An urchin-shaped covalent organic framework with rich nitrogen for efficient removal of neonicotinoid insecticides in honey and fruits

Neonicotinoid insecticides (NEOs) are widely used because of their high efficiency, low dosage and long duration. However, the residues of NEOs could cause the collapse of bee population and even threaten human health. Herein, an urchin-shaped covalent organic framework with rich nitrogen (U-COF) was synthesized with 2,4,6-tri(4-aminophenyl)-1,3,5-triazine (TZT) and 2,5-divinyl-1,4-benzaldehyde (DVA) by adjusting the catalyst (acetic acid) concentration for adsorptive removal of NEOs. This U-COF with hierarchical structure showed good adsorption capacities for imidacloprid, acetamiprid and thiamethoxam at 217.2, 177.2 and 147.5 mg/g, respectively. The nitrogen-rich structure and abundant π electron system of U-COF also improved the adsorption capacity for NEOs. π-π interaction, hydrophobic interaction, and hydrogen bonding between adsorbent and target are the main reasons for the good adsorption effect. After five adsorption-desorption cycles, U-COF still shows good adsorption capacity. What is more important is that the high adsorption capacity of NEOs from honey and fruits was achieved by using U-COF, illustrating the great potential as sorbents for real samples.