Preparation And Application In Liquid Separation Of MXene Membrane

Separation process is an important section in chemical industry,which consumed enormous energy resources every year.Membrane separation is a new kind of separation technology with high efficiency and less energy consuming.It is expected to become a substitute for traditional thermal separation technologies.Traditional membrane materials have many drawbacks,such as short lifetime,high cost,trade-off between permeability and selectivity etc.Most researches of membrane separation technology were mainly focused on the preparation of high performance membrane materials.Two-dimensional（2D）membrane is a new kind of membrane material developed in recent years.Consists of 2D nanosheet units with atomic thickness,2D membranes have regular nanometer channels and unique physical and chemical properties.They have shown potential applications in gas and liquid separation,which are widely favored by researchers.Transition metal carbides,carbonitrides and nitrides（MXene）is a type of young 2D material successfully synthesised in 2011.It is prepared by selectively etching and peeling of its ternary MAX compound.MXene has special electrochemical properties and exhibited excellent performance in electrochemical energy storage components.On the other hand,MXene has abundant oxygen-containing functional groups and hydrophilicity.MXene membranes consisted of MXene nanosheet units have good mechanical properties and regular separation channels,which can transmit water and other solvent and reject molecules depend on there size at the same time.To further expand the application of MXene membrane in liquid separation,a kind of MXene membrane for alcohol-water separation was studied in this paper.LiF and HCl were chosen as etchants.Solution of Ti₃C₂T_X MXene nanosheets was obtained by etching and ultrasonic delaminating.MXene membrane with thickness of 2μm was assembled by vacuum filtration of the solution of Ti₃C₂T_X MXene nanosheets.The 2-μm-thick MXene membrane was applied for the separation of ethanol and water in pervaporation process.Effects of the feed ethanol concentration dehydration performance of the MXene membrane were investigated by changing the concentration of ethanol in feed from 75%to 95%.The water/ethanol separation factor of the MXene membrane increased with increasing feeding ethanol concentration.The MXene membrane gave a water/ethanol separation factor of 135.2 with a total flux of 263.4 g m^-2 h^-1 at room temperature for the azeotrope dehydration（95%ethanol mixed with 5%water）.Additionally,effects of the operating temperature on the ethanol dehydration performance of the MXene membrane were investigated by changing the the operating temperature from room temperature to 70 ^oC.As a result,MXene membrane exhibited better ethanol dehydration performance at room temperature compared with that at elevated temperatures.Therefore,such MXene membranes are more suitable for the separation of high-concentration ethanol solution at room temperature.The performance of MXene membrane to separate ethanol-water azeotrope with low energy consumption make it promising for practical use.Further,in order to improve the permeability and separation performance of MXene membranes,we reduced the thickness of MXene membranes to 100 nm,and added multi-walled carbon nanotubes（CNT）into MXene membranes to form composite membranes.The water permeance,dye rejection and pressure resistance of pure MXene membranes and 4%,6%,8%,10%MXene-CNT membranes were investigated.It was shown in the result that the interlayer space of MXene membranes increased due to the addition of CNT.The water permeance of MXene-CNT membranes increased with an increasing CNT content.MXene-CNT membranes also have a higher rejection to methylene blue（MB）and methyl orange（MO）than that of the pure MXene membranes.The MXene-CNT membranes can also maintain the growth of water permeance under an increasing pressure between 1to 5 bar,which showed a better pressure resistance.