Effect Of Surface Charge On Ion Selective Transport Performance Of Pillared Ti₃C₂T_x Nanochannels And Its Mechanism

Membrane technology is one of the most important means in modern separation science.Its application covers many technical fields including environment,electronics,energy,and so on.It plays an indispensable role in human life and industrial development.In recent years,nanotechnology,especially two-dimensional nanomaterials,has been developed by leaps and bounds.Its rich functional group structure and powerful functionality have shown great potential in the field of membrane separation.Among them,the separation function membrane with nano-and sub-nano-sized membrane pores constructed by two-dimensional materials has become the frontier in the field of membrane technology and nanotechnology due to its special transmission and sieving behavior for molecules and ions in solution.Among them,the two-dimensional layered membrane assembled by the parallel stacking of two-dimensional nanosheets provides a new platform for studying the transport behavior of ions at the angstrom scale.However,when a two-dimensional nano-layered film exists in an aqueous solution,the interlayer spacing is often increased due to the continuous entry of water molecules between the nanosheets.This swelling problem is common,which makes the spacing of the nanochannels formed by it very unstable.This problem also leads to a decrease in the stability and ion rejection rate of the two-dimensional membrane during the membrane separation process.This instability also seriously affects the study of ion transport characteristics as a nano-transport channel,and also limits its application in the field of membrane separation.Based on this,this article adopts a novel method to introduce sodium alginate gel and metal manganese ions between the large-size Ti₃C₂T_x nanosheets to form a columnar support structure,which has obtained good mechanical properties and stable interlayer spacing(<2nm)The MXene separation membrane achieves precise ion migration control by precisely adjusting the surface potential of the film to stabilize the nanochannel.In addition,it also explored its application in the field of forward osmosis.The main results obtained are as follows:(1)Single layer Ti₃C₂T_x nanosheet solution was prepare by the"MILD"etching method.Subsequently,a Ti₃C₂T_xlayered membrane was prepared by vacuum filtration on a bottom membrane with a pore size of 0.22mm.On this basis,sodium alginate was introduced into the interlayers to form a stable interlayer structure through manganese ion cross-linking.Finally,the technical conditions and parameters for the preparation of Ti₃C₂T_x layered films modified by manganese cross-linking sodium alginate gel were obtained.(2)A self-made filter device is designed,which can be connected to an electrochemical workstation to construct a typical three-electrode system.The manganese cross-linked sodium alginate modified Ti₃C₂T_x layered membrane with stable interlayer spacing was used as a nanochannel,and the surface potential of the nanochannel was precisely controlled through a three-electrode system to explore the mechanism of the channel surface potential on the ion transport behavior.The effect of the change of the channel surface potential on the transmission behavior of the ions passing through different nanochannels was compared.The results show that the external potential of the Ti₃C₂T_x nanochannel modified by manganese cross-linked sodium alginate has the best control effect,by adjusting the external voltage the ion penetration rate can be instantly and reversibly regulated,in which the penetration rate of Na⁺ions can be increased by up to 17 times under the 0.8V voltage;and the penetration rate of Mg²⁺ions can be inhibited by up to 17 times under the-0.8V voltage.(3)A self-made forward osmosis device is designed,which can be connected to an electrochemical workstation to accurately apply an external voltage to the forward osmosis films,thereby improving the forward osmosis performance of the films.The film shows excellent performance under a voltage of-0.8 V.When 0.5M sucrose solution is used as the draw solution and 4.75 g/L magnesium chloride solution is used as the feed solution,salt interception rate can reach 99.4%,the water flux can reach0.49 L m^-2bar^-1 h^-1.