Preparation Of Magnetic Metal-organic Framework Composites And Their Adsorption Properties For Organic Pollutants In Water

The pollution of organic pollutants in water to the aquatic environment and human health has attracted great attention.Due to its high toxicity,difficult degradation and low content,the removal and detection of organic pollutants has become a difficult task and also an important research direction,in which the key bottleneck problem is the development of efficient adsorbents.Therefore,this paper combines the excellent adsorption characteristics of metal-organic framework materials?MOFs?with the advantages of simple and rapid separation of magnetic materials to develop magnetic MOFs?MMOFs?for efficient adsorption and enrichment of organic pollutants in wastewater and separation analysis methods.In this paper,three MMOFs were prepared with Fe₃O₄ as the center:MZIF-67?Co?,MMOF-235?Fe?and MMOF-5.The prepared MMOFs have good adsorption effects on ciprofloxacin,methylene blue,and phenols,respectively,and the adsorption mechanism and adsorption characteristics are studied.Among them,MMOF-5 combined with HPLC-UV established a detection method for separation and enrichment of phenolic pollutants in water.Chapter 1:The harm of organic pollutants in water and its research progress are briefly introduced,and the preparation method and application of magnetic metal-organic framework composites are summarized.Chapter 2:Based on the method of polydopamine modified magnetic particles and surface layer-by-layer self-assembly;a new method for preparing magnetic metal-organic framework composite material?MZIF-67?Co??was developed.Combining Fe₃O₄ coated with polydopamine and cobalt ion,and then mixed with 2-methylimidazole ethanol solution and stir at room temperature to obtain Fe₃O₄@PDA@ZIF-67?Co??abbreviated as MZIF-67?Co??.The material was characterized by SEM,XRD,FT-IR,TG,VSM.At the same time,the adsorption performance of MZIF-67?Co?for ciprofloxacin?CIP?antibiotics in aqueous solution was evaluated.The Freundlich model fits the equilibrium adsorption data well.The results of adsorption kinetics show that MZIF-67?Co?can quickly adsorb CIP,and the adsorption kinetics follows a pseudo-second-order kinetic model.The adsorption capacity of CIP is up to 381.4 mg g^-1.Moreover,MZIF-67?Co?showed no significant CIP removal loss after five cycles.Chapter 3:How to effectively and conveniently remove organic dye pollutants from wastewater is a challenge for public health and ecosystem protection.Here,we selected MOF-235?Fe?as MOF materials to disperse the Fe₃O₄@PDA in the reagents for the preparation of MOF-235?Fe?to synthesize magnetic-metal organic framework composites?MMOF-235?Fe??by a simple solvent method.The material performs well in methylene blue?MB?adsorption.the results show that the MB equilibrium adsorption capacity is 138.2 mg g^-1(when pH=8.0,the contact time is 6 h,the adsorbent dose is 5 mg,the initial MB concentration is 100 mg L^-1).The adsorption kinetics follows the pseudo-second-order kinetic model,and the adsorption isotherms are more suitable for the Freundlich model,indicating that the adsorption of MB in MMOF-235?Fe?is suitable for multilayer adsorption,and the adsorption binding sites on the adsorbent surface are heterogeneous.Chapter 4:Selecting the MOF-5 as the MOF material,disperse the Fe₃O₄@PDA in the reagent of the synthetic MOF-5,embed the Fe₃O₄@PDA in the MOF-5 by simple stirring,and synthesize the composite.Simultaneously,using it as magnetic solid phase extraction?MSPE?adsorbents to enrich three phenolic compounds from environmental wastewater,phenol?Phenol?,?-Naphthol??-NP?,o-Nitrophenol?O-NP?.It followed by high performance liquid chromatography?HPLC-UV?detection.Various parameters of extraction were optimized,including the amount of pH,MMOF-5 adsorbent for the sample matrix,adsorption time,salt concentration and elution solvent.The recovery of these phenols in the standard-added water samples was 67.9-101.5%,and the relative standard deviation was2.1-5.6%,which indicated that magnetic solid phase extraction with high performance liquid chromatography has good reliability;the adsorption mechanism of MMOF-5 was fully elucidated.Hydrophobic interaction was found between phenol and MMOF-5 in water,?-?stacking and hydrogen bonding interaction,in which hydrophobic interaction dominated the magnetic solid phase extraction performance.