Preparation Of Functionalized Metal-organic Frameworks And Its Application In Analysis And Removal Of Environmental Water Contaminant

Metal Organic Frameworks（MOFs）are a class of porous materials with metal node or clusters interconnected by organic linkers.MOFs possess many advanteges,such as large specific surface area,controlled porosity,and easy postsynthetic modification.Thus,their excellent adsorption properties exhibit broad application prospects.However,there are still some limits of the applications of MOFs.For example,the separation of MOFs crystals from aqueous solutions is always laborious.On the other hand,since the positive charges of the metal ion in MOFs are exactly coordinated with electronegative organic ligands like carboxylate-based linkers,most of the reported MOFs are electrically neutral,which limited their selective adsorption toward polar substances.Therefore,developing novel functionalized MOFs materials is a significant project,to extend their applicability as adsorbents for the enrichment of trace contaminants before analysis and adsorption removal of pollutions in environment waters.The main results are summarized as follows:（1）Basing on the chemical structure of heterocyclic pesticides,MOFs were used for the extraction of heterocyclic pesticides,due to the benzene rings in their organic linkers could interact heterocyclic rings by p-p interactions.Magnetic MOF-5 were prepared and used as adsorbents for magnetic solid-phase extraction（MSPE）of four kinds of heterocyclic pesticides in environmental water samples,coupled with high performance liquid chromatography（HPLC）determination.The materials were thoroughly characterized and several main parameters influencing MSPE efficiency were investigated.Under optimal conditions,the MSPE-HPLC method presented high sensitivity with limits of detection ranging from 0.04–0.11 μg/L.As well as good precision with relative standard deviations of 2.9%–7.1%（intra-day）and 3.3%–7.1%（inter-day）.Furthermore,the method was successfully applied to reservoir and river water samples,and satisfactory recoveries at three spiked concentration levels were between 80.2% and 108.3%.The magnetic MOF-5 composites based MSPE followed by HPLC proved promising for convenient and efficient determination of heterocyclic pesticides in environmental water samples.（2）For the analysis of anionic phenoxy carboxylic acid herbicides（PCAs）in water samples,a novel kind of cationic MOFs mixed-matrix membrane（MMM）was firstly designed,and it was used for simultaneous dispersive membrane extraction（DME）of six phenoxy carboxylic acid herbicides from water samples,followed by ultrahighperformance liquid chromatography tandem mass spectrometry determination.The prepared cationic MOFs-MMM was characterized and several main variables influencing the DME efficiency were investigated and optimized in detail.Low limits of detection in the range of 0.03–0.59 ng/L and satisfactory recoveries within 80.1%–117.4% for all the PCAs were a reliable witness to demonstrate supreme sensitivity and the applicability of the developed method.By relying on the obtained results,the present work implied cationic MOF-MMM based DME can be a versatile and worthy utility for the extraction of polar pollutants in environmental water samples.（3）Antibiotic contaminants were difficult to be degraded in environmental waters.Thus,MOFs with high adsorption properties were used for adsorption removal of antibiotics,combining with magnetic nanoparticles for convenient solid-liquid separation.Fe₃O₄/HKUST-1 were synthesized for the adsorption removal of two widely used ciprofloxacin（CIP）and norfloxacin（NOR）fluoroquinolone antibiotics（FQAs）from aqueous solutions.The adsorption equilibrium time was achieved within 30 min,and the maximum adsorption capacities of the magnetic composites toward CIP and NOR reached as high as 538 mg g-1 and 513 mg g-1,respectively.The main adsorption mechanism were p-p interactions and electrostatic interaction.The saturation magnetization value of Fe₃O₄/HKUST-1 was 44 emu g-1,which was sufficient for the separation of the Fe₃O₄/HKUST-1 adsorbent from aqueous solution by an external magnetic field.Additionally,this magnetic material showed a good reusability with the slight derease of adsorption capability after reuse for ten cycles.These results indicated that the magnetic composites Fe₃O₄/HKUST-1 may be a promising adsorbent in the decontamination of FQAs from wastewater.（4）2,4-dichlorophenoxyacetic acid（2,4-D）is one of the most widely used anionic phenoxy carboxylic acid herbicides.For the removal of 2,4-D pollutants in environmental waters,a novel kind of quaternary amine anionic-exchange MOFs UiO-66 namely UiO-66-NMe₃⁺ was synthesized for adsorptive removal of 2,4-D from aqueous solutions.The maximum adsorption capacity of UiO-66-NMe₃⁺ toward 2,4-D reached as 279 mg g-1,higher than that of pristine UiO-66 and aminated UiO-66.Additionally,the UiO-66-NMe₃⁺ could be well regenerated by simple solvent washing and exhibited a slight decline of adsorption capacity after seven successive recycle.Comparing with reported activated carbon and resin materials,the UiO-66-NMe₃⁺ MOFs possessed higher adsorption capacity and shorter equilibrium time,as well as good reusability and practicality.The developed ion-exchange functionalized MOFs provided an ideal alternative for efficient adsorptive-removal of 2,4-D from aqueous environment.