Preparation Of Polyamide/Carbon-Nanomaterial Composite Membranes And Their Application In Pervaporation Desalination

Pervaporation desalination has been widely studied due to its various advantages such as wide range of treatable salt concentration and low energy consumption.Satisfactory membrane materials are the key to achieve high pervaporation performances.So far,a variety of materials have been used in this desalination technology.Among them,the carbon-based graphene oxide and carbon nanotubes composite membranes have acquired much attention due to their good separation ability and high water permeation.Pure graphene oxide and carbon nanotubes membranes are susceptible to swelling under a large amount of aqueous solution,leading to the reduction in separation performance.In this thesis,graphene oxide or multi-walled carbon nanotubes were used as the intermediate layer,a top-layer of polyamide was introduced by interfacial polymerization for preparation of polyamide-graphene oxide and polyamide-multi-walled carbon nanotubes composite membranes with further applications in pervaporation desalination to achieve ideal separation performances.The polyamide-graphene oxide composite membranes were successfully developed on polyacrylonitrile substrate by vacuum-assisted filtration with subsequent interfacial polymerization.Through various characterization methods proved that the composite membranes possessed a complete surface structure and enhanced hydrophilicity.When subjected to pervaporation desalination,the effects of graphene oxide interlayer thickness,feed temperature and concentration on the separation performance were investigated.At the same time,the membrane stability of polyamide-graphene oxide composite membrane was studied.A series of experimental results indicated that the optimal graphene oxide interlayer thickness was determined to be 100nm.In this interlayer thickness,the water flux through prepared membranes could reach up to 26.7 kg m^-2 h^-1 with 99.99%salt rejection for 3.5 wt%Na Cl aqueous solution under 70°C.When the feed salt concentration was increased to 10 wt%,the high water flux(24.0 kg m^–2 h^–1)and the ideal rejection（99.99%）were still kept,which demonstrated the potential of the prepared composite membrane in the treatment of hypersaline solution.Moreover,satisfactory performance could be preserved in the long-term test for the prepared polyamide-graphene composite membrane.Polyamide-mulit-wall carbon nanotubes composite membranes were fabricated on hydrolyzing polyacrylonitrile substrate,and the influence of the substrate modification on the properties of the composite membranes was explored.In addition,the pervaporation desalination performance of the composite membranes for different feed temperatures,concentrations and salt solutions of different systems were also investigated.For 3.5 wt%Na Cl aqueous solution solution under 70°C,the highest permeability water flux of the composite membrane prepared with the modified substrate could reach 88.5 kg m^–2 h^–1,which was much higher than that of the composite membrane prepared with original substrate(33.1 kg m^–2 h^–1),the rejection of both were99.99%.Even with 10 wt%hypersaline solution as feed,the composite membrane also could achieve high permeation flux(40.8 kg m^–2 h^–1)and excellent ion rejection（99.99%）,which also could effectively deal with acidic brine.All the results demonstrate that polyamide-multi-wall carbon nanotubes composite membranes prepared in this study have great application prospects in practical pervaporation desalination of hypersaline seawater or aqueous solutions.