Study On Enrichment And Separation Of Polycyclic Aromatic Hydrocarbons And Organic Nitrogen Pesticides By Metal-organic Framework Materials

The analytical process of environmental sample includes sample collection,pretreatment,sample analysis and data processing of experimental results.Sample pretreatment is very important in environmental analytical chemistry,especially for complex matrix samples.Avoiding the influence of the matrix in the pretreatment process and separating and enriching the analyte from the interfering impurities are the key steps to improve the sensitivity and accuracy of the analysis and reduce the detection limit.At present,some safe,reliable,green and low-cost new sample pretreatment technologies,such as,solid-phase extraction（SPE）,magnetic solid-phase extraction（MSPE）and solid-phase microextraction（SPME）and others have been widely used in separation and enrichment of environmental samples.As the key of sample pretreatment technology,adsorbent materials with high selectivity and strong enrichment ability are the focus of current research.Metal-organic frameworks（MOFs）and their composite materials have the advantages of simple preparation,novel structure,stable properties,uniform pore size distribution,large specific surface area,and easy surface modification,etc.Therefore,it has attracted great attention,especially in the field of sample pretreatment technology has a broad development prospect.In this thesis,g-C₃N₄/ZIF-8 composites and new hollow Ni O/Co@C magnetic nanocomposites were designed and prepared as adsorption materials for separating and enriching persistent organic pollutants（POPs）and organic nitrogen pesticides（ONPs）from environmental samples by SPE and MSPE,high performance liquid chromatography（HPLC）was used to analyze and detect polycyclic aromatic hydrocarbons（PAHs）and organic nitrogen pesticides（ONPs）.The research content of this thesis is divided into four chapters:Chapter one:The harm of persistent organic pollutants（POPs）to ecological environment and human health was introduced.The importance of sample pretreatment technology in the analysis of environmental pollutants was presented.The overview,classification,preparation methods and application of MOFs in sample pretreatment were reviewed in detail,and the adsorption mechanism of organic pollutants by MOFs was briefly introduced.Chapter two:Graphite phase carbon nitride（g-C₃N₄）incorporating zeolitic imidazolate framework-8（ZIF-8）nanocomposite（g-C₃N₄/ZIF-8）with hierarchical structure was synthesized successfully by simple and rapid in situ growth method at room temperature.The composites were used as an adsorbent of solid-phase extraction（SPE）and the superior adsorptive removal of polycyclic aromatic hydrocarbons（PAHs）for the first time.Under several optimum conditions,the g-C₃N₄/ZIF-8-SPE-HPLC-FLD method showed low detection limits(0.006-3.41μg L^-1)and limits of quantification(0.02-11.3μg L^-1),wide linear ranges from 0.02 to 1000μg L^-1for all compounds,linear correlation coefficients（R²）of more than 0.9968,and satisfying reproducibility（relative standard deviations,RSDs<4.0%for intra-day,RSDs<8.3%for inter-day）,the spiked recoveries at two levels of 10.0,50.0μg L^-1 were in the range of 77.4%-114%with the RSDs less than 8.66%.In addition,the g-C₃N₄/ZIF-8 nanocomposites demonstrated excellent enrichment ability and extraction efficiency for PAHs compared with commercial adsorbents,which might since there were strongπ-πstacking force,hydrophobic interaction,hydrogen bonding,and more adsorption sites compared with other adsorbents.Finally,the g-C₃N₄/ZIF-8 based SPE method was combined with high-performance liquid chromatography（HPLC）to detect fifteen PAHs in environmental water samples successfully.Chapter three:In this paper,a kind of bimetallic MOFs composite（Ni/Co-MOF）was prepared by one-step solvothermal method,and it was transformed into magnetic MOFs derived nanocomposites（Ni O/Co@C）after heat treatment without the preparation of Fe₃O₄.The structures of the materials were characterized by SEM,TEM,FT-IR,PXRD,TGA and VSM.The results show that the MOFs-derived spherical nanosheet magnetic composite（S-Ni O/Co@C）has good thermal stability,and has the dual characteristics of magnetic nanoparticles and MOFs material.Finally,the material was used as MSPE adsorbent to study the separation and enrichemnt performance of organic nitrogen pesticide（ONPs）.Chapter four:In this experiment,a novel hollow H-Ni O/Co@C magnetic nanocomposite was successfully prepared by simple solvothermal reaction,using Cobalt（Co）ions as inducers,regulating the chemical transformation process and utilizing its coordination effect.This composite was used as magnetic solid phase extraction（MSPE）adsorbent for the first time to remove organic nitrogen pesticides（ONPs）.Compared with the spherical nanosheet S-Nio/Co@C magnetic composites derived from MOFs,the adsorption equilibrium experiments show that the hollow H-Ni O/Co@C has more advantages than the spherical nanosheet S-Nio/Co@C adsorbent without the preparation of Fe₃O₄.The results showed that H-Ni O/Co@C had a high adsorption capacity of 62.2mg g^-1 for pesticides due to its hollow porous structure.In addition,the adsorption properties and mechanism of ONPs were discussed in detail from the aspects of adsorption kinetics and thermodynamics.More importantly,H-Ni O/Co@C can not only achieve simple solid-liquid separation,but also have good reproducibility and stability.After nine cycles,the extraction recovery remained above 90%.Therefore,H-Ni O/Co@C magnetic nanocomposites are promising adsorbents for the separation and enrichment of pollutants in environmental water samples.