Facile and large-scale synthesis of trifluoromethyl-grafted covalent organic framework for efficient microextraction and ultrasensitive determination of benzoylurea insecticides

Owing to the excessive usage of benzoylurea insecticide (BUs), ecological and environmental problem has been attracted increasing public attention. Herein, a novel trifluoromethyl-grafted covalent organic framework (COF), named COF-(CF3)2, was synthetized through Suzuki-Miyaura cross-coupling reaction based on post-synthetic modification (PSM) strategy under mild condition. The synthesized operation was simplified to make it suit-able for large-scale production and application. Characterization methods, such as fourier transform-infrared spectrum, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, were implemented to confirm the successful synthesis of COF-(CF3)2. Considering the enhanced electrostatic interaction and fluorine-fluorine interactions, COF-(CF3)2 was applied as solid phase microextraction (SPME) coating. An analytical method coupling direct immersion (DI)-SPME with ultra-high performance liquid chromatography-tandem mass spectrometrywas established for effective enrichment and ultrasensitive determination of seven BUs in environmental water. Satisfactory analytical parameters for target BUs were obtained, including wide linearity of 1-1000 ng L-1 with correlation coefficient (R2) of 0.9991-0.9999, low limits of detection (LOD) of 0.06-0.50 ng L-1, high enrichment factors (EFs) of 44-105 and satisfactory precision with relative standard deviations (RSD) <= 10.2%. The excellent performance of the proposed method was validated by the recovery test in real water samples with recoveries of 76.2-107.6% and RSD <= 11.1%. Furthermore, multiple interactions between COF-(CF3)2 and BUs molecules were analyzed combined with theoretical simulations to explain the adsorption mechanism. It illustrated that exceptional BUs adsorption performance of COF-(CF3)2 might be attributed to synergistic effect of mesoporous structure and trifluoromethyl modification. This work represents a rational design of functional materials through a novel and versatile PSM approach for the effective enrichment and ultrasensitive analysis of BUs in environmental water, and provides a multiscale understanding of high-performance adsorbent.

Automated summary

In this study, a novel trifluoromethyl-grafted covalent organic framework (COF) was synthesized and applied for solid phase microextraction (SPME) of benzoylurea insecticides in environmental water. The successful synthesis of COF-(CF3)2 was confirmed by various characterization methods, and an effective analytical method for the determination of benzoylurea insecticides was established. The study provides important insights for the rational design of functional materials and the understanding of high-performance adsorbents.