Preparation,structural Regulation And Preliminary Application Of Two-dimensional Ti₃C₂ MXene Membranes

The separation/purification is an essential part of chemical engineering process.However,traditional separation technologies,such as distillation,distillation,and extraction,require high energy consumption and do not comply with the environmental protection policies currently implemented by the government.Membrane separation technology is expected to replace traditional separation technology due to its advantages,such as efficient,environmental friendly and energy-saving.The development of membrane separation technology is limited by the shortcomings of traditional materials such as short lifespan,high cost,and difficult to break the balance of flux and selectivity.Therefore,developing new high-performance separation membrane materials remains a top priority in promoting the development of membrane technology.As one of the fundamental platforms for the development of membrane,2D materials have attracted much attention due to their unique atomic thickness,micrometer scale sheet size,and rich surface functional groups.Different 2D nanomaterials provide different material properties in separation membranes to meet the needs of different applications.MXene,the transition metal carbides（nitrides）generated by selective etching of MAX phase layered ceramic materials,has stood out among 2D nanomaterials due to its surface functional groups such as-O,-OH,and-F.With these hydrophilic groups,MXene has great potential for application in water treatment.Moreover,the layered 2D membrane composed of MXene nanosheet units has regular and controllable nanoscale transport channels,which can achieve the transport of liquid/gas molecules and effectively screen molecules of different sizes.Therefore,this paper systematically studied the effects of various factors on the thickness,lateral size,interlayer distance,and surface functional groups of the Ti₃C2MXene nanosheets during the preparation process,and explored the preparation,testing,and structural regulation of MXene membranes.（1）Preparation,characterization,and storage of Ti₃C₂ MXene nanosheetsThis work uses the experimental route of preparing MXene using HCl/LiF in-situ method,and investigates the effects of different etchants,the ratio of Al³⁺and F^-in HCl/LiF etchant and the ultrasonic power and time during the etching process on the MXene material by using characterization methods such as scanning electron microscopy,X-ray diffraction,and particle size distribution analyzer.The results shown that the intercalation of cations（such as Li⁺and NH₄⁺）can effectively promote the detachment of MXene nanosheets and compared to the other two etchants,the etching environment generated by HCl/LiF is more conducive to the exfoliating and layering of large MXene layers.When the molar mass of F^-is 7 times or more than that of Al³⁺,the obtained MXene material has an obvious single layer structure,and the d-spacing distance between the nano layers can increase with the increase of F^-concentration in the etchant(When the molar mass ratio of Al³⁺to F^-ion is 1:9,the d-spacing distance of MXene is 14.33（?）and the one-time production is more than60%).Ultrasonic treatment can affect the lateral size of MXene nanosheets and promote layering of MXene layers（improving single-layer production）.（2）Preparation,characterization,performance testing,membrane structure and regulation of Ti₃C₂ MXene self-supporting membraneThe microstructure and chemical composition of MXene layered membrane prepared by vacuum assisted suction filtration were observed and analyzed using characterization methods such as X-ray diffraction,X-ray photoelectron spectroscopy,and scanning electron microscopy.It was demonstrated that MXene layered membrane has good layered transport channels,hydrophilic surface properties,interlayer distance of molecular size（0.37 nm）,stability,and can be applied in gas separation/nanofiltration technology.After dye rejection and gas separation tests of self-stacking MXene layered membranes supported by nylon-66,the results showed that MXene had a 100%rejection rate for Congo Red dye with penetration rate of11.02 L·m^-2·h^-1·bar^-1 and exhibited gas separation performance using molecular sieves as the separation mechanism.In addition,by combining self-linking reaction and etching concentration,the interlayer spacing of MXene 2D membranes can be controlled.After heat treatment at170℃for 30 h,the d-spacing of The MXene self-supporting membrane obtained by the molar mass ratio of Al³⁺to F^-ion is 1:9 is adjusted from 14.33（?）to 13.54（?）,and the membrane structure is more stable.（3）Preparation and performance study of Ti₃C₂ MXene composite membrane and mixed matrix membraneUsing interfacial polymerization method,single-layer Ti₃C₂T_X nanosheets were successfully doped into the polyamide skin.The doping of Ti₃C₂T_X in the polyamide layer improved the hydrophilicity of the membrane surface and increased the water flux by 31.67%while only 3.81%decrease in Na₂SO₄ rejection rate.In order to construct a defect free and orderly 2D nano channel in MXene mixed matrix membrane,we added the high molecular weight CMC into MXene solution,which served as covalent bond agent to bridge the MXene nanosheets in sequence.By testing the rejection of the MXene mixed matrix membrane with Congo Red and Methylene Orange,we found that the membrane had a rejection rate of over 60%in a short period of time for the Methylene Orange dyes,which could not be rejected by self-stacking MXene membrane.