Construction Of Composite System Based On Metal-organic Frameworks For Removal Of Organic Pollutants

With the rapid development of global industrialization and population explosion,water pollution caused by different pollutants had become a serious global problem,affecting the lives of people.Organic pollutants,such as dyes and oils,were a major pollutant of sewage and generated through the printing and textile industries,automobiles,and petrochemical industries.The treatment methods of organic pollutants were mainly divided into physical methods,chemical methods and biological methods.Physical adsorption method has attracted much attention due to its advantages such as simple operation,low cost and easy regeneration.Currently,various porous materials have been used to adsorb organic pollutants,such as zeolite,activated carbon,chitosan,etc.Among them,metal-organic frameworks（MOFs）had become emerging adsorbents in recent years due to their large specific surface area and diversity of chemical components.In this paper,three kinds of composite material systems were constructed based on MOF for adsorbing organic molecules in wastewater,such as dyes and oils.The main research contents are as follows:（1）MIL-53（Fe）was difficult to remove from water completely due to its small size,which would cause secondary pollution to the environment in sewage treatment.In view of the above problems,carbon nanotubes/ethylene vinyl acetate fiber（CNTs/EVA,abbreviated as CE）was selected as carrier to prepare MIL-53（Fe）/CE composite fiber by in situ growth method（MIL-53（Fe）:60.56 wt%）.The adsorption results showed that both MIL-53（Fe）and MIL-53（Fe）/CE had good adsorption properties for anionic dye Congo red（CR）and neutral dye medium Orange 1（MO1）,with removal were above 90%,and the composite fiber had good dye release ability,which could release all adsorbed dyes within 1 h.In addition,MIL-53（Fe）/CE composite fiber still had dye adsorption rate of more than 80%after 9 cycles,while the adsorption rate of MIL-53（Fe）decreased to 68.40%after 4 cycles,indicating that the composite fiber not only maintained the dye adsorption performance of MIL-53（Fe）,but also improved its cycling ability.Therefore,MIL-53（Fe）/CE fiber has a certain development prospect in dye adsorption.（2）In order to improve the selective adsorption ability of Ui O-67 on cationic dyes,a metal polyphenol compound Fe-TA（TA is tannin）with negative electrical properties was selected for surface modification.The modified material Ui O-67@Fe-TA（abbreviated as UFT-X,where X represents the number of modifications）exhibited significant selective adsorption of cationic dye MB,and UFT-3 had the best effect.The selective adsorption properties of Ui O-67 and UFT-3on ionic mixed dyes were tested,and the results showed that the modification of Ui O-67 was beneficial for enhancing the materials selective adsorption for cationic dyes.In addition,the adsorption of cationic dyes by UFT-3 was evaluated through isothermal adsorption and kinetics.The study showed that its adsorption process followed the Freundlich isotherm model and quasi second-order kinetics model,indicating that the adsorption process was a multi molecular layer chemical adsorption,and the maximum adsorption amounts for MB and BG were 213.20 mg/g and 1415.56 mg/g.This work provides a strategic and theoretical basis for construction of materials with selective adsorption or materials surface modification.（3）To choose hydrophobic adsorbents is more conducive to the removal of oil in the application of oil-water separation.Therefore,a metal-organic framework ZJU-64-CH₃containing hydrophobic groups was selected for the adsorption of oil in water.However,ZJU-64-CH₃had a low contact angle to water,and it is difficult to separate powdered adsorbent from oil-water mixed solutions,which could easily cause environmental pollution,so this material cannot be effectively applied.Therefore,ZJU-64-CH₃was combined with a polyvinylidene fluoride membrane（PVDF）containing hydrophobic groups（-F）to prepare ZJU-64-CH₃/PVDF composite membrane and improve oil-water separation effect of ZJU-64-CH₃.The composite membrane not only increased the contact angle of ZJU-64-CH₃to water（from 80.40°to 130°）and enhanced its hydrophobicity,but also increased the elongation of PVDF and improved its mechanical properties.The oil adsorption and oil-water separation effects were tested using adsorbents ZJU-64-CH₃,PVDF,and composite membranes.The results showed that compared to ZJU-64-CH₃,the composite membrane had better oil adsorption and oil-water separation performance,with the maximum oil flux of 333.33 L/（m²·h）and the maximum separation efficiency of 99%.In addition,the composite membrane had good recyclability and satisfactory cycling performance.It still had high separation efficiency and oil flux after 12 cycles,indicating that the composite membrane is expected to be applied in the field of oil-water separation.