A Two‐Dimensional Lamellar Membrane: MXene Nanosheet Stacks

Abstract

Two-dimensional (2D) materials are promising candidates for advanced water purification membranes. A new kind of lamellar membrane is based on a stack of 2D MXene nanosheets. Starting from compact Ti AlC , delaminated nanosheets of the composition Ti C T with the functional groups T (O, OH, and/or F) can be produced by etching and ultrasonication and stapled on a porous support by vacuum filtration. The MXene membrane supported on anodic aluminum oxide (AAO) substrate shows excellent water permeance (more than 1000 L m h bar ) 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. Long-time operation also reveals the outstanding stability of the MXene membrane for water purification.

A Regularly Channeled Lamellar Membrane for Unparalleled Water and Organics Permeation

“…[2c] However,t he currently available lamellar membranes possess generally irregular channels because they are formed via disordered stacking of the existing flexible sheets. [7] Recently, Wang et al synthesized small-sized single layers of Ti 3 C 2 T x to prepare an Fe(OH) 3 -intercalated lamellar membrane with ah igh water permeance of 1084 Lm À2 h À1 bar À1 . [6] Recently,r igid sheets have attracted research interests as promising building blocks because they can be orderly stacked into regular and straight channels without curling.M oreover,r igid sheets can form stable channels with adequate strength.…”

Ti2Au2C and Ti3Au2C2 formed by solid state reaction of gold with Ti2AlC and Ti3AlC2

“…These phases can also be exfoliated to form a recently established class of two-dimensional materials labelled MXene. [11][12][13][14][15][16] The introduction of Au in M n+1 AX n phases by hightemperature-induced exchange can be used for Ga-containing MAX phases (Mo 2 GaC and Mo 2 Ga 2 C 17,18 ) to synthesize Mo 2 AuC and Mo 2 (Au 1Àx Ga x ) 2 through an Au substitution reaction with Ga. 19 The question remains whether this mechanism can be generally applied to other M n+1 AX n phases, and beyond. We chose thin films of Ti 2 AlC and Ti 3 AlC 2 as model system to address this question.…”

Fluoride‐Free Synthesis of Two‐Dimensional Titanium Carbide (MXene) Using A Binary Aqueous System

“…Hydroxyl functional groups on Ti 3 C 2 layers result from the nucleophilic attack by the surrounding OH À anions.Because OH À has smaller ionic radius (0.11 nm) [22] than that of Cl À (0.18 nm), it is easier to intercalate and attack at the basal plane of Ti 3 C 2 sheets.T he functionalization of Ti atoms leads to the sharp reduction of Ti À Al bonding strength (ELF % 0.1), facilitating the removal of Al atoms from the anode. [4,23] TEM image (Figure 3d)d isplays at ypical Ti 3 C 2 T x sheet with welldefined and clean edges.T he high-resolution image confirms at ypical bilayer flake (Supporting Information, Figure S9). [20a] Some large flakes reach up to 18.6 mmindiameter, thanks to the mild etching conditions.Based on the statistical analysis of 187 individual sheets (Figure 3c), the average flake size (2.4 mm) is comparable to that prepared by modified LiF/HCl etching method.…”

“…Fore xample,w hen C OH < 0.1m,t he etching was incomplete after 10 hours;when C OH > 0.5 m,only amorphous carbon was obtained after as hort timescale (1 hour) (Supporting Information, Figure S3). [4] Notably,t he stacked films fabricated by filtrating the dispersions exhibit an electrical conductivity of 1330 AE 110 Scm À1 ,s imilar to those prepared from LiF/HCl etching method (1500 Scm À1 ). This is ak ey step to delaminate etched Ti 3 C 2 T x into individual 2D sheets,because the positive charged TMA + ions can weaken the interactions between 2D layers.…”

“…[4] Moreover,t hanks to the fluoride-free etching, the exfoliated Ti 3 C 2 T x (T = O, OH) flakes do not contain any fluorine terminations.F or the application in supercapacitors,a dditive-free films exhibit aremarkable areal capacitance (220 mF cm À2 ), outperforming those made from traditional wet-chemical approaches. [4] Moreover,t hanks to the fluoride-free etching, the exfoliated Ti 3 C 2 T x (T = O, OH) flakes do not contain any fluorine terminations.F or the application in supercapacitors,a dditive-free films exhibit aremarkable areal capacitance (220 mF cm À2 ), outperforming those made from traditional wet-chemical approaches.…”