Ionic liquids accelerate the crystallization of a magnetic fluorine-functionalized 3D covalent organic framework for efficient capture of trace benzoylurea insecticides in juices and beverages

Abstract

The fabrication of functionalized three-dimensional covalent organic frameworks (3D COFs) involves intricate and demanding synthetic procedures, which has significantly restricted their broad applications. However, ionic liquids (ILs) have demonstrated the capability to facilitate COF crystallization, shorten reaction durations, and achieve functional modification of COFs. Furthermore, the excessive utilization of benzoylurea insecticides (BUs) in agricultural products is substantially hazardous to ecological systems and human health. Herein, we proposed for the first time a mixed ILs-mediated Schiff base polymerization strategy. It enabled one-step synthesis of a highly crystalline NH₂-Fe₃O₄@F-3D COF at room-temperature conditions, specifically designed for the detection of BUs in complex food matrixes. NH₂-Fe₃O₄@F-3D COF contained a distinctive and well-connected porous structure as well as a high specific surface area (361.4 m²/g). It also contained abundant exposed F groups and a small quantity of -COOH functionalized groups, which were introduced by the 2,3,5,6-tetrafluorobenzaldehyde monomer and ILs. NH₂-Fe₃O₄@F-3D COF exhibited a favorable affinity toward BUs via fluorine‑fluorine affinity and hydrogen bonding interaction. The approach manifested a wide linear scope (25–10,000 ng/L) and possessed low detection thresholds (0.42–2.93 ng/L) regarding the nine analytes being examined. Its effectiveness was further assessed by employing it for detecting BUs in juices and beverages, thus corroborating its adequacy in quantifying trace amounts of BUs in complex food matrixes. The devised high-performance polymerization and functionalization strategy, specifically engineered to fabricate 3D COFs, exhibits extraordinary potential utility in the identification and quantification of contaminants present within practical samples.