Preparation And Performance Regulation Of Nanofiltration Membranes Based On MXene

Facing the serious situation of dye wastewater pollution in China,membrane separation technology has become an important method to treat dye wastewater.Among them,nanofiltration membrane,as a kind of pressure driven membrane,can effectively separate single polyvalent ions and small organic molecules with molecular weight range of 200.0-1000.0 Da.Nanofiltration shows great application prospects in dye wastewater treatment,seawater desalination and organic solvent treatment.Traditional nanofiltration membranes are mainly thin film composite（TFC）membranes prepared by interfacial polymerization（IP）,they have been faced with a“trade-off”limitation between permeability and selectivity,the membranes permeability and selectivity are mutually dependent.Therefore,the thin film nanocomposite（TFN）membrane composed of the nanofillers embedded into polyamide（PA）layer is considered to be a new type of membrane promising to enhance the performance of membrane separation.As an emerging nanofillers,two-dimensional materials MXene has great potential in the design of TFN membranes due to its rich functional groups,good flexibility and hydrophilic surface.However,the serious expansion problem of two-dimensional structure and the selection of wrong preparation will destroy the separation performance of the membrane.Therefore,this paper provides some effective optimization methods to solve these problems,and the specific contents are as follows:（1）MXene nanosheets were prepared by etching MAX precursor in a mixture of Li F and HCl.MXene nanosheets were embedded into a polyamide layer formed by polyethyleneimine（PEI）monomer and trimesoyl chloride（TMC）.The positively charged PEI monomer and negatively charged MXene nanosheets ensure good compatibility,and the optimal membrane has a pure water flux of 20.9 L m^-2 h^-1 bar^-1 and dyes rejection of 99.4%,99.0%and 98.8%for Congo red（CR）,Reactive blue 19（RB19）and Methyl blue（MB）,respectively.Meantime,the membrane exhibited low rejections towards Na₂SO₄ and Na Cl.The enhanced performance of the MXene-based membrane is mainly due to the amplified interlayer distance and the appropriate crosslinking degree,which promotes the water molecules transport.（2）By controlling the content of ZIF-8 nanoparticles grown in-situ,the interlayer distance of MXene nanosheets was tailored to optimize the permeability of the modified membranes.The high hydrophilic MXene nanosheets and the controllable size of ZIF-8 nanoparticles make PA layer have strong molecular sieve separation ability.The experimental results show that the optimal membrane has a rejection rate of more than 99.0%for CR,RB19,Xylene brilliant cyanin G250（G250）and MB solutions,with a pure water flux of up to 40.8 L m^-2 h^-1 bar^-1.Furthermore,the optimal membrane showed excellent separation performance in acid-base stability and long run stability operation.（3）By extracting Silk nanofibers（SNFs）from silkworm cocoons and combining with MXene nanosheets,one-dimension/two-dimension（1D/2D）heterojunction membrane was designed using vacuum filtration combined with interfacial polymerization.The heterogeneous structure constructed by SNFs and MXene nanosheets expands the interlayer space of MXene nanosheets.The content of SNFs was adjusted to control the degree of crosslinking.The experimental results show that the separation membrane has a pure water flux of 24.5 L m^-2 h^-1 bar^-1,while maintaining high removal of dye solution and low rejection of salt solution.This research provides additional feasibility for assembling heterojunction membrane of different dimensions nanomaterials（e.g.,0D-2D,1D-2D and 2D-2D）for environmental sustainability development.