Few-layer MXene Research Articles

Room temperature gas sensors for NH3 detection based on the heterojunction of 2D Ti3C2Tx MXenes and Bi2S3.

Bi2S3/Ti3C2Tx nanomaterials were successfully prepared through a simple hydrothermal method. Various methods were used for their characterization, including XRD, XPS, SEM, EDS, and BET, along with testing their gas-sensing properties. The results showed that the response value to 100ppm ammonia at room temperature reached 107%, which was 14.1 times higher than that of pure few-layer MXene. After undergoing anti-humidity interference testing, we observed that Bi2S3/Ti3C2Tx exhibited a higher response value in real-time monitoring of ammonia as humidity increased. Specifically, under 90% humidity conditions, its response value reached 1.32 times that of normal humidity conditions. This exceptional moisture resistance ensures that the sensor can maintain stability, and even exhibit superior performance, in harsh environments. Therefore, it possesses excellent selectivity, high-moisture-resistance, and long-term stability, making it significant in the field of medical and health monitoring.

Multiple Heterointerfaces and Heterostructure Engineering in MXene@Co-P-S Hybrids Promote High-Performance Sodium-Ion Half/Full Batteries.

In this paper, heterogeneous cobalt phosphosulfide (Co4S3/Co2P) nanocrystals anchoring on few-layered MXene nanosheets (MXene@Co4S3/Co2P) were prepared by in situ growth and the subsequent high-temperature phosphorization/sulfidation processes. Thanks to the synergistic effect and the abundant phase interfaces of Co4S3, Co2P, and MXene, the electron transfer and Na+ diffusion processes were greatly accelerated. Meanwhile, the high electrical conductivity of MXene nanosheets and the heterogeneous structure of Co4S3/Co2P effectively avoided the MXene restacking and the agglomeration of phosphosulfide particles, thus mitigating volumetric expansion during charging and discharging. The results show that the MXene@Co4S3/Co2P heterostructure presents good rate capability (251.08 mAh g-1 at 1 A g-1) and excellent cycling stability (198.69 mAh g-1 after 407 cycles at 5 A g-1). Finally, the storage mechanism of Na+ in the heterostructure and the multistep phase transition reaction were determined by ex situ X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS) analyses. This study provides a new perspective on the formation of metal phosphosulfide and MXene hybrids with multiple heterointerfaces as well as demonstrates MXene@Co4S3/Co2P composites as the promising anode material in sodium-ion batteries.

Augmented surface terminations on few-layer MXene (Ti3C2Tx) with superior electrochemical behavior for energy storage applications

Augmented surface terminations on few-layer MXene (Ti3C2Tx) with superior electrochemical behavior for energy storage applications

Harnessing niobium-based MXenes for sensors and energy storage applications: The past, the present and the future

Niobium carbide MXenes belong to a class of metal carbide MXenes with niobium as the early transition metal. The transformation of niobium carbide MXene sheets in to few-layer MXene sheets, the combination of the niobium-based MXene with other materials, delamination, intercalation, and partial oxidation of the niobium carbide MXene sheets have resulted in the formation of a material with excellent energy storage and sensing potentials. Herein, the synthesis and classification of the niobium-based MXenes (NBM), their application as sensing materials for a wide range of analytes, and their energy storage potentials are discussed exhaustively. The various transformations of niobium carbide MXenes over the last two decades are also established in this timely review. Essentially, this review is a searchlight on the prospects of NBM, the current state of their application, and their relevance in the materials research community.

Constructing a hierarchical MoS2/MXene heterostructure for efficient capacitive deionization of saline water

Well-dispersed and few-layered molybdenum disulfide (MoS2) has been considered as a suitable electrode material for pseudocapacitive capacitive deionization (CDI) due to its lamellar structure, flexible interlayer intercalation, and high theoretical capacity. However, the serious aggregation, low electrical conductivity and poor hydrophilicity of MoS2 have limited its desalination application. To address these issues, few-layered MXene is used as a conductive and hydrophilic skeleton to support MoS2 nanosheets. In this study, a hierarchical MoS2/MXene heterostructure is fabricated for highly efficient CDI of saline water. The designed heterostructure effectively inhibits the agglomeration of MoS2 and MXene nanosheets, exposes more active electrochemical sites, and improves the wettability, thereby enhancing ion/charge transport. The MoS2/MXene heterostructure electrode exhibits low electrical resistance (3.2 Ω), along with a high specific capacitance of 171.8 F·g-1 at 2 A·g-1. Furthermore, the MoS2/MXene-based CDI electrode demonstrates an excellent desalination capacity of 55.8 mg·g-1 and a fast desalination rate of 13 mg·g-1·min-1. This study paves the way for novel applications in the CDI field.

Improvement of hydrogen evolution catalytic performance of MoS2 nanoflowers by constructing MoS2/MXene Ti3C2 heterostructure petals

In this paper, we report a special [Formula: see text] nanoflower synthesized by hydrothermal approach, in which a heterostructure petal of [Formula: see text] [Formula: see text] is constructed by growing the [Formula: see text] active layers onto the few-layered MXene [Formula: see text] substrate. Compared with the pristine [Formula: see text] nanoflowers, the heterostructure [Formula: see text] nanoflowers exhibit a lower onset overpotential of 207 mV and a lower Tafel slope of 28 mV dec[Formula: see text]. This can be explained by the heterostructure [Formula: see text] nanoflowers providing a great number of exposed surfaces of [Formula: see text], and increasing more active sites, and strengthening the interlayer coupling between [Formula: see text] and MXene [Formula: see text] to accelerate the charge transfer. All the merits are beneficial to the performance enhancement for hydrogen evolution catalytic.

Solid-lubrication performance of Ti3C2Tx - Effect of tribo-chemistry and exfoliation

Multi-layer Ti3C2Tx coatings have demonstrated an outstanding wear performance with excellent durability due to beneficial tribo-layers formed. However, the involved formation processes dependent on the tribological conditions and coating thickness are yet to be fully explored. Therefore, we spray-coated Ti3C2Tx multi-layer particles onto stainless steel substrates to create coatings with two different thicknesses and tested their solid lubrication performance with different normal loads (100 and 200 mN) and sliding frequencies (1 and 2.4 Hz) using linear-reciprocating ball-on-disk tribometry. We demonstrate that MXenes’ tribological performance depends on their initial state (delaminated few-layer vs. multi-layer particles), coating thickness, applied load and sliding frequency. Specifically, the best behavior is observed for thinner multi-layer coatings tested at the lower frequency. In contrast, coatings made of delaminated few-layer MXene are not as effective as their multi-layer counterparts. Our high-resolution interface characterization by transmission electron microscopy revealed unambiguous differences regarding the uniformity and chemistry of the formed tribo-layers as well as the degree of tribo-induced MXenes’ exfoliation. Atomistic insights into the exfoliation process and molecular dynamic simulations quantitatively backed up our experimental results regarding coating thickness and velocity dependency. This ultimately demonstrates that MXenes’ tribological performance is governed by the underlying tribo-chemistry and their exfoliation ability during rubbing.

The synthesis and supercapacitor application of flexible free-standing Ti3C2Tx, Mo2TiC2Tx, and V4C3Tx MXene films.

MXenes represent a fascinating category of two-dimensional materials made up of transition metal carbides and nitrides, currently attracting significant research attention, especially in energy storage. However, the electrochemical properties of MXene materials with varying elemental compositions may exhibit significant differences. In order to optimally select types of MXenes that are more suitable for energy storage and explore their energy storage mechanisms, three kinds of different elemental compositions of delaminated MXenes (d-Ti3C2Tx, d-Mo2TiC2Tx, and d-V4C3Tx) were prepared by solid-phase synthesis, liquid-phase etching, and mechanical exfoliation method, successively. The obtained single-layer or few-layer MXene nanosheets were self-assembled into flexible free-standing film electrodes via vacuum-assisted filtration, and the detailed material preparation and characterization can guide the synthesis of more MXenes. Furthermore, we conducted a comprehensive study on the effects of various aqueous electrolytes (3 M H2SO4, 3 M KOH, and 3 M Na2SO4) and temperatures (0 °C, 20 °C, and 40 °C) on their electrochemical performance. This work optimized the MXene types that are more suitable for electrochemical energy storage application (d-Ti3C2Tx and d-V4C3Tx), and also found that the V4C3Tx MXene has excellent rate performance and long cycling performance, and has guiding significance for the development of MXene materials in energy storage. More significantly, the d-V4C3Tx MXene exhibits exceptional specific capacitance in both acidic and alkaline electrolytes, reaching 292.0 F g-1 in 3 M H2SO4, the highest among the three types of MXenes, and 184.3 F g-1 in 3 M KOH, far surpassing the performance of the d-Mo2TiC2Tx and d-Ti3C2Tx MXenes (less than 100 F g-1 at 2 mV s-1). Furthermore, this reveals that H+ intercalation/deintercalation, showing pseudocapacitance characteristics, along with the large interlayer spacing play a vital role in energy storage for MXenes, and an asymmetric configuration is an effective means to improve the energy density of aqueous supercapacitors. The comparative analysis aims to enhance the understanding of MXene materials' potential in advanced energy storage systems.

Immobilizing Bimetallic RuCo Nanoalloys on Few-Layered MXene as a Robust Bifunctional Electrocatalyst for Overall Water Splitting.

Doping Co atoms into Ru lattices can tune the electronic structure of active sites, and the conductive MXene can adjust the electrical conductivity of catalysts, which are both favorable for improving the electrocatalytic activity of the catalyst for water splitting. Here, ruthenium-cobalt bimetallic nanoalloys coupled with exfoliated Ti3 C2 Tx MXene (RuCo-Ti3 C2 Tx ) have been constructed by ice-templated and thermal activation. Due to the strong interaction between the RuCo nanoalloys and conductive MXene, RuCo-Ti3 C2 Tx not only exhibits an excellent hydrogen evolution reaction (HER) performance with a low overpotential and Tafel slope (60 mV, 34.8 mV dec-1 in 0.5 M H2 SO4 and 52 mV, 38.7 mV dec-1 in 1 M KOH), but also good oxygen evolution reaction (OER) performance in an alkaline electrolyte (266 mV, 111.1 mV dec-1 in 1 M KOH). The assembled RuCo-Ti3 C2 Tx ||RuCo-Ti3 C2 Tx electrolyzer requires a lower potential (1.56 V) than does the Pt/C||RuO2 electrolyzer at 10 mA cm-2 . A boosted catalytic HER activity from immobilizing the RuCo nanoalloys on MXene was unveiled by density functional theory calculations. This study provides a feasible and efficient strategy for developing MXene-based catalysts for overall water splitting.

Upgrading the electrochemical performance of Li-rich Mn-based cathodes through additional fast Li storage assisted by few-layer MXene

Li-rich Mn-based [xLi2MnO3·(1-x)LiMO2] (LR) cathodes are low cost and have high energy density, indicating high commercialization potential. However, the low initial coulombic efficiency, poor rate performance, and inferior cycling durability of LR cathodes confer difficulty in such commercialization. Herein, we proposed the use of a few-layer MXene (Ti3C2) to improve electrochemical performance. We found that the few-layer MXene can improve the conductivity and provide additional capacity at low voltage (2.25 V), thereby greatly increasing the initial coulombic efficiency, rate, and cycle performance. The additional capacity may have originated from an interface space-charge storage with capacitive properties, that is, the storage and transport of ions and electrons at the interface of Ti3C2 and LR particles. The modified sample exhibited an initial coulombic efficiency of 94.3 % and 158 mAh g–1 at 5C. Even after 300 cycles at 5C, it retained 87.3 % of its capacity. This novel strategy can serve as a reference for the modification of other electrode materials and can also expand the application of MXene in the field of batteries.

Preparation of cathode materials with excellent electrochemical performance by composite of few-layer MXene and LiFePO4

Preparation of cathode materials with excellent electrochemical performance by composite of few-layer MXene and LiFePO4

Enhancing structure and cycling stability of single crystal LiNi0.5Mn1.5O4 cathode via multifunctional MXene surface modification

Single crystal LiNi0.5Mn1.5O4 (LNMO) has gained increasing attention due to its cobalt-free composition, low rolling resistance, and high energy density. However, its high voltage operating range renders it susceptible to electrolyte dissolution and side reactions, limiting its large-scale practical application as it exhibits poor cycling stability and rate performance. In this study, a novel composite material, LNMO@MXene, was developed by electrostatic self-assembly of single or few-layered MXene (Ti3C2Tx) onto the surface of LNMO. Among them, LNMO coated with 3 wt% MXene exhibited a discharge capacity of up to 130.86 mAh·g−1 at 1C, and a specific capacity of 109.80 mAh·g−1 at 5C after 500 cycles. After 200 cycles at 55 °C, the specific capacity was 114.4 mAh·g−1 with a retention rate as high as 86.99 %. The electrostatic self-assembly of MXene is a simple and effective coating strategy, which creates a conductive network, increases the capacity through Li+ intercalation, and forms a protective cathode electrolyte interphase (CEI) layer to inhibit interfacial side reactions. The synergistic effect between MXene and LNMO enhances the electrochemical performance of LNMO materials. This coating strategy can also be applied to the design of other cathode materials.

Ultra-sensitive trace NO2 detection based on quantum dots-sensitized few-layer MXene: A novel convincing insight into dynamic gas-sensing mechanism

It is critical for MXene to overcome the constraints of weak gas adsorption capacity, poor sensitivity and limited selectivity properties. Herein, quantum dots (QDs)-sensitized few-layer Ti3C2Tx was successfully constructed for efficient NO2-sensing. The ideal doping content was investigated according to multiple structural analysis and sensing-properties. Impressively, the FLTS-2 sensor displays a significant 42.05-fold response (60.38%, 500-ppb NO2) compare to pure MXene (1.43%). It also exhibits ideal selectivity, well long-term stability and lower detection limit (0.83-ppb), demonstrating its considerable potential for trace-level monitoring and practical applications. Meanwhile, a novel convincing dynamic gas-sensing mechanism is proposed to elucidate the enhancement of sensing-capabilities, including gas diffusion/adsorption, selective mechanisms, DFT calculations (37 models, 100 images) and QDs-sensitization mechanisms. Strikingly, dynamic gas-sensing mechanism proves that the surface functionalization of QDs modifications strongly improves the adsorption behavior and significantly facilitates the electron transfer of NO2 molecules, thus enhancing the sensing performance. The present experiment and mechanism analysis not only highlight the promising combination of 2D/0D MXene/PbS heterostructures, but also provide a theoretical perspective for designing of MXene-based sensors for trace NO2 detection.

Self-Assembled 2D VS2 /Ti3 C2 Tx MXene Nanostructures with Ultrafast Kinetics for Superior Electrochemical Sodium-Ion Storage.

Constructing nanostructures with high structural stability and ultrafast electrochemical reaction kinetics as anodes for sodium-ion batteries (SIBs) is a big challenge. Herein, the robust 2D VS2 / Ti3 C2 Tx MXene nanostructures with the strong Ti─S covalent bond synthesized by a one-pot self-assembly approach are developed. The strong interfacial interaction renders the material of good structural durability and enhanced reaction kinetics. Meanwhile, the enlarged and few-layered MXene nanosheets can be easily obtained according to this interaction, providing a conductive network for sufficient electrolyte penetration and rapid charge transfer. As predicted, the VS2 /MXene nanostructures exhibit an extremely low sodium diffusion barrier confirmed by DFT calculations and small charge transfer impedance evidenced by electrochemical impedance spectroscopy (EIS) analysis. Therefore, the SIBs based on the VS2 /MXene electrode present first-class electrochemical performance with the ultrahigh average initial columbic efficiency of 95.08% and excellent sodium-ion storage capacity of 424.6mAhg-1 even at 10Ag-1 . It also shows an outstanding sodium-ion storage capacity of 514.2mAhg-1 at 1Ag-1 with a capacity retention of nearly 100% within 500 times high-rate cycling. Such impressive performance demonstrates the successful synthesis strategy and the great potential of interfacial interactions for high-performance energy storage devices.

Adsorption of azo dyes and Naproxen by few-layer MXene immobilized with dialdehyde starch nanoparticles: Adsorption properties and statistical physics modeling

Novel Eco-friendly composite materials (DSP-M) were organized by combining few-layer MXene with the hydrophilic biomaterial dialdehyde starch nanoparticles (DASNP) and immobilizing DASNP on the surface of few-layer MXene by the dialdehyde-based cross-linking method. In addition to the study on the adsorption performance and mechanism of prohibited dyes (Rhodamine B, RB and Congo Red, CR) in food industry, the removal and mechanism of non-steroidal anti-inflammatory drug (Naproxen, NPX) residues in pharmaceutical field were also investigated. DSP-M was physiochemically characterized via series of analytical techniques and the dye adsorption isotherms at three temperatures were quantified. The results show that DSP-M exhibited excellent adsorption performance for all three selected adsorbates, and the Langmuir maximum monolayer adsorption capacity were 678.19 mg/L for RB, 754.41 mg/L for CR and 166.71 mg/L for NPX, respectively, and it agreed well with the Langmuir, pseudo–second order and intraparticle diffusion models. The statistical physics model was employed to further explore the adsorptive mechanism. The characteristics of DSP-M after adsorption and the simulation results indicate that the removal of RB, CR and NPX by DSP-M was mainly a physical adsorption process involved with hydrogen bonding, electrostatic force and van der Waals force.

Synergistic integration of MXene nanosheets with CdS@TiO2 core@shell S-scheme photocatalyst for augmented hydrogen generation

In order to ensure continuous and stable production of hydrogen (H2), the development of hierarchical nanostructures within a few-layer Mxene nanosheet, incorporating an ultrathin TiO2 shell material, is essential. This shell material plays a crucial role in maintaining the long-term stability of the core and preventing photo-corrosion, thus enabling uninterrupted H2 generation. To evaluate their potential as visible-driven photocatalysts for high H2 production, we conducted a comparative analysis of CdS cores covered with three different shell transition metal oxides (TiO2@NiO@ZnO), supported by Mxene. Structural and morphological characterizations through XRD and TEM confirmed the formation of pure CdS@TiO2@NiO@ZnO core–shell nanostructures, characterized by spherical shapes with a core diameter of 187 nm and a shell thickness of 19.2 nm. XPS experiments demonstrated the structural integrity of the individual elements within the nanocomposite, existing in their respective oxidation states within the core@shell structure. The hierarchical nanostructure exhibited optical characteristics with an absorption edge ranging from 480 to 580 nm. Among the three different shell materials, TiO2 displayed the highest photocatalytic activity under visible light irradiation, followed by NiO and ZnO. Based on our findings, the CdS@TiO2 core@shell photocatalyst supported by Mxene exhibited the highest efficiency, with a production rate of 16.2 mmol.h−1.g-1cat. This can be attributed to enhanced charge separation, the spatial distribution of carriers, and favorable structural properties. Our DFT calculations further supported the efficacy of coupling Mxene with CdS/TiO2, as it facilitated efficient water splitting, with CdS favoring H2O dissociation and Mxene favoring HER. These results highlight the potential of developing highly efficient photocatalysts for water splitting by integrating Mxene with CdS/TiO2. Additionally, The prepared CDTM (Mxene@CdS/TiO2) photocatalyst existing S-scheme heterojunction for efficient water splitting. This underscores the system's effective functioning across diverse sceneries, Overall, our study presents a feasible and effective strategy for constructing an S-scheme heterojunction system that utilizes photo charge carrier separation to enhance the utilization and conversion of solar energy.

Interfacial properties and strengthening mechanisms of few-layered MXene reinforced Mg-based composites

In the present study, MXene-reinforced Mg matrix composites were manufactured via the electrostatic self-assembly protocol and spark plasma sintering (SPS) process to develop lightweight materials with high mechanical performance. Uniform dispersion of MXene sheets was achieved in MXene/AZ91 composites. A unique interfacial structure was confirmed in these composites, which exhibited an ultrafine MgO interlayer (grain size of ∼10 nm) coherently incorporated or intercalated into MXene layers. The unique interfacial structure contributed to robust interfacial bonding between MXene sheets and Mg matrix, resulting in a substantial mechanical performance enhancement. The yield strength of 325.3 ± 7.9 MPa and elongation of 8.8 ± 0.2% were achieved in 0.3vol% MXene/AZ91 composites, showing a significantly high strengthening efficiency of 159.1 without sacrificing ductility. Quantitatively investigation of strengthening behavior manifested that the load-transfer effect was the primary strengthening mechanism in MXene/AZ91 composites, and the simulated strength was well-matched with experimental results due to the special interfacial structure and excellent dispersion properties. This study could offer significant guidance for developing novel lightweight materials with high mechanical performance for structural applications.

Resistive-type sensors based on few-layer MXene and SnO2 hollow spheres heterojunctions: Facile synthesis, ethanol sensing performances

High-performance and low-cost gas sensors are highly desirable and involved in industrial production and environmental detection. The combination of highly conductive MXene and metal oxide materials is a promising strategy to further improve the sensing performances. In this study, the hollow SnO2 nanospheres and few-layer MXene are assembled rationally via facile electrostatic synthesis processes, then the SnO2/Ti3C2Tx nanocomposites were obtained. Compared with that based on either pure SnO2 nanoparticles or hollow nanospheres of SnO2, the SnO2/Ti3C2Tx composite-based sensor exhibits much better sensing performances such as higher response (36.979), faster response time (5 s), and much improved selectivity as well as stability (15 days) to 100 ppm C2H5OH at low working temperature (200 °C). The improved sensing performances are mainly attributed to the large specific surface area and significantly increased oxygen vacancy concentration, which provides a large number of active sites for gas adsorption and surface catalytic reaction. In addition, the heterostructure interfaces between SnO2 hollow spheres and MXene layers are beneficial to gas sensing behaviors due to the synergistic effect.

Facile Tailoring of Surface Terminations of MXenes by Doping Nb Element: Toward Extraordinary Pseudocapacitance Performance.

MXenes show promising potential in supercapacitors due to their unique two-dimensional (2D) structure and abundant surface functional groups. However, most studies about MXenes have focused on tailoring surface structures by alternating synthesis methods or post-etch treatments, and little is known about the inherent relationship between surface groups and M elements. Herein, we propose a simple and novel strategy to adjust the surface structure of few-layered MXene flakes by adding a small amount of Nb element. Because of the strong affinity between Nb and O elements, the as-received V1.8Nb0.2CTx and Ti2.7Nb0.3C2Tx MXenes have much fewer -F functional groups and a higher O content than V2CTx and Ti3C2Tx MXenes, respectively. Thus, both V1.8Nb0.2CTx and Ti2.7Nb0.3C2Tx MXenes show enhanced pseudocapacitance performance. Especially, V1.8Nb0.2CTx delivers an ultrahigh volumetric capacitance of 1698 F/cm3 at a scan rate of 2 mV/s. Moreover, benefiting from the high activity of MAX precursors obtained through a fast self-propagating high-temperature synthesis, the etching time to produce V-based MXenes is much shorter than that in previous reports. Therefore, the results presented here are applicable to the surface engineering and rational design of 2D MXene materials and develop them into promising, cost-effective electrode materials for supercapacitors or other energy-storage equipment.

Natural oxidation of Ti3C2Tx to construct efficient TiO2/Ti3C2Tx photoactive heterojunctions for advanced photoelectrochemical biosensing of folate-expressing cancer cells

The rapid-charge carrier recombination and low conductivity are critical in devising an efficient photoelectrochemical (PEC) sensor. Herein, we propose partial oxidation of few-layered MXene (Ti3C2Tx) to construct a photo-active TiO2/Ti3C2Tx platform that could be configured for PEC sensing of folate receptors (FR), particularly, FR-expressing breast cancer cells (MDA-MB-231). MXene-Ti3C2Tx dispersion was oxidized in natural-open air conditions, where continuous exposure for six (06) days allowed for homogeneous in-situ growth of TiO2 over MXenes nanosheets (MX-06). This exposure enabled partial oxidation of MXene-sheets with a balanced TiO2 to MXene content that could exhibit improved photoresponsive characteristics owing to the synergism of redox-active TiO2 and highly conductive underlying Ti3C2Tx. The photoelectrode was then adapted for biorecognition by conjugating chitosan and folic acid (FA) networks, which permitted selective detection of FR-expressed cells with significant antifouling capabilities against common proteins such as bovine serum album (BSA), hemoglobin, and immunoglobulin G. (Ig G). The detection mechanism relies on FA's strong affinity for cancer cell folate receptors, which proportionally inhibited the photoelectrodes PEC oxidation response to ascorbic acid (AA)(mediator). The proposed inhibition strategy enabled sensitive detection of FR-expressed MDA-MB-231 cells in the concentration range of 1 × 102 to 2 × 107 cells/mL with a detection limit of 1.01 cells/mL (S/N = 3).