Selective Mass Transport Mechanism And Properties Of Graphene Oxide Membranes

The worldwide deepening crisis of clean and safe freshwater shortage and contamination has driven the rapid development of membrane-based filtration and separation technologies.The great progresses achieved by nanotechnologies in new materials field have provided possibilities for the fabrication of next-generation functional membranes with precisely designed composition and structure and tunable filtration and separation performances.Among the newly emerging materials,nanocarbon materials represented by carbon nanotubes,graphene and its derivatives are focused on and developed fast.In this thesis,the modified Hummers’ method and liquid exfoliation process were adopted to synthesize monolayer graphene oxide(GO)nanosheets.Using a series of liquid-phase membrane formation techniques such as drop-casting and vacuum filtration,GO membranes were prepared.Their selective mass transport properties and potential applications in filtration and separation were investigated.The mass transport properties and related mechanism were systematically investigated.The results indicate that liquid water experienced an ultrafast permeation through the nanocapillary channels within GO membrane,with a diffusivity ~5 orders of magnitude greater than the bulk diffusion case.These results might lay a foundation for the application of GO membranes in solution-based mass transport.On the other hand,significant selectivity could be achieved by a wide range of solutes dissolved in water permeating through GO membrane.A novel mechanism in relation to the excellent selectivity of GO membrane was proposed,which was confirmed by first-principles calculations and the different permeation rates of various ions through the target functional group decorated graphene membranes.The excellent selective mass transport properties of GO membrane resulted in potental applications in membrane separation,showing promises in wastewater treatment and reutilization,and the recovery of high purity acids from waste iron-based electrolytes in steel industry.By uniformly intercalating layered double hydroxide(LDH)nanosheets into the interlayer galleries of GO membranes,hetero-superlattice membranes based on two different kinds of nanosheets were fabricated and their ion transport properties were studied.The results reveal that cations bearing various valences could be effectively separated strictly according to their charges,independent of the cation and anion species.The excellent charge-guided ion separation performances of GO/LDH hybrid membranes endow great potential in areas such as wastewater purification and reutilization,chemical refinement and biomimetic selective ion transport.Water desalination properties of GO membranes were investigated,indicating that GO membranes exhibited intrinsic high water/ion selectivity in concentration gradientdriven diffusion,while the salt rejection(i.e.water/ion selectivity)was poor in pressuredriven filtration.This controversy was confirmed both experimentally and theoretically to be a result of the strong correlation of water/ion selectivity with the GO nanochannel length and applied pressure.The above results might lay a foundation for the optimization of GO membranes in water desalination.By uniformly intercalating titania(TO)nanosheets into GO laminates,assisted with UV reduction,novel hybrid membranes of reduced GO(RGO)/TO nanosheets were prepared,whose water desalination performances were greatly improved compared to pristine GO membranes.Comparing with the unreduced case,water permeation of RGO/TO hybrid membrane after 3 days of UV reduction could be preserved by ~60%,while salt permeation could be reduced to <5%,showing great promises in water desalination applications.