Preparation Of Metal-Organic Framework Composite Membrane And Study On Its Anti-fouling Property

Membrane separation technology,a new kind of modern separation technology,cannot only effectively intercept and remove the impurities and pollutants,but also recycle the available material in the waste water.At the same time,this technology has the advantages of low energy consumption,non-secondary pollution,simple device,easy operation and high efficiency and so on,which has been widely applied to effluent treatment and has good development prospects.But membrane fouling phenomenon inevitably exists in the membrane separation technology,which restricts its development.But membrane fouling phenomenon inevitably exists in the membrane separation technology,which restricts its development.Membrane pollution phenomenon is usually presented as the reduction of membrane permeation flux and separation efficiency,which will result in the increase of energy consumption and the decrease of the service life of the membrane.In turn,theprocessing costs will increase.Therefore,the preparation of membrane materials with better antifouling properties is of great significance in the water treatment,desalination and other fields.In this paper,in allusion to the problems about organic pollution of membrane and low efficiency of seawater desalination in the process of membrane separation,metal organic framework ZIF-8 was used as loading material.A novel layer-by-layer(LbL)technique was employed to sandwich ZIF-8 to prepare metal organic framework composite membrane with antipollution performance and high permeation flux.the seawater desalination properties of the prepared membrane materials studied in FO system.NOM used as a foulant,in a terminal filtration system,membrane fouling resistance was also studied,and its fouling mechanisms were discussed by virtue of XDLVO approach.The main research contents and results in this paper are presented as follows.(1)A novel layer-by-layer(LbL)technique was employed to sandwich ZIF-8 to prepare metal organic framework FO membrane.The characterization of SEM,AFM and XPS has proved that the membrane material has been successfully prepared,and a well-intergrown layer of ZIF-8 film was deposited and grew seamlessly from the FO support.simultaneously,the membrane surface became coarser.Metal organic framework FO membrane displayed a smaller contact angle,indicating that the active surfaces of ZIF-8 membranes were slightly more hydrophilic than that of the FO membrane,which result in organic pollutants deposition and adhesion on the surface of the membrane material prevented.In the forward osmosis device,the rejection of different valence salt ion for metal organic framework FO membrane was tested.KCl、NaCl、MgCl2 and CaCl2 was selected as the driving solution,deionized water as raw water,when 0.5%(w/v)ZIF-8 was loaded,the water flux of the membrane materials increased from 20LMH to 31LMH,and the increase was as high as 55%.Compared with FO membrane,it shows a low reverse salt flux,and has the best rejection of the salt ions in different valence states,which shows that the loading of ZIF-8 not only improves the permeation flux of membrane material,but also has good universality for the removal of salt ions in different valence state.(2)In the same way,to test the effect of ZIF-8 seeds on antifouling properties,HA、BSA and the mixture of HA/BSA solutions were filtrated using modified membrane in a terminal membrane system.It was found that compared with PES membrane,the water flux increased by 47%(from 82.18 L·m-2 ·h-1 to 120.78 L·m-2·h-1).When there was a precipitate layer of ZIF-8 on the membrane,the membrane fouling caused by NOM was significantly mitigated.J/J0 was increased,And with increasing the dose of ZIF-8,membrane flux decline was correspondingly decreased.The size and distribution of humic acid molecules in the filtrate were determined by GPC.It showed larger MW HA molecules were more easily rejected compared to the smaller MW HA molecules.Moreover,after physical and chemical cleaning the flux recoveries of the metal organic framework PES membrane is 84.5%and 95.9%.While the permeation flux of PES membrane was only 49.5%and 60.8%.The results showed that the metal organic framework PES membrane has good reversibility of the pollution.(3)According to XDLVO theory,the AGTOT of the metal organic framework PES membrane surfaces showed positive values,which signifies the resistance to membrane fouling,whereas a negative value would aggravate membrane fouling.After the deposition of HA on membrane surfaces,the zeta potential increased slightly but still remain negative.because the surface of the polluted membrane is deposited with more hydrophobic humic acid,which makes the hydrophilicity of the membrane decrease,but which still showed a good antipollution performance.