A Study On Graphene Oxide Nanocomposite Membrane

With the rapid development of nano-technology in recent years, nanomaterials have been used to prepare membranes with enhanced performance, which provides a new direction for the progress of membrane technology. For the first time, we adopted the nano-sheets of graphene oxide in the preparation of graphene oxide/polysulfone (PSf) composite ultrafiltration membrane and graphene oxide/Nafion composite proton exchange membrane, and investigated their properties respectively.Graphene oxide were prepared by using a modified Hummers method combined with ultrasonication. Results showed that the prepared nanoplatelets of graphene oxide have rough surface and both single-layer and multi-layer platelets exist. The nanoplatelets can form stable dispersions in water and polar solvents such as DMAc, NMP because of electrostatic repulsion. It presents similar chemical structure to graphite oxide, which indicated that ultrasonication just exfoliate the layer and did not destroy oxygen-containing functional groups on the layer's surface. It also has good thermal stability and the complete weight loss temperature can reach 630℃.Graphene oxide is not a good electronic conductor because it lacked an extendedπ-conjugated orbital system. The electrical conductivity of graphene oxide product is 1.74×10^-9S/m. But it conducts proton much better, with a proton conductivity of 6.85×10^-5S/cm.Immersion phase inversion method was adopted to prepare graphene oxide/PSf composite UF membranes. Results revealed that graphene oxide could affect membrane's interior structure evidently, the porocity and mean pore size had been changed accordingly. In addition transverse pores present when the content of graphene oxide was high. The contact angle of the composite membrane was decreased, indicating improved hydrophilicity of the membrane. The composite membranes showed 1.3 times higher pure water flux than PSf membrane with inapparent decline of BSA rejection. Breaking strength of the composite membrane increased dramatically, which can be 2 times as high as that of PSf membrane. The increase of mechanical strength resulted from graphene oxide embedment is more markedly in dense membrane than in porous membrane. Both PSf and composite membranes have high thermal stability.Graphene oxide/Nafion composite proton exchange membrane had been prepared. The composite membrane has good thermal stability and presents better dimensional stability at high temperature. The contact angle of the composite membrane becomes smaller which indicated the hydrophilicith of the composite membrane is improved. The breaking strength of the composite membrane can reach to 22.39MPa, a 44% increase compared with recast Nafion membrane. All the composite membranes have better methanol resistance and they retain high proton conductivity as Nafion. When the temperature is higher than 120℃, the proton conductivity of recast Nafion membrane begin to decrease, while that of composite membrane continue to rise.