Preparation Of UiO-66-NH₂ Based Composite Membrane And Its Application In Water Treatmen

Water environment pollution and water shortage have become difficulties and challenges facing the world.Membrane technology has been widely used and developed as an environmentally friendly new generation of water treatment method.Due to its own limitations,polymer membranes need to be further optimized and improved.The introduction of nanomaterials can greatly improve the separation performance and anti-pollution ability of polymer membranes.Metal organic frameworks(MOFs),as a type of frame structure material formed by combining metal ions and organic links,have the characteristics of high surface area and pore volume,low density and abundant adsorption sites.With the emergence of waterstabilized MOFs,its own structural characteristics and its adsorption,photocatalytic properties have been fully applied in water treatment.By choosing a suitable MOF material—UiO-66NH2,nanocomposite membranes based on the material were prepared with adsorption characteristics,photocatalytic characteristics and physical structure as the separation and purification mechanism.The three kinds.of nanocomposite membranes were applied to different types of wastewater treatment to evaluate the separation and purification performance of the corresponding nanocomposite membranes.The specific research contents of this paper are as follows:(1)A PAA@UiO composite material was obtained by combining UiO-66-NH2 and polyacrylic acid(PAA),and a PAA@UiO/GO composite membrane was prepared by inserting PAA@UiO into GO nanosheets.The addition of PAA@UiO expands the interlayer distance between GO nanosheets,forming a larger water channel,which helps the passage of water molecules.Instead,PAA@UiO forms a lateral distribution between GO nanosheets with screening and adsorption.The PAA@UiO/GO composite membrane prepared by increasing the functional structure of the membrane reached a flux of about 100 L·m-2·h-1 when performing separation experiments on three dye wastewaters(MB,CR,and RB)which can be completely removed.In addition,the PAA@UiO/GO composite membrane maintains a stable removal rate of the dye molecules in water environment with certain acidity,alkalinity or ionic strength.The prepared composite membrane was used to perform a cyclic separation experiment which find the removal rate and flux of dye wastewater by the PAA@UiO/GO composite membrane can be maintained at 95%and 85 L·m-2·h-1 or more after 10 cycles,respectively.(2)AgCO@UiO photocatalytic composite material with good visible light response were prepared by depositing silver carbonate(Ag2CO3)on UiO-66-NH2.AgCO@UiO photocatalytic material embedding in GO nanosheets to obtain AgCO@UiO/GO photocatalytic composite membrane.The addition of AgCO@UiO photocatalytic material can expand the water channel between GO nanosheets which can screen and adsorb some pollutants due to the presence of UiO-66-NH2.In addition,AgCO@UiO has photocatalytic properties that can degrade organic pollutants or reduce high-value heavy metals by photocatalysis in the water channels in the membrane and membrane surfaces.GO can further promote the separation of photo-generated electrons and holes,which can enhance the photocatalytic effect to increase the removal effect of the membrane on pollutants.Under light conditions,the AgCO@UiO/GO photocatalytic composite membrane can completely remove MB,RB,MR and Cr(Ⅵ),while the flux can reach 50 L·m-2·h-1.The dye and Cr(Ⅵ)wastewaters were used for 10 consecutive filtration experiments in the presence and absence of light,it was found that the removal rate of the above pollutants by the AgCO@UiO/GO composite membrane was higher in the light condition than no light condition.In addition,the former’s final flux loss rate is less than 10%,while the latter reaches about 30%.(3)UiO-66-NH2 was loaded on a polymer membrane with chitosan(CS)as an adhesive to prepare a UiO/CS composite membrane for oil-water separation.A large number of amino groups and framework structures on the surface of UiO-66-NH2 can well penetrate water molecules and retain oil droplets.UiO/CS composite membrane showed good stability in extreme acidity,alkalinity or high salinity water environments.When dichloromethane,petroleum ether,dodecane,and gasoline oil-water emulsions were used as separation objects,the UiO/CS composite membrane showed significantly better removal effect than the original membrane.Taking gasoline oil-water emulsion as the object,after 10 cycles of experiments,the flux of the UiO/CS composite membrane in the filtration process can finally be maintained at about 500 L·m-2·h-1,while the flux of the original membrane was only about 100 L·m-2·h-1.