Mechanochemical synthesis of covalent organic framework for the efficient extraction of benzoylurea insecticides

A covalent organic framework named TpAzo was successfully fabricated by a simple and environmentally friendly mechanochemical grinding method based on the Schiff base aldehyde-amine condensation reaction between 1,3,5-triformylphloroglucinol (Tp) and 4,4′-azodianiline (Azo), with p-toluene sulphonic acid as a molecular organizer. The TpAzo was characterized by scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, nitrogen adsorption-desorption isotherms, and thermogravimetric analysis. The TpAzo possessed a sheet-like morphology, rich porosity and high thermal stability. The extraction performance of the TpAzo was investigated by using it as the solid phase extraction adsorbent for the extraction of benzoylurea insecticides (BUs) from juice, tomato and white radish samples prior to high performance liquid chromatographic analysis. Under the optimal conditions, a good linearity for the BUs existed in the range of 1.0–160.0 ng mL−1 for juice sample and 0.5–80.0 ng g−1 for tomato and white radish samples with the correlation coefficients of 0.9956–0.9999. The limits of detection for the analytes were 0.1–0.2 ng mL−1 for juice sample and 0.05–0.1 ng g−1 for tomato and white radish samples. The method recoveries for the analytes fell in the range of 84.1%–108.6%. The adsorption mechanism of the TpAzo was investigated by using it to extract different types of organic compounds, including phthalates, phenylurea herbicides and carbamate insecticides. The results showed that the π-stacking and hydrophobic interactions between the TpAzo and the analytes played an important role for the adsorption.