Synthesis Of Magnetic COFs And Their Adsorption Properties For Triphenylmethane Pollutants In Aquatic Products

As aquaculture fungicides,malachite green,crystal violet and other triphenylmethane dyes were repeatedly banned,and new triphenylmethane dyes such as bright green and victoria blue are gradually appearing in the market and being abused.Therefore,the detection of multi-residues of triphenylmethane pollutants in aquatic products is particularly important.Traditional adsorbent materials have the key problems of low adsorption efficiency and non-reusability,while covalent organic framework?COFs?materials are gradually used in the pretreatment of toxic and hazardous substances in food,because of their excellent adsorption capacity,and show outstanding effect.Therefore,this paper designed and constructed a kind of magnetic separation medium with stable structure and excellent adsorption performance.This polymer can separate five kinds of triphenylmethane dyes from actual samples such as fish meat,and realize multi-residue detection and analysis through high-performance liquid phase.The results as follows:Synthesis of magnetic covalent organic framework materials.The carboxylmodified magnetic nano-Fe₃O₄-COOH was synthesized by solvothermal method.Subsequently,aldehyde-based monomers and amino monomers were added,and the Schiff base reacted to form imine COFs.At the same time,the Fe₃O₄-COOH was coated with COFs as functional groups by precipitation polymerization method to for Fe₃O₄-COOH@COF material.By investigating the key factors affecting the morphology and adsorption performance of the material,the monomer type,magnetic nanoscale and reaction solvent were optimized.And the monomer with the best adsorption performance was determined to be 3,3'-dihydroxybenzidine?BHBD?.The ratio of magnetic nanometer to amino monomer is 200 mg: 0.4 mmol.The reaction solvent is a mixed solvent of odichlorobenzene and absolute ethanol?V : V=9 : 1?.It is also determined that the growth process of magnetic COFs tends to start to grow uniformly on the surface of Fe₃O₄-COOH,and then after the magnetic core is completely covered,a short rod shape appears,gradually interweaving into a network,and finally becoming a block structure.Compared with the monomer type,the reaction solvent has a greater influence on the morphology of the material,and the adsorption performance of the mixed solvent is better than that of the single solvent.Characterization and performance testing of Fe₃O₄-COOH@COF.The successful synthesis of Fe₃O₄-COOH@COF was confirmed by SEM observation,elemental analysis,and FT-IR analysis,and the material was found to be a "bouquet network" structure.Through nitrogen adsorption and thermogravimetric analysis,it was found that the material has a high specific surface area of 165.6 m2/g and the thermal stability.The rapid magnetic responsiveness of the material was confirmed by the measurement of saturation magnetic strength.By studying the adsorption process of MG by Fe₃O₄-COOH@COF,it was found that the material has excellent adsorption properties.Among them,the maximum adsorption capacity of malachite green by Fe₃O₄-COOH@COF was 500 mg/g,which was in accordance with the kinetics of the second kinetics,belonging chemical adsorption.Through thermodynamic analysis,it was found that the Langmuir model had a good fitting effect on the adsorption process.That is monomolecular layer adsorption,the adsorption sites are relatively uniform,and the adsorption process was a spontaneous thermodynamic reaction.Discussed the adsorption behavior between the adsorbent and the dye molecule,and it was found that the material had a higher adsorption capacity of five triphenylmethane dyes from 42.8 to 500 mg/g.The repeatability test verifies that the material was repeatable usability.Magnetic solid phase extraction?MSPE?optimization and actual sample detection.By optimizing the main parameters of MSPE,the best pre-processing method was determined.The adsorption conditions were: each adsorption was 15 minutes,the adsorbent was added 5 mg,and the elution condition were: the eluent was 3% methanol acetate,each time the eluent was added 4 m L,and the elution was 10 minutes,and the elution was twice.In the actual sample detection,the linear correlation coefficients?R2?of the five dyes are all higher than 0.9990,achieving good linearity;the detection limit and the limit of quantification were 0.67?8 ?g/kg and 3?30 ?g/kg,respectively.The recovery rates of the five dyes in carp,grass carp,crucian carp and fish culture water were in the range of 84.1 to 117.2%,and the relative standard deviation was in the range of 0.6 to 13.4%.It can realize the rapid detection of five triphenylmethane dyes in complex samples at the same time.