Research And Application Of Lead Ion-imprinted Polymer Based On Magnetic Graphene Oxide

With the development of industrial and agricultural production and the acceleration of urbanization,heavy metal pollution is becoming more and more serious,and the heavy metal content of agricultural products exceeds the limit frequently.Lead and cadmium are two typical representatives of heavy metals,which can accumulate in organisms directly or through the food chain.It will endanger the life and health of humans and aquatic organisms when the content exceeds the allowable limit.The degree of heavy metal pollution and the effect of biological toxicity in environmental samples is directly related to the chemical forms of heavy metal,and different forms show different biological toxicity and environmental behavior.Therefore,the building of a high-efficiency and timesaving method to remove lead from complex matrices and assess of heavy metal contamination in biological samples have become significantly urgent.Currently,various technologies have been developed to detect and remove metallic lead and cadmium ions from aqueous systems,among which adsorption has become more and more widely used due to its simplicity,flexibility,ease of operation,low cost,and wide material selectivity.Based on these magnetic graphene oxide(GO)was sybthesized and explored its adsorption capacity for lead and cadmium,and used as a matrix material to perform lead ion imprinting polymerization on its surface in this article.The adsorption properties and application of resulting polymer material were studied and optimized to selectively adsorb lead ions from biological samples.The specific works are as follows1.MnFe2O4 magnetic nanoparticles(MNPs)were synthesized by the co-precipitation method and introduced amino functional groups on the surface.The functionalized MNPs were grafted to the surface of the layered GO to obtain the magnetic GO matrix material(MnFe2O4@SiO2-NH2@GO)through the dehydration condensation reaction between the amino group and the carboxyl group of GO.The structure and properties of materials were explored with X-ray diffractometer(XRD),scanning electron microscope(SEM),thermogravimetric analysis(TGA),Fourier transform infrared(FT-IR),and magnetic measurement system.After optimizing the adsorption conditions,the adsorption of Pb(Ⅱ)and Cd(Ⅱ)can reach equilibrium within 30 minutes,and the maximum adsorption capacity is 42.48 and 18.28 mg·g-1,respectively.The series of adsorption data can be well fitted by Langmuir adsorption isotherms and pseudo-second-order kinetic models,which proves that adsorption is a single-layer chemical adsorption on uniform adsorption sites.The calculation of thermodynamic parameters proves that adsorption is an endothermic reaction that proceeds spontaneously.2.Based on magnetic GO,a new surface ion-imprinted polymer(MnFe2O4/SiO2/GO-ⅡP)was fabricated successfully with 4-vinylpyridine as functional monomer and 2-(2-aminophenyl)-1H-benzimidazole as ligand to self-assembly with Pb(Ⅱ)through cross-linking polymerization.The structure and performance of the prepared adsorbent were explored through varieties of characterization methods.The adsorption experiments exhibited the MnFe2O4@SiO2/GO-ⅡP possessed a good adsorption performance for Pb(Ⅱ)ions and the maximum adsorption capacity reached 58.82 mg·g-1.The adsorption could be accomplished within 30 min and the adsorbents could be separated quickly by external magnetic field.The Langmuir adsorption isotherm and pseudo-second-order kinetic models could describe the adsorption procedure appropriately and the result demonstrated that the chemisorption was the rate-limiting step.The selectivity coefficient of Pb(Ⅱ)/Ni(Ⅱ),Pb(Ⅱ)/Zn(Ⅱ),Pb(Ⅱ)/Cd(Ⅱ),Pb(Ⅱ)/Co(Ⅱ)were 25.37,19.71,33.07 and 45.7,respectively.In addition,the regeneration experiments confirmed the high stability and reproducibility of adsorbents.Lastly,X-ray photoelectron spectroscopy(XPS)proved the bonding mechanisms of the material and Pb(Ⅱ)ions with a coordination N-Pb bond.3.Based on the prepared lead ion-imprinted material and SPE technology,an analytical method was established to separate different forms of heavy metal lead in actual samples(tobacco leaves and soil).The soluble and insoluble lead content in of biological samples(8 tobacco leaf samples and 9 soil samples)were separated after ultrasonic extraction and centrifugation.After lead in the soluble sample solution was adsorbed in MSPE with the prepared MGO@Pb-IIP,the organic and inorganic lead were eluted with organic eluent(70%ethanol)and inorganic eluent(1M HCl)and detected with Inductors Coupled Plasma-Mass Spectrometer(ICP-MS).The recovery rate of inorganic Pb is above 85.0%,indicating that this MnFe2O4@SiO2/GO-ⅡP magnetic solid phase extraction combined with ICP-MS detection method can accurately and reliably analyze the content and form distribution of Pb in biological samples.