Preparation Of GO/PVA Composite Membrane And Its Asymmetric Permeation Behavior

Graphene oxide have a good performance in the field of water treatment because of their excellent hydrophilicity and special two-dimensional nanochannels.However the individual graphene oxide film can’t be used alone in water treatment because it is unstable.In order to take full advantage of the excellent properties of graphene oxide,we obtained composite separation membranes with asymmetric permeation behavior by a layer-by-layer self-assembly method.Polyvinyl alcohol(PVA)and graphene oxide(GO)were crosslinked to polyvinylidene fluoride(PVDF)microfiltration membrane through glutaraldehyde(GA).We used improved Hummers method to prepare the GO dispersion.The GO dispersion was further prepared into graphene oxide with different reduction degrees(RGO)by hydrothermal reduction.The GO were charactered by XRD,XPS,TEM,FTIR and Raman.With the hydrothermal reaction time increased,the degree of reduction of graphene oxide increased.In a certain range,it showed reductive controllability,which provided the research foundation for the GO composite membrane with different reduction degree.Asymmetric permeability GO/PVA composite films with different layers were obtained by changing the number of assembly layers.The morphology and structure of the composite membrane were characterized by various test methods.It was found that GO/PVA was successfully cross-linked on the surface of PVDF membrane,and the structure became more perfect as the number of assembly layers increased.The water flux,interception and contact angle were used to study the performance of the composite membrane.The composite membrane with three layers was the best,and it had the obvious asymmetric permeability.Under the positive and negative pressure,its water flux value and rejection of PEG-20000 differed by about 25.0 times,respectively.Effects of PVA concentration on the morphology and structure of the three-layer composite membrane were also studied.The results showed that the low-concentration PVA was difficult to deposited on the membrane surface,while the high-concentration PVA was likely to cause the surface densification.The effect of the reduction degree of graphene oxide on the structure and separation performance of the composite membrane was investigated.The asymmetric permeability GO composite film with a low reduction degree can still maintain a good permeability under long-term operation for 6 h,and the recovery rate of water flux after pollution was 89.71%.It was showed that the GO composite membrane with lower reduction degree had better structural stability and anti-fouling performance.This work will provide a research basis for extending the working life of composite membranes and a new strategy for designing high-performance GO based separation membranes.