Chitosan-coated fluoro-functionalized covalent organic framework as adsorbent for efficient removal of per- and polyfluoroalkyl substances from water

Covalent organic frameworks (COFs) are a class of newly developed crystalline porous materials that show great potential toward environmental applications. Most of COFs exhibit high hydrophobicity, which restrict their applications in aqueous environment. In this article, a novel covalent organic framework (COF) was developed and used as an efficient adsorbent for highly removal of per- and polyfluoroalkyl substances (PFASs) from water. Firstly, a fluoro-functionalized COF (F-COF) was synthesized at room temperature by Schiffbase reaction. A layer of chitosan was then modified on the surface of F-COF via cross-linking polymerization reaction. The obtained chitosan/F-COF possesses desirable hydrophilicity, surface wettability, and high specific surface area, showing high adsorption capacity towards PFASs via electrostatic interaction, hydrogen bond interaction, fluorine-fluorine interactions, and channel size selection. The adsorption performances of chitosan/F-COF toward typical PFASs such as perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), and ammonium perfluoro(2-methyl-3-oxahexanoic) acid (GenX) were investigated, and extremely perfect adsorption performances were obtained, with maximum adsorption capacities (qmax) of 8307.1, 6177.1, and 4603.3 mg/g as well as rate constants of 2.3 × 10−3, 1.3 × 10−3, and 6.4 × 10−4 g/mg min−1 for PFOS, PFOA, and GenX, respectively. Moreover, the chitosan/F-COF shows good simultaneous uptake ability for PFASs with the simultaneously removal efficiencies over 88.4% for three PFASs in lake water and sewage samples. Our study reveals a great application prospect of chitosan/F-COFs in pollutant removal and environmental remediation.