2D Transition Metal Carbides Research Articles

Antiviral Effects of Heparan Sulfate Analogue-Modified Two-Dimensional MXene Nanocomposites on PRRSV and SARS-CoV-2.

Due to the worldwide impact of viruses such as SARS‐CoV‐2, researchers have paid extensive attention to antiviral reagents against viruses. Despite extensive research on two‐dimensional (2D) transition metal carbides (MXenes) in the field of biomaterials, their antiviral effects have received little attention. In this work, heparan sulfate analogue (sodium 3‐mercapto‐1‐propanesulfonate, MPS) modified 2D MXene nanocomposites (Ti3C2‐Au‐MPS) for prevention of viral infection are prepared and investigated using severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) pseudovirus and porcine reproductive and respiratory syndrome virus (PRRSV) as two model viruses. Ti3C2‐Au‐MPS nanocomposites are shown to possess antiviral properties in the different stages of PRRSV proliferation, such as direct interaction with PRRS virions and inhibiting their adsorption and penetration in the host cell. Additionally, Ti3C2‐Au‐MPS nanocomposites can strongly inhibit the infection of SARS‐CoV‐2 pseudovirus as shown by the contents of its reporter gene GFP and luciferase. These results demonstrate the potential broad‐spectrum antiviral property of Ti3C2‐Au‐MPS nanocomposites against viruses with the receptor of heparin sulfate. This work sheds light on the specific antiviral effects of MXene‐based nanocomposites against viruses and may facilitate further exploration of their antiviral applications.

Nanoscale MXene Interlayer and Substrate Adhesion for Lubrication: A Density Functional Theory Study.

Understanding the interlayer interaction at the nanoscale in two-dimensional (2D) transition metal carbides and nitrides (MXenes) is important to improve their exfoliation/delamination process and application in (nano)-tribology. The layer–substrate interaction is also essential in (nano)-tribology as effective solid lubricants should be resistant against peeling-off during rubbing. Previous computational studies considered MXenes’ interlayer coupling with oversimplified, homogeneous terminations while neglecting the interaction with underlying substrates. In our study, Ti-based MXenes with both homogeneous and mixed terminations are modeled using density functional theory (DFT). An ad hoc modified dispersion correction scheme is used, capable of reproducing the results obtained from a higher level of theory. The nature of the interlayer interactions, comprising van der Waals, dipole–dipole, and hydrogen bonding, is discussed along with the effects of MXene sheet’s thickness and C/N ratio. Our results demonstrate that terminations play a major role in regulating MXenes’ interlayer and substrate adhesion to iron and iron oxide and, therefore, lubrication, which is also affected by an external load. Using graphene and MoS2 as established references, we verify that MXenes’ tribological performance as solid lubricants can be significantly improved by avoiding −OH and −F terminations, which can be done by controlling terminations via post-synthesis processing.

2D Ti3C2Tx MXene/MOFs composites derived CoNi bimetallic nanoparticles for enhanced microwave absorption

The emerging two-dimensional (2D) transition metal carbide (MXene) has been a hot topic due to its special structure and high dielectric loss. However, the inevitable stacking phenomenon and lack of magnetic loss of the related MXene materials seriously restrict their application in electromagnetic (EM) absorption. Herein, Ti3C2Tx (a typical material of MXene family) modified with metal–organic frameworks (MOFs) is prepared via simple electrostatic self-assembly and consequent heat treatment. The lamellar MXene provided the substrate for anchoring the MOFs, and the Ni nanoparticles catalytically derived carbon nanofibers (CNFs) served as bridges to construct the cross-linked network. Based on this network structure, the extensive heterogeneous interfaces effectively facilitate the dielectric loss ability, and the addition of magnetic CoNi nanoparticles can enhance the additional magnetic loss capacity. It is worth noting that when the matching thickness is only 1.76 mm, the minimum reflection loss (RLmin) value of the sample (Ti3C2Tx/CNFs/TiO2/CoNi) reaches –54.6 dB, and the corresponding effective absorption bandwidth (EAB, RL < –10 dB) is 4.0 GHz (11.9–15.9 GHz). These results show that magnetic-dielectric synergistic, interfacial polarization, and multilayer structure, were conducive to the improvement of microwave absorption (MA) properties. This study envisions a novel strategy for constructing efficient MXene-based microwave absorbers.

Electrochemiluminescence bioassays based on carbon nitride nanomaterials and 2D transition metal carbides

Electrochemiluminescence (ECL) is a powerful technique for bioassays. To meet the growing demand for bioassays, it is necessary to develop new ECL emitters and co-reaction acceleration strategies to improve detection sensitivity and expand the application scope. Carbon nitride nanomaterials and 2D transition metal carbides, as newly emerging carbon-based nanomaterials, have been increasingly used for ECL bioassays due to their attractive optical and electrochemical properties as well as diversity. In this minireview, we summarized the latest advances in ECL bioassays using carbon nitride nanomaterials and 2D transition metal carbides in the past two years. Finally, we briefly discuss the future trends and challenges of carbon-based nanomaterials for ECL bioanalysis.

Improved lithium ion storage capacity of Ti2SnC via in-situ formation of SnO2

MAX phase materials, the precursors of MXenes (2D transition metal carbides, carbon nitrides, and nitrides), have become increasingly popular in electrochemical applications. In this study, we have successfully prepared Ti2SnC with high lithium capacity via the in-situ formation of SnO2. Results show that there are TiC nanowhiskers and SnO2 inside the Ti2SnC MAX calcined at 800 ℃, and the initial specific capacity could reach 377 and 371 mAh·g−1 at high current densities of 400 mA·g−1 and 1.0 A·g−1, respectively. These values are higher than those of most MAX phase materials reported in previous studies, such as Ti3SiC2 and Nb2SnC, but the stability and rate performance are inferior, which is a direction for the future. This paper provides a new pathway for the application of MAX phases in electrochemistry, which has more in-depth application prospects.

V4C3TX MXene: First-principles computational and separator modification study on immobilization and catalytic conversion of polysulfide in Li-S batteries

Many attempts have recently used rationally-designed Ti3C2Tx MXene-based materials to increase sulfur utilization and tackle the detrimental shuttle effect in Li–S batteries (LSBs) due to their merits of high electronic conductivity, considerable catalytic activity, and sulfur immobilization. Nevertheless, the investigation of applying other two-dimensional (2D) transition metal carbides in LSBs is comparatively rare. In this work, the first-principles computations predicted that V4C3Tx could boost the “adsorption-diffusion-conversion” process of lithium polysulfides (LiPSs) over that of most other metal carbides of the MXene family. Inspired by this, we prepared the V4C3Tx MXene by hydrofluoric acid (HF) etching and then used it as a functional material coating on a polypropylene (PP) separator for LSB. As expected, the V4C3Tx modified PP separator (V4C3Tx-PP) can effectively prevent the shuttle effect of LiPSs via physical blocking, chemical adsorption, and catalytic conversion, as confirmed by visual polysulfide adsorption and diffusion tests, XPS analysis, and a series of electrochemical evaluations. As a result, the LSB with a V4C3Tx-PP enabled a high capacity and enhanced cycling performance (927 mAh g−1 at 1 C and 516 mAh g−1 retained for over 800 cycles, 1 C = 1675 mA g−1). More encouragingly, the cell achieves a superior rate capability of 725 mAh g−1 at 2 C and 586 mAh g−1 at 4 C, respectively. In addition, the V4C3Tx-PP-based LSB shows a high areal capacity of 4.3 mAh cm−2, even with the sulfur loading up to 4 mg cm−2. This work expands the application types and scope of MXenes from theoretical and experimental points of view. The first use of the V4C3Tx MXene modified separator in Li-S batteries creates high potential for practical application.

A Supercapacitor Electrode Synthesis Strategy: Proton Acid‐Treated Ti3C2TX Film with Single‐walled Carbon Nanotubes as a Reinforcement

AbstractHigh‐performance electrode materials are the key to advances in the energy storage area. 2D transition metal carbide Ti3C2TX is the most widely studied MXene with a unique two‐dimensional structure, exhibiting excellent electrochemical properties and becoming a new choice electrode material for supercapacitors in many studies However, the poor mechanical properties of pure the Ti3C2TX film has become the bottlenecks for the application. Ti3C2TX with less Li+ was prepared by proton acid colloid treatment, and then the single‐walled carbon nanotubes (SWCNTs) were used as interlayer barriers in the films to prevent Ti3C2TX layers from restacking to prepare Ti3C2TX and SWCNTs composite films. The composite films were tested and analyzed by different electrochemical techniques. The results showed that the film formed by MXene colloidal filtration after proton acid treatment was denser and the electrical conductivity reached 608700 S/m, which was 3.2 times higher than that of the original Ti3C2TX film. The composite film was prepared by mixing MXene colloidal proton acid treatment and SWCNTs, followed by filtration showd good capacitive capacity, reaching 270.5 F/g by testing in the 1 m H2SO4 electrolyte with the CV cycle of 5 mV/s. And the specific capacitance retention reaches 97.6 % under 5000 CV cycles. The tensile test of composite film shows that the ultimate strength up to 50.3 MPa, which is about 2.3 times compared to original Ti3C2TX film.

Microwave-pulse sugar-blowing assisted synthesis of 2D transition metal carbides for sustainable hydrogen evolution

Electrocatalytic hydrogen evolution reaction (HER) is crucial to clean fuel production. Two-dimensional (2D) transition metal carbides (TMCs) are promising HER electrocatalysts by their excellent intrinsic catalytic activity. However, the synthesis of 2D TMCs requires prolonged high-temperature conditions or rigorous etching processes. Here we achieved an ultra-fast and facile synthesis of ultra-thin carbon-terminated 2D TMCs via a microwave-pulse sugar-blowing method. A series of 2D TMCs are obtained rapidly within 3 min. This method accurately adjusts carbon-layer thickness and facilitates the formation of 2D structures. Accordingly, the electrocatalytic HER activity and stability of TMCs are significantly improved. The 2D W2C with 1 nm carbon-layer thickness shows high HER activity and ultra-long durability (100 h) in both acidic and alkaline electrolytes. Furthermore, this microwave-pulse method is a generic synthesis strategy that is demonstrated by the successful preparation of 2D WC, Mo2C and MoC.

Activating lattice oxygen of two-dimensional MnXn−1O2 MXenes via zero-dimensional graphene quantum dots for water oxidation

The poor oxygen evolution reaction (OER) activity of two-dimensional (2D) transition metal carbides (MXenes) is a major obstacle to their application in highperformance water splitting and fuel cells due to the high energy barriers for the absorption of intermediates. Here, we demonstrate that the lattice oxygen of MnXn−1O2 MXenes can be activated by 0D graphene quantum dots (GQDs), thereby activating the OER via the lattice-oxygen oxidation mechanism (LOM) instead of the conventional adsorbate evolving mechanism. The pH-dependent OER activity of MnXn−1O2@GQDs and 18O isotope-labelling experiments with time-of-flight secondary-ion mass spectrometry (TOF-SIMS) provide the direct evidence of LOM. Interestingly, the activated lattice oxygen amount can be controlled by the GQDs. The as-prepared 0D/2D Ti3C2O2@GQDs heterostructure delivers a highly reduced overpotential of 390 mV (bare Ti3C2O2: 530 mV) at a benchmark current density of 10 mA cm−2. Through optimizing the thickness and the additional conductive substrate, the overpotential at 10 mA cm−2 decreases to 250 mV, while the Tafel slope is reduced to 39 mV dec−1; these values indicate the as-prepared heterostructure is superior to the state-of-the-art MXene-based OER catalysts. This work provides a new strategy to enhance the OER activity of MnXn−1O2 and extends the application of LOM from perovskite to MXenes.

Surface termination effects on the terahertz-range optical responses of two-dimensional MXenes: Density functional theory study

Two-dimensional (2D) transition metal carbides referred to as MXenes show excellent terahertz (THz) shielding performance and stealth effectiveness. Differently from other 2D materials, MXenes inherently have surface functionality and consequently, surface termination engineering has been a powerful means to manipulate their physical properties greatly in a predictable way. Despite MXenes’ great potential in THz technology, the surface engineering issue has not been examined to date. For the first time, using density functional theory calculations, this study investigated the THz-range optical responses of the most popular MXene, Ti3C2Tx by systematically varying surface termination species among -O, -OH, -F, -Cl, and -Br. We found that O-terminated MXenes showed the highest THz absorption performance of 180,000 cm−1. Meanwhile, OH-terminated MXenes exhibited seven-to-eight times magnitude smaller THz absorption efficiency and F-terminated MXenes showed significantly deteriorated two-order magnitude smaller performance than that of O-terminated MXene. For recently developed surface halogen alternatives, Cl-terminated MXenes have almost the same but slightly lower terahertz absorption efficiency compared to F-terminated MXenes, while Br-terminated MXenes have remarkably enhanced one-order magnitude greater performance. O, OH, and Br-terminated MXenes belong to a good THz absorbing materials in a descending order of O, Br, and OH. We revealed that the THz absorption capacity is intimately related with metallicity that can be recognized by the exceedingly large refractive index at the ultralow photon energy of 0.001–0.002 eV. This study strongly indicated the promising potential of surface termination engineering for tailoring the THz photonics of MXenes.

Termination-Property Coupling via Reversible Oxygen Functionalization of MXenes.

MXenes are a growing family of 2D transition-metal carbides and nitrides, which display excellent performance in myriad of applications. Theoretical calculations suggest that manipulation of the MXene surface termination (such as =O or −F) could strongly alter their functional properties; however, experimental control of the MXene surface termination is still in the developmental stage. Here, we demonstrate that annealing MXenes in an Ar + O2 low-power plasma results in increased =O functionalization with minimal formation of secondary phases. We apply this method to two MXenes, Ti2CTx and Mo2TiC2Tx (Tx represents the mixed surface termination), and show that in both cases, the increased =O content increases the electrical resistance and decreases the surface transition-metal’s electron count. For Mo2TiC2Ox, we show that the O content can be reversibly altered through successive vacuum and plasma annealing. This work provides an effective way to tune MXene surface functionalization, which may unlock exciting surface-dependent properties.

Advances of MXenes; Perspectives on Biomedical Research.

The last decade witnessed the emergence of a new family of 2D transition metal carbides and nitrides named MXenes, which quickly gained momentum due to their exceptional electrical, mechanical, optical, and tunable functionalities. These outstanding properties also rendered them attractive materials for biomedical and biosensing applications, including drug delivery systems, antimicrobial applications, tissue engineering, sensor probes, auxiliary agents for photothermal therapy and hyperthermia applications, etc. The hydrophilic nature of MXenes with rich surface functional groups is advantageous for biomedical applications over hydrophobic nanoparticles that may require complicated surface modifications. As an emerging 2D material with numerous phases and endless possible combinations with other 2D materials, 1D materials, nanoparticles, macromolecules, polymers, etc., MXenes opened a vast terra incognita for diverse biomedical applications. Recently, MXene research picked up the pace and resulted in a flood of literature reports with significant advancements in the biomedical field. In this context, this review will discuss the recent advancements, design principles, and working mechanisms of some interesting MXene-based biomedical applications. It also includes major progress, as well as key challenges of various types of MXenes and functional MXenes in conjugation with drug molecules, metallic nanoparticles, polymeric substrates, and other macromolecules. Finally, the future possibilities and challenges of this magnificent material are discussed in detail.

Growth of self-aligned nonlayered TaC nanosheets on liquid copper by a solid phase diffusion strategy

Compared with layered 2D materials, nonlayered 2D materials combine atomic thickness and high-activity surface, leading to many unique properties. Herein, a solid phase diffusion strategy is raised to obtain self-aligned nonlayered TaC single crystals on liquid copper. Because of the immiscibility of Cu and Ta, a β-Ta nanolayer with a thickness of ∼7 nm would form on the surface of liquid copper by a long-time solid phase diffusion process. After introducing CH4, the β-Ta nanolayer could be converted into 10 μm TaC single crystals with a thickness of 10 nm. With the extension of the reaction time, TaC single crystals would form an ordered self-aligned state spontaneously under the action of lateral capillary force. Finally, the self-aligned TaC nanosheets are assembled into large-size TaC films with a thickness of 10 nm. This strategy paves a new way to grow large-size nonlayered 2D transition metal carbides.

Approaching intrinsic dynamics of MXenes hybrid hydrogel for 3D printed multimodal intelligent devices with ultrahigh superelasticity and temperature sensitivity

Hydrogels are investigated broadly in flexible sensors which have been applied into wearable electronics. However, further application of hydrogels is restricted by the ambiguity of the sensing mechanisms, and the multi-functionalization of flexible sensing systems based on hydrogels in terms of cost, difficulty in integration, and device fabrication remains a challenge, obstructing the specific application scenarios. Herein, cost-effective, structure-specialized and scenario-applicable 3D printing of direct ink writing (DIW) technology fabricated two-dimensional (2D) transition metal carbides (MXenes) bonded hydrogel sensor with excellent strain and temperature sensing performance is developed. Gauge factor (GF) of 5.7 (0 − 191% strain) and high temperature sensitivity (−5.27% °C−1) within wide working range (0 − 80 °C) can be achieved. In particular, the corresponding mechanisms are clarified based on finite element analysis and the first use of in situ temperature-dependent Raman technology for hydrogels, and the printed sensor can realize precise temperature indication of shape memory solar array hinge.

Two-dimensional tetragonal and hexagonal lattices of transition metal carbides MC (M = Ti, Zr, Hf): Observation of two nodal loops and strong light-harvesting ability

Two-dimensional (2D) transition metal carbides (TMCs) have captured immense interest for their fascinating physical and chemical properties. Among them, bare carbide MXenes exhibit a metallic feature, greatly limiting the potential applications in optoelectronic devices. Herein, based on the particle swarm optimization and first-principles calculations, we predicted the existence of two single layer (SL) TMCs, namely, tetragonal β-MC and hexagonal γ-MC (M = Ti, Zr, Hf). The two structures are more stable than previously reported α-MC and possess semimetal and semiconductor properties, respectively. We further reveal that the β-MC monolayers have two nodal loops around the Fermi level. SL γ-TiC, ZrC, and HfC have a bandgap of 1.59, 1.24, and 1.57 eV, respectively, and display strong light-harvesting ability in the visible light range. Our research expands the 2D TMCs family beyond the extensively existing MXenes and greatly enriches the carbon chemistry.

Toward Room-Temperature Electrical Control of Magnetic Order in Multiferroic van der Waals Materials.

Electrical control of magnetic order in van der Waals (vdW) two-dimensional (2D) systems is appealing for high-efficiency and low-dissipation nanospintronic devices. For realistic applications, a vdW 2D material with ferromagnetic (FM) and ferroelectric (FE) orders coexisting and strongly coupling at room temperature is urgently needed. Here we present a potential candidate for nonvolatile electric-field control of magnetic orders at room temperature. Using first-principles calculations, we predict the coexistence of room-temperature FM and FE orders in a 2D transition metal carbide, where the spatial distribution of magnetic moments strongly couples with the orientation of out-of-plane electric polarization. Furthermore, an electric-field switching between interfacial FM and ferrimagnetic orders is realizable through constructing a multiferroic vdW heterostructure based on this material. These findings make a significant step toward realizing room-temperature multiferroicity and strong magnetoelectric coupling in 2D materials.

The Emergence of 2D MXenes Based Zn-Ion Batteries: Recent Development and Prospects.

Rechargeable zinc-ion batteries (ZIBs) with exceptional theoretical capacity have garnered significant interest in large-scale electrochemical energy storage devices due to their low cost, abundant material, inherent safety, high specific energy, and ecofriendly nature. Metal carbides/nitrides, known as MXenes, have emerged as a large family of 2D transition metal carbides or carbonitrides with excellent properties, e.g., high electrical conductivity, large surface functional groups (e.g., F, O, and OH), low energy barriers for the diffusion of electrolyte ions with wide interlayer spaces. After a decade of effort, significant development has been achieved in the synthesis, properties, and applications of MXenes. Thus, it has opened up various exciting opportunities to construct advanced MXene-based nanostructures for ZIBs with excellent specific energy and power. Herein, this review summarizes the advances across multiple synthesis routes, related properties, morphological and structural characteristics, and chemistries of MXenes for ZIBs. The recent development of MXene-based electrodes is introduced, and electrolytes for ZIBs are elucidated in detail. MXene-based rocking chair ZIBs, strategies to enhance the performance of MXene-based cathodes, suppress the dendrites in MXene-based anodes, and MXene-based flexible ZIBs are pointed out. A rational design and modification of the MXenes as well as the production of composites with metal oxides exhibits promise in solving issues and enhancing the electrochemical performance of ZIBs. Finally, the present challenges and future prospects for MXene-based ZIBs are discussed.

High-Performance Flexible Piezoresistive Sensor Based on Ti3C2Tx MXene with a Honeycomb-like Structure for Human Activity Monitoring.

Wearable and flexible pressure sensors have sparked great interest due to their unique capacity to conformally attach to the surface of the skin and quantify human activities into recordable electric signals. As a result, more and more research efforts are being devoted to developing high-sensitivity and cost-effective flexible sensors for monitoring an individual’s state of activity. Herein, a high-performance flexible piezoresistive sensor was designed and fabricated by combing 2D transition metal carbides, nitrides, and carbonitrides (MXene) with a honeycomb-like structure formed by femtosecond filamentating pulses. The sensing mechanism is attributed to the change of the connecting conductive paths between the top interdigital electrodes and the bottom microstructured films coated with MXene. The obtained sensing device demonstrates high sensitivity of 0.61 kPa−1, relatively short response time, and excellent reliability and stability. Benefiting from the aforementioned extraordinary sensing performance, the sensor can be used with success to monitor tiny physiological signals, detect large deformations during human movement, and distinguish finger gestures, thus demonstrating its broad prospects in physiological analysis systems, health monitoring systems, and human–machine interaction.

Friction between MXenes and other two-dimensional materials at the nanoscale

Two-dimensional (2D) materials have unique friction properties that are different from their 3D counterparts. MXenes, a large family of 2D transition metal carbides, carbonitrides, and nitrides, have recently attracted attention as solid lubricants on the macroscale. Here we experimentally investigate the friction of Ti3C2Tx and Ti2CTx MXenes against Ti3C2Tx and Ti2CTx MXenes, graphene, and MoSe2 at the nanoscale, using atomic force microscopy (AFM). Ti3C2Tx and Ti2CTx MXene coated SiO2 spherical AFM probes were used to slide against films of these materials with varying number of monolayers deposited on the substrate. We have found that over the 15 nm sliding distance the measured nanoscale coefficients of friction (COFs) for all the investigated 2D interfaces are below 0.01. At the same time, hydrogen bonding involving -O- and –OH surface terminating groups on MXenes induced higher friction forces for the MXene/MXene contacts compared to other contacts. Moreover, a less significant number-of-monolayers effect on the friction was observed for MXenes due to their thicker monolayers compared with other 2D materials in this study. These results further contribute to our understanding of the mechanisms of friction of MXenes and reveal the potential of MXenes as tunable lubricants at the nanoscale.

Low-temperature carbonized biomimetic cellulose nanofiber/MXene composite membrane with excellent microwave absorption performance and tunable absorption bands

2D transition metal carbides and nitrides (MXenes) have gained much interest in microwave absorption. However, the high conductivity of MXenes results in inferior absorption performance. To solve this problem, Cellulose nanofiber (CNF) is compounded with MXenes to build membranes with biomimetic structures. CNF not only contributes to adjusting the electromagentic parameters, but also enhances the microwave attenuation and regulates the absorption band. In this work, nacre-like and loofah-like carbonized CNF/MXenes membranes were successfully prepared. The self-assembly of CNF and MXene avoids the impedance mismatch, and the biomimetic structures enhance conductive loss, polarization loss and multiple reflection. The results show that nacre-like carbonized CNF/MXene membrane (CCM) exhibits absorbing performance with the minimum reflection loss (RLmin) of −42.2 dB and the Effective absorption band (EAB) of 7.12 GHz. Meanwhile, the absorption peaks are mainly concentrated on X-band. Further, as the morphology changes to porous layers, the RLmin of loofah-like CCM increases to −63.8 dB, whose EAB is 7.32 GHz at 2.5 mm, and the main absorption peaks shift to Ku-band. Besides, the possible absorption mechanism of biomimetic composite membranes has been expounded. This work provides a versatile strategy for CNF/MXene composite membrane with biomimetic structures on excellent and tunable microwave absorption performance.