Heteroporous 3D covalent organic framework-based magnetic nanospheres for sensitive detection of bisphenol A

Covalent organic frameworks (COFs) showed great promise in effective adsorption of target molecule via size selectivity. Although various magnetic 2D COFs composites have been studied and exhibited the intensive applications, the incorporation of 3D COFs and magnetic nanoparticles to form a new class of magnetic adsorbents with enhanced function still has no reports. Herein, a novel Fe₃O₄@3D COF with heteroporous structure matching to the sizes of bisphenol A (BPA) was firstly synthesized for better adsorption of BPA than common magnetic 2D-COFs. Three Fe₃O₄@3D COFs nanospheres were synthesized under the solvothermal conditions in autoclave, and the optimum Fe₃O₄@3D-COF denoted as Fe₃O₄@COF-TpTAM (Tp, 1,3,5-triformylphloroglucinol; TAM, tetra(p-aminophenyl)-methane) was selected and employed. Detailed characteristics of Fe₃O₄@COF-TpTAM were evaluated via various techniques including TEM, FTIR, TGA, XRD and BET. Excellent chemical and thermal stability, high surface area (294.6 m² g^-1) and pore volume (0.2 m³ g^-1) with multiple pore sizes comparable with the simulated three-dimensional sizes of BPA were exhibited. A high adsorption capacity of BPA up to 209.9 mg/g that was better than common 2D-COFs was achieved, and the sensitive MSPE-LC-MS method with wide linear range (10-5000 pg/mL), low detection limit (4 pg/mL, S/N = 3) was built. Satisfactory recoveries of BPA as 93.8 ± 1.4%-101.4 ± 5.1% (n = 3) and 100.4 ± 1.9% ~ 107.3 ± 1.2% (n = 3) were obtained in milk and river water samples, respectively. This work demonstrates the promising application of Fe₃O₄@3D COF as efficient adsorbents of trace BPA, and opens up a new access for the efficient MSPE in sample pretreatment for food or environmental safety analysis.