time-integrated monitoring of low-level contaminants. This study highlighted the potential of COF materials as effective binding phases for DGT and provided a promising approach for reliable monitoring of PFAS in complex aquatic systems.