Preparation And Performance Regulation Of Graphene Based Filter Membrane

The pollution caused by industrial development and the demand caused by the increase of the total population has accelerated the shortage of water resources,and it is urgent to find a sustainable source of fresh water.Pressure-driven nanofiltration membranes shine in water treatment applications due to their simple operation,low investment cost,and low energy consumption.Two-dimensional sheet graphene oxide（GO）membranes are simple to fabricate and contain numerous functionalizable reaction sites,which have broad application prospects in membrane separation.However,when graphene oxide is used to prepare a separation membrane,because the oxygen-containing functional groups on graphene oxide are easy to bond with water molecules,the d-spacing between graphene oxide nanosheets increases,which weakens the force between the sheets and leads to oxidation.The retention rate of the graphene membrane is reduced,and the stability is weakened,which seriously reduces the service life of the membrane.In order to improve the stability of the membrane and obtain good retention performance,GO is the main raw material,and the following two different methods are used to prepare different nanofiltration membranes to achieve the above purpose.（1）Graphene oxide was prepared by the modified Hummers method,and polyethyleneimine（PEI）and 1-（3-dimethylaminopropyl）-3-ethylcarbodiimide（EDC）were used to prepare graphene oxide.PGO was successfully prepared by cross-linking.The composite membrane of PGO/GO/PGO"sandwich"structure was prepared by vacuum-assisted filtration using PGO and GO as materials.The research shows that the cross-linked PGO dispersion is positively charged and can be well complexed with negatively charged GO,and the PGO film has high stability under the cross-linking of PEI chains.The interlayers of PGO are relatively loose,mainly because the addition of PEI chains increases the d-spacing,which results in a relatively weak retention rate of the PGO film;in contrast,the d-spacing of the GO layer is relatively tight,and there are two layers of PGO.The swelling phenomenon of the middle GO layer was alleviated,so the retention rate of the GO layer was relatively good.In general,the PGO/GO/PGO film played the main retention role in the middle GO layer.With the reduction of hydrophilic functional groups,the hydrophilicity of PGO is slightly lower than that of GO,but it still exhibits hydrophilic characteristics,which can improve the flow rate of water and prevent pollution.By testing the water flux and rejection rate of PGO/GO/GPO membranes with different loadings（400μg,800μg,1 mg and 1.2 mg）,after comprehensive analysis,it is concluded that when the loading is 1mg,PGO/GO/GPO-3 The retention rate and retention rate of the membrane reached the optimal equilibrium point.At this time,the water flux reached 42.02L/m²·h·bar,the rejection rate of salt was 84%,and the rejection rate of dye was 100%.The PGO/GO/GPO-3 films were not damaged under long-term soaking（30days）,while the GO film showed signs of damage after soaking for 3 days.In addition,the membrane was operated in a free diffusion system for 120 hours,and the rejection rate of the membrane for dyes and salts remained relatively stable,indicating that this structure has an outstanding improvement in membrane performance.（2）Holes graphene oxide（HGO）was prepared by the reaction of H₂O₂ and GO by etching method.Methylene blue（MB）was used as intercalation agent to mix in HGO dispersion,and HGO/MB composite was prepared by vacuum filtration.membrane.The specific surface area of HGO is larger than that of GO through characterization,which can explain the existence of HGO nanopores,and the pore size of these nanopores is concentrated between 1-3 nm.And the existence of nanopores leads to the increase of defects and wrinkles in the HGO membrane,but the addition of MB can reduce the existence of these wrinkles,which will correspondingly reduce the water flux of the membrane.The insertion of MB did not increase the d-spacing of the membrane in the dry condition,and the d-spacing of the membrane decreased slightly when the content of MB was increased to 300μL.The hydrophilicity of HGO is lower than that of GO.After adding a certain amount of MB,the hydrophilicity is improved,but as the amount continues to increase,the hydrophilicity is weakened.By testing the performance of HGO/MB membranes with different amounts of MB,we found that the membrane water flux of HGO/MB-100 can reach 21.34 L/m²·h·bar,which is 7 times that of GO membrane.And the rejection rate of Na2SO4 reaches 83.2%,the rejection rate of methyl orange is above 93%,the highest can reach 95.9%,the rejection rate of Rhodamine B is above 97%,and the highest is 98.9%.In the water environment,the HGO/MB membrane was not damaged by ultrasound for 15 min,and the GO membrane started to be damaged at 5 min.