Structural Design Of Carbon Nanomaterial/polymer High Flux Composite Forward Osmosis Membrane

Forward osmosis is a very promising membrane separation technology,which has many advantages that other membrane separation processes do not have,such as low energy consumption,low cost of membrane formation,high efficiency,wide separation range and so on.These characteristics make it has great application prospect in seawater desalination and wastewater treatment.However,phenomenon of concentration polarization exists in the process of forward osmosis.Nanoparticles have been introduced into the preparation of forward osmosis membranes to improve the performance of forward osmosis membranes.However,these studies were focused on the doping of single one-dimensional or two-dimensional nanomaterials,and nanomaterials were prone to agglomeration in the interfacial polymerization layer.This topic will be continued on the basis of the existing researches by using polyethersulfone membrane as substrate membrane.The polyvinyl alcohol(PVA)layer was set up to improve hydrophilicity of membrane,and graphene oxide was added into the interfacial polymerization layer to further increase water channels and enhance hydrophilicity.It could be concluded that all the peak-and-valley structures of interfacial polymerization were obtained.The surface of the forward osmosis membrane became smoother and the surface roughness decreased after addition of graphene oxide.The hydrophilicity of forward osmosis membrane after coated by PVA was stronger than that coated without PVA,while the water flux showed a lower value.The water flux of the forward osmosis membrane increased when graphene oxide was added to the interfacial polymerization layer.The salt flux reached the lowest value when the content of graphene oxide reached 500 ppm,and meanwhile the water flux and salt flux reached the balance.On the basis of above researches,further modification was carried out by reducing the content of polyethersulfone in the support layer and removing PVA layer.The interfacial polymerization layer was modified by synergistic reaction of carbon nanotubes and graphene oxide(GO).The results from X-ray photoelectron spectroscopy(XPS)showed that the ratio of C=O increased from 5%to 5.81%with the cooperation of GO and OCNTs,indicating that synergistic reaction of GO and OCNTs reduced the crosslinking degree of interfacial polymerization layer.The results from scanning electron microscopy and transmission electron microscopy showed that GO and OCNT linked together and evenly distributed in the interfacial polymerization layer.The surface morphology of interfacial polymerization layer is based on structure of GO and OCNTs instead of independent peak-and-valley structure,which indicates that GO and OCNTs join interfacial polymerization reaction and reduce the crosslinking degree.The water flux and salt flux of forward osmosis membrane reached 114 LMH and 5.17 gMH respectively under the synergistic effect of GO and OCNT,and the structure coefficient S value(201.8 um)was lower.Finally,a forward osmosis membrane with ideal comprehensive performance was obtained.One-dimensional carbon nanotubes and two-dimensional graphene oxide can be connected by functional groups and polymer chains,and carbon nanotubes support graphene oxide sheets to form unique channels to enhance water flux.