Preparation and extraction property study of corn cob-like magnetic mosaic carbon materials derived from MOF-on-MOF composites

Large accumulations of pesticide residues in the environment eventually enter the human body with food. Based on magnetic solid-phase extraction (MSPE) technology, it is possible to achieve efficient extraction of trace pesticide residues in foodstuffs, and the construction of MSPE adsorbents with excellent magnetic properties and many active sites is still one of the main research topics. Based on this, we developed a new strategy for the preparation of "MOF-on-MOF" composites, which were carbonized and used as adsorbents for the extraction of pesticide residues in cereals. A novel corn cob core-shell composite Fe2O3@C@ZIF-8 was created by embedding ZIF-8 onto the surface of Fe2O3@C derived from MIL-88A(Fe), and used for the extraction of benzoylurea insecticides(BUs) from cereals. The adsorption behaviour between Fe2O3@C@ZIF-8 and BUs was investigated by static and kinetic experiments and the adsorption mechanism was elaborated. For the trace analysis of BUs, a magnetic solid-phase extraction combined with high performance liquid chromatography-ultraviolet detector (HPLC-UV) approach was also developed. Under the optimized experimental conditions, the limits of detection and quantification were 0.015–0.03 μg L−1 and 0.05–0.1 μg L−1, and the relative standard deviations for the intra-day and inter-day ranges were 1.82%–2.13 % and 3.85%–4.59 %, respectively. The spiked recoveries of the four cereals ranged from 82.72% to 104.45 %. After 10 cycles of use of Fe2O3@C@ZIF-8, the recoveries of BUs ranged from 77.90% to 96.74 %. The analytical method based on Fe2O3@C@ZIF-8 as adsorbent has a low limit of detection, a wide linear range and is highly applicable to the analysis of real samples. In addition, the strategy developed in this study for the preparation of thermoplastic polymer-assisted "MOF-on-MOF" composites has promising applications.