Preparation Of Novel Magnetic Adsorbents And Application In The Detection And Removal Of Nitrogen-Containing Heterocyclic Pesticide Residues

Nitrogen-containing heterocyclic pesticides are pesticides with nitrogen atoms in the molecular ring-forming structure,mainly including triazole fungicides,imidazole fungicides,benzimidazole fungicides,etc.,and have been widely used for the prevention and control of a variety of pests in agricultural production.Nevertheless,unscientific and irrational applications of pesticides in actual production also pose potential threats to non-target organisms and the environment.Thus,it is crucial to conduct research on the detection and removal of nitrogen-containing heterocyclic pesticide residues in the environment.This research combines magnetic nanoparticles with functional materials to independently prepare four multifunctional magnetic adsorbents,and new methods for the detection and removal of nitrogen-containing heterocyclic pesticides in complex matrices have been established around these adsorbents.The specific results are as follows:The magnetic metal organic framework（MOF）adsorbent Fe₃O₄@DUT-5 was successfully prepared and combined with high performance liquid chromatography to establish a multi-residue analytical method for nitrogen-containing heterocyclic pesticides（epoxiconazole,tebuconazole,prochloraz and flusilazole）in a variety of fruit and vegetable samples.Characterization analysis showed that Fe₃O₄@DUT-5 had an excellent saturation magnetization（41.44 emu/g）and was rapidly separated by an external magnetic field.Under optimal circumstances,the limit of detection（LOD）range was0.054μg/L-0.313μg/L,and the enrichment factor was 69.6-96.4.The method was applied to the multi-residue analysis of nitrogen-containing heterocyclic pesticides in three vegetables（cucumber,pepper and tomato）and three fruits（mango,banana and kiwi）,and the recoveries of the four nitrogen-containing heterocyclic pesticides satisfied the requirements for pesticide residue analysis with RSDs in the range of 1.0%-6.4%.（2）Fe₃O₄@PDA@Ui O-67 was successfully synthesized by solvothermal and room-temperature stirring methods,and applied to the removal of nitrogen-containing heterocyclic pesticides（flusilazole,metconazole,tebuconazole and epoxiconazole）from water column.The characterization analysis demonstrated that the Ui O-67 functionalized modified magnetic PDA could significantly expand the specific surface area of the synthesized material（173.03 m²/g）.The adsorption experimental parameters were optimized by batch adsorption experiments,and the adsorption process was consistent with the Langmuir isothermal model and pseudo-second-order kinetic model.Meanwhile,Fourier transform infrared（FT-IR）and X-ray photoelectron spectroscopy（XPS）characterization analyses combined with density functional theory（DFT）calculations indicated that hydrogen bonding forces were the main adsorption mechanism between the adsorbent and the pesticide molecules.Furthermore,the prepared Fe₃O₄@PDA@Ui O-67had good reusability and the spiked removal rates of the target analytes in the four natural water samples were all over 90%.（3）The bimetallic organic framework（MOF）composite Fe₃O₄@Ce O₂@MOF-5（Zn-Co）was successfully prepared by solvothermal method and used as an adsorbent for the rapid decontamination of nitrogen-containing heterocyclic pesticides（epoxiconazole,flusilazole,triazolone and myclobutanil）in water.The characterization results indicated that the specific surface area of the bimetallic adsorbent（SSA,399.43 m²/g）was significantly higher than that of the single metal MOF material（SSA:Fe₃O₄@Ce O₂@MOF-5（Zn）=27.02 m²/g;Fe₃O₄@Ce O₂@MOF-5（Co）=35.48 m²/g）when Zn and Co were present simultaneously.The adsorption properties and adsorption behavior were investigated under the optimal adsorption conditions.The adsorption reaction was mainly a physical adsorption process with single surface layer.In addition,the adsorption mechanism of Fe₃O₄@Ce O₂@MOF-5（Zn-Co）for nitrogen-containing heterocyclic pesticides involved pore filling,surface complexation,covalent bonding,hydrogen bonding andπ-πinteractions.The spiked removal of the target pesticides in three paddy water samples（Henan,Anhui and Hubei paddy water）were all over 83%.（4）Fe₃O₄@ZIF-90@MIL-68（Al）was successfully synthesized by solvothermal method and"one pot method",and it was applied to the removal of nitrogen-containing heterocyclic pesticides（triazolone,imazalil,epoxiconazole,flusilazole and prochloraz）in water.The characterization results revealed that the material has a microporous and mesoporous structure with a saturation magnetization intensity of 44.63 emu/g;the introduction of the functional material ZIF-90 resulted in a more stable adsorbent structure and a larger specific surface area（392.31 m²/g）.The adsorption experiments showed that the adsorption of Fe₃O₄@ZIF-90@MIL-68（Al）for nitrogen-containing heterocyclic pesticides was consistent with the pseudo-second-order kinetic and Langmuir isothermal model;at the optimal adsorption conditions,the maximum adsorption capacity of prochloraz was 352.32 mg/g;adsorption mechanisms include pore filling,surface complexation,covalent bonding,π-πinteraction,and hydrogen bonding.Additionally,the functional group structure of the material surface was still maintained after 10 cycles.The spiked removal rates of the five target agents in three paddy water samples were higher than 90%.