Preparation Of Magnetic Covalent Organic Framework Nanocomposites And Their Application In Determination Of Trace Environmental Pollutants

With the magnetic nanomaterials continuous progress,many novel magnetic nanomaterials have been synthesized and applied to various research fields.Among them,Covalent organic frameworks?COFs?was an emerging type of porous crystal-structured materials,which have become an brilliant star in modern materials science research since first report in 2005.COFs are composed of covalent bonds,low density,high surface area,good thermal and solvent stability,excellent structural regularity,and adjustable pore structure.They are favored by researchers,among which magnetic covalent organic frameworks?MCOFs?are one of the most novel covalent organic frameworks?COFs?materials.Combining MCOFs with different analytical pretreatment techniques and detecting environmental pollutants is the focus of this paper.In particular,the detection of trace environment pollutants in complex matrices must meet the requirements of effectively removing interference from complex matrices and efficiently enriching for analytes.Among the analytical pretreatment technologies that are constantly being developed and used,the ones that best meet these requirements are effervescent reaction-enhanced microextraction?MNER-EM?with green chemical characteristics and solid-phase microextraction?SPME?technology.In this paper,core-shell magnetic covalent organic frameworks?MCOFs?were prepared and characterized,combined with green,highly efficient enrichment microextraction system,effervescent reaction-enhanced microextraction?MNER-EM?and solid phase microextraction?SPME?technology,and use this combined system for trace environmental pollutant detection.The main research contents are as follows:1.Preparation and characterization of three core-shell magnetic covalent organic frameworks?MCOFs?materials,which were used for the first time as magnetic separation adsorbent and independent adsorbent in effervescent reaction enhanced microextractioncombined with HPLC-FLD.The extraction and enrichment technology of endocrine disruptors?EDs?in liquid matrix samples were constructed.This innovative technology combines the efficient adsorption/extraction based on MCOFs,fast effervescent dispersion and convenient magnetic separation into one step.Through the isothermal adsorption and kinetic adsorption experiments,the equilibrium adsorption capacities?Q_e?of six EDs on the MNCs were 38.3-88.1 mg/g.At the same time,several factors affecting the extraction efficiency were strictly optimized,such as the molar ratio of effervescent tablet composition,kind and dosage of adsorbent,kind of elution solvent,p H,extraction temperature and salt addition.Under optimized conditions,the MNER-EM/HPLC-FLD method had a good linear range 0.1?0.5-200?g L^-1,and the correlation coefficients are all greater than 0.9991,good recoveries?83.4-106.2%?,low limits of detection(LODs based on S/N=3,0.019-0.096?g L^-1)and high precision?intra-and inter-day RSDs,3.11-5.73%?for six EDs in real-world water,beverage and human urine and serum samples.Thus,the Ni Fe₂O₄@COF MNCs provide a good alternative for replacing traditional magnetic separation and adsorbent materials,and also this proposed method shows a great potential in conventional monitoring of trace EDs in liquid matrices.2.Using the successfully prepared new magnetic Ni Fe₂O₄@COF nanocomposites,mixing with dimethyl siloxane?PDMS?and silicone rubber curing agent,Ni Fe₂O₄@COFs coating quartz fiber SPME extraction head was made.Combined with GC-ECD method,an analytical method for extraction and enrichment of TCS and MTCS in environmental water samples and human urine samples was constructed.The extraction efficiency of Ni Fe₂O₄@COFs nano-coatings for seven environmental pollutants was studied.The Ni Fe₂O₄@COFs nano-coatings gave the mean extraction recovery for triclosan,methyl triclosan,fenpropathrin,bifenthrin,permethrin,fenvalerate,and deltamethrin,which were 88.80%,91.82%,36.57%,43.74%,25.07%,32.73%and 46.51%,respectively.The experiment results show that the Ni Fe₂O₄@COFs nano-coating has the highest extraction efficiency for triclosan and methyl triclosan than pyrethroid pesticides.The factors affecting SPME/GC-ECD technology were strictly optimized,such as extraction temperature,extraction time,salt effect,p H and thermal desorption time.Under the optimal experimental conditions,the linear range of TCS and MTCS were 0.1-1000?g L^-1,and the correlation coefficients are greater than 0.9995;the intra-day RSD?n=6?is2.53-3.55%,intre-day RSD?n=6?is 2.37-5.06%;SPME extraction coating based on Ni Fe₂O₄@COFs can be reused 120 times and the extraction efficiency is basically unchanged.In short,the combined technology is simple,sensitive,efficient and green,so it has important application value in routine monitoring of TCS pollutants in complex liquid matrices.