Preparation Of MOF-derived Magnetic Porous Materials And Their Application In Sample Pretreatment

Sample preparation is the most critical and difficult part of the process of analyzing complex samples（e.g.environmental,biological,pharmaceutical or food samples）.If there have many possible compound interferences in a complex sample,or there has a trace or ultra-trace level in the target analyte,direct analysis of the sample is impractical,lacking selectivity and sensitivity.Choosing the appropriate sample preparation technology not only eliminates the effects of interfering substances,but also improves the selectivity and sensitivity of the analytical method,and also prevents to damage the analysis instruments.Magnetic solid-phase extraction（MSPE）is an innovative solid phase extraction（SPE）technology that has received considerable attention in sample preparation techniques.MSPE not only has the advantages of SPE,such as the ability to extract organic analytes from polar to non-polar in various samples without altering the concentration or characteristics of the analyte and to remove matrix interference.MSPE also overcomes the limitations of traditional SPE.Because of its magnetic properties,the MSPE adsorbent can be separated from the sample solution by an external magnetic field.It does not need to be installed in any type of device.There is no problem of high back pressure or packed bed blockage.And phase separation can be achieved quickly without the need for inefficient steps such as centrifugation or filtration.The MSPE method simplifies the extraction process in sample pretreatment and improves extraction efficiency.Metal-organic frameworks（MOFs）is composed of metal ions or metal clusters assembled by coordination with organic ligands.They are crystalline porous materials with a hybrid network structure,with extremely high surface area and pore volume,permanent porosity,controlled pore size or shape,and high thermal and mechanical stability.The properties of MOFs make it suitable as a candidate for adsorbent materials.The synergy between the porous MOFs material and the magnetic nanoparticles can be used as a high performance MSPE adsorbent.Moreover,the large surface area and high porosity of MOFs allow the analyte to diffuse within the framework and interact with the adsorption site,improving extraction efficiency.Most of the MOF-derived materials are obtained by carbonization,and a small part is obtained by surface modification of MOFs.Most of the obtained derivative materials retain the skeleton and pore size of MOFs.Therefore,the exploration and preparation of magnetically derived materials that retain the structural properties of MOFs are of great significance for MSPE.The research content of the paper is as follows:1.Magnetic hybrid carbon materials（Co@NC/CNTs）,with Co nanoparticles encapsulated by carbon shells which include the inner loose porous nitrogen-doped carbon（NC）and the short carbon nanotubes（CNTs）on surface layer,was synthesized by exploiting the one-step pyrolysis strategy.The as-synthesized Co@NC/CNTs is provided with the nanopores,a large specific surface area,and strong magnetic response.The obtained Co@NC/CNTs was used as magnetic solid-phase extraction adsorbents to extract flurbiprofen and ketoprofen.The parameters of extraction efficiency,involving adsorbents amount,extraction time,sample solution volume,ionic strength,p H and the conditions of desorption efficiency,were optimized in detail.After determined by high-performance liquid chromatography-ultraviolet（HPLC-UV）,the results evinced that Co@NC/CNTs showed a high extraction efficiency and enrichment factors.The good linear range of both flurbiprofen and ketoprofen were all 5.0-1000 ng L^-1 with the limit of detection of 0.60 ng L^-1 and 0.70 ng L^-1,respectively.Furthermore,a valid method for the extraction of flurbiprofen and ketoprofen from human serum was established.The spiking recoveries of two profens were between 86.74%and 97.22%the relative standard deviation less than 6.55%.Co@NC/CNTs can be repeatedly used at least 10 times,indicating its excellent regeneration and reusability.The results demonstrated that the Co@NC/CNTs materials exhibits high enrichment ability and extraction efficiency,playing great promise in MSPE.2.Using core-shell ZIFs（ZIF-8@ZIF-67）as a precursor,a large number of magnetic carbon nanotubes（Co@CNTs）were formed by high-temperature pyrolysis under the flowing Argon.The morphology,structure and properties of Co@CNTs were confirmed by scanning/transmission electron microscopy,X-ray diffraction,X-ray photoelectron spectroscopy and Raman spectroscopy and so on.The as-synthesized Co@CNTs is provided with a large specific surface area,a suitable pore size,and a strong magnetic response.In order to verify the extraction performance of Co@CNTs,an effective method was established to use it as an MSPE adsorbent to extract pyrethroid pesticides.The Co@CNTs mainly adsorbs analytes byπ-πinteraction and van der Waals force.The extraction efficiency parameters such as the amount of Co@CNTs,extraction time,volume of sample solution,and desorption efficiency and so on were optimized in detail.The results obtained by high performance liquid chromatography showed that this method has good linear range(0.05-10μg L^-1)and low LODs(0.029μg L^-1,0.018μg L^-1 and 0.039μg L^-1).In addition,the method was used for extracting pyrethroid pesticides in soil,and a pesticide was enriched and detected in the soil.The spiking recoveries of three pyrethroid pesticides were in the range of 92.76-105.72%,and the RSD was less than 3.25%.The experimental results show that Co@CNTs have excellent extraction performance and good regeneration stability,and can be used as adsorbents for MSPE.3.Using the principle that the catechol group of polydopamine can chelate with the metal ion in the crystal of MOFs,the magnetic metal-polydopamine frameworks was prepared by using magnetic ZIF-67（Fe₃O₄@ZIF-67）as a template which was etched by PDA.The morphology,structure and properties of Fe₃O₄@Z67D were confirmed by scanning/transmission electron microscopy,X-ray photoelectron spectroscopy and IR spectroscopy,ect.The introduction of PDA modified the hydrophobic surface of ZIF-67 to be hydrophilic and increased the pore size of the material.Fe₃O₄@Z67D has a hydrophilic surface,a nanometer-scale pore size,and a magnetic response.In addition,an effective method was established to verify the extraction performance of Fe₃O₄@Z67D,which was used as an MSPE adsorbent to extract two cationic dyes（methylene blue and crystal violet）by hydrophilic,π-πstacking,electrostatic,hydrogen bonding and so on.The extraction efficiency parameters such as Fe₃O₄@Z67D dosage,extraction time,sample solution volume,and desorption efficiency and so on were optimized in detail.After determined by high-performance liquid chromatography,the linear range of methylene blue and crystal violet were 0.5-200μg L^-1 and 0.01-50μg L^-1,respectively,and the detection limits were 0.04μg L^-1 and0.008μg L^-1,respectively.The method was used for adsorption and detection of dyes in fish pond water,the spiking recoveries of two cationic dyes ranged from 81.99-109.01%,and the RSD was lower than 2.88%.The experimental results verify that Fe₃O₄@Z67D has excellent reproducibility and reusability,and has good extraction efficiency for enrichment of methylene blue and crystal violet,and has a good application prospect in MSPE.