Controlled Preparation Of Graphene-based Membrane And Study On Its Separation Performance

In recent years,membrane separation technology has received extensive attention in solving environmental and resource problems.Compared with traditional separation methods,membrane-based separation technology has the advantages of high selectivity,energy saving and environmental protection.High permeability,high selectivity,strong thermal stability and chemical stability are the main properties required for ideal membranes.As a derivative material of graphene,graphene oxide（GO）has the advantages of single-atom layer two-dimensional structure,containing a large number of oxygen-containing functional groups,good hydrophilicity,antifouling,stable mechanical and chemical properties,and has great application potential in gas purification,pervaporation and wastewater treatment of membrane technology.However,the structure of pure GO membrane is dense,and water m olecules will form hydrogen bonds with oxygen-containing functional groups when passing through the oxidation region,which increases the flow resistance of water,resulting in low permeability.In addition,GO is prone to swelling in aqueous solution and has poor circulation stability.Therefore,for the above problems,we modified and optimized the GO membrane,and the main contents are as follows:（1）A separation membrane was prepared by combining porous graphene（PG）and GO using vacuum filtration method.The planar pores on PG shortened the mass transfer path and increased the interlayer spacing.At the same time,the hydrophobicity of PG itself can inhibit membrane swelling.The effects of different pore sizes（0 nm,30 nm,70 nm）and different mass ratios of PG（0 wt%,5 wt%,10 wt%,20 wt%,40 wt%,60wt%,80 wt%,and 100 wt%）on the performance of separation membranes were studied.Through performance testing,it was found that the optimal pore size and composite ratio were PG with a pore diameter of 70 nm and a mass ratio of about 40 wt%.The water permeance of the pure GO membrane increased from 3.08 L m^-2 h^-1 bar^-1 to 45.52 L m^-2h^-1 bar^-1.The prepared GO/PG composite membrane has excellent separation performance for dye molecules,can intercept dye molecules with molecular weight as low as 373 g mol^-1,and has a rejection rate of up to 99%for dyes such as Victoria Blue（VB）,and can operate continuously and stably for 150 h.In addition,the GO/PG composite membrane was used for the separation of drug molecules in organic solvents,and it was found that the rejection rate of Vitamin B12（VB12）molecules in propionic acid reached 93%,reflecting the potential application of this composite membrane in organic solvent filtration.（2）A separation membrane with layer-by-layer structure was successfully prepared by using the layer-by-layer assembly method（LBL）to assemble GO and positively chargedα-Ni（OH）₂ nanosheets on the PES substrate membrane sequentially.The surface charge of the membrane can be adjusted by changing the number of assembly layers.The prepared odd and even layers have negative and positive charges on their membrane surfaces,respectively,and exhibit excellent rejection and stability for molecules with t he same charge.The experiment found that the rejection rate of the negatively charged 3-layer membrane for the negatively charged Eriochrome Black T（EBT）dye was 99.7%,while the rejection rate of the positively charged 4-layer membrane for the positively charged VB dye was 99.8%.Using EBT and VB dye molecules as target molecules,the cyclic stability of the 3-layer and 4-layer membranes was tested.The filtration time was up to 228 h,the permeance was stable,and the rejection remained around 99%.