Preparation And Properties Of Graphene Oxide-Polyacrylonitrile Based Nanofiltration Membranes

Membrane separation technology has the advantages of efficient separation,concentration,purification.Recently,with the increasing of wastewater treatment from the growing demand for water resources and water standards,nanofiltration membrane research has been greatly improved.Nanofiltration(NF)membrane owns separation characteristics boundary between reverse osmosis(RO)and ultrafiltraton(UF)membrane,which can intercept solute with molecular weight between 200-1000 Da.NF membrane has wide applications including demineralization of water,small organic molecular separation,dyeing wastewater treatment,food industry and so on.Traditional NF preparation methods such as nonsolvent-induced phase separation(NIPS)and interfacial polymerization may cause some problems,i.e.low membrane strength,poor structural controllability and peeling of active layer,which lead to instability of the membrane structure and performance.Polyacrylonitrile(PAN)has been used to prepare ultrafiltration membrane and support membranes of RO owing to it high glass transition temperature,high hydrophilicity,good solvent and thermal stability.Due to the strong polarity of cyan in polyacrylonitrile structure,the molecular chain is difficult to rotate,which lead to poor mechanical strength and toughness and limits its further application.Organic-inorganic hybrid membranes are believed to own the advantages originated from both the organic and the inorganic component,which is an importance development direction of membranes.Graphene oxide(GO),a derivative of graphene,has two dimensional structure,good hydrophilicity,high specific surface area and mechanical properties,which is an ideal modified material of polymer membranes.Our present work focuses on preparing NF membranes with proper structure,good separation performance,excellent mechanical and antifouling properties via TIPS and molecular layer-by-layer assembly(m Lb L)process.GO/PAN blend membrane was prepared via TIPS,which show excellent overall performance,i.e.high permeation,good antifouling,wonderful mechanical strength and dye rejection,etc.The blend membrane is suitable for dye waste-water treatment and dye/salt fractionation.The effect of the additives,polymer concentration and quenching bath on structure and performance of the PAN membranes were investigated.It was found that the membrane prepared with glycerol has better performance due to it poor compatibility with PAN,low polar fraction and molecular weight.With the increasing of polymer concentration,the structure of membranes becomes denser and the phase separation temperature rise.The morphology of the membranes become loose with the decreasing of cooling rate,which leads to high porosity and water flux.GO/PAN membranes were prepared by mixing GO with diluent via a solvent-exchange method.The incorporation of 0.2 wt% GO endowed membrane with excellent performance,the water flux increased by 83% compared to the pure membrane.The blend membrane shows high dye rejection and low salt rejection.The flux recovery ratio and tensile strength reached to 84% and 12.46 MPa respectively due to the hydrophilic and enhancement effect of GO.High-flux GO/PAN blend membrane was aminating modificated and applied as substrate membrane.NF membranes were prepared via interfacial polymerization(IP)and m Lb L process,amino on amination modified membrane can improve adhesion strength between substrate and active layers.In contrast to IP method,NF membrane prepared by m Lb L process is more stable and easy to control the charge of membrane surface.NF membranes prepared by m-phenylenediamine with rigid structure show better separation performace than diethylenetriamine with flexible structure.With the increase of the layer number,the water flux decrease and the salt rejection increase.GO was deposited on m Lb L NF membrane to enhance membrane performance,the optimal concentration of graphene oxide solution was 1 mg/ml.The concentration of monomers,polymerization time,heat treatment temperature were modulated to improve membrane performance.The composite NF membrane exhibited high salt rejection of 74.7 for Na2SO4 and excellent antifouling properties,the water flux recovery rate is up to 91.3% due to the good fouling resistance of GO on the membrane surface.