(399q) Two-Dimensional Mxene Membrane for Water Purification

Li Ding, Yanying Wei, Haihui Wang*

South China University of Technology, School of Chemistry and Chemical Engineering, No. 381 Wushan Road, Guangzhou 510640, Guangdong, China

Corresponding author: hhwang@scut.edu.cn Introduction

Two-dimensional (2D) materials are considered to be promising candidates for advanced membrane separation process. Several 2D materials, such as graphene and graphene oxide (GO),^[1] exfoliated nanosheets of metal-organic frameworks (MOFs)^[2] and zeolite nanosheets,^[3] and the transition metal dichalcogenides (TMDs),^[4] have attracted increasing attention in preparing for future functional separation membranes due to their outstanding mechanical properties, excellent thermal stability and superior flexibility. Nowadays, a novel kind of 2D layered material named MXenes - a family of early transition metal carbides, has received increasing attention. MXene is normally produced by selectively etching the A layer from MAX phases. Owing to its flexibility, superior structural stability, high electrical conductivity and hydrophilic surfaces, MXene has been widely used in super capacitors,^[5] Lithium-ion batteries,^[6] oxygen-evolution reaction,^[7] and heavy metal adsorption.^[8] However, there so far no report on the inorganic MXene-based membranes till now, except the paper by Gogotsi et al. for ion sieving.^[9] Herein, we propose a kind of 2D lamellar membranes with Ti₃C₂T_X MXene nanosheets, and its application in water purification.

Keywords: Two-dimensional • MXene • Ti3C2TX • membrane • separation • water purification Experimental

The preparation of the MXene membrane for water purification is as follows. First, Ti₃AlC₂ particles were first etched by HF solution to generate Ti₃C₂T_X powder. By extracting Al as AlF₃, the interaction between the layers is weakened. The MXene nanosheets can be obtained by sonication-assisted exfoliation. Second, the positively charged Fe(OH)₃ colloidal solution was chosen to intercalate the negatively charged MXene nanosheets to create expanded nanochannels. Subsequently, after a simple vacuum filtration process and hydrochloric acid solution (HCl) treatment to remove the Fe(OH)₃ nanoparticles, the ultimate MXene membrane can be obtained. Results and discussion

The MXene membrane supported on anodic aluminum oxide (AAO) substrate shows excellent water permeance (more than 1000 L m^-2 h^-1 bar^-1) and favorable rejection rate (over 90 %) for molecules with sizes larger than 2.5 nm. The water permeance through the MXene membrane is much higher than that of the most membranes with similar rejections. Additionally, the long-time operation reveals the outstanding stability of the MXene membrane for water purification.