Preparation Of Two-dimensional Laminar MXene Memebrane And Its Application On Ionc Sieving

With the sustaintable development of modern industry,it is becoming more and more challengable for water pollution.At present,the treatment methods of industrial sewage mainly include precipitation filtration,activated carbon adsorption,electrodialysis,distillation and so on.However,due to their high cost and energy consumption and probable secondary pollution,some severe challenges are faced in the control of water pollution.Membrane separation has been increased more intrests because of these advantages including simple device,easy operation,low energy consumption,easy control and maintenance,and high separation efficiency.Nervertheless,the two-dimensional layered GO and MXene membranes witha facile hydrophilicity are easily swellen in the water environment,and therefore it is limited on the application of water treatment for these membrane.To solve it,here,the two-dimensional layered MXene membrane were prepared using a vacuum filtration combined with thermal crosslinking.the ion sieving and the removal of heavy metal ions were investagted under pressure driving and applied voltage.After vacuum heat treatment,due to the dehydration of interlayer hydroxyl groups,self-cross-linked reation facilitate the formation of Ti-O-Ti bond between the two-dimensional layered MXene nanosheets.Therefore,the interlayer distance of the obtained MXene membrane is fixed at 7.6?8?,resulting in little swelling.In watertreatment,the water flux of 484 L·bar^-1·h^-1·m^-2 is obtained through the MXene membrane under a pressure difference of 1atm.Based on pressure driving,the ion sieving is carried out using the two-dimensional laminar MXene membrane sieving.The separation coefficients of mixed ions K⁺/Na⁺,K⁺/Pb²⁺,K⁺/Ca²⁺,K⁺/Ca²⁺and K⁺/Cu²⁺for the resultant MXene membrane were 1.069,1.267,1.271 and 1.280,respectively,while the rejection of single cation including Na⁺,Pb²⁺,Ca²⁺and Cu²⁺were just 28%,39%,40%and 40%,respectively.Because of the negative charge on the surface of MXene membrane,the cations is easily adsorbed on the surface of MXene membrane.Therefore,it is expected that the applied voltage can further improve the ion sieving of the membrane.The MXene membrane with a thickness of365nm has arrived at a separation belance for 50 min in the ion sieving under a applied voltage of 16.5 V,which indicates the improving separation in comparation with the previous reports.The separation coefficients of K⁺/Na⁺,K⁺/Pb²⁺,K⁺/Ca²⁺,K⁺/Ca²⁺and K⁺/Cu²⁺are significantly increased up to 1.172,78.144,80.344 and 83.1,respectively.The rejection rates of Na⁺,Pb²⁺,Ca²⁺and Cu²⁺are 87%,99%,99%and 99%,respectively.The larger difference in the diameter of the two ions,the higher separation coefficient,and the larger diameter of cations,the higher of rejection rate.Further,the stable separation of cations is maintained in ion sieving.These results show that the MXene membrane prepared by thermal crosslinking method has good performance of ion sieving and removal of metal ion,especially heavy metal ions,under applied voltage,and it is promising for thermal-crosslinked MXene membrane to apply in water treatment and rejection of heavy metal ions.