Synthesis of Olefin-Linked high stability covalent organic frameworks for the removal of perfluoroalkyl acids from water

Covalent organic frameworks (COFs) are promising adsorbents due to their designable functionality, but their applications are hampered by poor chemical stability. Herein, a series of novel high stability olefin-linked (C = C) COFs with different ratios of OMe, as the adsorbent to remove perfluoroalkyl acids (PFAAs), were firstly synthesized by a three-component strategy under solvothermal conditions. The synthesized COFs showed strong resistance toward acid (6 M HCl) and base (6 M NaOH) because of the robust C = C linkage which can be achieved reversibly under stringent synthetic conditions. Among the four [OMe]x-COF adsorbents, [OMe]100-COF exhibited the highest adsorption affinities and adsorption capacities for perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). The theoretical maximum adsorption capacity of [OMe]100-COF for PFOA and PFOS, calculated by Langmuir isotherm, were 601.2 mg g−1 and 1106.1 mg g−1, respectively. This could be ascribed to the synergistic combination of electrostatic interaction and hydrophobic-hydrophobic interaction. Moreover, [OMe]100-COF can be efficiently regenerated during the adsorption–desorption cycles. This study provides a novel strategy to fabricate olefin-linked COFs for the effective adsorption of perfluorinated compounds in water. Perfluorinated compounds (PFAAs) were shortlisted for persistent organic pollutants (POPs) in 2009 due to their persistence, bioaccumulation, toxicity, and long-distance mobility. Adsorption is one of the promising ways with advantages of simplicity and low energy consumption for removing PFAAs from aqueous environment. Herein, a series of olefin-linked COFs with high chemical stability was synthesized using a three-component strategy. And they showed rapid uptake and high capacity for the removal of PFAAs. This study provides a novel strategy to fabricate olefin-linked COFs for the effective adsorption of perfluorinated compounds in water.