Effective extraction of pyrethroid pesticides from cabbages using Fe3O4@NU-1000 and adsorption mechanism: An experimental and theoretical study

In this paper, a magnetic zirconium-based MOFs (Fe3O4@NU-1000) with good water stability was prepared for effective extraction of pyrethroid pesticides from vegetables. Characterization results showed Fe3O4@NU-1000 has a high specific surface area (435.34 m2 center dot g- 1) and a large pore size (4.88 nm), which provides abundant adsorption sites for pesticides molecules. Fe3O4@NU-1000 can achieve rapid magnetic separation from solution within 1 min, greatly reducing the extraction time of pyrethroid pesticides. The results of adsorption kinetics and isotherms showed that the adsorption process of pyrethroid pesticides on Fe3O4@NU-1000 was monolayer adsorption and physisorption. The maximum adsorption capacities of Fe3O4@NU-1000 for beta-cyfluthrin, lambda-cyhalothrin, permethrin, and bifenthrin were up to 1159.11, 1194.16, 1151.48, and 1181.74 mg center dot g- 1, respectively. Molecular dynamics simulations showed that adsorption is driven by hydrophobic interaction. Van der Waals forces and hydrogen bonding accelerate pesticide molecules to approach the surface, and pi-pi interactions enable stable adsorption of pesticide molecules within the triangular and hexagonal micropores of NU1000. DFT calculations confirmed that pesticide molecules predominantly adsorb stably within the pores of Fe3O4@NU-1000 through pi-pi interactions, with additional contributions from CH3-pi and Cl-pi interactions. Finally, a simple and sensitive method was established for the determination of pyrethroid pesticides in cabbage samples using Fe3O4@NU-1000 based magnetic solid-phase extraction and high-performance liquid chromatography. It provided low limit of detection (0.0011-0.0058 mu g center dot mL-1), a wide linear range (1-25 mu g center dot mL-1), and satisfactory recoveries (81.35-98.64 %), which can achieve effective extraction and trace detection. This study provides a magnetic MOFs material for extraction of pesticides and reveals its adsorptive mechanism at molecular level, which is helpful for rational design of more pretreatment materials for pesticides detection in complex food matrices.