Recent progress of two-dimensional nanosheet membranes and composite membranes for separation applications

Cutting-edge developments in MXene-derived functional hybrid nanostructures: A promising frontier for next-generation water purification membranes

A novel family of multifunctional nanomaterials called MXenes is quickly evolving, and it has potential applications that are comparable to those of graphene. This article provides a current explanation of the design and performance assessment of MXene-based membranes. The production of MXenes nanosheets are first described, with an emphasis on exfoliation, dispersion stability, and processability, which are essential elements for membrane construction. Further, critical discussion is also given to MXenes potential applications in Vacuum assisted filtration, casting method, Hot press method, electrospinning and electrochemical deposition and layer-by-layer assembly for the creation of MXene and MXene derived nanocomposite membranes. Additionally, the discussion is carried forward to give an insight to the modification methods for the construction of MXene-based membrane are described in the literature, including pure or intercalated nanomaterials, surface modifiers and miscellaneous two-dimensional nanomaterials. Furthermore, the review article highlights the potential utilization of MXene and MXene based membranes in separation and purification processes including removal of small organic molecules, heavy metals, oil-water separation and desalination. Finally, the perspective use of MXenes strong catalytic activity and electrical conductivity for specialized applications that are difficult for other nanomaterials to accomplish are discussed in conclusion and future prospectus section of the manuscript. Overall, important information is given to help the communities of materials science and membranes to better understand the potential of MXenes for creating cutting-edge separation and purification membranes.

Advancements in defect engineering of two-dimensional nanomaterial-based membranes for enhanced gas separation

The advent of two-dimensional nanomaterials, a revolutionary class of materials, is marked by their atomic-scale thickness, superior aspect ratios, robust mechanical attributes, and exceptional chemical stability. These materials, producible on a large scale, are emerging as the forefront candidates in the domain of membrane-based gas separation. The concept of defect engineering in 2D nanomaterials has introduced a novel approach in their application for membrane separation, offering an effective technique to augment the performance of these membranes. Nonetheless, the development of customized microstructures in gas separation membranes via defect engineering remains nascent. Hence, this review is designed to serve as a comprehensive guide for the application of defect engineering in 2D nanomaterial-based membranes. It delves into the most recent developments in this field, encompassing the synthesis methodologies of defective 2D nanomaterials and the mechanisms underlying gas transport. Special emphasis is placed on the utilization of defect-engineered 2D nanomaterial-based membranes in gas capture applications. Furthermore, the paper encapsulates the burgeoning challenges and prospective advancements in this area. In essence, defect engineering emerges as a promising avenue for enhancing the efficacy of 2D nanomaterial-based membranes in gas separation, offering significant potential for advancements in membrane-based gas separation technologies.

Ion Transport Behavior in van der Waals Gaps of 2D Materials

2D materials, with advantages of atomic thickness and novel physical/chemical characteristics, have emerged as the vital building blocks for advanced lamellar membranes which possess promising potential in energy storage, ion separation, and catalysis. When 2D materials are stacked together, the van der Waals (vdW) force generated between adjacent layered nanosheets induces the construction of an ordered lamellar membrane. By regulating the interlayer spacing down to the nanometer or even sub-nanometer scale, rapid and selective ion transport can be achieved through such vdW gaps. The further improvement and application of qualified 2D materials-based lamellar membranes (2DLMs) can be fulfilled by the rational design of nanochannels and the intelligent micro-environment regulation under different stimuli. Focusing on the newly emerging advances of 2DLMs, in this review, the common top-down and bottom-up synthesis approaches of 2D nanosheets and the design strategy of functional 2DLMs are briefly introduced. Two essential ion transport mechanisms within vdW gaps are also involved. Subsequently, the responsive 2DLMs based on different types of external stimuli and their unique applications in nanofluid transport, membrane-based filters, and energy storage are presented. Based on the above analysis, the existing challenges and future developing prospects of 2DLMs are further proposed.

Permselectivity and Ionic Conductivity Study of Na+ and Br- Ions in Graphene Oxide-Based Membranes for Redox Flow Batteries

Permselectivity of a membrane is central for the development of electrochemical energy storage devices with two redox couples, such as redox flow batteries (RFBs). In RFBs, Br3-/Br- couple is often used as a catholyte which can cross over to the anolyte, limiting the battery's lifetime. Naturally, the development of permselective membranes is essential to the success of RFBs since state-of-the-art perfluorosulfonic acid (PFSA) is too costly. This study investigates membranes of graphene oxide (GO), polyvinylpyrrolidone (PVP), and imidazole (Im) as binder and linker, respectively. The GO membranes are compared to a standard PFSA membrane in terms of ionic conductivity (Na+) and permselectivity (exclusion of Br-). The ionic conduction is evaluated from electrochemical impedance spectroscopy and the permselectivity from two-compartment diffusion cells in a four-electrode system. Our findings suggest that the GO membranes reach conductivity and permselectivity comparable with standard PFSA membranes.

Rapid growth of MXene-based membranes for sustainable environmental pollution remediation

Water consumption has grown in recent years due to rising urbanization and industry. As a result, global water stocks are steadily depleting. As a result, it is critical to seek strategies for removing harmful elements from wastewater once it has been cleaned. In recent years, many studies have been conducted to develop new materials and innovative pathways for water purification and environmental remediation. Due to low energy consumption, low operating cost, and integrated facilities, membrane separation has gained significant attention as a potential technique for water treatment. In these directions, MXene which is the advanced 2D material has been explored and many applications were reported. However, research on MXene-based membranes is still in its early stages and reported applications are scatter. This review provides a broad overview of MXenes and their perspectives, including their synthesis, surface chemistry, interlayer tuning, membrane construction, and uses for water purification. Application of MXene based membrane for extracting pollutants such as heavy metals, organic contaminants, and radionuclides from the aqueous water bodies were briefly discussed. Furthermore, the performance of MXene-based separation membranes is compared to that of other nano-based membranes, and outcomes are very promising. In order to shed more light on the advancement of MXene-based membranes and their operational separation applications, significant advances in the fabrication of MXene-based membranes is also encapsulated. Finally, future prospects of MXene-based materials for diverse applications were discussed.

A Review of Advancing Two-Dimensional Material Membranes for Ultrafast and Highly Selective Liquid Separation

Membrane-based nanotechnology possesses high separation efficiency, low economic and energy consumption, continuous operation modes and environmental benefits, and has been utilized in various separation fields. Two-dimensional nanomaterials (2DNMs) with unique atomic thickness have rapidly emerged as ideal building blocks to develop high-performance separation membranes. By rationally tailoring and precisely controlling the nanochannels and/or nanoporous apertures of 2DNMs, 2DNM-based membranes are capable of exhibiting unprecedentedly high permeation and selectivity properties. In this review, the latest breakthroughs in using 2DNM-based membranes as nanosheets and laminar membranes are summarized, including their fabrication, structure design, transport behavior, separation mechanisms, and applications in liquid separations. Examples of advanced 2D material (graphene family, 2D TMDs, MXenes, metal-organic frameworks, and covalent organic framework nanosheets) membrane designs with remarkably perm-selective properties are highlighted. Additionally, the development of strategies used to functionalize membranes with 2DNMs are discussed. Finally, current technical challenges and emerging research directions of advancing 2DNM membranes for liquid separation are shared.

Graphene oxide membranes with a confined mass transfer effect for Li+/Mg2+ separation: a molecular dynamics study

Molecular dynamics simulations were used to investigate the influence of the confined mass transfer effect on the separation of Mg2+ and Li+ from graphene oxide membranes, both in terms of layer spacing and degree of oxidation.

Experimental study of carbon dioxide absorption by Fe2O3@glutamine/NMP nanofluid

In this study, for the first time, the nanoparticle (NP) of Fe₂O₃@glutamine (C₅H₁₀N₂O₃) was synthesized to improve the Fe₂O₃ properties in absorbing carbon dioxide (CO₂) using the base fluid of hydrous N-methyl-2-pyrrolidone (NMP) solution (50 wt%), as a physically powerful CO₂ absorbent. To do this, several nano-NMP solutions, in different weight percentages of NPs, were first prepared. Then, in a batch setup, the nano-NMP solutions were directly exposed to CO₂ gaseous (at the pressures of 20, 30, and 40 bar) to clarify the effects of the mass percentage of NPs and initial pressure on CO₂ absorption. Results clearly illustrated that Fe₂O₃ nanofluid was not stable more than 0.025 wt%. However, Fe₂O₃@glutamine nanofluid was stable approximately two times more than Fe₂O₃ nanofluid due to the presence of glutamine as a hydrophilic agent in the structure of Fe₂O₃@glutamine. Moreover, in comparison to the base fluid (NMP solution), although Fe₂O₃ increased CO₂ absorption up to 9.14%, Fe₂O₃@glutamine NPs caused the CO₂ absorption to increase up to 19.41%, which can be determined as the chemical reactions of two amino groups in the glutamine structure with CO₂ and also higher stability of Fe₂O₃@glutamine NPs compared to bare Fe₂O₃ NPs. To achieve accurate results, all the mentioned experiments were repeated 5 times. The performance of Fe₂O₃ and Fe₂O₃@glutamine NPs after the fifth trial reduced by less than 3.5%, which reveals that the synthesized NPs had almost stable efficiency throughout their applications.

Supported MXene/GO Composite Membranes with Suppressed Swelling for Metal Ion Sieving

Novel two-dimensional (2D) membranes have been utilized in water purification or seawater desalination due to their highly designable structure. However, they usually suffer from swelling problems when immersed in solution, which limits their further applications. In this study, 2D cross-linked MXene/GO composite membranes supported on porous polyamide substrates are proposed to improve the antiswelling property and enhance the ion-sieving performance. Transition-metal carbide (MXene) nanosheets were intercalated into GO nanosheets, where the carboxyl groups of GO combined the neighboring hydroxyl terminal groups of MXene with the formation of -COO- bonds between GO and MXene nanosheets via the cross-linking reaction (-OH + -COOH = -COO- + H₂O) after heat treatment. The permeation rates of the metal ions (Li⁺, Na⁺, K⁺, Al³⁺) through the cross-linked MXene/GO composite membrane were 7-40 times lower than those through the pristine MXene/GO membrane. In addition, the cross-linked MXene/GO composite membrane showed excellent Na⁺ rejection performance (99.3%), which was significantly higher than that through pristine MXene/GO composite membranes (80.8%), showing improved ion exclusion performance. Such a strategy represents a new avenue to develop 2D material-derived high-performance membranes for water purification.