The Influene Of Ti₃C₂T_x Sheet Lateral Size On Interlayer Space Of The Corresponding Membrane

Currently the environmental and energy problems such as oily wastewater,antibiotic wastewater and CO₂ separation draw wide attention across the world.The design of efficient separation membrane is expected to solve the above difficulties and expand the application scope of membrane materials.The emergence and development of two-dimensional material membranes provide new ideas and research directions in material selection and pore design of high-performance membranes,making it possible to prepare the membrane with high permeance and high retention at the same time.The two-dimensional materials membranes are mainly composed of the interlaminar channels formed by the restacking of nanosheets to screen and selectively transfer particles.The surface properties and geometric dimensions of the nanosheets directly determine the diffusion path and mass transfer resistance.In this paper,we focus on Ti₃C₂T_x membrane,aiming to use the uniform functional group distribution on the surface and the adjustment of the sheet size to expand the application scope of two-dimensional membrane separation.At the same time,the effect of the sheet size on the structure of regular interlaminar channels is investigated to achieve the goal of perfect interlaminar screening.The model relationship between the nanosheet size and the separation performance was established to further understand the mass transfer mechanism of the two-dimensional membrane.The paper is divided into four parts:（1）The Ti₃Al C₂ MAX phase was selectively etched with HCl and LIF as mixed etchants to obtain Ti₃C₂T_x nanosheets with the lateral size of 1μm.Then,the ultra-thin Ti₃C₂T_xnanosheets membrane with the thickness of about 30 nm was prepared on the polyetherselfone（PES）support by vacuum suction.The as-fabricated membrane can separate oil-in-water emulsion with the size of oil drop ranging from 50 nm to 250 nm.The oil content in the permeate side after single filtration is less than 10 ppm.In 50-cycle test,the permeability and selectivity of the membrane have no obvious decay and fluctuation,showing excellent antifouling property and operation stability.The results of experiments and molecular dynamics simulation show that the membrane has hydrophilic and low oil drop adhesion.Such excellent screening performance is mainly attributed to hydrophilic surface and sub-nanometer interlayer channel.What’s more,the Ti₃C₂T_x membrane exhibits better screening performance facing with oil-in-salty water emulsions,which is mainly due to the shrinkage of interlayer galleries induced by ion intercalation,resulting in better screening.（2）A well-aligned Ti₃C₂T_x nanosheets membrane is constructed with high aspect ratio block with the lateral size ranging in 2-4μm.Compared with the precursor of Ti₃Al C₂ MAX precursor,Ti₃C₂T_x membrane shows a brighter diffraction ring on the（002）crystal surface,and this ring has light and shadow alternation patterns in 2D XRD.All results above indicate that the prepared Ti₃C₂T_x membrane has regular and well-aligned interlayer channels,and the calculated height of interlayer channels are 0.35 nm in dry state,which can also be proved by results of the transmission electron microscope and the fast inverse Fourier profiles.Compared with the polymer nanofiltration membrane,no matter antibiotics dissolved in water and organic environment,the solvent permeation flux of Ti₃C₂T_x membrane is at least one order of magnitude higher under the similar retention in aqueous and ethanaol solution.This excellent increasing performance is mainly ascribed to the regular interlayer channels assembled with high aspect ratio of nanosheets.（3）By further improving the preparation method of the Ti₃C₂T_x nanosheet,the ultra-large nanosheets with lateral size in 4-9μm can be obtained.The regular Ti₃C₂T_x membrane formed by the ultra-large nanosheets via vacuum filtration was used to separate H₂/CO₂ gas pair.The m^-2 s^-1 Pa^-1,respectively,and the selectivity is 85.The membrane also demonstrates some water vapor stability at a certain level.These properties are mainly due to the regular interlayer channels assembled with large aspect ratio of Ti₃C₂T_x nanosheets,which can ensure the fast transfer of small molecules of gas mixture,and strictly screen the large molecules.This method can provide guidance for other similar nanostructures with regular interlayer screening channels.（4）A series of Ti₃C₂T_x membrane constructed with different lateral size nanosheets were prepared by adjusting the preparation methods of nanosheets.The influence of the lateral size of Ti₃C₂T_x on the structure and then separation performance of the corresponding membranes were investigated.The results show that the small nanosheets lead to disordered stacking,resulting in increased permeance;the large one can construct more regular interlayer galleries,resulting in better retention performance with a compromise permeance.The perfect separation membrane requires Ti₃C₂T_x nanosheet membrane assembled with a few layers of nanosheet stacking,which needs to be further improved in the membrane preparation method.This will provide a guidance to balance the relationship between the screening performance of the two-dimensional membrane and the geometric size.