Properties Of MXenes Research Articles

Application of Two-Dimensional MXene materials in sensors

Transition metal carbides and nitrides/carbonitrides (MXenes) with satisfactory conductivity, high specific surface area and excellent hydrophilicity have attracted the attention of many researchers in the field of electrochemical sensors in recent years. Etched MXenes usually show an accordion-like morphology; moreover, monolayer MXenes exhibit better electrical conductivity and mechanical properties. The electronic and chemical properties of MXenes can be significantly changed by means of compounding, hybridization and modification. MXenes with large surface areas can be used in biosensors as carriers for recognition elements to achieve direct electron transfer to target analytes. In addition, MXenes exhibit excellent biological compatibility so that they can be incorporated into biological receptors without affecting biological activity. MXenes can be combined with other metal oxide nanoparticles to expand the electrode surface area while reducing the overpotential effect in the electroanalysis process to enhance catalytic activity. MXene-based sensors for detecting strain, pressure, temperature, gas, various biomarkers, and some environmental pollutants, and for use in other major research fields are summarized. The future challenges in MXenes research, development and applications of electrochemical sensing are discussed.

Interactions of Ti3C2 MXene with Aqueous Zwitterionic Biological Buffers: Implications for Applications in Biological Systems

MXenes, a family of ultrathin layered two-dimensional (2D) transition-metal carbides, nitrides, and carbonitrides, are steadily advancing as novel inorganic nanosystems for a broad range of applications. While high conductivity, solution processability, hydrophilic nature, and the presence of various surface functional groups enable the use of 2D MXenes in aqueous systems, applications that involve the use of MXenes in aqueous systems and biological solutions, including but not limited to water treatment, water desalination, and biological assays, are only beginning to emerge. For the successful application of MXene in aqueous systems, their interactions with common aqueous solution constituents must be better understood. This paper describes the structural and functional properties of Ti3C2Tx (Tx = O−, OH−, F−) MXenes in N-substituted commonly used biological buffers like N-(2-hydroxyethyl)-piperazine-N′-ethanesulfonic acid (HEPES) and 3-(N-morpholino)-propane sulfonic acid (MOPS) and with a series of piperazine-based molecules dissolved in phosphate buffer solutions. Dissolving MXenes in these buffers significantly impacts their optical, structural, and electrical properties. The interactions of Ti3C2Tx MXenes with N-substituted zwitterionic buffer molecules are structure-dependent and mostly but not fully reversible. X-ray photoelectron spectroscopy measurements reveal small but measurable surface oxidation through the formation of Ti–O bonds. Our results suggest a complex interaction pattern where some interactions are driven by hydrogen bonding and electrostatic forces, while others involve chemisorption, which results in a permanent impact on the MXene nanosheets. This study is an important step toward understanding the stability of MXenes in complex aqueous media and the impact of interactions of MXenes with nitrogen-containing molecules on MXene properties, which are especially important in applications of MXenes in biological systems. The nature of interactions between MXenes and biological buffer molecules, revealed in our study, suggests that surface chemistry modifications of MXenes are required to preserve their chemical stability and enable their applications in complex biological solutions.

MXene-based electrochemical (bio) sensors for sustainable applications: Roadmap for future advanced materials

MXenes are emerging transition metal carbides and nitrides-based 2D conductive materials. They have found wide applications in sensors due to their excellent valuable properties. This paper reviews the recent research status of MXene-based electrochemical (bio) sensors for detecting biomarkers, pesticides, and other aspects. The first part of this paper introduced the synthesis strategy and the effect of surface modification on various properties of MXenes. The second part of this paper discussed the application of MXenes as electrode modifiers for detecting pesticides, environmental pollutants, and biomarkers such as glucose, hydrogen peroxide, etc. Hope this review will inspire more efforts toward research on MXene-based sensors to meet the growing requirements.

Latest advances on MXenes in biomedical research and healthcare.

The unique combination of physical and chemical properties of MXenes has propelled a growing number of applications in biomedicine and healthcare. The expanding library of MXenes with tunable properties is paving the way for high-performance, application-specific MXene-based sensing and therapeutic platforms. In this article, we highlight the emerging biomedical applications of MXenes with specific emphasis on bioelectronics, biosensors, tissue engineering, and therapeutics. We present examples of MXenes and their composites enabling novel technological platforms and therapeutic strategies, and elucidate potential avenues for further developments. Finally, we discuss the materials, manufacturing, and regulatory challenges that need to be synergistically addressed for the clinical translation of MXene-based biomedical technologies.

Structural Stability and Electronic Transport Properties of Nb2C‐MXenes under High Pressure

AbstractThe extraordinary electronic properties of MXenes are closely associated with their surface terminations and external strain. Herein, by applying pressure, the structural and electronic properties of Nb2C‐MXenes with two different terminations F (Nb2CFx) and Cl (Nb2CClx) are reported. Through high‐pressure X‐ray diffraction and scanning electron microscopy, it is observed that Nb2CFx loses its layered structure and becomes disordered above 20 GPa, while Nb2CClx remains as layered structures up to 42.5 GPa. Surprisingly, the stable Nb2CClx shows the axial compression coefficients with 1174.5 ± 39.2 GPa along the c axis and 1234.8 ± 25.8 GPa along the a axis, even larger than that of its precursor Nb2AlC MAX phase. It is also found that the resistance of Nb2CFx exhibits a drop of two orders of magnitude from the ambient pressure. Accompanied by a slight increment of the superconducting transition temperature, the superconductivity of Nb2CClx survives up to 50.5 GPa. The results uncover the effects of surface terminations on structural stability and electronic properties of Nb2C‐MXenes under high pressure.

Surface and Interface Regulation of MXenes: Methods and Properties.

Since the discovery of Ti3 C2 Tx in 2011, 2D transition metal carbides, nitrides, and carbonitrides, known as MXenes, have been attracting great attention as the emerging member of 2D materials. The surface terminations, intercalants, and the interfaces between MXenes and other substances are of importance for tuning the properties of MXenes. For instance, surface termination of MXenes can change the density of states at the Fermi levels to make MXenes electronically tunable. Different terminations can lead to band opening and changes in behavior from metallic to semiconducting, as well as dramatic changes in the work function of MXenes. On the other hand, electron transfer occurring at the interface between MXenes and other substances due to the physical interaction/chemical bonding, changes the electron configuration of MXenes and realizes the functionalization. In this review, the most up-to-date progress of the surface and interface regulation of MXenes is comprehensively summarized, introducing the effect of various synthesis methods on the surface and interface chemistry, the routes on tuning the surface and interface chemistry, and the related potential applications. Finally, the perspective of the future research directions and challenges on surface and interface regulation is outlined.

Maximizing Electron Channels Enabled by MXene Aerogel for High-Performance Self-Healable Flexible Electronic Skin.

Among the increasingly popular miniature and flexible smart electronics, two-dimensional materials show great potential in the development of flexible electronics owing to their layered structures and outstanding electrical properties. MXenes have attracted much attention in flexible electronics owing to their excellent hydrophilicity and metallic conductivity. However, their limited interlayer spacing and tendency for self-stacking lead to limited changes in electron channels under external pressure, making it difficult to exploit their excellent surface metal conductivity. We propose a strategy for rapid gas foaming to construct interlayer tunable MXene aerogels. MXene aerogels with rich interlayer network structures generate maximized electron channels under pressure, facilitating the effective utilization of the surface metal properties of MXene; this forms a self-healable flexible pressure sensor with excellent sensing properties such as high sensitivity (1,799.5 kPa-1), fast response time (11 ms), and good cycling stability (>25,000 cycles). This pressure sensor has applications in human body detection, human-computer interaction, self-healing, remote monitoring, and pressure distribution identification. The maximized electron channel design provides a simple, efficient, and scalable method to effectively exploit the excellent surface metal conduction of 2D materials.

Nature‐Inspired Interconnected Macro/Meso/Micro‐Porous MXene Electrode

AbstractThe geometric multiplication development of MXene has promoted it to become a star material in numerous applications including, but not limited to, energy storage. It is found that pore structure modulation engineering can improve the inherent properties of MXene, in turn significantly enhancing its electrochemical performance. However, most of the current works have focused on exploring the structure‐effective relationships of the single‐scale pore structure regulation of MXene. Inspired by Murray's law from nature where a highly graded structure of the organisms is discovered and used to achieve effective diffusion and maximize mass transfer, a hierarchically interconnected porous MXene electrode across micro‐meso‐macroporous is constructed. This MXene‐based electrode provides large amounts of active sites while greatly shortening the ion diffusion channel. Finally, the zinc ion microcapacitor based on this MXene electrode exhibits an ultrahigh area‐specific capacitance up to 410 mF cm−2 and an energy density up to 103 µWh cm−2 at a power density of 2100 µW cm−2. The areal energy density outperforms the currently reported zinc ion microcapacitors. This study supports an effective strategy for electrode materials (including but not limited to MXene) to achieve ultra‐short ion diffusion channels and maximum transport efficiency for next‐generation high‐performance energy storage.

Recent advances in MXenes: a promising 2D material for photocatalysis

We focus on the recent development of the synthesis and properties of MXene, current challenges and the future possible directions to develop and enhance the catalytic performance of MXene for various environmental and energy demands.

MXene-based chemical gas sensors: Recent developments and challenges.

The long-running Covid-19 pandemic has forced researchers across the globe to develop novel sensors and sensor materials for detecting minute quantities of biogenic viruses with high accuracy in a short period. In this context, MXene galleries comprising carbon/nitride two-dimensional nanolayered materials have emerged as excellent host materials in chemical gas sensors owing to their multiple advantages, including high surface area, high electrical conductivity, good thermal/chemical conductivity and chemical stability, composition diversity, and layer-spacing tunability; furthermore, they are popular in clinical, medical, food production, and chemical industries. This review summarizes recent advances in the synthesis, structure, and gas-sensing properties of MXene materials. Current opportunities and future challenges for obtaining MXene-based chemical gas sensors with high sensitivity, selectivity, response/recovery time, and chemical durability are addressed. This review provides a rational and in-depth understanding of the relationship between the gas-sensing properties of MXenes and structure/components, which will promote the further development of two-dimensional MXene-based gas sensors for technical device fabrication and industrial processing applications.

A systematic study of work function and electronic properties of MXenes from first principles.

Functional 2D materials are interesting for a wide range of applications. The rapid growth of the MXene family is due to its compositional diversity, which, in turn, allows significant tuning of the properties, and hence their applicability. The properties are to a large extent dictated by surface terminations. In the present work, we demonstrate the influence of termination species (O, NH, N, S, F, Cl, Br, I) on the changes in electronic structure, work function, dynamical stability, and atomic charges and distances of MXenes (Ti2C, Nb2C, V2C, Mo2C, Ti3C2, and Nb4C3). Among these systems, the work function values were not previously reported for ∼60% of the systems, and most of the previously reported MXenes with semiconducting nature are here proven to be dynamically unstable. The results show that the work function generally decreases with a reduced electronegativity of the terminating species, which in turn is correlated to a reduced charge of both the metal and terminating species and an increased metal-termination distance. An exception to this trend is NH terminations, which display a significantly reduced work function due to an intrinsic dipole moment within the termination. Furthermore, the results suggest that halogen terminations improve the electrical conductivity of the materials.

Chalcogen (S, Se, and Te) decorated few-layered Ti3C2Tx MXene hybrids: modulation of properties through covalent bonding.

2D carbides and nitrides of transition metals (MXenes) have shown great promise in a variety of energy storage and energy conversion applications. The extraordinary properties of MXenes are because of their excellent conductivity, large carrier concentration, vast specific surface area, superior hydrophilicity, high volumetric capacitance, and rich surface chemistry. However, it is still desired to synthesize MXenes with specific functional groups that deliver the required characteristics. This is due to the fact that a considerable amount of metal atoms is exposed on the surface of MXenes during their synthesis through an etching procedure; hence, other anions and cations are uncontrollably implanted on their surfaces. Because of this situation, the first invented Ti3C2Tx MXene suffers from low photoresponsivity and detectivity, large overpotential, and small sensitivity in photoelectrochemical (PEC) photodetectors, hydrogen evolution reaction (HER), and sensing applications. Therefore, surface modification of the MXene structure is required to develop the device's performance. On the other hand, there is still a lack of understanding of the MXene mechanism in such cutting-edge applications. Thus, the manipulations of MXenes are highly dependent on understanding the device mechanism, suitable modification elements, and modification methods. This study for the first time reveals the conjugation effect of pre-selected S, Se, and Te chalcogen elements on a few-layered Ti3C2Tx MXene to synthesize new composites for PEC photodetector, HER, and vapor sensor applications. Also, the mechanism of the chalcogen decorated few-layered Ti3C2Tx MXene composites for each application is discussed. The selection of a few-layered Ti3C2Tx MXene is due to its fascinating characteristics which make it capable to be considered as an appropriate substrate and incorporating chalcogen atoms. The Te-decorated few-layered Ti3C2Tx MXene composite provides better performances in PEC photodetector and vapor sensing applications. Although the potential value of the Se-decorated few-layered Ti3C2Tx composite is slightly lower than that of the Te-decorated sample in HER application, its overpotential is still greater than that of the Te-decorated sample. The acquired results show that the S-decorated few-layered Ti3C2Tx composite demonstrates the lowest performance in all three examined applications in comparison with the other two samples.

Can Surface Structure Manipulate Mechanical and Thermal Properties of MXenes?

Can Surface Structure Manipulate Mechanical and Thermal Properties of MXenes?

Solution-free synthesis of MXene composite hybrid nanostructures by rapid Joule heating

A rapid Joule heating technique enables the successful synthesis of a wide range of hybrid materials without compromising the unique properties of MXenes making them suitable for various applications where the synergistic effect of MXene composites can yield significant performance enhancements.

A robust COF@MXene membrane for ultra-high flux of water-in-oil emulsion separation.

A facile covalent assembly strategy is proposed for the preparation of superhydrophobic COF-stabilized MXene separation membranes. Ultra-high separation fluxes of up to 54 280 L m-2 h-1 and 643 200 L m-2 h-1 bar-1 are obtained for emulsified water-in-oil mixtures by adopting gravity and external pressure, respectively. Moreover, the challenges of easy swelling and oxidation properties of MXene have been effectively overcome via the COF-stabilized mechanism.

Bioinspired 3D-Printed MXene and Spidroin-Based Near-Infrared Light-Responsive Microneedle Scaffolds for Efficient Wound Management.

Biomedical dressings have been comprehensively explored for wound healing; however, the complicated manufacturing process and mono-function of the dressing remain critical challenges for further applications. Here, a versatile extrusion three-dimensional (3D) printing strategy to prepare MXene and spidroin-incorporated microneedle scaffolds with photothermal responsive and self-healing properties for promoting wound healing is proposed. Inspired by the cactus, the microneedle scaffold is composed of a top porous scaffold, and microneedles whose inverse opal (IO) photonic crystal (PC) structure and the ample space between the scaffold gaps endow the microneedle scaffold with high drug-carrying capacity. Furthermore, the excellent electrical and photothermal properties of MXene allow the microneedle scaffold to perform sensitive wound movement monitoring and controlled drug release under near-infrared irradiation. Moreover, the extensive hydrogen bonding and Schiff base between the spidroin, polyurethane (PU), and aloe vera gel (avGel) molecules conferred high self-healing and mechanical performance to the microneedle scaffold. In vivo experiments with rat models of wounds have shown that drug-laden microneedle scaffolds under near-infrared (NIR) light can promote the recovery of full-skin wounds. These unique characteristics suggest that 3D-printed multifunctional microneedle scaffolds show great potential for applications in facilitating wound healing and will find widespread applications in wound management.

Toward Smart Sensing by MXene.

The Internet of Things era has promoted enormous research on sensors, communications, data fusion, and actuators. Among them, sensors are a prerequisite for acquiring the environmental information for delivering to an artificial data center to make decisions. The MXene-based sensors have aroused tremendous interest because of their extraordinary performances. In this review, the electrical, electronic, and optical properties of MXenes are first introduced. Next, the MXene-based sensors are discussed according to the sensing mechanisms such as electronic, electrochemical, and optical methods. Initially, biosensors are introduced based on chemiresistors and field-effect transistors. Besides, the wearable pressure sensor is demonstrated with piezoresistive devices. Third, the electrochemical methods include amperometry and electrochemiluminescence as examples. In addition, the optical approaches refer to surface plasmonic resonance and fluorescence resonance energy transfer. Moreover, the prospects are delivered of multimodal data fusion toward complicated human-like senses. Eventually, future opportunities for MXene research are conveyed in the new material discovery, structure design, and proof-of-concept devices.

Investigating suitable medium for the long-duration storage of Ti2CTx MXene

Recently, 2D material MXene gained a significant attention due to its unique properties like chemical diversity, hydrophilicity, 2D morphology, metallic conductivity, etc. Despite the promising properties of MXenes, these materials are not gaining momentum in various applications because of their poor chemical or oxidation stability. Earlier reports stated that organic solvents with low temperature storage could prevent the oxidation of Ti3C2Tx MXene flakes due to less number of dissolved oxygen molecules in the solvents. Due to the lack of a suitable storage media, Ti2CTx MXene is still receiving less attention despite having equivalent physio-chemical properties to Ti3C2Tx. To address this issue, this paper reports a suitable medium for preventing or delaying the degradation or oxidation of Ti2CTx MXene. Herein, Ti2CTx MXene was dispersed in different solvents for a duration of 3 months at ambient (room temperature) and freezing conditions (−20 °C and −80 °C) and characterized thereafter using XRD, Raman, SEM, TEM and XPS techniques. The results are suggested that polar solvents with a high surface tension, high viscosity, high boiling point, and high dielectric constant and in case of “Dry MXene”, keep it in a vacuum or inert atmosphere, will be suitable for long duration storage of Ti2CTx MXene at room temperature. However, it is not the best option for storing the material for a long duration of time. Finally, we have successfully find out the suitable storage medium to avoid the degradation and oxidation of Ti2CTx MXene for a long period of time and it is recommended that it should be dispersed in polar solvents and stored in a frozen condition like − 20 °C temperature or below (−80 °C). In case of “Dry MXene”, the storage condition should be at subzero temperature (−20 °C), and/or freezing conditions should be maintained to avoid degradation as well as oxidation.

Current Understanding of the Wettability of MXenes

AbstractSince the first report regarding the successful fabrication of few‐layer transition metal carbides (known as MXenes) of 2011, their intrinsic properties, such as mechanical strength and electrical conductivity, are intensively studied. Though the hydrophilic nature of MXenes is widely reported and utilized to fabricate various functional materials, there is a lack of systematic study with respect to the science behind the wetting phenomena of MXene‐based materials. The goal of this manuscript is to provide some useful guidelines in the design of novel MXene‐based systems with desirable wetting properties by analyzing the current understanding of the wettability of MXenes. Specifically, after the introduction of the fundamental concepts in wetting theory, the wettability of pure MXene films is summarized based on the recently published results from both theoretical and experimental studies. Then, the determining factors in the wetting properties of MXenes associated with surface architectures and chemical compositions are clarified, which is followed by the effect of hybridization strategies discussed in detail. In the end, a summary of the abundant applications relying on the wetting properties of MXene‐based systems is presented along with the current challenges and the corresponding future research directions in this field.

MXene-Based Ink Design for Printed Applications

MXenes are a class of two-dimensional nanomaterials with a rich chemistry, hydrophilic surface and mechano-ceramic nature, and have been employed in a wide variety of applications ranging from medical and sensing devises to electronics, supercapacitors, electromagnetic shielding, and environmental applications, to name a few. To date, the main focus has mostly been paid to studying the chemical and physical properties of MXenes and MXene-based hybrids, while relatively less attention has been paid to the optimal application forms of these materials. It has been frequently observed that MXenes show great potential as inks when dispersed in solution. The present paper aims to comprehensively review the recent knowledge about the properties, applications and future horizon of inks based on 2D MXene sheets. In terms of the layout of the current paper, 2D MXenes have briefly been presented and followed by introducing the formulation of MXene inks, the process of turning MAX to MXene, and ink compositions and preparations. The chemical, tribological and rheological properties have been deeply discussed with an eye to the recent developments of the MXene inks in energy, health and sensing applications. The review ends with a summary of research pitfalls, challenges, and future directions in this area.