Preparation And Properties Of Graphene Oxide-Modified Nanofiltration Membrane

Nanofiltration has many advantages of partial removal of monovalent ions,low-pressure operation,low osmotic-pressure,and energy saving.The technology shows great prospect of application in sea water desalination and sewage disposal.In this research the polysulfone?PSF?hollow fiber ultrafiltration membrane was appliedas the basement membrane to prepare composite nanofiltration membrane via interfacial polymerization reaction and bidirectional coating process.The hydrophilic modification of composite nanofiltration membrane was conducted,and the effect of GO on the structure and properties of the modified membrane was discussed with graphene oxide?GO?as the modifier.In this paper,firstly,the optimum process conditions for preparation of polysulfone nanofiltration membrane were first discussed.The best preparation process was determinedby investigating the effect of piperazine?PIP?dosage,water phase coating time,trimesoyl chloride?TMC?dosage,interfacial polymerization time and heat treatment temperature on membrane properties.And thebest-optimizedparameterswerethat the concentration of PIP is1wt%;Water phase reaction time is 6 min,and water phase coating pressure is 0.05 MPa;The concentration of TMC is 0.22wt%;Interfacial polymerization time is 5 min;Reaction and heat treatment temperature are 20? and 60?.The pure water flux is about 13.4L/?m²·h?under 0.5Mpa,and removal rate of MgSO₄ is about 90%.The amide functional group was confirmed by IR.And it was found by SEM and AFM that the inner surface of composite nanofiltration membrane was relatively rough.There is a prominent mountain ridge on the surface,which indicated that an ultra-thin functional layer was formed.GO was synthesized by improved Hummers method,and was characterized by TEM,XRD and FTIR.Hydroxyl,carboxyl and carbonyl oxygen hydrophilic functional groups were observed in laminar-structure GO.Then GO was blended into coating solution.The effect of the content of GO on membrane structure and permeability was investigated.It is found that When the content of GO was 0.05wt%,the membrane with optimal performance was obtained.The membrane water flux was 20.8L/?m²·h?,and removal rate of MgSO₄ is about76.8%.The membrane modified by GO shows the lower adsorption amount of BSA,and presents higher flux recovery ratio and lower flux decline rate than pure membrane.At last,the NF membrane was used for treatment of sewage.The experiment shows that compared to the unmodified membrane,the water flux of the modified membrane decreases slowly;and the rejection rate of COD,hardness and chroma are 83.0%,77.1%and 91%,respectively,which lower than that of unmodified membrane.The membrane modified by GO showed lighter polluting than unmodified membrane.And the membrane fouling is mainly resulted from loosed cake layer formed on the membrane surface.