Research On The Design, Preparation And Performance Of Graphene-based Nanofiltration Membranes Based On Three-dimensional Channels

Graphene,as a material with two-dimensional of dense honeycomb crystal lattices structure,can be acted a good barrier material which is impermeable to any molecules,showing a great application potential in the field of membrane separation.The nanofiltration graphene-based membrane was prepared by layer-by-layer self-assembly to form the functional layer,which is supported on the surface of based-membrane.The three-dimensional water transport nanochannels,which formed by the defects and interlayer gaps of reduced graphene oxide(rGO)in the graphene-based membrane,can perform as a molecular sieve for water treatment.Only substances with a molecular radius smaller than the nanochannels size can pass.However,both the hydrophilic groups contained in the channels and narrow channels would also cause a considerable resistance for water permeation,limiting the flux of graphene-based membrane.It has become a main bottleneck for the current graphene-based membrane or other membrane.Given these deficiencies and based on the deep understanding membrane separation process,a novel-graphene-based membrane with stereo channels of three-dimensional structure was designed and fabricated,to obtain superior water flux and maintain its excellent exclusion performance.Besides,in-depth study on the membrane separation process was carried,which proposed to couple the membrane process and electrocatalytic technology to make the channel with electrocatalytic activity,achieving the functional graphene-based membrane development.In order to gain the dual purpose:reducing the resistance from hydrophilic groups for water permeation and expanding the interlayer spacing between graphene sheets for a wider nanochannel,the moderately reduced graphene oxide(rGO)was obtained by one-step hydrothermal treatment,and nanoparticles TiO2 were simultaneously loaded on the surface of rGO,forming rGO-TiO2 composites dispersion.Then 1-dimensional oxygen-functionalized carbon nanotubes(oCNT)were used to co-assembly with rGO-TiO2 to construct a novel three-dimensional water channels in the graphene-based membrane.Comprehensive characterization and permeation test showed that the nanoparticles oCNT and TiO2 are introduced in the interlayer spacing of rGO sheets,so that the rGO-TiO2/oCNT membrane has more pronounced 3-dimensional water channels.Further,we put forward using the water molecule as a secondary soft layer to support the rGO sheets,the graphene-based wet-membrane was fabricated by simple immersing water.Compared with the corresponding graphene-based dry-membrane,the morphology structure occurred a great change and the wet-membrane formed a dense surface and a larger interlayer spacing.The pure water flux of the wet-membrane and its rejection for Methyl blue(MB)achieves an astonishing improvement,far more than the current graphene-based membrane.Remarkably,the rejection of membrane for Methyl orange(MO)with smaller molecular radius was also investigated,and it was found that the wet-membrane possesses excellent adsorption property for organic contaminants.According to the results of membrane stability and adsorption tests,the mechanism of separation processes of graphene-based membrane was deeply analyzed.Based on the prepared graphene-based membrane structure and separation process,TiO2 was utilized to intercalate the interlayer space,more importantly,it can be simultaneously performed as electrocatalyst.TiO2 as catalyst shows excellent photoelectrocatalysis performance due to their special band structure.The graphene-based membrane was performed as both a filter and an anode.Combined with electrocatalytic technology,the membrane can give the channel with electrocatalytic activity,which can improve the removal for small-molecule contaminants by degradation.The way of membrane separation coupling electrocatalysis is promising to break the limit of the"trade-off'effect in the field of membrane.Compared to the non-electrocatalytic graphene-based membrane,the MO removal for membrane increased by more than 52%after coupling.The optimum component ratio of the membrane was investigated,suggesting that there is a suitable TiO2 and oCNT intercalation range for a stable catalytic performance.