Fabrication Of Graphene Oxide Based Forward Osmosis Membrane And Its Separation Performance

As atomic thick 2D nanometer material,Graphene Oxide?GO?has many excellent performances,such as good mechanical property,high specific area,favorable structure stability etc.Graphene oxide laminar membrane,an ideal membrane material,shows good hydrophilicity,high water permeability and selective solute retention.It has aroused wide attention in fields,like seawater desalination,oil/water and gas separation etc.Forward Osmosis?FO?technique,driven by the osmosis pressure difference????between two sides of semi-permeable membrane,is a novel membrane separation technique.Compared with traditional membrane technique,FO technique has many advantages,such as low energy consumption,low membrane fouling,high recovery rates and zero emission etc.,those make it one hot spot in the field of membrane separation technique.However,because of the structure of FO membrane,the water flux decreases dramatically for the Internal Concentration Polarization?ICP?in supporting layer and solute reverse osmosis phenomenon in active layer,that limits the development of FO technique in practical application.Therefore,it is important to search for the novel FO membrane for reducing the effect of ICP and solute reverse osmosis phenomenon to popularize the application of FO technique.In this dissertation,GO and porous graphene oxide were used as starting materials,based on thermallyinduced chemical crosslinking,different types of graphene oxide based forward osmosis membranes have been prepared,and a series of performances have been tested in FO process.The research contents included in the following two aspects:?1?Preparation of ultrathin freestanding graphene oxide laminar membrane and its separation performance in FO process.The Ultrathin Freestanding Graphene Oxide Laminar?UFGOL?membrane,with thickness ¹ ?m,has been prepared by self-assembling through vacuum filtration and then cross-linked with Propanedioic Acid?PA?.The chemical structure analyzing show that graphene oxide sheets in UFGOL membrane has been successfully cross-linked by PA and also partially reduced during the annealing treatment.The XRD spectrums in dry and wet state illustrates the interlayer spacing between graphene oxide layers can be effectively controlled by PA and the stability enhanced.The prepared UFGOL membranes were evaluated in FO separation process,the result demonstrates the water flux of it is 35 L m^-2h^-1,while the reverse permeation rate for Na⁺ is 0.56 mol m^-2h^-1 when using 2 mol L^-1 Na Cl as brine solution and pure water as feed solution.By contrast,the water flux of membrane with support layer is 13.4 Lm-2h-1,which illustrates that ICP in FO process can be greatly diminished by removing support layer in UFGOL membrane.When engineered in organic dye and heavy metal solution separation process,UFGOL membrane can retain the organic dye?MO,RO?and Cu²⁺ completely,and shows excellent water purification property.?2?Engineering nano-pores on graphene oxide sheets via irradiation ‘etching',preparation of porous graphene oxide laminar composite membrane and its separation performance in FO process.HO· radical,one of the gamma-ray radiolysis products,was used to etch defects on the edge and in-plane of graphene oxide sheet,as a result,the nanoscale pores were emerged on it.The mechanism of etching nanopore on graphene oxide has been investigated and it has been demonstrated oxygen-containing groups were bonded to could be oxidized and removed by HO· radicals,leaving defects on graphene oxide sheets.Furthermore the diameter of nano-pore can be easily tuned by varying the ‘etching' time.Porous graphene oxide has been used as starting materials,Porous Graphene Oxide Laminar Composite?PGOLC?membrane was prepared by self-assembling through vacuum filtration then cross-linked with PA.The Contact angel and XRD measurements illustrate that the hydrophilicity of graphene oxide sheets has been enhanced and the interlayer spacing of graphene oxide sheets in wet state has been narrowed effectively by PA.Furthermore,the results of FO process test show that the water flux of PGOLC membrane is 34.7 L m^-2h^-1,while 14.2 L m^-2h^-1 for the normal graphene oxide laminar membrane when using 1 mol L^-1 Na Cl as brine solution and pure water as feed solution.Lastly,PGOLC membrane has been engineered in Rh.B solution FO separation process,the water flux of PGOLC membrane was 21.7 Lm-2h-1,while 6.7 L m^-2h^-1 for normal graphene oxide laminar membrane.That is because the nano-pores on porous graphene sheets provide more vertical channel for water molecule,which largely shorten the effective pass way in graphene oxide laminar membrane.In this dissertation,UFGOL membranes were prepared and effectively diminished the effect of ICP in FO process,which provides new research ideas for developing novel forward osmosis membrane.Meanwhile,engineering nanopore on graphene oxide sheets via irradiation etching to obtain PGOLC membrane with higher permeability was investigated,and provides new technical line for preparation highperformance graphene oxide laminar membrane.