Preparation Of Iron Oxide/graphene Composite Nanofiltration Membranes And Their Application In Water Treatment

Among the many water treatment methods,nanofiltration membrane separation technology has received extensive attention due to its advantages of high efficiency,low cost,low energy consumption and easy operation.Compared with traditional polymer nanofiltration membrane materials,the inorganic nanofiltration membrane material has many advantages,such as corrosion resistance,high-temperature resistance,stable chemical properties,stable appearance,easy to clean and has a long service life.Therefore,research on inorganic nanofiltration membrane materials has received more and more attention.Among them,graphene material has advantages of the unique two-dimensional layered structure,rich surface oxygen-containing functional groups,good flexibility,chemical stability and strong hydrophilicity,so it has become the choice for the preparation of nanofiltration membranes.Although the dense layered-stacking structure of graphene nanofiltration membranes can ensure a high rejection rate for the contaminant molecules,there are also problems of low flux and contamination of the nanofiltration membrane during the long-term separation experiment.These problems have limited their application in the field of sewage treatment.In order to solve the above problems,this subject is mainly to improve the separation performance and anti-fouling property of graphene nanofiltration membranes by uniformly loading iron oxide(?-Fe-2O3)with photocatalytic property on graphene sheets The specific research contents are as follows(1)In view of the low flux and membrane fouling problems of graphene-based nanofiltration membranes,the ?-Fe2O3/GO composite nanofiltration membrane is prepared by uniformly loading ?-Fe2O3 on the graphene oxide(GO)sheets by vacuum filtration.The addition of ?-Fe2O3 can appropriately adjust the interlayer spacing of the nanofiltration membrane,thereby improving the separation performance.The separation experiment results show that after adding 0.15 mg ?-Fe2O3 to the 0.25 mg GO nanofiltration membrane,the interlayer spacing increases from 0.73 nm to 0.83 nm,and the permeation flux to 20 ppm methyl orange(MO)solution is increased from 2.99 L m-2 h-1 bar-1 to 6.03 L m-2 h-1 bar-1,and the rejection rate is maintained above 97%.At the same time,this composite nanofiltration membrane has better separation performance for low concentration of 2 ppm MO solution,and the permeation flux is as high as 16.92 L m-2 h-bar-,and the rejection rate is 98.53%.In addition,the photocatalytic property possessed by ?-Fe-O3 can also endow "self-cleaning" function to the composite nanofiltration membrane,thereby improving the anti-fouling property.Anti-fouling test results show that this ?-Fe2O3/GO composite nanofiltration membrane after separating 20 ppm MO solution for five cycles,its rejection rate can recover to 94.70%of initial rejection rate only by 4 h visible light irradiation,and the permeation flux remains unchanged.This indicates that the addition of ?-Fe2O3 is suitable for improving the separation performance and anti-fouling property of graphene-based nanofiltration membranes.(2)When the graphene-based nanofiltration membrane is in an aqueous environment for a long time,structural instability occurs.Therefore,in order to solve this potential problem,GO is reduced to reduced graphene oxide(RGO)by hydrothermal method,and ?-Fe2O3/RGO composite nanofiltration membrane is prepared by vacuum filtration.The characterization results show that the hydrophilicity of the RGO surface decreases after GO is reduced,and this can help solve the problem of swelling and redissolution.Moreover,the number of oxygen-containing function groups on the surface of RGO is decreasing,and this will reduce the transmission resistance of water molecules during the membrane separation process,which is beneficial to increase the permeation flux.At the same time,?-Fe2O3 is uniformly embedded in the RGO sheets,which is beneficial to improve the separation performance and anti-fouling property of the composite nanofiltration membrane.The separation experiment results show that the permeation flux of ?-Fe2O3/GO composite nanofiltration membranes to 20 ppm MO solution reaches 38.01 L m-2 h-1 bar-1,and the rejection rate is 93.52%.Anti-fouling test results show that this composite nanofiltration membrane remains stable during cycling process,and after being contaminated,its permeation flux could return to 91.90%of the initial permeation flux only after 4 h visible light irradiation,and the rejection rate remains above 94%.The excellent separation performance and cycle performance of ?-Fe2O3/RGO composite nanofiltration membranes are mainly due to the proper reduction of graphene,so the proper reduction of graphene material and the addition of ?-Fe2O3 can both be used to improve the performance of graphene-based nanofiltration membranes.