Developing brake pad friction materials is critical to enhancing the automotive brake system's performance. Solid lubricants play a crucial role in reducing wear and maintaining friction under demanding conditions. While molybdenum disulfide (MoS 2 ) remains widely used, recent progress in 2D materials has opened new possibilities. Among these, titanium-based MXenes (Ti 3 C 2 T x ) have emerged as promising candidates due to their mechanical strength, thermal resilience, and inherent self-lubricating properties. This study presents the first comprehensive evaluation of Ti 3 C 2 T x and MoS 2 as a solid lubricant in automotive brake pad composites. A fixed matrix composition of steel fibers, barium sulfate, phenol-formaldehyde resin, and iron oxide is maintained across three formulations: a MoS 2 -based, a Ti 3 C 2 T x -based, and a hybrid combining both additives. The samples are fabricated adopting powder metallurgical techniques. Samples evaluation is conducted to analyze their thermal, mechanical, physical, and tribological properties. Microstructural analyses are performed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Tribological performance is assessed through pin-on-disk against a gray cast iron disk. Results show that Ti 3 C 2 T x -containing composites excel in all aspects compared to MoS 2 . The hybrid formulation composite reduces specific wear rate by 16.5%, while the Ti 3 C 2 T x -only composite achieves a 48.5% reduction relative to the MoS 2 composite.

MXenes are a rapidly expanding family of two-dimensional transition metal carbides and nitrides whose exceptional compositional, structural, and surface-chemical tunability has driven rapid growth across materials science, chemistry, physics, and engineering. This roadmap consolidates the current state of MXene research, spanning synthesis, processing, fundamental properties, computation, electrochemical energy storage, biomedical applications, electronics, optoelectronics, membranes, sensing, tribology, and extreme-environment technologies. By identifying key advances, persistent challenges, and emerging opportunities, the roadmap provides a forward-looking outlook for guiding MXenes from laboratory discovery toward transformative applications.

Two-dimensional transition metal carbides and nitrides (MXenes) are an important family of electrochemically active 2D materials. MXenes combine high conductivity with hydrophilicity, making them attractive materials for many applications, including electrochemical energy storage, sensing, desalination, and others. In order to better understand the role of structure on MXene properties, here, we investigated the vibrational properties and diffusion of water in MXenes with differing layer thicknesses and transition metal compositions using inelastic, quasi-elastic, and small-angle neutron scattering. We found that all of the Mo-containing MXenes studied here exhibited comparable vibrational dynamics and diffusion coefficients to each other and to previously studied Ti3C2T x . However, Ti2CT x was distinguished by its faster diffusion and more hydroxyl groups compared to the other MXenes studied. These results can help guide the selection of appropriate MXenes for energy storage and electrochemical water purification applications.

Understanding the structure-property relationships in layered transition-metal carbides or nitrides, known as MXenes, is of critical importance for their rational design, synthesis, and application. However, the vast chemical and structural diversity of MXenes, stemming from their wide range of M and X elements, surface terminations, and different atomic coordination environments, makes it challenging to clearly understand these structure- property relationships. In this work, we perform first-principles density functional theory (DFT) calculations and molecular dynamics (MD) simulations to comprehensively investigate the stability and a variety of physical properties of MXenes with different coordination environments. Using Ti- and Mo-based carbide MXenes as model systems, energetic calculations reveal that Ti-based MXenes are most stable in octahedral coordination, whereas Mo-based MXenes preferentially adopt prismatic coordination. This fundamental difference in preferred atomic coordination gives rise to markedly distinct properties between these two systems as a function of the fraction of octahedral and prismatic sites. For instance, the in-plane stiffness of Ti-based MXenes increases as octahedral coordination becomes dominant, but it decreases in the Mo-based MXenes under the same conditions. Additional stability analyses based on mechanical, lattice-dynamical, and temperature-dependent thermodynamic properties demonstrate that many metastable MXenes not only satisfy the strict stability criteria but can also undergo phase transitions among different structures and even become stabilized at elevated temperatures. Although surface terminations, such as F and O atoms, do not alter the energetic ordering or the overall stiffness trends among stable and metastable MXenes, they influence other material properties. For instance, O termination can induce semiconducting behavior in both stable and metastable Ti2CO2 MXenes. This study significantly advances the fundamental understanding of structure-property relationships in MXenes and provides valuable guidance for developing coordination-based design principles to precisely engineer MXenes with improved properties.

There is a need for new electrochemical energy storage materials that can handle high cycling rates (high power) for rapid charging without compromising high energy density, such as high-power Li-ion batteries (LIBs) and Li-ion capacitors (LICs). Electrically conductive and redox-active two-dimensional (2D) materials, such as transition metal carbides and borides, are promising candidates for these applications. Tailoring in-plane chemically ordered MAB phases (i-MAB) has facilitated the synthesis of their 2D derivatives (i-MBenes), which possess ordered vacancies at the metal sites. The first reported i-MBene paper is Mo4/3B2Tx, which is derived from the parent i-MAB phase (Mo2/3Y1/3)2AlB2 by the selective etching of Al and Y. In this study, we report on the synthesis of 2D Mo4/3B2Tx aerogel and its electrochemical performance as an electrode material for LIBs. Our aerogel exhibits remarkable stability during life-cycling testing at high applied specific currents, maintaining a specific capacity of 260 mAh g-1 even after completing 500 cycles under a high specific current of 2 A g-1. At a moderate specific current of 100 mA g-1, it delivers an energy density of 363 Wh kg-1, while at a high specific current of 2 A g-1, it achieves a specific power of 1300 W kg-1. Complementary density functional theory calculations further reveal that Li preferentially occupies hexagonal Mo sites in Mo4/3B2Tx, supporting the observed stable lithiation behavior and excellent high-rate capability. These results suggest that 2D Mo4/3B2Tx aerogel is a promising candidate for high-power LIBs and LICs.

MXenes, an emerging class of two-dimensional van der Waals materials, have become the focus of research, demonstrating exceptional potential in electrochemical, biochemical and electronic applications. This chapter provides a brief overview of MXenes, covering their fundamental characteristics, synthesis methods and current challenges, with particular attention on synthesis methods.

The increasing occurrence of pharmaceutical residues in treated wastewaters, together with the emergence of MXene-based composites as novel and promising catalysts for advanced oxidation processes (AOP), motivates the development of more efficient and selective treatment technologies. In this study, a novel Nb4C3Tx-Co3O4 nanohybrid AOP catalyst was synthesized for peroxymonosulfate (PMS) activation under dark conditions to degrade four pharmaceutical pollutants including caffeine (CAF), ibuprofen (IBU), paracetamol (PAR), and sulfamethoxazole (SMX). Structural and morphological characterization confirmed successful integration of Co3O4 nanoparticles onto the Nb4C3Tx MXene surface. Under optimized conditions, complete degradation of the pharmaceuticals was obtained within 60 min, except for IBU, which required >100 min due to steric hindrance in its molecular structure, resulting in fewer sites available for attack by reactive species. The contribution of reactive species differs among the pharmaceutical where degradation of IBU and PAR was predominantly governed by sulfate radicals (SO4 center dot-), contributing over 50% while CAF and SMX followed a degradation mechanism involving singlet oxygen (O-1(2), up to 30%), SO4 center dot- (20-40%) and (OH)-O- center dot (20-40%). The AOP involved a redox-mediated PMS activation mechanism predominantly on Co and Nb surface sites. The Nb4C3Tx-Co3O4 catalyst exhibited robust performance in cocktail of pollutants and maintained satisfactory degradation efficiency, especially for SMX and PAR in tertiary effluents from wastewaters treatment plant (WWTP) collected in Bratislava. In addition, the chemical structure of degradation by-products was characterized by LC-MS analysis and a degradation mechanism was proposed. Colorimetric MTT assays of the treated waters showed no acute cytotoxicity from either the PhACs or their degradation products on short-term exposure. This study provides new insights into pollutant-specific oxidation mechanisms and reactive species profiles in PMS-based AOPs, establishing Nb4C3Tx-Co3O4 as a promising non-conventional catalyst for potential quaternary treatment in WWTP technology.

MBenes are a class of two-dimensional transition-metal borides derived from layered MAB phases. Here, we use first-principles calculations to predict a new tetragonal MB (1 : 1) MBene phase featuring a diamond-shaped B-B lattice and systematically assess its phase stability, synthetic accessibility, and catalytic performance towards the CO2 reduction reaction (CO2RR). Four tetragonal configurations are benchmarked against known hexagonal and orthorhombic phases, and a multi-tier screening identifies six robust members (CrB, FeB, MoB, WB, IrB, and PtB). Exploration of the I4/mmm MAB space reveals 11 viable precursors, including the experimentally synthesized Ir2ZnB2, which validates our screening approach. CO2RR free-energy diagrams show that CrB favors CH3OH while FeB, MoB, WB, IrB, and PtB preferentially yield HCOOH. The corresponding limiting potentials are competitive with, and in some cases superior to, those reported for state-of-the-art orthorhombic and hexagonal MBenes. These findings expand the MBene landscape by establishing a tetragonal phase with structural, synthetic, and catalytic promise.

MXene-based coatings offer a promising route to multifunctional neural interfaces for in vivo neurochemical sensing. Here, we develop Ti(3)C(2)Tx MXene/poly(3,4-ethylenedioxythiophene) (MXene/PEDOT) composite coatings for glassy carbon (GC) and platinum (Pt) flexible microelectrode arrays (MEAs), enabling multianalyte neurochemical sensing and electrophysiological recording. MXene/PEDOT forms uniform nanostructured films that increase charge storage capacity by one order of magnitude, reduce impedance by similar to 84% at 1 kHz, and enhance charge transfer efficiency for square-wave voltammetry (SWV). Using an optimized SWV waveform, functionalized GC-MEAs detect dopamine (DA) and serotonin (5-HT) individually and simultaneously with low limits of detection (9.6 nM for DA; 4.7 nM for 5-HT), high selectivity, and exceptional resistance to electrochemical fouling (>120 h DA; >40 h 5-HT) and biofouling. In vivo measurements resolve basal extracellular DA in the striatum (99 +/- 29 nM) and 5-HT in the amygdala and prefrontal cortex (20 +/- 7 nM), with their simultaneous striatal detection validated by pharmacological manipulation of neurotransmitter levels. Extending this strategy to Pt-MEAs confers neurochemical sensitivity while preserving single-unit recordings, establishing MXene/PEDOT as a versatile functional coating for multimodal, multianalyte interfaces.

Dual polarity photodetection devices are an important building block for multifunctional devices. In particular, photoelectrochemical photodetectors (PEC PDs) show great promise due to their ability to control photocurrent polarity by varying the incident light wavelength and the choice of electrolyte. However, achieving broadband dual-polarity PEC PDs that deliver high responsivity and bias switchable operation remains a significant challenge. 2D transition metal carbides, nitrides, and carbonitrides (MXenes) are emerging materials that combine high electrical conductivity, excellent electrochemical properties, and ease of solution processing, making them suitable for constructing multifunctional PEC PDs. Herein, we report the broadband dual-polarity photoelectrochemical photocurrent switching (PEPS) in Ti3CNTx MXene/GO operating under a small external bias. We employ a solid-solution Ti3CNTx MXene, which exhibits featureless optical absorption and high electrical conductivity, and hybridize it with semiconducting GO, which possesses abundant surface states and a tunable bandgap, to construct PEC PDs that exhibit the PEPS effect. Notably, Ti3CNTx/GO heterostructures show excellent bidirectional photoresponse across the UV-to-visible light, with responsivity tunable by the Ti3CNTx-toGO ratio. The optimized heterostructure achieves high photoresponsivity values of 0.16 mA W- 1 (cathodic) and 0.45 mA W- 1 (anodic), corresponding to 360-fold and 4-fold enhancements compared to pristine GO and Ti3CNTx, respectively. We untangle the strong PEPS effect, showing that Ti3CNTx facilitates efficient chargecarrier transfer and interfacial charge separation at the metal/semiconductor interfaces. These intriguing results highlight the potential of MXenes as building blocks for the design of highly sensitive optoelectronic devices that leverage the PEPS effect.

Abstract The capture of volatile radioiodine from nuclear fuel reprocessing off-gas streams remains a critical challenge due to the high volatility, long half-life, and biological uptake of 129I from the environment. Although silver-based sorbents provide strong iodine chemisorption, their high cost and regulatory classification as mixed radioactive-hazardous waste motivate the development of alternative materials. Here, we report a silver-free Cu2O–Ti3C2Tx MXene hybrid for iodine gas capture at 150 °C. Structural and compositional analyses confirm the formation of Cu2O nanoparticles on Ti3C2Tx nanosheets and their subsequent conversion to thermodynamically stable CuI upon static iodine gas exposure. The nanohybrid achieves an iodine mass loading of up to 1115 mg/g. The iodine-loaded hybrid was further consolidated by spark plasma sintering into a mechanically self-supporting CuI–Ti3C2Tx monolith that retained the CuI phase and exhibited a seven-day cumulative normalized iodine loss of 1.64 g/m2, corresponding to only 0.076% of the initial iodine inventory during modified ASTM C1308–21 leach testing. These results demonstrate the potential of Cu2O–Ti3C2Tx MXene as a copper-based alternative to silver sorbents for elevated-temperature iodine gas capture.

MBenes, a novel class of transition metal borides, represent an exciting advancement in two-dimensional (2D) materials. This study introduces a novel and mild microwave-assisted hydrothermal method. A multilayered (ML) MoAlB@MBene structure is achieved when a mixture of hydrochloric acid (HCl) and hydrogen peroxide (H2O2) is used in combination with acid (0.1 M HCl) or base (0.1 M NaOH) pre-treatment. This method differs from reported etching techniques, which require long reaction times and highly concentrated acids (or bases). Also, they demonstrated that instead of selectively etching, the MAB phases dissolve, incompletely etch, or even oxidize. Achieving a multilayer structure within 4 hours was previously challenging. The current process allows for ML MBene formation and controlled oxidation in 4 hours. This leads to a distinct bandgap opening in ML MoAlB@MBene, with energy levels of 3.54, 3.58, 3.65, and 3.88 eV. The study also explores the optical absorption characteristics and time-resolved photoluminescence (TRPL) behavior of ML MoAlB@MBene. This demonstrates its tunable optical properties and significant potential for applications in high-performance light-emitting diodes, photovoltaics, photocatalysts, laser diodes, and more.

Two-dimensional van der Waals heterostructures with exotic quantum phenomena have garnered a huge surge in the field of optoelectronic devices. Herein, we report spectroscopic evidence of efficient interfacial charge transfers at the interface of a novel 2D/2D V4C3Tx MXene/protonated g-C3N4 (PCN) heterostructured thin film, demonstrating robust photosensitivity and a large exciton activation energy of 139.5 meV. Through temperature-dependent photoluminescence (PL) and time-resolved PL spectroscopy, we unravel the photophysical mechanism driving efficient charge transfer and photosensitivity in V4C3Tx/PCN heterostructures. These heterostructures exhibit superior photosensitivity to white and UV light compared with either PCN or V4C3Tx pristine materials. Additionally, we observed significant PL quenching with unusual negative thermal quenching and extended charge carrier lifetime in the V4C3Tx/PCN heterostructures across a broad temperature range of 70-370 K. Notably, at the elevated temperature of 370 K, the carrier lifetime was enhanced by more than 2-fold, making the heterostructures promising for optoelectronic applications. This work provides critical insight into the charge transfer mechanism between V4C3Tx MXene and PCN, opening a new avenue for rationally designing g-C3N4-based heterostructures for highly photosensitive optoelectronic devices.

Two-dimensional (2D) transition metal carbides and nitrides, known as MXenes, possess unique physical and chemical properties, enabling diverse applications in fields ranging from energy storage to communication, catalysis, sensing, healthcare, and beyond. Despite extensive research and notable advancements, a fundamental understanding of MXenes' phase diversity and its connection to their hierarchical precursors, including the intermediate MAX phases and the ancestral bulk phases, remains limited. Here, it is hypothesized that the atomic coordination environments adopted by transition metal and nonmetallic atoms in their three-dimensional (3D) bulk precursors may persist in 2D MXenes to govern their phase diversity. Using high-throughput modeling based on first-principles density functional theory, a wide range of MXene phases is unveiled and comprehensively evaluate their relative stabilities across a large chemical space. The key to the approach lies in considering various atomic coordination environments drawn from four types of ancestral bulk phases. Through this comprehensive structural library of MXenes, general guiding principles are uncovered, such as a close alignment between the phase stability of MXenes and that of their 3D precursors. These findings introduce a new design strategy in which the atomic coordination environments in bulk phases can serve as reliable predictors for accessing the diverse structural landscape of MXenes.

The development of advanced solid lubricants is critical for enhancing energy efficiency and durability in mechanical systems. In this study, we investigate the tribological performance of hybrid solid lubricant coatings composed of two-dimensional titanium carbide (Ti₃C2Tx)- and niobium carbide (Nb₂CTx)-based MXenes. Coatings were applied via spray deposition onto AISI 304 stainless steel substrates and tested under dry sliding conditions against Al₂O₃ counterbodies. While individual MXene coatings exhibited limited friction stability, the hybrid Ti₃C2Tx/Nb₂CTxcoating demonstrated a significantly reduced and stable coefficient of friction (COF < 0.2) throughout the test duration. Comprehensive surface and structural analyses of the wear tracks including SEM-EDS, Raman spectroscopy, and TEM revealed the formation of a compact, stratified tribofilm. We propose as a phenomenological model that under tribological stress, the hybrid system undergoes adaptive reconfiguration: Ti₃C2Tx anchors to the substrate, enhancing adhesion and mechanical integrity, while Nb₂CTx migrates to the sliding interface, acting as a sacrificial layer. This dynamic redistribution results in a synergistic interaction that enhances tribochemical resilience and wear resistance. These findings establish hybrid MXene coatings as a promising strategy for engineering next-generation solid lubricants, offering new pathways for the design of high-performance, energy-efficient coatings in demanding industrial applications.

Two-dimensional (2D) layered materials such as transition metal dichalcogenides (e.g., MoS2, WS2) and MXenes (e.g., Ti3C2Tx), as well as hybrids of these materials are the focus of current research in solid lubrication due to their outstanding performance. Transition metal carbo-chalcogenides (TMCCs), consisting of an MXene core and a TMD-like surface, represent an inherent combination of TMDs and MXenes without the need to construct hybrids out of the individual layers. Due to their layered structure and surface chemistry, favorable tribological properties can be expected from these novel materials. Here, multilayer Ta2S2C and Nb2S2C TMCCs are deposited solely as a powder onto a steel substrate and their tribological properties under linear sliding against different counterbodies, i.e., Al2O3, SiC, 100Cr6, and polytetrafluoroethylene (PTFE) are discussed. Advanced materials characterization techniques are used to detect the presence of TMCCs inside the wear tracks and to reveal their 2D structure within the tribofilm. Finally, density functional theory (DFT) simulations are used to unravel the easy shearability of TMCCs at the nanoscale. The results demonstrate the great potential of this new 2D material family, which also offers many possibilities for defined tuning of the solid-solid interface.

Herein, we report the synthesis of two-dimensional Ta2Se2C (2D-Ta2Se2C) nanosheets using electrochemical lithiation in multilayer Ta2Se2C followed by sonication in deionized water. Multilayer Ta2Se2C was obtained via solid-state synthesis of FexTa2Se2C followed by chemical etching of Fe. 2D-Ta2Se2C exhibited promising electrocatalytic activity for the hydrogen evolution reaction from water compared to multilayer Ta2Se2C and 2D-TaSe2. 2D-Ta2Se2C showed an overpotential at 10 mA·cm-2 (η10) of 264 mV, a Tafel slope of 91 mV·dec-1, and an electrochemically active surface area of 17.61 mECSA2·gcatalyst-1. The high performance could be attributed to the large surface area of single sheets which hence maximizes the number of exposed catalytic sites and increased density of vacancies, observed with transmission electron microscopy, during synthesis and processing.

Despite their remarkable optical, adsorption, and photocatalytic properties, MXenes face handling challenges that hinder their application in photocatalysis. In this study, we encapsulated Ti3C2Tx and Nb2CTx MXenes with magnetite in macro-scale sodium alginate capsules. Capsules containing 1 % magnetite and 0.1 % Ti3C2Tx MXene demonstrated a 60 % removal rate of 25 mg L- 1 methylene blue solution under UV and white light exposure. Additionally, magnetite incorporation facilitated easier handling and collection of the capsules. Tests on factorydelivered industrial dye (E133) showed an almost 80 % degradation rate. Furthermore, high dye degradation rates were maintained even after 4 cycles of regeneration, and in various pH conditions, ranging from 4 to 12. The exceptional performance was attributed to dye absorption and degradation within capsules, where ROS are generated under UV light. Our capsules offer an optimal, reusable solution for fully degrading industrial dyes in wastewater while protecting the active material and allowing its reusability.

Two-dimensional transition metal carbides and/or nitrides (MXenes), especially their few-layered nanosheets, have triggered burgeoning research attentions owing to their superiorities including extraordinary electrical conductivity, accessible active surface, and adjustable processability. Molten salts etching route further achieves their controllable surface chemistry. However, the method encounters challenges in achieving few-layered structures due to more complex delamination behaviors. Herein, we present an efficient strategy to fabricate Cl- or Br-terminated MXene nanoflakes with few-layers, achieved by electrochemical intercalation of Li ions and concomitant solvent molecules from the electrolyte solution, with gaseous propylene molecules to disrupt interlayer forces. By controlling cut-off voltages, the optimal protocol results in nanosheets with a recovery rate of ~93% and preserved surface chemistry. The resultant MXenes dispersions were employed as lubricants to enhance tribovoltaic nanogenerators, where Ti3C2Br2 displayed superior electrical output. These findings facilitate the understanding of MXenes' intrinsic physical properties and enable the nanoengineering of advanced electronic devices.