Preparation And Separation Properties Of Graphene Oxide Crosslinked Composite Membrane

With the rapid development of China’s economy,technology and industrialization,the problem of water pollution is becoming more and more serious,which poses a serious threat to the natural environment and human health.Therefore,how to solve the problem of water pollution has become a hot topic.Among many water treatment methods,membrane separation technology is widely used in the field of wastewater treatment because of its advantages of simple operation,energy saving,environmental protection and less chemical residue,among which membrane separation material is the key.Graphene oxide（GO）,as a new two-dimensional material in the field of membrane materials,has attracted much attention due to its unique lamellar stacking structure,rich oxygen-containing functional groups and extremely stable chemical structure-However,the application of pure go membrane is greatly limited by the defects of compact stacking,low permeation flux and poor membrane stability.Based on this,this paper proposes a new method to improve the above problems of pure go Carbon nanotubes（CNTs）and silicon dioxide（SiO₂）nanoparticles are inserted into go lamelluc as "wedge",and the lamellar spacing is widened,so as to increase the permeation channel and coxstruct graphenc oxide compositc membrane structure with high permeation flux,high separation and high chemical stability.GO/CNTs and GO/SiO₂ composite membranes were prepared by vacuum filtration technology.The morphology,composition.wettability,oil-water separation performance and chemical stability of go based composite membranes before and after modification were compared:（1）Graphene oxide was prepared by improved Hummer’s method and freeze-drying technology The morphology and structure of graphene oxide were characterized.The results showed that the graphene oxide lamellae were single layer and thin yarn,and the thickness of graphene oxide was about 1.6 nm.The dispesions of graphene oxide dispersions were prepared by vacuum filtration to prepare the separation membranes.The effects of different GO content on the permeation flux and retention rate were studied.The results showed that the separation flux decreased from 756 L·m^-2·h^-1 to 165 L·m^-2·h^-1,and the retention rate of the toluene emulsion increased from 83.2%to 99.8%.Moreover,when the amount of graphene oxide is 3mL,the permeation flux and retention rate of the separation membrane can reach a equilibrium point,and the separation performance is the best.（2）The composite separation film of GO/SiO₂ was prepared by the combination of silica nanoparticles with small molecular crosslinker ethylenediamine,and then introduced into graphene oxide film by vacuum filtration.The microstructure observation shows that silica particles open the go layer and generate nanochannels,which increases the layer spacing of the original film from 0.81nm to 0.98nm,which significantly increases the permeability channel.Furthermore,the results of contact angle show that the surface hydrophilicity of the composite film is improved,and the contact angle decreases from 70.61 ° to 45.42 ° and the oil drainage performance is improved.The specific surface area of go composite film can be increased by silica modification,from 8.66 m²/g to 22.82 m²/g.At the same pressure,the permeability flux increased from 466 L·m^-2·h^-1 to 892 L·m^-2·h^-1 with the increase of silica addition.The retention rate of oil-water emulsion is above 99.0%,and the highest reaches 99.5%.The results of cyclic test show that the retention rate of GO/SiO₂ composite film can still be kept 99.6%after 6 cycles,and the structure stability is high.（3）The dispersion and hydrophilicity of CNTs were improved by pre oxidation treatment.GO/CNTs composite separation films were prepared by vacuum filtration method.The micro morphology observation showed that CNTs successfully acted as "nano wedges" to support the original tight go layers and form three-dimensional network channels.The results showed that the interlayer spacing of GO/CNTs composite membrane increased from 0.81nm to 0.96nm;the specific surface area（8.66 m²/g,21.14 m²/g）and pore volume（0.000653 cm³/g,0.004037 cm³/g）of GO and GO/CNTs composite membrane also increased,which improved the porosity of composite membrane and effectively increased the permeation channel during separation.After modification,the water contact angle of GO/CNTs composite film decreased from 71.17°to 19.62 ° and its hydrophilicity improved.The permeation flux can reach 1132 L·m^-2·h^-1 and the retention rate of oil-water emulsion reaches over 99%.