Multi-dimensional Carbon Nano/COFs Hybrid Material Preparation And Its Organophosphorus Pesticide Adsorption Performance And Recognition Mechanism

With the rapid development of social and economic development and the general improvement of living standards,the quality and safety of agricultural products are increasingly concerned by consumers,the establishment of a simple,accurate and rapid organophosphorus pesticide detection system,to regulate the use of organophosphorus pesticides,to ensure product quality and safety of vegetables has a more far-reaching practical significance.At present,there are still some technical bottlenecks in the accurate detection of organophosphorus pesticides in China,resulting in the ineffective treatment of complex matrices such as pigments and polysaccharides in fruit and vegetable agricultural products.In this study,COFs materials,two-dimensional carbon materials and magnetic nanoparticles were used to prepare functionalized COFs composites by material functional hybridization,molecular recognition modification and layer self-assembly techniques,and their structural characteristics,adsorption properties and recognition mechanisms were resolved by physical-chemical characterization,and they were applied as solid adsorbents in sample pretreatment for the purification of fruit and vegetable agricultural products,and finally Combined with high performance liquid chromatography tandem mass spectrometry,an organophosphorus pesticide detection method with high sensitivity,good selectivity and reproducibility was successfully developed,which provides a strong guarantee for the supervision of the quality and safety of agricultural products.The main research contents are as follows:1.The flexible surface control technique of 3D graphene was used to regulate the polymerization rate of monomers at the early stage of the reaction,followed by a 3D space-guided in situ synthesis strategy to successfully create COFs modified layers on the surface of 3D graphene.The physicochemical properties and potential adsorption mechanism of 3DGA@COFs were investigated in depth using nanomaterial characterization techniques,and it was found that they have a large specific surface area(127.95 m²/g),regular pore volume(0.0344 cm³/g)and 3D anisotropic structure with good adsorption potential for organophosphorus pesticides.The effects of target concentration,adsorbent dosage,extraction time,p H value,ion concentration and the adsorption conditions on the adsorption performance of 3DGA@COFs materials were investigated by single-factor optimization experiments,respectively.The maximum sorption amounts(Q)of 3DGA@COFs materials were found to be 1.91,1.95 and 1.97mg/g for malathion,triazophos and quinpirole pesticides,respectively,and the recoveries of the composites remained above 70%after seven times of reuse,indicating their good reusability,stability and economic applicability.3DGA@COFs composites can be be used as a solid phase extractant to adsorb triazophos,malathion and quinpirole pesticides,laying the foundation for the construction of functionalized COFs materials for efficient identification of pretreatment technology.2.Magnetic covalent organic skeleton composites(Fe₃O₄@g-C₃N₄@COFs)were successfully prepared with the help of solution-assisted exfoliation,co-precipitation and layer-by-layer self-assembly techniques,and the spatial structure and characteristic functional groups of the composites were analyzed using BET,TEM,SEM,XRD,FTIR and VSM characterization,and the results showed that the specific surface area of the composites was 56.6560 m2/g,an average pore size of about 21.08959 nm,a pore volume of 0.311247 cm3/g and a magnetic specificity response value of 36.60 eum/g,indicating that the composites have good potential for specific adsorption of organophosphorus pesticides.The nonlinear fitting of static adsorption isotherms(Langmuir and Freundlich model)and kinetic equations(fitted first-order and fitted second-order kinetic equations)revealed the single-molecule layer chemisorption process between the composites and propamocarb pesticide.The maximum adsorption amount(Q)of Fe₃O₄@g-C₃N₄@COFs material for propylbromophos pesticide was found to be 31.02 mg/g by single-factor optimization experiments,and it was not affected by p H and ion concentration;the reusability test revealed that the recovery rate of the composite material remained above 75%after 7 times of reuse,saying that the composite material has good reusability,stability.The Fe₃O₄@g-C₃N₄@COFs composite can be used as a magnetic solid-phase extractant for specific adsorption of propylbromide pesticide,laying the foundation for the construction of a highly specific recognition pretreatment technology for functionalized COFs materials.3.A sample pretreatment technique based on multidimensional carbon nano/COFs hybrid materials developed in combination with high performance liquid chromatography tandem mass spectrometry(HPLC-MS)was successfully used for the highly specific and accurate detection of malathion,triazophos,quinpirole and propamocarb pesticide residues in fruit and vegetable agricultural products.The experimental results showed that the concentration of organophosphorus pesticides in the concentration range of 0.5-200?g/L showed good linearity with the relative abundance,and the detection limits(signal/noise=3)of the method were 0.01-0.14?g/L.Three concentrations of malathion,propamocarb and triazophos were spiked into lettuce,tomato and cucumber under the optimal conditions,and the experimental analysis revealed that The recoveries of the samples spiked by the method ranged from75.40%-102.13%,and the RSDs were in the range of 0.08-8.24%.The recoveries of the samples spiked with three concentrations of propamocarb in apples,grapes and oranges under the optimal conditions were in the range of 74.33%-116.59%with the RSDs of 0.27-7.55%.In conclusion,this study combined solid phase extraction and magnetic solid phase extraction sample pretreatment techniques to construct a precise detection method for malathion,triazophos,quinpirole and propamocarb pesticides,and successfully applied to the qualitative and quantitative analysis of organophosphorus pesticides in fruit and vegetable agricultural products,highlighting the great potential of COFs-based composites as solid sorbents in sample pretreatment,and providing a development for ensuring the quality and safety of agricultural products.The results show the great potential of COFs-based composites as solid adsorbents in sample pretreatment,and provide technical support for the development of ensuring the quality and safety of agricultural products.