| At present,the over-standard rate of pesticide residues in major agricultural products is high.In order to effectively remove the organic pesticide residues in fruits and vegetables,the preparation of an efficient,low-cost and environmentally friendly adsorbent is imperative.In this study,soybean protein separation,peanut protein separation and rice bran protein,three different types of plant proteins with low added value,were selected as the substrate,and a protein-cerium complex with the adsorption of omethoate pesticide was prepared by cross-linking with cerium nitrate through substitution reaction.The process parameters of the cross-linking reaction between three plant proteins and cerium ammonium nitrate were optimized respectively.The adsorption isotherm and kinetic equation were further fitted to study the adsorption methods and mechanisms of three protein-cerium complexes,so as to realize the recycling of the protein/cerium complex,increase the comprehensive utilization rate of the protein,and lay a solid theoretical foundation for industrial application research.The main contents and results are as follows:1.The single factor was used to optimize the technological parameters of the substitution reaction between protein and cerium ammonium nitrate.With cerium content as the index,the effects of four factors on the crosslinking reaction were investigated,including the cross-linking ratio,the cross-linking pH,the cross-linking temperature and the cross-linking time.The results showed that the crosslinking ratio of the three protein-cerium complexes was 1:1,the crosslinking pH was 7.5,5.5 and 4.5,the crosslinking temperature was 45?,35? and 35?,and the crosslinking time was 14 h,respectively.2.Fourier infrared spectroscopy(FT-IR),scanning electron microscope(SEM),X-ray diffraction(XRD),differential scanning calorimetry(DSC),SDS-PAGE gel electrophoresis and other techniques were used to analyze the structure of protein-cerium complex.The results show that new chemical bond is cerium-oxygen bond and new crystal peak are produced by FT-IR and XRD.SEM can observe the porous structure,rough structure and loose structure of the composite surface,which can enhance its adsorption capacity.DSC can indicate that the enthalpy of protein decreases,the hydrogen bond is weakened,and the structure of protein becomes loose.SDS-PAGE gel electrophoresis showed that the complex still had the typical bands of proteins.Several characterization methods proved that the proteins successfully reacted with cerium ions and obtained the unsaturated sites for the oamethoate pesticide.3.Three kinds of protein-cerium complexes were used to conduct adsorption experiments on methoxide pesticide.Different adsorption conditions were explored and two isotherms were fitted with two kinetic models(The experimental models were the Langmuir and Freundlich isotherm models and the first and second order kinetic models,respectively).The adsorption efficiency of the three protein-cerium complexes on oamethoate pesticide was much higher than that of the original protein,and the fitting degree of the three protein-cerium complexes was higher on the Langmuir isotherm and the second order kinetic model,respectively.This proves that the surface of protein-cerium complex is uniform and more inclined to monolayer adsorption.The adsorption capacity may be related to the chemical actions such as chelating electrostatic force,valence force and ion exchange.The adsorption rate of the compound can still reach more than 60% after repeated test for 5 times,which proves that the adsorption property is good and has practical application value. |
PDF Full Text Request