Preparation Of Nanocomposite Adsorbent Based On Modified Multi-walled Carbon Nanotubes And Its Application In Detection Of Bisphenol A In Food

In recent years,it has been paid more and more attention on the impact of endocrine disruptors on human health and ecosystem.Bisphenol A?BPA?is one of the noteworthy endocrine disruptors,which is mainly used in food and beverage packing,surface water and soil.Series of studies have shown that prolonged exposure to low concentration BPA can damage the immune,endocrine and nervous system of human body to warying degrees,and even induce cancer.BPA often exists at trace level in food.Due to the low sensitivity and selectivity of direct analysis of bisphenol A in complex matrix,proper sample pretreatment is necessary to improve the detection ability and analysis efficiency of the instrument.Solid phase extraction?SPE?is the most widely used sample pretreatment technology,and adsorbent is the core of SPE.The most commonly used C18 bonded silica can achieve good enrichment efficiency for specific targets,but for some relatively polar targets,the recovery rate is relatively low.Therefore,the development of new,simple,economical and effective adsorbents to improve the selectivity or sensitivity of BPA is still continuing.Carbon nanotubes?CNTs?are an effective solid-phase extraction adsorbent with excellent adsorption and screening properties for many organic and inorganic substances.As a similar or more effective material for silica-based adsorbents,CNTs have great analytical potential for BPA.In this paper,new solid-phase extraction and magnetic solid-phase extraction adsorbents were prepared and solid-phase extraction and magnetic solid-phase extraction techniques were developed.MWCNTs-MnO₂ and MWCNTs-Fe₃O₄-MnO₂composite nanoparticles were successfully prepared by loading MnO₂ and Fe₃O₄.A new solid-phase extraction-high performance liquid chromatography method was established for the determination of BPA.The adsorption thermodynamics and kinetics experiments were carried out to study the adsorption performance of adsorbents and the adsorption equilibrium process of BPA.The morphology,element and magnetic properties of the adsorbent were characterized by means of scanning electron microscopy,transmission electron microscopy,infrared spectroscopy,vibrating sample magnetometer,specific surface area and pore analyzer.The application of adsorbent as solid phase extraction material in food analysis was verified.The main contents of this paper are as follows:1.Introduction:This paper briefly introduces the existence of BPA in environment and food,summarizes the hazards of BPA and the limitations of various countries;lists common sample pretreatment technologies,including liquid-liquid extraction,solid-phase extraction,dispersive solid-phase extraction and magnetic solid-phase extraction developed from solid-phase extraction;and then summarizes the materials used in solid-phase extraction,which are divided into common solid-phase extraction,multi-walled carbon nanotubes,modified multi-walled carbon nanotubes and magnetic multi-walled carbon nanotubes,as well as common detection methods and applications for BPA.Multi-walled carbon nanotubes?MWCNTs?are often used as adsorbents because of their special properties.This chapter introduces the application prospects of MWCNTs and their applications in solid phase extraction and magnetic solid phase extraction.Finally,based on the application status of solid phase extraction adsorbents,modified multi-walled carbon nanotubes were proposed as solid phase extraction adsorbents for food analysis,and the research contents of this paper were briefly summarized,indicating the significance of the research.2.Preparation and application of manganese dioxide-modified multi-walled carbon nanotubes?MWCNTs-MnO₂?solid phase extraction adsorbent:In this chapter,MWCNTs-MnO₂ was prepared as a carrier,and manganese dioxide was loaded on the surface to improve the adsorption capacity of the material.The prepared MWCNTs-MnO₂ was filled in the empty column of solid phase extraction for sample pretreatment.Through the study of the concentration of adsorbate,adsorption time,pH and other factors,it was found that the adsorption thermodynamics conformed to Langmuir adsorption model,and the maximum adsorption capacity of BPA was 114.7 mg/g.The adsorption equilibrium reached at 300 min.The adsorption kinetics conformed to the quasi-second-order kinetic model.The adsorption capacity was the largest at pH=6.0 and could be reused?the recovery rate was still greater than 94%after 30 reuses?.The morphology,structure and element composition of the adsorbent were characterized by scanning electron microscopy,X-ray diffraction,specific surface area and void analyzer and Fourier transform infrared spectroscopy.The conditions of solid phase extraction?SPE?were optimized,the recovery and precision of SPE column were investigated,and the extraction effect of SPE column was investigated by high performance liquid chromatography?HPLC?and ultraviolet spectroscopy?UV?.The results showed that the enrichment factor of BPA in vegetables was 50 times,and the detection limit of the method was 0.050ng/mL,which could be used for trace analysis of BPA in vegetables.3.Preparation and application of manganese dioxide modified magnetic multi-walled carbon nanotubes?MWCNTs-Fe₃O₄-MnO₂?:Manganese dioxide nanocomposites supported by functionalized multi-walled carbon nanotubes?MWCNTs-Fe₃O₄-MnO₂?were synthesized,and the magnetic solid phase extraction?SPE?properties of the materials were studied comprehensively,which were applied to trace analysis of BPA in bottled beverages.By fitting the adsorption model,the data conform to Langmuir adsorption model and quasi-second-order kinetic model.The maximum adsorption capacity of BPA is 137.6 mg/g,the adsorption equilibrium time is150 min,and the maximum adsorption capacity is at pH=5.0.The morphology,element composition and magnetic properties of the material were characterized by scanning electron microscopy,transmission electron microscopy,Fourier transform infrared spectroscopy and vibrating sample magnetometer.The results showed that ferric oxide was successfully loaded on the surface of multi-walled carbon nanotubes to achieve magnetic separation,while manganese dioxide was successfully coated to increase adsorption sites and adsorption capacity.The detection limit of BPA in bottled drinking water was 0.092 ng/mL.The recovery was 96.0-102.2%and the relative standard deviation was less than 7.7%.The method can be used for trace analysis of BPA in bottled drinking water.