Preparation And Evaluation Of Graphene Oxide Composite Forward Osmosis Membrane

Forward osmosis（FO）technology has attracted great attention due to its low energy consumption and no external pressure drive.At present,the simultaneous improvement of the water flux（J_v）and the salt rejection rate（R）of the FO membrane and the reduction of the internal concentration polarization（ICP）have become practical requirements.The key to solving such problems lies in the membrane material itself.In this project,graphene oxide（GO）was selected to dope and modify thin film composite forward osmosis（TFC-FO）membranes,in order to obtain the high-permeability graphene oxide TFC-FO（GO-TFC-FO）membranes.The quantum size effect of nanoparticles,the physical and chemical properties of GO of different sizes are significantly different.Three sizes of GO（50～150 nm,0.2～10μm and over 10μm）were doped in polysulfone（PSF）support layer of TFC-FO membrane to form GO-TFC-FO membrane by interfacial polymerization（IP）reaction.After GO modification,the nano-water channels of GO-doped membranes with 50～150 nm and 0.2～10μm increased,the porosity increased,and the hydrophilicity was significantly enhanced.The results of the forward osmosis experiment show that:at the optimal doping amount,the 0.2～10μm GO-doped membrane had the largest J_v(95.9 L·m^-2·h^-1),and R reached 96.8%;the J_v of the50～150 nm GO-doped film reached the upper middle level(51.5 L·m^-2·h^-1),and R was greater than 99%,which indicated that the difference between J_v and R was related to the formation of membrane structure.The SEM image shows that the increase of membrane pores in 0.2～10μm GO-doped membrane was conducive to the increase of J_v,but the anti-salt flux（J_s）also increased(9.5 g·m^-2·h^-1).The membrane pores formed by the GO-doped membrane of 50～150 nm were slightly uniform and dense,which was helpful for the retention of impurity ions,and J_s was less than 1g·m^-2·h^-1.Among the above three GO-TFC-FO membranes with different GO sizes,GO-doped membranes with 50～150 nm have a higher J_v,the largest R,and the smallest J_s.Then,50～150 nm GO was selected to modify the active layer of the composite film,and the support layer and active layer of the TFC-FO film were simultaneously doped,which were compared with the GO-doped support layer composite film.FTIR and XPS characterization proved that GO reacted with MPD and TMC to form polyamide groups.When the support layer and active layer were respectively doped with GO,the percentages of C=O（15.07%,10.15%）and N-C=O（44.73%,42.90%）were higher than those of the bilayer composite film doped with GO（C=O:9.79%;N-C=O:32.14%）.SEM images show that the GO single layer doping of the support or active layer can form the uniform water channel perpendicular to the surface of the film,which was conducive to reducing ICP and improving the water flux,but the bilayer doping with GO was not beneficial to the structure of the TFC-FO film formation.At the optimal doping amount,J_v(54.854 L·m^-2·h^-1)of the GO-doped composite film in the active layer was slightly higher than J_v(51.47 L·m^-2·h^-1)of the GO-doped composite film in the support layer.Lastly,0.2～10μm and 50～150 nm GO was respectively doped in the PSF support layer composite film,and 50～150 nm GO was doped in the PA active layer composite film were used to evaluate the desalination effect of simulated seawater(0.6 mol·L^-1 Na Cl).Compared with the control group（12.66%）,1 mol·L^-1 Mg Cl₂was used as the draw solution,the water fluxes of the above three membranes increased by 33.82%,21.17%,and 32.35%,respectively.The salt fluxes of the three membranes tested with 2.5 mol·L^-1 Mg Cl₂ as the draw solution,the results showed thant the salt fluxes were all lower than 20 g·m^-2·h^-1 during the 9 h experiment.Therefore,the 0.2～10μm GO modified PSF support layer composite membrane and the 50～150 nm GO modified PA active layer composite membrane have practical application value in seawater desalination.