Facile synthesis of a core-shell structured magnetic covalent organic framework for enrichment of organophosphorus pesticides in fruits.

A facile strategy was developed for the fabrication of a magnetic covalent organic framework (COF) via grafting of the monomers, 2,5-dihydroxyterephthalaldehyde (Dt) and 1,3,5-tris(4-aminophenyl) benzene (Tb) onto surface-modified Fe3O4 nanoparticles. The magnetic COF, named as magnetic COF-DtTb, was readily fabricated without high temperature or harsh reaction conditions. The synthesized magnetic COF-DtTb nanoparticles were fully characterized, presenting a regular core-shell spherical structure, large specific surface area, superparamagnetism, and good thermal stability. Their potential as an enrichment adsorbent was investigated to establish an efficient magnetic solid-phase extraction method for the determination of organophosphorus pesticide residues in fruits. Systematic method validation revealed good linearity in the concentration range of 1-200 µg L-1 (correlation coefficient >0.9957). The method limits of detection were in the range of 0.002-0.063 µg kg-1, the method limit of quantification was 1.00 µg kg-1 and recoveries ranged from 72.8% to 111% with RSDs lower than 12.3%. The results indicated that magnetic COF-DtTb possesses superior trace enrichment properties for organophosphorus pesticides in fruits.

Relevance of an electrochemical process prior to a biological treatment for the removal of an organophosphorous pesticide, phosmet.

The aim of this study was to examine the feasibility of coupling an electrochemical pre-treatment with a biological step in order to degrade phosmet, an organophosphorous pesticide. Preliminary biodegradation experiments showed that the target molecule was not assimilated by activated sludge. The pre-treatment consisted of potentiostatic electrolysis (-1.3 V/SCE) in a flow cell. After only one pass (1 mL min(-1)), cyclic voltammetry with a vitreous carbon electrode showed a total phosmet reduction in neutral medium confirmed by thin layer chromatography, which also highlighted the presence of several by-products. H NMR spectra of the main by-product showed the absence of the aromatic ring, only the phosphorus part of phosmet has been identified and phosmet-oxon, a very toxic derivative, was not formed. Lower toxicity and higher biodegradability characterized the electrolyzed solution, EC(50) value increased from 7% to 58% and BOD(5) value increased from 4 to 9 mg O(2) L(-1) after electrolysis leading to an increase of the BOD(5) on COD ratio from 0.19 to 0.42 (limit of biodegradability, 0.4). These encouraging results were confirmed during activated sludge culture since an almost total mineralization of the electrolyzed solution was recorded (97%), confirming the feasibility of the proposed coupled process.