Preparation Of Magnetic Molecular Imprinted Polymers For Microcystic-LR Recognition

Microcystins are a class of the most common and harmful algal toxins during algal blooms.Microcystins can be passed to human through water or food chain and consequently pose a great threat to human health by endangering the liver,kidney and other organs.Therefore,it is of great significance to determine and monitor the microcystins.A magnetic molecular imprinted polymer（MMIPs）was synthesized in the thesis using the most toxic MC-LR as template.The MMIPs showed specific adsorption to template molecule and was utilized to detect MC-LR in water.The main contents and results of the thesis are as follows:A stable Fe₃O₄@GO@DA polymer was synthesized by chemical coprecipation using ultrasonic dispersive graphene oxide（GO）solution as solvent,dopamine（DA）as modifier.Prior to polymerization,GO was prepared by the Hummers method.Afterwards A magnetic molecularly imprinted polymer（MMIPs）was synthesized through surface molecular imprinting technique with the obtained magnetic material as carrier,MC-LR as template molecule,dopamine as functional monomer and crosslinking agent,azodiisobutyronitrile（AIBN）as initiator,10 mM 3 hydroxymethyl aminomethane solution（TRIS-HCl,pH 8.5）as solvent.The amount of graphene,dopamine and initiator were optimized and the results were as follows:when 50 mg of graphene synthesis of Fe₃O₄@GO@DA,5 mg of dopamine and 100 mg of initiator were used,the resultant magnetic molecularly imprinted polymers（MMIPs）showed largest adsorption capacity.X-ray diffraction（XRD）was employed tocharacterize the crystalline structure of GO and MMIPs,Fourier infrared spectrum（FT-IR）was used to characterize the functional structure of MMIPs,thermogravimetric analyzer（TGA）was used to characterize the thermal stability of MMIPs,andvibrating sample magnetometer（VSM）was used to characterize the saturated magnetic field intensity of MMIPs,transmission electron microscopy（TEM）was used to characterize the surface morphology structure of MMIPs.The eluent type,elution time,static adsorption,adsorption kinetics and selective adsorption capacity of MMIPs were investigated.the experimental results are as follows:when the mixture of methanol and acetic acid（8:2,V/V）was used as the elution,the adsorption performance of the MMIPs was the best.The template molecule could be removed completely after 160 min of elution.The static adsorption was adopted to demonstrate the good selectivity of the MMIPs toward the template molecule MC-LR.When the concentration of MC-LR solution was 3 g/mL,the saturated adsorption capacity of the MMIPs was 3.16mg/g,which was greater than that of the magnetic non-molecularly imprinted polymer（MNIPs,Q=1.97 mg/g）.Different mathematical model were used to describe the static adsorption of the MMIPs.the results showed that the Freundlich model（R²=0.8041）was fitted to the equilibrium data better than the Langmuir model（R²=0.0416）and the Langmuir Freundlich model（R²=0.7811）.The Lagergren pseudo-first-order and pseudo-second-order equation were used to fit adsorption kinetics.The results indicated that the pseudo-first-order kinetic model with a higher R² value was more suitable to predict the adsorption process of MMIPs.In addition,selective recognition experiment was performed by using MC-RR and MC-YR as competitive compounds,and the selectivity coefficients of MC-RR,MC-YR and MC-LR were 1.02,1.05 and 1.85 respectively.Repetitive experiments showed that the MMIPs had a good regeneration capacity and the recovery could still remain 82.3%after six adsorption-desorption-adsorption cycles.The method was applied to the detection of MC-LR in water samples.The recovery was 86%¹13%,and the relative standard deviation（RSD）was 1.0%⁶.81%with a detection limit of 0.08μg/L（n=7,RSD=2.7%,C=1μg/L）.The prepared MMIPs can be used to effectively collect MC-LR and detect the actual samples.