Electrocatalytic/photocatalytic properties and aqueous media applications of 2D transition metal carbides (MXenes)

The 2D transition metal carbides (MXenes) are increasingly considered among of the most promising 2D nanomaterials, because of their unique properties such as hydrophilic nature, metallic conductivity, large surface-area-to-volume ratio, and active surface functionalities. This has led to their growing utilization in water/wastewater treatment and environmental remediation applications, including water purification membranes, heavy metal removal, capacitive deionization, and bactericidal agents. This account will focus on the key characteristic properties of MXenes such as high metallic/electronic conductivity, and catalytic activity, and their utilization for the electrocatalytic and photocatalytic-based environmental remediation applications. We will also address the key challenges facing MXene-based materials in aqueous media and possible mitigation routs.     

MXene-based nanomaterials as adsorbents for wastewater treatment: a review on recent trends

The wastewater treatment is a challenging research area to reduce the increasing pressure on limited fresh water resources. Amongst several techniques adopted and practiced, adsorption is one of the most effective and sustainable eco-friendly processes. In recent years, MXene nanomaterials, a new family of transition metal carbides, have gained increasing attention as the potential adsorbent for pollutants due to their unique features such as large surface area with abundant active sites and hydrophilicity. A wide range of pollutants viz. heavy metal ions, organic dyes, radionuclides, and toxic gas molecules have been sensed by 2D MXenes. An inclusive understanding on the adsorptive behavior of MXene-based materials is needed to explain the removal mechanism and effects of different adsorption parameters. This review gives a general overview on recent research progress on MXene materials with special reference to their applications for the adsorptive removal of different pollutants. The general trends in the synthesis of MXenes, their stability and different factors affecting the adsorption process along with the main challenges in understanding the full potential of MXenes for environmental applications are discussed.     

Review of MXenes as new nanomaterials for energy storage/delivery and selected environmental applications

Energy and environmental issues presently attract a great deal of scientific attention. Recently, two-dimensional MXenes and MXene-based nanomaterials have attracted increasing interest because of their unique properties (e.g., remarkable safety, a very large interlayer spacing, environmental flexibility, a large surface area, and thermal conductivity). In 2011, multilayered MXenes (Ti₃C₂T_x, a new family of two-dimensional (2D) materials) produced by etching an A layer from a MAX phase of Ti₃AlC₂, were first described by researchers at Drexel University. The term “MXene” was coined to distinguish this new family of 2D materials from graphene, and applies to both the original MAX phases and MXenes fabricated from them. We present a comprehensive review of recent studies on energy and environmental applications of MXene and MXene-based nanomaterials, including energy conversion and storage, adsorption, membrane, photocatalysis, and antimicrobial. Future research needs are discussed briefly with current challenges that must be overcome before we completely understand the extraordinary properties of MXene and MXene-based nanomaterials.

     

Emerging applications of MXenes for photodetection: Recent advances and future challenges

The development and applications of transition metal carbides, nitrides and carbonitrides, commonly denoted as MXenes, have during the last few years rapidly expanded in various technological fields owing to their unique and controllable properties. These materials exhibit competing performance comparing with traditional materials and have created numerous opportunities for technology markets. Taking the advantage of excellent optoelectronic features, MXenes have been utilized for the construction of photodetectors with various structures and unique functionalities. While the application of MXenes in this area can be traced back to 2016, we have during the recent three years witnessed a dramatic development of MXene-based photodetectors, calling for a timely review to guideline their future direction. In this work, synthetic strategies of pristine MXenes are briefly introduced and their properties are discussed focusing on the optoelectronic aspects that are fundamental for the photoelectric conversion. Recent advances of MXene-based photodetectors are comprehensively summarized based on different types of MXenes and innovative designs of device construction. Finally, we provide perspectives for future challenges and opportunities of MXene-based photodetectors, which may enlighten their further development.     

MXene基水凝胶复合材料的研究进展

MXenes是一类新型二维纳米片,随着MXenes材料的迅速发展,近年来,兴起了一种新型材料,即MXene基水凝胶复合材料,其在生物医学、能源、电磁干扰屏蔽、传感器等方面均具有广泛的应用前景。但目前MXene基水凝胶复合材料的制备和应用仍处于起步阶段。本文主要回顾MXene基水凝胶复合材料的最新进展,详细梳理MXene基水凝胶复合材料的制备方法,并重点介绍其潜在应用前景。最后,针对MXene基水凝胶复合材料领域中所面临的机遇和挑战进行展望。      

MXenes Antibacterial Properties and Applications: A Review and Perspective

The mutations of bacteria due to the excessive use of antibiotics, and generation of antibiotic-resistant bacteria have made the development of new antibacterial compounds a necessity. MXenes have emerged as biocompatible transition metal carbide structures with extensive biomedical applications. This is related to the MXenes’ unique combination of properties, including multifarious elemental compositions, 2D-layered structure, large surface area, abundant surface terminations, and excellent photothermal and photoelectronic properties. The focus of this review is the antibacterial application of MXenes, which has attracted the attention of researchers since 2016. A quick overview of the synthesis strategies of MXenes is provided and then summarizes the effect of various factors (including structural properties, optical properties, surface charges, flake size, and dispersibility) on the biocidal activity of MXenes. The main mechanisms for deactivating bacteria by MXenes are discussed in detail including rupturing of the bacterial membrane by sharp edges of MXenes nanoflakes, generating the reactive oxygen species (ROS), and photothermal deactivating of bacteria. Hybridization of MXenes with other organic and inorganic materials can result in materials with improved biocidal activities for different applications such as wound dressings and water purification. Finally, the challenges and perspectives of MXene nanomaterials as biocidal agents are presented.     

Ultrathin Cellulose Nanofiber Assisted Ambient-Pressure-Dried,Ultralight, Mechanically Robust,Multifunctional MXene Aerogels

Ambient-pressure-dried (APD) preparation of transition metal carbide/nitrides (MXene) aerogels is highly desirable yet remains highly challenging. Here, ultrathin, high-strength-to-weight-ratio, renewable cellulose nanofibers (CNFs) are efficiently utilized to assist in the APD preparation of ultralight yet robust, highly conductive, large-area MXene-based aerogels via a facile, energy-efficient, eco-friendly, and scalable freezing-exchanging-drying approach. The strong interactions of large-aspect-ratio CNF and MXene as well as the biomimetic nacre-like microstructure induce high mechanical strength and stability to avoid the structure collapse of aerogels in the APD process. Abundant functional groups of CNFs facilitate the chemical crosslinking of MXene-based aerogels, significantly improving the hydrophobicity, water resistance, and even oxidation stability. The ultrathin, 1D nature of the CNF renders the minimal MXenes’ interlayered gaps and numerous heterogeneous interfaces, yielding the excellent conductivity and electromagnetic interference (EMI) shielding performance of aerogels. The synergies of the MXene, CNF, and abundant pores efficiently improve the EMI shielding performance, photothermal conversion, and absorption of viscous crude oil. This work shows great promises of the APD, multifunctional MXene-based aerogels in electromagnetic protection or compatibility, thermal therapy, and oil-water separation applications.     

Recent advances in MXenes: From fundamentals to applications

The family of MAX phases and their derivative MXenes are continuously growing in terms of both crystalline and composition varieties. In the last couple of years, several breakthroughs have been achieved that boosted the synthesis of novel MAX phases with ordered double transition metals and, consequently, the synthesis of novel MXenes with a higher chemical diversity and structural complexity, rarely seen in other families of two-dimensional (2D) materials. Considering the various elemental composition possibilities, surface functional tunability, various magnetic orders, and large spin–orbit coupling, MXenes can truly be considered as multifunctional materials that can be used to realize highly correlated phenomena. In addition, owing to their large surface area, hydrophilicity, adsorption ability, and high surface reactivity, MXenes have attracted attention for many applications, e.g., catalysts, ion batteries, gas storage media, and sensors. Given the fast progress of MXene-based science and technology, it is timely to update our current knowledge on various properties and possible applications. Since many theoretical predictions remain to be experimentally proven, here we mainly emphasize the physics and chemistry that can be observed in MXenes and discuss how these properties can be tuned or used for different applications.     

Mechanotribological Aspects of MXene-Reinforced Nanocomposites

MXenes are recently discovered 2D nanomaterial with superior mechanical, thermal, and tribological properties, being commonly employed in a wide variety of critical research areas, ranging from cancer therapy to energy and environmental applications. Due to their special properties, such as mechanoceramic nature with excellent mechanical performance, thermal stability and rich surface properties, MXenes have tremendous potential as advanced composite structures, especially those based on polymers due to a great affinity between macromolecules and the terminating groups of 2D MXenes. MXenes have been extensively explored in metal matrix nanocomposites as well as in solid- or liquid-based lubrication systems owing to the 2D structure and antifriction characteristics. The purpose of the this paper is to provide a comprehensive insight into the material, mechanical, and tribological properties of the MXene nanolayers with discussions on the recent advancements attained from MXene-reinforced nanocomposites starting with the synthesis, fabrication techniques, intricacies of the underlying physics and mechanisms, and finally focusing on the progress in computational studies. This analysis of MXene-based composites will stimulate an emerging field with innumerable opportunities and ample potentials to produce newfangled materials and structures with targeted properties.     

Emerging MXene-Based Flexible Tactile Sensors for Health Monitoring and Haptic Perception

Due to their potential applications in physiological monitoring, diagnosis, human prosthetics, haptic perception, and human–machine interaction, flexible tactile sensors have attracted wide research interest in recent years. Thanks to the advances in material engineering, high performance flexible tactile sensors have been obtained. Among the representative pressure sensing materials, 2D layered nanomaterials have many properties that are superior to those of bulk nanomaterials and are more suitable for high performance flexible sensors. As a class of 2D inorganic compounds in materials science, MXene has excellent electrical, mechanical, and biological compatibility. MXene-based composites have proven to be promising candidates for flexible tactile sensors due to their excellent stretchability and metallic conductivity. Therefore, great efforts have been devoted to the development of MXene-based composites for flexible sensor applications. In this paper, the controllable preparation and characterization of MXene are introduced. Then, the recent progresses on fabrication strategies, operating mechanisms, and device performance of MXene composite-based flexible tactile sensors, including flexible piezoresistive sensors, capacitive sensors, piezoelectric sensors, triboelectric sensors are reviewed. After that, the applications of MXene material-based flexible electronics in human motion monitoring, healthcare, prosthetics, and artificial intelligence are discussed. Finally, the challenges and perspectives for MXene-based tactile sensors are summarized.     

Rational design of MXene-based films for energy storage: Progress,prospects

Two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides (MXenes) have been synthesized and developed into a wide range of applications including energy storage, optoelectronics, electromagnetic interference shielding, biomedicine, and sensors, etc. Compared to other 2D materials, MXenes possess a unique set of properties such as superior mechanical strength, outstanding hydrophily, and excellent dispersion quality, making them particularly suitable for fabricating films/membranes featuring designed microstructures and tunable nanochannels. 2D MXene-based films (MBFs) have demonstrated excellent ion storage, electron transport and ionic selectivity properties for electrochemical energy storage and have received enormous interest in recent years. Compared with conventional electrode materials and structures, MBFs show great advantages in the aspects of flexibility, tailorability and functionality, which are suitable for flexible, portable, and highly integrated energy storage systems. This review summarizes recent advances and well-developed strategies of the MBFs design and fabrication toward applications of metal-ion batteries (MIBs, including Li, Na, K-ions), lithium-sulfur (Li-S) batteries and supercapacitors (SCs). Special attentions are given to the design principles of MBFs based microstructures, inter-layer nanochannels and in-plane nanochannels for energy storage. Finally, the current challenges and promising perspectives of the MBFs for energy storage devices are presented.     

炭分子筛膜的制备及应用研究进展

炭分子筛膜(CMSM)是用于气体分离的一种高效节能新型材料,在气体分离中具有极大的工业化应用潜力.综述了炭分子筛膜的前躯体选择、制备工艺及气体分离应用方面的研究进展,并对炭分子筛膜的发展方向进行了展望.     

MXenes的制备、性质及其在肿瘤诊疗中的研究进展

二维过渡金属碳化物、氮化物或碳氮化物(MXenes)已成为二维材料中一个新兴的热点领域。MXenes材料具有优异的电子传递性能、出色的光热转换性能、较高的比表面积、良好的生物相容性和低毒性等特点, 在肿瘤诊疗中显示出良好的应用前景。本文简要总结了MXenes的制备方法, 包括氢氟酸法、氟盐法、熔融盐法、碱辅助水热法和化学气相沉积法, 及其稳定性、机械性质、光学性质和电学性质。重点综述了MXenes在肿瘤诊疗中的应用, 包括光热治疗、多模式联合治疗、构建MXenes表面介孔材料的联合治疗和MXenes主动靶向联合治疗, 以及建立MXenes诊断-治疗一体化平台。最后简要介绍了MXenes可能辅助肿瘤诊疗的其他特性及其应用, 并阐述了MXenes在肿瘤诊疗中存在的挑战以及未来发展前景。     

Emerging 2D nanomaterials for biomedical applications

Two-dimensional (2D) nanomaterials are an emerging class of biomaterials with remarkable potential for biomedical applications. The planar topography of these nanomaterials confers unique physical, chemical, electronic and optical properties, making them attractive candidates for therapeutic delivery, biosensing, bioimaging, regenerative medicine, and additive manufacturing strategies. The high surface-to-volume ratio of 2D nanomaterials promotes enhanced interactions with biomolecules and cells. A range of 2D nanomaterials, including transition metal dichalcogenides (TMDs), layered double hydroxides (LDHs), layered silicates (nanoclays), 2D metal carbides and nitrides (MXenes), metal–organic framework (MOFs), covalent organic frameworks (COFs) and polymer nanosheets have been investigated for their potential in biomedical applications. Here, we will critically evaluate recent advances of 2D nanomaterial strategies in biomedical engineering and discuss emerging approaches and current limitations associated with these nanomaterials. Due to their unique physical, chemical, and biological properties, this new class of nanomaterials has the potential to become a platform technology in regenerative medicine and other biomedical applications.     

Superhigh and Robust Ion Selectivity in Membranes Assembled with Monolayer Clay Nanosheets

It is crucial to control the ion transport in membranes for various technological applications such as energy storage and conversion. The emerging functional two-dimensional (2D) nanosheets such as graphene oxide and MXenes show great potential for constructing ordered nanochannels, but the assembled membranes suffer from low ion selectivity and stability. Here a class of robust charge-selective membranes with superhigh cation/anion selectivity, which are assembled with monolayer nanosheets of cationic/anionic clays that inherently have permanent and uniform charges on each layer is reported. The transport number of cations/anions of cationic vermiculite nanosheet membranes (VNMs)/anionic Co-Al layered double hydroxide (CoAl-LDH) nanosheet membranes is over 0.90 in different NaCl concentration gradients, outperforming all the reported ion-selective membranes. Importantly, this excellent ion selectivity can persist at high-concentration salt solutions, under acidic and alkaline conditions, and for a wide range of ions of different sizes and charges. By coupling a pair of cation-selective vermiculite membrane and anion-selective CoAl-LDH membrane, a reverse electrodialysis device which shows an output power density of 0.7 W m⁻² and energy conversion efficiency of 45.5% is constructed. This work provides a new strategy to rationally design high-performance ion-selective membranes by using 2D nanosheets with inherent surface charges for controllable ion-transport applications.     

Recent Developments in Graphene‐Based Membranes: Structure,Mass‐Transport Mechanism and Potential Applications

Significant achievements have been made on the development of next‐generation filtration and separation membranes using graphene materials, as graphene‐based membranes can afford numerous novel mass‐transport properties that are not possible in state‐of‐art commercial membranes, making them promising in areas such as membrane separation, water desalination, proton conductors, energy storage and conversion, etc. The latest developments on understanding mass transport through graphene‐based membranes, including perfect graphene lattice, nanoporous graphene and graphene oxide membranes are reviewed here in relation to their potential applications. A summary and outlook is further provided on the opportunities and challenges in this arising field. The aspects discussed may enable researchers to better understand the mass‐transport mechanism and to optimize the synthesis of graphene‐based membranes toward large‐scale production for a wide range of applications.     

Recent Progress in Emerging Novel MXenes Based Materials and their Fascinating Sensing Applications

Early transition metals based 2D carbides, nitrides and carbonitrides nanomaterials are known as MXenes, a novel and extensive new class of 2D materials family. Since the first accidently synthesis based discovery of Ti₃C₂ in 2011, more than 50 additional compositions have been experimentally reported, including at least eight distinct synthesis methods and also more than 100 stoichiometries are theoretically studied. Due to its distinctive surface chemistry, graphene like shape, metallic conductivity, high hydrophilicity, outstanding mechanical and thermal properties, redox capacity and affordable with mass-produced nature, this diverse MXenes are of tremendous scientific and technological significance. In this review, first we'll come across the MXene based nanomaterials possible synthesis methods, their advantages, limitations and future suggestions, new chemistry related to their selected properties and potential sensing applications, which will help us to explain why this family is growing very fast as compared to other 2D families. Secondly, problems that help to further improve commercialization of the MXene nanomaterials based sensors are examined, and many advances in the commercializing of the MXene nanomaterials based sensors are proposed. At the end, we'll go through the current challenges, limitations and future suggestions.     

MXene Printing and Patterned Coating for Device Applications

As a thriving member of the 2D nanomaterials family, MXenes, i.e., transition metal carbides, nitrides, and carbonitrides, exhibit outstanding electrochemical, electronic, optical, and mechanical properties. They have been exploited in many applications including energy storage, electronics, optoelectronics, biomedicine, sensors, and catalysis. Compared to other 2D materials, MXenes possess a unique set of properties such as high metallic conductivity, excellent dispersion quality, negative surface charge, and hydrophilicity, making them particularly suitable as inks for printing applications. Printing and pre/post-patterned coating methods represent a whole range of simple, economically efficient, versatile, and eco-friendly manufacturing techniques for devices based on MXenes. Moreover, printing can allow for complex 3D architectures and multifunctionality that are highly required in various applications. By means of printing and patterned coating, the performance and application range of MXenes can be dramatically increased through careful patterning in three dimensions; thus, printing/coating is not only a device fabrication tool but also an enabling tool for new applications as well as for industrialization.     

Laser-induced graphene and carbon nanotubes as conductive carbon-based materials in environmental technology

Nanotechnology and nanomaterials have attracted interest due to their potential in mitigating contemporary environmental challenges, such as the stressors imposed by increased industrial and agricultural activities, and the deterioration of air, soil and water quality. In particular, advanced technologies that harness carbon-based nanomaterials are poised to emerge as tools that provide new solutions for the global water crises. These tools include, electrically conductive membrane processes, which uniquely combine a separation process with a functional surface. In this respect, laser-induced graphene (LIG) and carbon nanotubes (CNTs) are electrically conductive carbon nanomaterials that hold great utility in a multitude of environmental applications, including the development of fouling-resistant systems for desalination and water treatment, enhanced separation methods, and innovative pollutant sensing and electrocatalytic platforms. Consequently, this review article describes and compares some important recent advances in LIG- and CNT-based electroactive surfaces. The discussion of LIG as an emerging carbon material set in context with CNTs is intended to shed light on future directions and development possibilities to meet the growing global challenges in terms of water treatment applications of both materials as well as other electrically conductive carbon-based nanomaterials exhibiting exceptional performance and versatility.     

Charged Layered Boron Nitride‐Nanoflake Membranes for Efficient Ion Separation and Water Purification

2D layered nanomaterials have attracted considerable attention for their potential for highly efficient separations, among other applications. Here, a 2D lamellar membrane synthesized using hexagonal boron nitride nanoflakes (h‐BNF) for highly efficient ion separation is reported. The ion‐rejection performance and the water permeance of the membrane as a function of the ionic radius, ion valance, and solution pH are investigated. The nonfunctionalized h‐BNF membranes show excellent ion rejection for small sized salt ions as well as for anionic dyes (>97%) while maintaining a high water permeability, ≈1.0 × 10^?3 L m m^?2 h^?1 bar^?1). Experiments show that the ion‐rejection performance of the membrane can be tuned by changing the solution pH. The results also suggest that the rejection is influenced by the ionic size and the electrostatic repulsion between fixed negative charges on the BN surface and the mobile ions, and is consistent with the Donnan equilibrium model. These simple‐to‐fabricate h‐BNF membranes show a unique combination of excellent ion selectivity and high permeability compared to other 2D membranes.