Ion‐Selective MXene‐Based Membranes: Current Status and Prospects

Abstract

On the other hand, membrane separation has attracted attention, as an environmentally safe, simple, sustainable, and energy-efficient alternative separation technology. [4][5][6][7][8][9] Furthermore, compared to conventional separation processes, membrane separation has been found to be promising in water and wastewater treatment, [10,11] gas separation, [12][13][14] oil refinement, [15,16] food processing, [17] biology, [18][19][20] solid-phase extractions, [21,22] ion separation, [23] and pharmaceutical industries. [24] Ion-separation membranes have been widely used in various fields, such as electroplating, treatment of electronic waste, precious metal recovery, and metallurgical and battery industries. [25][26][27][28] The fabrication of highly-selective ion-separation membranes is still challenging in spite of many advances in the past few decades. [29,30] These membranes separate a targeted ion by isolating it from other ions. When ions that are present are of the same type and valence, [31,32] the separation is very difficult due to the similar permeabilities of the ions. Ion-separation membrane processes have been classified into nanofiltration (NF), [33] reverse osmosis (RO), [34,35] forward osmosis (FO), [36,37] electrodialysis, [38] and ion exchange membranes. [39] Among these, NF has exhibited good potential for selective separation of ions based on their charge and size, [40] allowing for the separation of ions with a specific diameter (larger than membrane nanochannels). [41] However, its solution flux decreases, as the size of its membrane nanochannels decreases. This relationship does not allow for achieving simultaneously high permeation and selectivity because of the inherent rejection/permeance tradeoff of the membranes. [42] Hence, the fabrication of ion-separation membranes with simultaneously high ion rejection and high permeation is of great interest. [40,43,44] To achieve simultaneously high ion rejection and high permeation, in recent years several materials have been investigated, including metal-organic frameworks (MOFs), [45][46][47] carbon nanotubes, [48] metal coated polymer, [49] metal nanotubes, [50] and porous carbon. [51] In particular, 2D materials have received attention [52] due to their quantum confinement effect and unique micro-structures [53] that contribute to their high separation performance. So far, phosphorene, layered double hydroxides, [54][55][56] transition metal dichalcogenides, [57][58][59][60][61][62] Water pollution is a major global challenge, as conventional polymeric membranes are not adequate for water treatment anymore. Among emerging materials for water treatment, composite membranes are promising, as they have simultaneously improved water permeation and ions rejection. Recently, a new family of 2D materials called MXenes has attracted considerable attention due to their appealing properties and wide applications. MXenes can be incorporated into many polymeric materials due to their high compatibility. MXenes/polymer composite membranes have been found...

Thin Film Polyamide Nanocomposite Membrane Decorated by Polyphenol-Assisted Ti3C2Tx MXene Nanosheets for Reverse Osmosis

“…MXenes as a class of multifunctional two-dimensional (2D) transition-metal carbides, nitrides, or carbonitrides with a formula M n +1 X n T x (T = −OH, −O, or −F) have attracted noticeable attention for membrane-based separation application due to their fascinating properties such as hydrophilicity, diverse surface chemistry, superior thermal and mechanical stability, high antifouling and antibacterial activity, and large surface area. − Although the privilege and benefit of MXene-based membranes, as a filler , or selective layer, , have been confirmed, there are still several drawbacks on MXenes such as weak ambient stability, easy restacking, and poor processability, which constrain the further scalable development of MXene-based membranes . Also, an important issue regarding the production of a well-mixed MXene/polymer nanocomposite membrane is the interfacial interaction between the polymeric chain and MXene nanosheets.…”

Biomimetic Nanochannels: From Fabrication Principles to Theoretical Insights

“…During past few years, another 2D material-MXene has attracted increasing attention due to the unique structures and potential applications in ionic transport. [133] Generally, MXenes are 2D materials synthesized by selective etching of A (A is a III or IV A-group element, mostly Al or Ga) layers from the MAX phase where M represents an early transition metal and X is either C or N. The general composition of MXene is M n+1 X n T x , where T represents surface termination (O, OH, and/or F) and x is the number of termination groups. [134] Gao and Luo et al prepared stable aqueous MXene membranes for lightcontrolled ionic transport.…”

High-Performance and Stable Two-Dimensional MXene-Polyethyleneimine Composite Lamellar Membranes for Molecular Separation

“…Ti 3 C 2 T x is produced by T x termination, where T represents O, OH, and/or F groups . Ti 3 C 2 T x forms negatively charged 2D structures that have excellent properties such as high hydrophilicity, adjustable interlayer spacing, high mechanical strength, and structural stability. − They are used to build advanced membranes with improved separation performance and thus have broad application prospects in molecular separation . In a 2D lamellar membrane, the stacked structure of nanosheets improves the separation performance of the membranes .…”