Monodisperse fluorinated 3D covalent organic frameworks for enhanced adsorption and extraction of perfluorocarboxylic acids

Abstract

Advancements in covalent organic frameworks (COFs) in the field of adsorption and extraction are always limited by their non-uniform and irregularly aggregated morphology. Herein, we pioneer the preparation of monodisperse COFs with a regular shape and further explore their adsorption and extraction capabilities. As a proof of concept, a new monodisperse fluorinated 3D COF, named M-TAM-TFTA, featuring a nonpolar structure and uniform size and shape, is selected as the model COF for the adsorption and extraction of perfluorocarboxylic acids (PFCAs). M-TAM-TFTA, consisting of tetra(4-anilyl)methane (TAM) and 2,3,5,6-tetrafluoroterephthalaldehyde (TFTA), exhibits higher adsorption capacity (554.9 mg g⁻¹) and faster adsorption kinetics (5 min) compared to the same composition aggregated 3D COF A-TAM-TFTA as well as diverse reported materials. This remarkable adsorption performance of M-TAM-TFTA for PFCAs is proved to be dominantly caused by its lower mass transfer resistance structure and multiple specific interactions including F–F, hydrophobic, electrostatic and H-bonding interactions. M-TAM-TFTA is further applied to develop a probe nanoelectrospray ionization mass spectrometry (PESI-MS) method for direct and precise determination of PFCAs with a wide linear range (0.5–5000 ng L⁻¹) and low limits of detection (0.08–0.46 ng L⁻¹). This study provides robust support for the great potential of monodisperse COFs as adsorbents for the treatment of contaminants in complex samples.