Mocular-pillared Reduced Graphene Oxide Membrane And Its Permeation Performance

As a new separation technology,membrane separation technology holds the advantages of economy,cleanliness,less land occupation and mild operation conditions.Membrane is the core of membrane separation technology.However,at present,separation membranes are facing the trade-off effect,which makes it difficult to obtain separation membranes with both good flux and selectivity.Therefore,it is necessary to develop new membrane materials to overcome this challenge.Graphene-based materials,as a new type of carbon materials,with ultra-thin thickness,excellent mechanical properties and stable chemical properties,have become a new research hotspot in many fields,including membrane separation.As an important derivative of graphene,graphene oxide（GO）has the advantages of easy dispersion,convenient modification and economical large-scale preparation.Therefore,layer-by-layer self-assembled membranes prepared from GO have better application prospects.GO membranes with better osmotic separation performance can be obtained by modifying GO properly to improve the physical and chemical properties of interlayer channels.GO was prepared by improved Hummers method and GO nanosheets were pillared by2-methylimidazole.The rGO membranes pillared by imidazole（rGO-MeIm）were prepared by dispersion evaporation method and pressure-assisted self-assembly method,respectively.The microstructures of the membranes were characterized by XRD,FTIR,XPS,elemental analysis,thermogravimetry,AFM and FESEM.The gas permeability and ion permeability of the membranes were tested and the following results were obtained:1.The rGO-MeIm membrane with complete structure can be obtained by dispersion evaporation method.After heat treatment,some of the membranes have been effectively pillared.The gas permeation of rGO-MeIm membrane increases with the increasing of MeIm mass fraction.The selectivity of H₂/CO₂ and H₂/N₂ is slightly higher than that of Knudsen diffusion.2.rGO-MeIm membranes with complete structure and thinner thickness can be obtained by pressure-assisted layer-by-layer self-assembly.Compared with PVDF membrane,thinner membrane with PES as the substrate membrane can be more easily obtained.With the introduction of MeIm,the interlayer spacing of GO increases,and the interlayer spacing decreases with the increasing of heat treatment temperature.Dehydration and the ring opening reactions of carboxyl and epoxy groups occur between MeIm and GO nanosheet.Due to the introduction of MeIm,rGO-MeIm membrane is slightly reduced,but its reduction degree is not as high as the membrane reduced by hydrazine hydrate.3.The gas permeation of rGO-MeIm membrane is significantly higher than that of GO membrane and with the decrease of membrane thickness,the gas permeation of rGO-MeIm membranes increases gradually.The gas permeation of rGO-MeIm membrane is the highest when the heat treatment temperature is 120℃ and the membrane thickness is 25 nm,which is1174.4 GPU.The selectivity of H₂/CO₂ and H₂/N₂ of rGO-MeIm membrane is slightly higher than that of Knudsen diffusion.The selectivity of rGO-MeIm membrane can not be improved significantly by changing the preparation method.However,rGO-MeIm membrane has good selectivity for propane and butane gases with larger molecular sizes.The selectivity of H₂/n-C₄H₁₀ is 17.53.4.The ion permeation rate of rGO-MeIm membrane is lower than that of GO membrane because of their smaller interlayer channel size in wet state.The permeation rate of rGO-MeIm membrane for different types of metal ions is different from that of ordinary GO membranes,in which alkaline earth metal ions are the largest and transition metal ions are the smal est.This is related to the interaction between MeIm and metal ions.