Transition Metal Carbides Research Articles

Mesoporous MXene nanosheets/CNF composite aerogels for electromagnetic wave absorption and multifunctional response

To acquire excellent wave-absorbing materials with broadened applications, transition metal carbides (Ti3C2Tx, MXene) have been the research focus. However, the high conductivity of MXene limits its electromagnetic wave (EMW) absorption capability; meanwhile, the inferior mechanical properties of MXene-based aerogels severely restrict their applications. Here, porous MXene (PMXene) nanosheets were prepared by hydrogen peroxide etching, which was then physically and chemically crosslinked with cellulose nanofibres (CNF) to successfully prepare PMXene/CNF composite wave-absorbing aerogels with excellent mechanical properties. PMXene/CNF aerogel achieved a minimum reflection loss (RLmin) of − 72.27 dB and an effective absorption bandwidth (EAB) of 5 GHz at a thickness of 1.63 mm without any magnetic component. The aerogels exhibited excellent environmental stability at a density of 12.5 mg/cm3, including fatigue resistance (100 compression cycles, 0.075 energy loss efficiency) and low-temperature resistance. Refining the mechanical properties exploits the aerogel’s potential for motion monitoring and electronic skin applications. In addition, the aerogels integrate properties such as water–oil separation, photothermal conversion, and thermal insulation (thermal conductivity of 0.045 W/(m-K)). Therefore, multifunctional PMXene/CNF aerogels have a broad potential for future application in the defence industry, electronic devices, and smart wearable fields.

Two-Dimensional MXene-Based Functional Composites for Photocatalysts: Current Status and Perspectives

Abstract: MXenes, as novel two-dimensional (2D) transition metal carbides, nitrides or carbonitrides, have excellent metal conductivity, high carrier mobility, and surface-terminated groups regulated band structure. It can be thus used as a cocatalyst in photocatalytic systems to improve the photocatalytic properties. This review represented recent research progress on the controllable construction of MXene-based functional composites with zero-dimensional (0D), one-dimensional (1D), 2D, and three-dimensional (3D) semiconductor photocatalysts and their applications for photocatalysts. Extensive information related to 2D MXene-Based composites for photocatalysts and their associated patents were collected. The construction methods and photocatalytic enhancement mechanisms of 2D MXene-based composite photocatalysts were given. Due to their excellent physical and chemical properties, 2D MXene composites have been widely used in pollutant removal, hydrogen production, CO2 reduction, and nitrogen fixation. Through the construction of 2D MXene-based functional composite photocatalysts with novel structures and excellent performance, it provides a new perspective for the design and construction of high-efficiency photocatalysts. The future research directions of MXene-based composite photocatalysts was proposed.

Unique dual superlyophobic covalent organic frameworks (COF-TpBD) intercalated MXene composite membrane for efficient oil-water separation

The development of composite membranes utilizing transition metal carbides and nitrides, exemplified by Ti3C2Tx (MXene), has proven efficacious in the treatment of oily wastewater. However, challenges arise from the prolonged and convoluted transport paths within MXene interlayer nanochannels, significantly impeding mass transfer and diminishing membrane permeability. This investigation incorporated porous covalent organic frameworks (COFs) as intercalating agents into two-dimensional (2D) MXene-based membranes to expand the interlayer nanochannels. The resulting MXene@COF-TpBD functional layer polyethersulfone (PES) composite membrane exhibited a distinctive dual superoleophobic surface, concurrently manifesting underwater superoleophobicity and underoil superhydrophobicity (underwater oil contact angle > 150°, underoil water contact angle > 150°). The membranes exhibited excellent water flux (up to 4092.7 L·m-2·h-1·bar-1), efficient oil-water emulsion separation (up to 1908.4 L·m-2·h-1·bar-1, rejection rates >99.78%), noteworthy fouling resistance and structural stability, outperforming most of existing similar membranes. Furthermore, supported by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the incorporation of COF-TpBD improved the antifouling characteristics of the composite membrane. This work presents innovative insights into the improvement of 2D MXene membranes and the use of COF-TpBD for the specific remediation of oily wastewater.

Promising antibacterial performance of Ag-nanoparticles intercalated Nb2CTx MXene towards E. coli and S. aureus

MXenes are a group of two-dimensional (2D), atomically thin transition metal carbides, nitrides and carbon nitrides with a variety of desirable characteristics. Due to their exceptional physiochemical characteristics and ultrathin lamellar structure, MXenes have shown excellent antibacterial capabilities. Two-dimensional Nb2CTx MXene has been recently analyzed for potential applications in antibacterial materials. Due to the development of antibiotic-resistant bacteria further materials or composite materials need to be explored. In this work, we report the antibacterial properties of a composite of Nb2CTx and silver, synthesized using electrostatic self-assembly method. This work also demonstrates the optimization of the etching of Nb2CTx MXene for different time intervals and delamination of Nb2CTx MXene by using two different solvents i.e., tetramethylammonium hydroxide (TMAOH) and isopropyl amine. The antibacterial characteristics of Nb2CTx MXene, delaminated Nb2CTx MXene and Nb2CTx-Ag composite of 1:1 and 2:1 were tested and compared. This study demonstrates that Nb2CTx-Ag composite shows higher antibacterial properties than Nb2CTx and delaminated Nb2CTx MXene and could reach an antibacterial activity of 98.5 % for S. aureus and 100 % for E. coli.

Fabrication of MXene-TiO2 nanotube composite and their electrochemical study in acidic and alkaline medium

MXenes, a novel class of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, have emerged as promising electrocatalysts for the hydrogen evolution reaction (HER) due to their remarkable electrical conductivity, exceptional structural and chemical stability, and large active surface area. In this study, we synthesized a 1D/2D Ti3C2 MXene-TiO2 nanotube (TNT) composite via electrostatic self-assembly method. Field emission scanning electron microscopy (FE-SEM) confirmed the distinctive accordion-like, multilayered morphology of Ti3C2Tx MXene, while X-ray diffraction (XRD) provided the crystalline phase of the composite. High-resolution transmission electron microscopy (HR-TEM) revealed an average particle size of 38.41 nm for the MXene-TNT nanocomposite. Additionally, X-ray photoelectron spectroscopy (XPS) confirmed the composite composition, highlighting the synergistic integration of MXene and TiO2 nanotube that enhances electrical interactions and contributes to superior catalytic performance. Electrochemical performance was assessed using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) in both acidic and alkaline media. Among the composites, the MXene-TNT (1:10) loading demonstrated a low Tafel slope of 65 mV/dec in acidic media, indicative of enhanced mass transfer properties. In alkaline media, the MXene-TNT (1:5) composite exhibited a Tafel slope of 160 mV/dec for HER, with kinetic performance proving more favorable in the acidic environment. Additionally, the composite displayed a Tafel slope of 149 mV/dec for the oxygen evolution reaction (OER) in acidic media. This study demonstrates a feasible approach for developing high-performance, cost-effective electrocatalytic materials for efficient hydrogen production, utilizing MXene as a co-catalyst.

A Time‐Saving Method for Evaluating the Fatigue Strength of Carburized High‐Alloy Steel Containing Carbides

To propose a time‐saving method for evaluating the fatigue strength of carburized steel, the fatigue behavior and fracture mechanism of carburized 14Cr14Co13Mo5 steels are studied by the rotary bending fatigue tests. It is found that the fatigue crack initiation site changes from surface to internal after carburizing due to the residual compressive stress and carbide cluster caused by the carburization. Besides, a notable correlation between the stress intensity of the cracked carbides at fatigue crack initiation site and fatigue life is observed in the carburized samples. This correlation allows for the estimation of fatigue strength at long conditional life based on samples tested at relatively high stress amplitudes with short lives, achieving a prediction error within 10% for the material studied. A significant time saving of ≈65% compared to the staircase method is achieved. The proposed method has significant implications for improving the efficiency fatigue strength evaluation in carburized steels containing carbides.

Surface Plasmons in Two-Dimensional MXenes.

MXenes, a class of layered two-dimensional transition metal carbides and nitrides, exhibit excellent optoelectronic properties and show promise for fields ranging from photonics and communications to energy storage and catalysis. Some members of the MXene family are metallic and exhibit large in-plane conductivity, making them possibly suited for 2D plasmonics. The highly variable chemical structure of MXenes offers a broad chemical space to tune material properties for plasmonic applications, including plasmon-enhanced catalysis, surface-enhanced Raman spectroscopy (SERS), and electromagnetic shielding. However, this synthetic complexity has also presented several roadblocks in the process of moving MXene plasmonics into applications. For example, in the prototypical MXene Ti3C2Tx, there remains disagreement over the bulk plasmon energy and the assignment of a prominent resonance around 1.7 eV. We discuss fundamental models and theories of plasmon physics and apply these models to MXenes in order to clarify some of these problems. We outline the potential for hyperbolic plasmons in MXenes and propose new avenues for MXene photonics research.

Co-infiltration and dynamic formation of Pd3ZnCx intermetallic carbide by syngas boosting selective hydrogenation of acetylene

Transition metal carbide shows excellent performance in selective hydrogenation of acetylene, however, the carburization of Pd-based intermetallic compounds remains infeasible. Here we report the successful synthesis of an unprecedented Pd3ZnCx intermetallic carbide, via co-infiltration of zinc and carbon in one-step carburization by syngas. Utilizing state-of-the-art in situ characterizations and theoretical calculation, we unveil the dynamic evolution of Pd3ZnCx during carburization, forming a Pd3Zn like cubic phase carbide structure. A unique transitional state (Pdt) with low content of Zn/C co-infiltration is clearly identified facilitating phase transition and sustain incorporation of carbon and zinc at elevated temperatures. The Pd3ZnCx carbide shows by far the best catalytic performance in the selective hydrogenation of acetylene with a high selectivity (>90%) even at a high H2/C2H2 ratio. Our results therefore provide a co-infiltration strategy and dynamic insights for the one-step synthesis of Pd based intermetallic carbides, towards high-performance intermetallic compound for selective hydrogenation of acetylene.

Engineering MXene Surface via Oxygen Functionalization and Au Nanoparticle Deposition for Enhanced Electrocatalytic Hydrogen Evolution Reaction.

MXene, a family of 2D transition metal carbides and nitrides, presents promising applications in electrocatalysis. Maximizing its large surface area is key to developing efficient non-noble-metal catalysts for the hydrogen evolution reaction (HER). In this study, oxygen-functionalized Ti3C2Tx MXene (Ti3C2Ox) is synthesized and deposited gold nanoparticles (Au NPs) onto it, forming a novel composite material, Au-Ti3C2Ox. By selectively removing other functional groups, mainly -O functional groups are retained on the surface, directing electron transfer from Au NPs to MXene due to electronic metal-support interaction (EMSI), thereby improving the catalytic activity of the MXene surface. Additionally, the interaction between Au NPs and -O functional groups further enhanced the overall catalytic activity, achieving an overpotential of 62 mV and a Tafel slope of 40.1 mV dec-1 at a current density of -10 mA cm-2 in 0.5 m H2SO4 solution. Density functional theory calculations and scanning electrochemical microscopy with ≤150 nm resolution confirmed the enhanced catalytic efficiency due to the specific interaction between Au NPs and Ti3C2Ox. This work provides a surface modification strategy to fully utilize the MXene surface and enhance the overall catalytic activity of MXene-based catalysts.

Exploring the structural and electronic properties of N-doped Ti2C MXenes for novel applications in advanced materials and devices: A DFT study

MXenes, a category of two-dimensional transition metal carbides and nitrides, have attracted significant interest owing to their distinctive characteristics. This study utilizes Density Functional Theory (DFT) to examine the effects of nitrogen doping on the structural and electrical properties of Ti2C MXenes. N-doping induces significant alterations in the lattice structure and electronic properties, culminating in an elevated density of states at the Fermi level, indicating improved conductivity. Furthermore, optical characteristics such as reflectivity and loss function are affected by N-doping, resulting in a shift in the intensity of the reflectivity peak. The alterations provide N-doped Ti2C MXenes viable candidates for advanced applications in energy storage, catalysis, and electronic devices, facilitating future empirical and theoretical investigations in MXene-based materials.

Impact of PEDOT:PSS/Ti3C2Tx composite hole transport layer on the performance of perovskite light emitting diodes

The two-dimensional transition metal carbide MXenes, often designated by Ti3C2Tx, have garnered significant interest on account of their distinctive optoelectronic characteristics. In this paper, PEDOT:PSS/Ti3C2Tx composite hole transport layer (HTLs) was prepared by adding the MXenes material Ti3C2Tx into PEDOT:PSS, and quasi-two-dimensional perovskite light-emitting diodes (PeLEDs) were fabricated and investigated. While the addition concentration of Ti3C2Tx was 0.25 mg/mL, the optimal device shows the maximum luminance of 6250 cd/m2, and the current efficiency of 6.17 cd/A, which is 133 % and 112 % higher than the reference device without Ti3C2Tx, respectively. It is indicated that the additive incorporation of Ti3C2Tx in PEDOT:PSS can improve the efficiency of hole injection and conductivity of hole transport layer, and passivate the defects of perovskite film, thus enhancing the optoelectronic performance of PeLEDs. The findings of this study indicate that the PEDOT:PSS/Ti3C2Tx composite HTLs has considerable potential for application in PeLEDs.

Molten salts assisted one-pot synthesis of hollow transition metal carbides

Hollow transition metal carbides (TMCs) have broad potential applications due to their high melting point, low density, high specific surface area, and good electrical conductivity. However, the conventional preparation of TMCs often involves complex processes and requires high temperature, which limits their practical application. Herein, hollow TMC powders including NbC, VC, ZrC, and TiC were successfully prepared by one-pot molten salt synthesis (MSS) at relatively low temperatures. The formation mechanism and the influence of carbon crystallinity on the synthesis process were investigated. It was found that amorphous carbon precursors act as sacrificial templates in MSS, which can induce the Kirkendall effect to form the hollow structure. When using graphitized carbon microspheres as carbon precursors, the reaction between transition metals and carbon is uneven and relatively sluggish, which prevents the occurrence of the Kirkendall effect, thus hindering the formation of hollow structure. This work provides a facile method to prepare hollow TMCs with the advantages of low synthesis temperature and adjustable morphology.

Spray-on electronic tattoos with MXene and liquid metal nanocomposites

Electronic tattoos present appealing forms of wearable devices operated directly on the skin. Although two-dimensional transition metal carbides (MXenes) are promising material choices, their films are susceptible to fracturing when subjected to tensile deformations. This study presents electronic tattoos comprising MXenes and liquid metal microcapsules fabricated by spray deposition onto the skin. The resulting nanocomposite has a low sheet resistance of approximately 2.2 Ω/sq. and can be repetitively deformed to 50 % strain. The enhanced deformability is attributed to the release of liquid metal from the microcapsules upon stretching, facilitating the repair of cracks in the nanocomposite layer. In addition, the nanocomposite conforms to the skin, sticks well, and moves with the body. It is also resistant to friction and sweat, making it suitable for various applications. A bifunctional electronic tattoo has been further developed, showcasing its capability to acquire biopotential signals and deliver electrical stimulation. Our study effectively improves the deformability of MXene-based nanocomposites for electronic tattoos, achieving seamless device integration in the body.

Exploring the synergistic potential: A comprehensive review of MXene-Based composite electrocatalysts

MXenes, a prominent category of 2D materials consisting of transition metal carbides, nitrides, and carbonitrides, have garnered significant interest since the introduction of Ti3C2Tx. This fascination arises from their exceptional attributes like their high special surface area, superb electrical conductivity, and remarkable mechanical strength. These qualities have established MXenes as top materials for electrocatalysis, a critical component of clean energy conversion technologies. Crucially, MXenes serve as the foundation for the next generation of electrocatalysts, aiming at high activity, selectivity, and sustainability.In electrocatalysis, MXene composites enhance the performance of various reactions, such as water splitting and fuel cell operations. When combined with metals, metal oxides, or other conductive materials, MXenes exhibit improved electrical conductivity and catalytic activity. These composites can achieve higher efficiency and selectivity in electrochemical reactions, making them suitable for sustainable energy applications. MXene composites also play an significant role in the development of supercapacitors, which are energy storage devices characterized by rapid charge and discharge capabilities. The high special surface area and excellent conductivity of MXenes increase charge storage and improve energy and power density. When MXene composites are mixed with materials such as polymers or other nanomaterials, they can further optimize these properties, leading to increased performance and longevity. Also in battery technology, MXene composites are used to improve the performance of anodes and cathodes. Their high capacity for ion storage and conduction contributes to higher energy density and faster charge/discharge rates. By combining MXenes with other materials, researchers are able to create advanced battery systems that overcome traditional limitations, resulting in batteries that are more efficient, durable, and capable of delivering higher performance. In this study MXene–Carbon composites, MXene-LDH composites, MXene-Polymer composites, MXene-MOF composites are reviewed and discussed. The versatility of MXenes is further enhanced when they are composited with various other materials. Such compositions allow for tailoring their innate properties, enabling a widespread range of applications. In terms of environmental implications, MXenes and their composites boast excellent reducibility, conductivity, and biocompatibility, making them very appropriate for use in environmental clean-up and protection applications.

Biomimetic Porous MXene Antibacterial Adsorbents with Enhanced Toxins Trapping Ability for Hemoperfusion.

2D transition metal carbides and nitrides, i.e., MXene, are recently attracting wide attentions and presenting competitive performances as adsorbents used in hemoperfusion. Nonetheless, the nonporous texture and easily restacking feature limit the efficient adsorption of toxin molecules inside MXene and between layers. To circumvent this concern, here a plerogyra sinuosa biomimetic porous titanium carbide MXene (P-Ti3C2) is reported. The hollow and hierarchically porous structure with large surface area benefits the maximum access of toxins as well as trapping them inside the spherical cavity. The cambered surface of P-Ti3C2 prevents layers restacking, thus affording better interlaminar adsorption. In addition to enhanced toxin removal ability, the P-Ti3C2 is found to selectively adsorb more middle and large toxin molecules than small toxin molecules. It possibly originates from the rich Ti-deficient vacancies in the P-MXene lattice that increases the affinity with middle/large toxin molecules. Also, the vacancies as active sites facilitate the production of reactive oxygen under NIR irradiation to promote the photodynamic antibacterial performance. Then, the versatility of P-MXene is validated by extension to niobium carbide (P-Nb2C). And the simulated hemoperfusion proves the practicability of the P-MXene as polymeric adhesives-free adsorbents to eliminate the broad-spectrum toxins.

Optimized Design of Quinary High-Entropy Transition Metal Carbide Ceramics Based on First Principles

In this paper, we developed models for 21 quinary high-entropy transition metal carbide ceramics (HETMCCs), composed of carbon and the transition metals Ti, Zr, Mo, V, Nb, W, and Ta, employing the Special Quasirandom Structures (SQS) method. We investigated how the transition metal elements influence lattice distortion, mixing enthalpy, Gibbs free energy of mixing, and the electronic structure of the systems through first-principles calculations. The calculations show that 21 systems can form a stable single phase, among which (TiMoVNbTa)C5, (ZrMoNbWTa)C5, and (MoVNbWTa)C5 exhibit superior stability. The formation energy and migration energy of carbon vacancies in systems with strong single-phase stability were calculated to predict their radiation resistance. The formation energy of carbon vacancies is closely related to the types of surrounding transition metal elements, with values ranging between the maximum and minimum formation energies observed in binary transition metal carbides (TMCs). The range of migration energy for carbon vacancies is wider than that observed in TMCs, which can hinder their long-range migration and enhance the radiation resistance of the materials.

The importance of the vibrational entropy in the mixing stabilization for complex ceramics

AbstractThe concept of high‐entropy materials has been introduced based on the idea that multiple principal components can be mixed through the increase in configurational entropy. Implicit in this idea is that the vibrational entropy, the other component of the mixing entropy, is small compared to the configurational entropy. To explore this relationship, we examined the mixing enthalpy, configurational entropy, and vibrational entropy of two binary ceramic systems—the transition metal carbides and transition metal diborides. We computed the vibrational entropy directly using the dynamical matrices obtained from density functional theory and the quasiharmonic approximation. The mixing vibrational entropy of the mixed diborides is at least as large as the configurational entropy while it is smaller for the carbides. Utilizing the phonon density of states, we further demonstrate the origin of the high mixing vibrational entropy arises because of a large number of new low‐frequency modes that appear in the diborides. Similar modes occur in the carbides but occur at larger frequencies. These differences ultimately arise because of the structural differences where metal atoms share nearest neighbors in the diborides, while they do not in the carbides. This increased vibrational mixing entropy dramatically enhances the mixing of the diborides and demonstrates that this type of entropy cannot be neglected when considering what stabilizes mixtures and provides a new perspective on what is considered high entropy.

Chemically Stable Group IV-V Transition Metal Carbide Thin Films in Hydrogen Radical Environments.

Hydrogen is a crucial element in the green energy transition. However, its tendency to react with and diffuse into surrounding materials poses a significant challenge. Therefore, developing coatings to protect system components in hydrogen environments (molecular, radicals (H*), and plasma) is essential. In this work, we report group IV-V transition metal carbide (TMC) thin films as potential candidates for protective coatings in H* environments at elevated temperatures. We expose TiC, ZrC, HfC, VC, NbC, TaC, and Co2C thin films, with native surface oxycarbides/oxides (TMO x C y /TMO x ), to H* at elevated temperatures. Based on X-ray photoelectron spectroscopy performed on the samples before and after H*-exposure, we identify three classes of TMCs. HfC, ZrC, TiC, TaC, NbC, and VC (class A) are found to have a stable carbidic-C (TM-C) content, with a further subdivision into partial (class A1: HfC, ZrC, and TiC) and strong (class A2: TaC, NbC, and VC) surface deoxidation. In contrast to class A, a strong carbide reduction is observed in Co2C (class B), along with a strong surface deoxidation. The H* interaction with TMC/TMO x C y /TMO x is hypothesized to entail three processes: (i) hydrogenation of surface C/O atoms, (ii) formation of CH x /OH x species, and (iii) subsurface C/O atom diffusion to the surface vacancies. The number of adsorbed H atoms required to form CH x /OH x species (i) and the corresponding thermodynamic energy barriers (ii) are estimated based on the change in the Gibbs free energy (ΔG) for the reduction reactions of TMCs and TMO x . Hydrogenation of surface carbidic-C atoms is proposed to limit the reduction of TMCs, whereas the deoxidation of TMC surfaces is governed by the thermodynamic energy barrier for forming H2O.

The Impact of Metal Ions on MXene Membranes: Critical Role of Titanium Vacancies.

Two-dimensional transition metal carbides and nitrides (MXenes) and MXene-based membranes hold promise for applications including water purification and seawater desalination; however, their environmental behavior and fate in these matrices remain unknown. In this study, we systematically assessed the reaction efficiencies of Ti3C2Tx at varying important environmental conditions. Our experiments revealed that copper and iron ions accelerated the oxidation rate of Ti3C2Tx 55.4 and 33.4 times, respectively. TiO2 and amorphous carbon were identified as the primary solid products. Based on in situ water-phase atomic force microscopy, atomic high-angle annular dark-field scanning transmission electron microscopy, and theoretical results, we postulate that metal ions enhance Ti3C2Tx oxidation by spontaneously migrating and anchoring at Ti vacancies, which then become active sites for this reaction. This process increases the adsorption of H2O and oxygen, making the Ti vacancy-rich surface convex area the most vulnerable site to attack. The findings in this study provide useful information for a comprehensive understanding of the interaction between MXene structural defects and metal ions as well as for the design and modification of MXene membranes resistant to metal ion impact.

Exploring topological phases in superconducting transition metal (Sc, Ti, V)-carbides

The combination of non trivial band topology and superconductivity, resulting in topological superconductivity, igniting a fervent pursuit in the realm of quantum materials. Through density functional theory and maximally localized Wannier functions, we delve into the electronic and topological properties of transition metal carbides ΛC (with Λ= Sc, Ti, V). Phonon dispersions guarantee the structural stability of these superconductors. Witness the presence of band inversion within the Brillouin Zone of TiC and VC, contrasting the absence of such band inversion in ScC. In addition, the nonzero Z2 topological invariant as well as the occurrence of Dirac cone in the surface spectrum of TiC and VC, unveil their topologically nontrivial character. These transition metal carbides emerge as promising candidates for probing the depths of topological superconductivity and unraveling the associated Majorana bound states.