Preparation Of Surface Molecularly Imprinted Polymer And Its Application In The Removal Of Imidacloprid And Acetamiprid From Tea Polyphenols

Tea polyphenols(TP)is the general name of all the multi hydroxy classification substances in tea,and it is the main functional active substance in tea.Tea raw materials are usually extracted by pure water or ethanol/water in industry,and different purity products are prepared by ethyl acetate extraction or other methods.However,in the process of tea polyphenol processing,it is inevitable that pesticide molecules will be dissolved and enriched in the solvent,and finally remain in tea polyphenol products.Pesticide residues in tea polyphenols will do harm to human health and affect the export and sales of tea polyphenol products.In this study,dual-template surface molecularly imprinted polymer(DT-MIP)and dummy template surface molecularly imprinted polymer(DMIP)were prepared,and the dummy template surface molecularly imprinted polymer was selected as the packing to prepare a molecularly imprinted solid-phase extraction column for the removal of imidacloprid and acetamiprid from tea polyphenols.The main research contents were as follows:1.Use computer simulation to screen the best functional monomer.In order to efficiently and quickly screen out suitable functional monomer,the optimal configurations of three functional monomers(MAA,AA and 2-Vpy),imidacloprid and acetamiprid were simulated by Gaussian 09 software,and the binding energy of each polymer formed by three functional monomers and two template molecules in the molar ratio of 1:4 was calculated.MAA was selected as the best functional monomer according to the principle of minimum energy.Compared with the experimental exploration,this method greatly saved the experimental time and reduced the waste of reagents.2.Preparation,characterization and adsorption evaluation of dual-template surface molecularly imprinted polymer.In order to prepare molecularly imprinted polymer which can adsorb imidacloprid and acetamiprid at the same time,the dual-template surface molecularly imprinted polymer was synthesized based on silica gel using imidacloprid and acetamiprid as dual-templates,MAA as functional monomer,ethylene glycol dimethacrylate(EGDMA)as cross-linking agent and AIBN as initiator.The dual-template surface molecularly imprinted polymer was characterized by elemental analysis,scanning electron microscopy(SEM),fourier transform infrared spectroscopy(FT-IR),X-ray diffraction(XRD),thermogravimetry(TGA).Its static adsorption and adsorption selectivity were tested.The results showed that the dual-template molecularly imprinted polymer had better thermal stability,larger adsorption capacity and higher adsorption selectivity.The equilibrium adsorption capacity of imidacloprid and acetamiprid reached 33.01 ± 1.06 mg/g and 25.62±0.45 mg/g respectively in 200 ?g/mL aqueous solution of imidacloprid and acetamiprid.The adsorption specific factor(a)were 1.80±0.08 and 1.48±0.12,respectively.The adsorption fit was consistent with Langmuir adsorption isotherm model,and belongs to single molecular layer adsorption.3.Preparation,optimization and performance evaluation of dummy template surface molecularly imprinted polymer.In order to avoid the potential template leakage of DT-MIP and to better control the preparation conditions of materials,nicotinamide,a structural analogue of imidacloprid and acetamiprid,was selected as the dummy template molecule.MAA as the functional monomer,EGDMA as the crosslinking agent,AIBN as the initiator to synthesize the dummy template surface molecularly imprinted polymer based on the silica gel.The preparation conditions of the DMIP were optimized by single factor experiment and response surface analysis.The structure of the optimized DMIP was characterized by SEM,and its static adsorption experiment and adsorption selectivity experiment were carried out.The results showed that when the molar ratio of template molecule and functional monomer was 1:4 and the volume of solvent was 80 mL,the optimal synthesis conditions of DMIP were as follows:the molar ratio of crosslinker and functional monomer was 7:1,the amount of modified silica gel was 0.919 mg,and the volume ratio of methanol/water in solvent was 9:1.The adsorption capacity of DMIP to imidacloprid and acetamiprid reached 42.74±0.37 mg/g and 25.99±0.84 mg/g,respectively in 200 ?g/mL aqueous solution of imidacloprid and acetamiprid.The adsorption specific factor(a)were 1.95±0.12 and 1.91±0.05,respectively.The adsorption capacity and selectivity of DMIP were higher than those of the DT-MIP.The adsorption fit was in accordance with the quasi second-order adsorption kinetic model and Freundlich adsorption isotherm model,which belongs to chemical adsorption.4.Condition optimization,application and product evaluation of molecularly imprinted solid phase extraction.In order to investigate the applicability of the DMIP for industrial application,and further evaluate the property changes of tea polyphenol products before and after removal,the tea polyphenol sample with the most serious residues was selected for removal experiments.The solid phase extraction(SPE)column was prepared by using DMIP as the packing.Imidacloprid and acetamiprid were removed from tea polyphenols under the optimized conditions,and the reusability of SPE column was investigated.The results showed that when the ratio of height to diameter of molecularly imprinted solid phase extraction column was 5:1 and the column volume was 3.92 mL,the optimal removal conditions were as follows:10.20 times of column volume,1 mL/min of flow rate,14 mL of ethanol/acetic acid(9:1,V/V)as eluent.The removal rate of imidacloprid and acetamiprid were 94.35%and 95.53%,respectively,and the loss rate of tea polyphenols was 5.20%.The removal process did not significantly affect the functional components of tea polyphenol,and the residual organic reagents of tea polyphenol products met the relevant provisions of the Chinese Pharmacopoeia.The column showed good reusability in the experiment of reuse.