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Morphology regulation and composition design have proved to be effective strategies for the fabrication of desirable microwave absorbers. However, it is still challenging to precisely control the microstructure and components of MAX phases. Herein, an entropy-driven approach, a transition from irregular grains (low entropy) to sheet structure (high entropy), is proposed to modulate the morphology of MAX phases. The theoretical calculation indicates that the morphology evolution can be ascribed to the enlarged energy difference between (11_00) and (0001) facets. The enriched structural defects and optimized morphologies yield significant dipolar polarization, interfacial polarization, multiple reflections, and scattering, which all enhance the electromagnetic wave absorption performance of (V0.25 Ti0.25 Cr0.25 Mo0.25 )2 GaC. Specifically, its minimum reflection loss can reach up to -47.12 dB at 12.13 GHz, and the optimal effective absorption bandwidth is 4.56 GHz (2.03 mm). Meanwhile, (V0.25 Ti0.25 Cr0.25 Mo0.25 )2 GaC shows also pronounced thermal insulation properties affording it good reliability in the harsh working environment. This work offers a novel approach to designing and regulating the morphology of the high entropy MAX phase, and also presents an opportunity to elucidate the relationship between entropy and electromagnetic wave absorption performance.
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Tailoring of individual single-atom-thick layers in nanolaminated materials offers atomic-level control over material properties. Nonetheless, multielement alloying in individual atomic layers in nanolaminates is largely unexplored. Here, we report 15 inherently nanolaminated V2(A xSn1-x)C (A = Fe, Co, Ni, Mn, and combinations thereof, with x â¼ 1/3) MAX phases synthesized by an alloy-guided reaction. The simultaneous occupancy of the 4 magnetic elements and Sn in the individual single-atom-thick A layers constitutes high-entropy MAX phase in which multielemental alloying exclusively occurs in the 2-dimensional (2D) A layers. V2(A xSn1-x)C exhibit distinct ferromagnetic behavior that can be compositionally tailored from the multielement A-layer alloying. Density functional theory and phase diagram calculations are performed to understand the structure stability of these MAX phases. This 2D multielemental alloying approach provides a structural design route to discover nanolaminated materials and expand their chemical and physical properties. In fact, the magnetic behavior of these multielemental MAX phases shows strong dependency on the combination of various elements.
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Currently, less favorable C=O hydrogenation and weak concerted acid catalysis cause unsatisfactory catalytic performance in the upgrading of biomass-derived furfurals (i.e., furfural, 5-methyl furfural, and 5-hydroxymethyl furfural) to ketones (i.e., cyclopentanone, 2,5-hexanedione, and 1-hydroxyl-2,5-hexanedione). A series of partially oxidized MAX phase (i.e., Ti3 AlC2 , Ti2 AlC, Ti3 SiC2 ) supporting Pd catalysts were fabricated, which showed high catalytic activity; Pd/Ti3 AlC2 in particular displayed high performance for conversion of furfurals into targeted ketones. Detailed studies of the catalytic mechanism confirm that in situ hydrogen spillover generates Frustrated Lewis H+ -H- pairs, which not only act as the hydrogenation sites for selective C=O hydrogenation but also provide acid sites for ring opening. The close intimate hydrogenation and acid sites promote bifunctional catalytic reactions, substantially reducing the reported minimum reaction temperature of various furfurals by at least 30-60 °C.
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Due to their unique layered microstructure, the presence of various functional groups at the surface, earth abundance, and attractive electrical, optical, and thermal properties, MXenes are considered promising candidates for the solution of energy- and environmental-related problems. It is seen that the energy conversion and storage capacity of MXenes can be enhanced by changing the material dimensions, chemical composition, structure, and surface chemistry. Hence, it is also essential to understand how one can easily improve the structure-property relationship from an applied point of view. In the current review, we reviewed the fabrication, properties, and potential applications of MXenes. In addition, various properties of MXenes such as structural, optical, electrical, thermal, chemical, and mechanical have been discussed. Furthermore, the potential applications of MXenes in the areas of photocatalysis, electrocatalysis, nitrogen fixation, gas sensing, cancer therapy, and supercapacitors have also been outlooked. Based on the reported works, it could easily be observed that the properties and applications of MXenes can be further enhanced by applying various modification and functionalization approaches. This review also emphasizes the recent developments and future perspectives of MXenes-based composite materials, which will greatly help scientists working in the fields of academia and material science.
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MXenes-2D carbides/nitrides derived from their bulk nanolamellar Mn +1 AXn phase (MAX) counterparts-are, for the most part, obtained by chemical etching. Despite the fact that the MA bonds in the MAX phases are not weak, in this work it is demonstrated that relatively large MAX single crystals can be mechanically exfoliated using the adhesive tape method to produce flakes whose thickness can be reduced down to half a unit cell. The exfoliated flakes, transferred onto SiO2 /Si substrates, are analyzed using electric force microscopy (EFM). No appreciable variation in EFM signal with flake thickness is found. EFM contrast between the flakes and SiO2 not only depends on the contact surface potential, but also on the local capacitance. The contribution of the latter can be used to show the metallic character-confirmed by four-contact resistivity measurements-of even the thinnest of flakes. Because the A-layers are preserved, strictly speaking MXenes are not dealt with in this work, but rather MAXenes. This is important in the case where the "A" layers contain magnetic elements such as Mo4 Ce4 Al7 C3 , whose structure is a derivative of the MAX structure.
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We report a new type of MAX phase (M=transition metals, A=main group elements, and X=C/N), Nb3 As2 C, designated as 321â phase. It differs from all the previous Mn+1 AXn phases in that it consists of an alternate stacking of one MX layer and two MA layers in its unit cell, while only one MA layer is allowed in usual MAX phases. The new 321â phase exhibits a bulk modulus of Nb3 As2 C up to 225(3)â GPa as determined by high-pressure synchrotron X-ray diffraction, one of the highest values among MAX phases. Isostructural 321 phases V3 As2 C, Nb3 P2 C, and Ta3 P2 C are also found to exist. First-principles calculations reveal the outstanding elastic stiffness in 321â phases. Among all 321â phases, Nb3 P2 C is predicted to have the highest elastic properties. These 321â phases, represented by a chemical formula Mn+1 An X, were added as new members to the MAX family and their other properties deserve future investigations.
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A method for mapping elastic strains by TEM in plastically deformed materials is presented. A characteristic feature of plastically deformed materials, which cannot be handled by standard strain measurement method, is the presence of orientation gradients. To circumvent this issue, we couple orientation and strain maps obtained from scanning precession electron diffraction datasets. More specifically, orientation gradients are taken into account by 1) identifying the diffraction spot positions in a reference pattern, 2) measuring the disorientation between the diffraction patterns in the map and the reference pattern, 3) rotating the coordinate system following the measured disorientation at each position in the map, 4) calculating strains in the rotated coordinate system. At present, only azimuthal rotations of the crystal are handled. The method is illustrated on a Cr2AlC monocrystal micropilar deformed in near simple flexion during a nanomechanical test. After plastic deformation, the sample contains dislocations arranged in pile-ups and walls. The strain-field around each dislocation is consistent with theory, and a clear difference is observed between the strain fields around pile-ups and walls. It is further remarked that strain maps allow for the orientation of the Burgers vector to be identified. Since the loading undergone by the sample is known, this also allows for the position of the dislocation sources to be estimated. Perspectives for the study of deformed materials are finally discussed.
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Vanadium-carbide-based MXenes have bewitched the scientific community due to their distinctive characteristics, which make them potential candidates for several technological applications, such as supercapacitors (SCs), batteries, gas separation, biological sensors, and desalination. This article provides an overview of recent developments in the synthesis and applications of vanadium-carbide MXene in SCs. Vanadium carbide is one of the most difficult MXenes to synthesize, and various synthesis techniques, including electrochemical exfoliation and chemical etching, have been utilized to fabricate this material. Additionally, the review article also emphasizes the potential use of vanadium carbide MXene as SCs. Finally, the paper concludes with the challenges faced in the synthesis process and the prospects of vanadium carbide MXene-based material fabrication. Overall, this review article provides in-depth and detailed information on recent research on vanadium carbide MXene and its possible uses.
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Integrating ceramic and metallic properties in MAX phases makes them highly desirable for diverse technological applications. In this study, through first-principles density functional theory (DFT), we investigated the physical properties of two new 312 MAX compounds, M3GaB2 (M = Ti, Hf). Chemical stability is confirmed via formation energy assessment, while mechanical stability is established by determining elastic stiffness constants. A thorough analysis of mechanical behaviors includes bulk modulus, shear modulus, Young's modulus, and hardness parameters. M3GaB2 demonstrates elastic constants and moduli closely aligned with other 312 carbides. Understanding the electronic band structure and density of states (DOS) sheds light on metallic properties, with anisotropy in electrical conductivity clarified through energy dispersion analysis. Investigation of photon interaction with titled compounds, including dielectric constants (real and imaginary parts), refractive index, absorption coefficient, photoconductivity, reflectivity, and energy loss function, has been carried out. The potential of M3GaB2 borides as a coating to reduce solar is evaluated based on the reflectivity spectra. These findings deepen our understanding of material properties and suggest diverse applications for M3GaB2 in various technological domains.
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Solid electrolyte interphase (SEI) has significant role in controlling lithium (Li) dendrites. However, lack of chemical stability, mechanical strength and self-perfection for conventional SEI cannot persistently suppress Li dendrites, leading to inferior cycling life. Herein, MAX phases (Ti2SnC and Ti2SC) as triple functional artificial SEI (ASEI) with high modulus, chemical stability and self-smoothing ability are introduced on Li foils (Ti2SnC@Li and Ti2SC@Li) for ultralong life Li metal anodes (LMAs). The high mechanical strength with lithiophilicity of the MAX can induce uniform Li deposition and suppress dendrite growth, while the excellent chemical stability and self-smoothing ability of the MAX guarantee the consistency of the ASEI, achieving ultralong life of the LMAs. As a result, the Ti2SnC@Li||Li@Ti2SnC half-cells demonstrate ultralong cycling performance of 5000 h at 5 mAh cm-2 and 5 mA cm-2. The Ti2SnC@Li||LiFePO4(LFP) full-cells demonstrate ultralong stability up to 3000 cycles at 5C. At harsh conditions including 24.3 mg cm-2 of LFP, 6.0 g (Ah)-1 of electrolyte and 2.6 of negative/positive ratio, the Ti2SnC@Li||LFP full-cells maintain 2.9 mAh cm-2 after 130 cycles at 0.3C. This work demonstrates the MAX phases with high modulus, chemical stability and self-smoothing ability as triple functional ASEI for metal anode protection.
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BACKGROUND: MXenes have attracted intensive attention owing to their unique twodimensional (2D) layered structure, high specific surface area, excellent conductivity, superior surface hydrophilicity, and chemical stability. In recent years, selective etching of the A element layers from MAX phases by fluorine-containing etchants (HF, LiF-HCl, etc) is a common method to prepare multilayered MXene nanomaterials (NMs) with plentiful surface terminations. At present, many studies have been reported on the use of fluorine-free etchants (NaOH, ZnCl2, etc) to etch MAX phases. The properties of MXene NMs are dependent on their structures. OBJECTIVE: The purpose of this review is to focus on a comprehensive and systematical survey on the preparation, structure modulation, and applications of MXene NMs in electrochemical energy storage devices, including supercapacitors, lithium-ion battery, sodium-ion battery, potassium-ion battery, and aluminum-ion battery. METHODS: Extensive information related to the preparation and applications of 2D MXene NMs for electrochemical energy storage and their associated patents were collected. This review highlights the recently reported 2D MXene NMs which are used in supercapacitor and various metal ion. RESULTS: It is found that the preparation methods have great impacts on the layer spacing and surface terminations of MXenes, consequently affecting their performance. Hence, this paper summarizes the research progress of the preparation strategies, layer spacing and surface termination modulation of MXene NMs. CONCLUSION: The applications of 2D MXene NMs in electrochemical energy storage are outlined. The forward-looking challenges and prospects for the development of MXenes are also proposed.
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A new, sizable family of 2D transition metal carbonitrides, carbides, and nitrides known as MXenes has attracted a lot of attention in recent years. This is because MXenes exhibit a variety of intriguing physical, chemical, mechanical, and electrochemical characteristics that are closely linked to the wide variety of their surface terminations and elemental compositions. Particularly, MXenes are readily converted into composites with materials including oxides, polymers, and CNTs, which makes it possible to modify their characteristics for a variety of uses. MXenes and MXene-based composites have demonstrated tremendous promise in environmental applications due to their excellent reducibility, conductivity, and biocompatibility, in addition to their well-known rise to prominence as electrode materials in the energy storage sector. The remarkable characteristics of 2D MXene, including high conductivity, high specific surface area, and enhanced hydrophilicity, account for the increasing prominence of its use in storage devices. In this review, we highlight the most recent developments in the use of MXenes and MXene-based composites for electrochemical energy storage while summarizing their synthesis and characteristics. Key attention is paid to applications in supercapacitors, batteries, and their flexible components. Future research challenges and perspectives are also described.
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Human bones can suffer from various injuries, such as fractures, bone cancer, among others, which has initiated research activities towards bone replacement using advanced bio-materials. However, it is still challenging to design bio-scaffolds with bone-inducing agents to regenerate bone defects. In this regard, MAX-phases and MXenes (early transition metal carbides and/or nitrides) have gained notable attention due to their unique hydrophilicity, bio-compatibility, chemical stability, and photothermal properties. They can be used in bone tissue engineering as a suitable replacement or reinforcement for common bio-materials (polymers, bio-glasses, metals, or hydroxyapatite). To fabricate bio-scaffolds, additive manufacturing is prospective due to the possibility of controlling porosity and creating complex shapes with high resolution. Until now, no comprehensive article summarizing the existing state-of-the-art related to bone scaffolds reinforced by MAX-phases and MXenes fabricated by additive manufacturing has been published. Therefore, our article addresses the reasons for using bone scaffolds and the importance of choosing the most suitable material. We critically discuss the recent developments in bone tissue engineering and regenerative medicine using MAX-phases and MXenes with a particular emphasis on manufacturing, mechanical properties, and bio-compatibility. Finally, we discuss the existing challenges and bottlenecks of bio-scaffolds reinforced by MAX-phases and MXenes before deriving their future potential.
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Engenharia Tecidual , Alicerces Teciduais , Humanos , Alicerces Teciduais/química , Estudos Prospectivos , Regeneração ÓsseaRESUMO
The article describes the Ti3SiC2 powder synthesis process. The influence of the molar ratio and two forms of carbon on the phase composition of the obtained powders was investigated. The synthesis was carried out using a spark plasma sintering (SPS) furnace. In addition, using the obtained powders, composites reinforced with SiC particles were produced. The obtained results showed no effect of the carbon form and a significant impact of annealing on the purity of the powders after synthesis. The composites were also consolidated using an SPS furnace at two temperatures of 1300 and 1400 °C. The tests showed low density and hardness for sinters from 1300 °C (maximum 3.97 g/cm3 and 447 HV5, respectively, for composite reinforced with 10% SiC). These parameters significantly increase for composites sintered at 1400 °C (maximum density 4.43 g/cm3 and hardness 1153 HV5, for Ti3AlC2-10% SiC). In addition, the crack propagation analysis showed mechanisms typical for granular materials and laminates.
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Electromagnetic (EM) wave pollution is harmful to human health and environment, thus it is absolutely important to develop new electromagnetic wave absorbing materials. MAX phases have been attracted more attention as a potential candidate for electromagnetic wave absorbing materials due to their high conductivity and nanolaminated structure. Herein, two new magnetic MAX phases with multiprincipal elements ((Ti1/3 Nb1/3 Ta1/3 )2 FeC and (Ti0.2 V0.2 Nb0.2 Ta0.2 Zr0.2 )2 FeC) in which Fe atoms replace Al atoms in the A sites are successfully synthesized by an isomorphous replacement reaction of multiprincipal (Ti1/3 Nb1/3 Ta1/3 )2 AlC and (Ti0.2 V0.2 Nb0.2 Ta0.2 Zr0.2 )2 AlC MAX phases with Lewis acid salt (FeCl2 ). (Ti1/3 Nb1/3 Ta1/3 )2 FeC and (Ti0.2 V0.2 Nb0.2 Ta0.2 Zr0.2 )2 FeC exhibit ferromagnetic behavior, and the Curie temperature (Tc ) are 302 and 235 K, respectively. The dual electromagnetic absorption mechanisms that include dielectric and magnetic loss, which is realized in these multiprincipal MAX phases. The minimum reflection loss (RL) of (Ti1/3 Nb1/3 Ta1/3 )2 FeC is -44.4 dB at 6.56 GHz with 3 mm thickness, and the effective bandwidth is 2.48 GHz. Additionally, the electromagnetic wave absorption properties of the magnetic MAX phases indicate that magnetic loss also plays an important role besides dielectric loss. This work shows a promising composition-design strategy to develop MAX phases with good EM wave absorption performance via simultaneously regulating dielectric and magnetic loss together.
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Two-dimensional (2D) transition metal carbides and/or nitrides, MXenes, are prepared by selective etching of the A-site atomically thin metal layers from their MAX phase precursors. High entropy MXenes, the most recent subfamily of MXenes, are in their infancy and have attracted great interest recently. They are currently synthesized mainly through wet chemical etching of Al-containing MAX phases, while various MAX phases with A-sites elements other than Al have not been explored. It is important to embody non-Al MAX phases as precursors for the high entropy MXenes synthesis to allow for new compositions. In this work, it is reported on the design and synthesis of Ga-containing medium/high entropy MAX phases and then their corresponding medium/high entropy MXenes. Gallium atomic layer etching is carried out using a Lewis acid molten salt (CuCl2). The as-prepared (Ti1/4 V1/4 Nb1/4 Ta1/4 )2 CTx exhibits a Li+ specific capacity of ≈400 mAh g-1 . For (Ti1/5 V1/5 Nb1/5 Ta1/5 Mo1/5 )2 CTx a specific capacity of 302 mAh g-1 is achieved after 300 cycles, and high cycling stability is observed at high current densities. This work is of great significance for expanding the family members of MXenes with tunable chemistries and structures.
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MAX phases are layered solids with unique properties combining characteristics of ceramics and metals. MXenes are their two-dimensional siblings that can be synthesized as van der Waals-stacked and multi-/single-layer nanosheets, which possess chemical and physical properties that make them interesting for a plethora of applications. Both families of materials are highly versatile in terms of their chemical composition and theoretical studies suggest that many more members are stable and can be synthesized. This is very intriguing because new combinations of elements, and potentially new structures, can lead to further (tunable) properties. In this review, we focus on the synthesis science (including non-conventional approaches) and structure of members less investigated, namely compounds with more exotic M-, A-, and X-elements, for example nitrides and (carbo)nitrides, and the related family of MAB phases.
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Although 2D transition metal carbides and nitrides (MXenes) have fantastic physical and chemical properties as well as wide applications, it remains challenging to produce stable MXenes due to their rapid structural degradation. Here, unique metal-bonded atomic layers of transition metal carbides with high stabilities are produced via a simple topological reaction between chlorine-terminated MXenes and selected metals, where the metals enable them to not only remove partially Cl terminations, but also bond with adjacent atomic MXene slabs, driven by the symmetry of MAX phases. The films constructed from Al-bonded Ti3 C2 Clx atomic layers show high oxidation resistance up to 400 °C and low sheet resistance of 9.3 Ω sq-1 . Coupled to the multilayer structure, the Al-bonded Ti3 C2 Clx film displays a significantly improved electromagnetic interference (EMI) shielding capability with a total shielding effectiveness value of 39 dB at a low thickness of 3.1 µm, outperforming pure Ti3 C2 Clx film.
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Phenolic compounds that are naturally found in food samples are not only an important part of the human diet but also useful bioactive substances for health. Among these, para-coumaric acid (p-CA) has antibacterial and antioxidant properties and is used in many industrial processes. In this study, the novel MAX-phase material, Nb4AlC3, was successfully prepared and characterized in detail with various spectroscopic, microscopic and thermal techniques. The sensor performance of Nb4AlC3 modified glassy carbon electrode (Nb4AlC3@GCE) was evaluated and analytical parameters were calculated. Experimental conditions such as pH and amount of modifier were optimized with differential pulse voltammetry (DPV) measurements. The real samples analyses of lemon, apple and pomegranate were applied for determination of p-CA with Nb4AlC3@GCE sensing system under the optimized conditions. The accuracy was evaluated by spike/recovery and high-performance liquid chromatography analysis, which accounted for high accuracy of the Nb4AlC3@GCE sensing system. The limit of detection, limit of quantification, linear working range and relative standard deviation (%) of the Nb4AlC3@GCE sensing system were determined as 0.28 and 0.85 µmol/L, 0.8-80.0 µmol/L, 3.17 %, respectively. The results showed that the proposed sensing system has the high precision at lower concentration of p-CA.
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Técnicas Eletroquímicas , Nióbio , Humanos , Técnicas Eletroquímicas/métodos , Limite de Detecção , EletrodosRESUMO
Over the last decade MXenes have become a hotspot of materials science as one of the newest 2-dimensional (2D) materials. Upon the recognition of their distinctive features (e.g., superior optical characteristics, large surface area, excellent hydrophilicity, biocompatibility, ease of surface functionalization, and high conductivity), their potential in biosensing applications has also gained considerable attention. With versatility in MXene synthesis methods and suitable etching, MXenes can be easily transformed into quantum dots, nanosheets, and MXenes composites. As such, during the last decade optical biosensing platforms-based on MXenes have emerged along with electrochemical sensors and wearable sensors built from MXenes. Herein, we present a broad perspective on the optical properties of MXenes alongside recent findings on their biosensing applications, which are based on different optical transduction principles (e.g., photoluminescence, colorimetry, surface plasmon resonance, surface-enhanced Raman scattering, and electro chemiluminescence). Furthermore, the future perspective and challenges concerning MXenes-based optical sensing techniques are discussed.