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MXenes: A rising star in the constellation of two-dimensional materials
... MXenes are usually synthesized by MAX, and its general formula is M n+1 AX n , where M is a transition metal (e.g. Ti, V, Nb, etc), A is mainly an element of IIIA or IVA (i.e. group 13 or 14), X represents C and/or N, and T x represents surface functional groups [20][21][22]. The surface of MXene contains many active groups, such as hydroxyl, oxygen and fluoride ions [23][24][25]. ...
Polyacrylonitrile /Ti3C2Tx MXene/silver nanoparticles fiber membranes with different silver nanoparticles contents and thickness of porous structure have been successfully prepared by electrospinning. Through the measurement of terahertz time domain spectrum, the shielding effect of the fiber membrane with 1% silver nanoparticles content can reach up to 12 dB. Moreover, the thickness of the spinning fiber membranes is controlled by adjusting the spinning time, so as to better analyse the influence of the thickness of the shielding performance in terahertz band. We attribute this excellent phenomenon to porous structure of the spun fiber membrane and combination of Ti3C2Tx MXene with few-layers and silver nanoparticles to increase the absorption and conductivity of the fiber membrane, thereby enhancing the shielding effect in terahertz range. Meanwhile, the prepared polyacrylonitrile / Ti3C2Tx MXene/ silver nanoparticles fiber membranes show good stability and little change in terahertz shielding effect after high temperature annealing. This may provide potential ideas about the development of high-performance terahertz shielding materials, which are of great significance of terahertz electromagnetic shielding.
... Compared to transitional zero-dimensional (0D) and one-dimensional (1D) nanomaterials, 2D materials exhibited unique properties and advantages due to their atomic layer thickness, large surface area, high electrical conductivity, strong mechanical strength, and flat nano/micro-scale surface, which making them excellent candidates for the design and fabrication of multifunctional nanomaterials towards applications in energy science, [4,5] environmental science, [6] electronic devices, [7] sensors, [8,9] tissue engineering, [10] biomedicine, [11] and many others. Recently, more and more attentions have been attracted onto one of the members of 2D materials family, MXenes, which include typical emerging class of 2D transition metal carbides (MCs) and metal nitrides (MNs) [12][13][14]. It has been found that 2D MCs and MNs have similar physical, chemical, and biological properties to that of graphene-like 2D materials. ...
Two-dimensional (2D) nanomaterials have attracted increased interest and exhibited extended applications from nanotechnology to materials science, biomedicine, tissue engineering, as well as energy storage and environmental science. With the development of the synthesis and fabrication of 2D materials, a new family of 2D materials, metal carbides (MCs), revealed promising applications in recent years, and have been utilized for the fabrication of various functional 2D and three-dimensional (3D) nanomaterials for energy and environmental applications, ascribing to the unique physical and chemical properties of MCs. In this review, we present recent advance in the synthesis, fabrication, and applications of 2D and 3D MC-based nanomaterials. For this aim, we first summarize typical synthesis methods of MCs, and then demonstrate the progress on the fabrication of 2D and 3D MC-based nanomaterials. To the end, the applications of MC-based 2D and 3D materials for chemical batteries, supercapacitors, water splitting, photodegradation, removal of heavy metals, and electromagnetic shielding are introduced and discussed. This work provides useful information on the preparation, hybridization, structural tailoring, and applications of MC-based materials, and is expected to inspire the design and fabrication of novel and functional MXene materials with improved performance.
The main objective of this research is to explore the thermophysical properties and heat transfer performance of aqueous inhibited propylene glycol/MXene nanofluid for a solar photovoltaic/thermal cooling system. A thorough characterization analysis of the nanofluid was conducted, assessing its morphology, chemical structure, stability, thermal conductivity, viscosity, specific heat capacity, and density. The findings indicate that the addition of MXene nanosheets significantly enhances the thermal conductivity and specific heat capacity while maintaining stability, despite a moderate increase in viscosity and density. The maximum thermal conductivity and specific heat capacity of the nanofluid are around 0.81 Wm−1K−1 and 9.1 kJ kg−1K−1, respectively, at 60 °C and a MXene loading concentration of 0.2 mass%. In comparison with the aqueous IPG, the density increase of the nanofluid is no greater than 0.5%. The nanofluid’s viscosity increases with increasing MXene concentration but decreases with temperature. However, the value is still low with no more than 7.4 mPa·s. An optimization study reveals that the optimal MXene concentration is 0.1664 mass% for maximizing the nanofluid heat transfer efficiency. Application in a PV/T system demonstrated that the nanofluid improves overall system efficiency by enhancing thermal and electrical efficiencies and reducing the PV module surface temperature. As the Reynolds number increases from 200 to 700, the heat transfer rate increases, but the Prandtl number decreases. A figure of merit, which compares increase in the heat transfer with the corresponding pumping power, gives the overall effectiveness of the nanofluid in the system. The value ranges from 0.8 to 2.1, where the higher value signifies a better advantage. The results suggest that the aqueous inhibited propylene glycol/MXene nanofluid is a promising candidate for advanced cooling solutions in photovoltaic/thermal systems.
First-principle investigations Terminations Structural stability Electronic properties a b s t r a c t As a new type of two-dimensional layered carbides, nitrides or carbonitrides, MXenes have attracted widespread attention due to their excellent physical/chemical properties and huge potential functions. This work theoretically investigates the compositional dependence of M nþ1 X n T 2 and their electronic properties; where the series of M nþ1 X n T 2 (M ¼ Sc, Ti, V; X ¼ C; n ¼ 1, 2; T ¼ O, OH, F, Cl, Br, I) is employed as a case study. It is found that the Sc-based MXenes have the largest lattice constants, illustrating the weak interactions between the surface functionalized groups and Sc atoms. According to the mechanical stability analysis, it is found that except for Ti 3 C 2 O 2 , all the others are stable. Mechanically, the halogen functionalized (F, Cl, Br, and I) M 2 CT 2 series have relatively large c 11 values; and the Ti 3 C 2 Br 2 has the largest c 11 value. It is also found that the band gaps of Sc 2 CCl 2 and Sc 2 CBr 2 are 0.8734 and 0.6976 eV, respectively; both of which show their potential applications as indirect band gaps semiconductors.
The family of MAX phases and their derivative MXenes are continuously growing in terms of both crystalline and composition varieties. In the last couple of years, several breakthroughs have been achieved that boosted the synthesis of novel MAX phases with ordered double transition metals and, consequently, the synthesis of novel MXenes with a higher chemical diversity and structural complexity, rarely seen in other families of two-dimensional (2D) materials. Considering the various elemental composition possibilities, surface functional tunability, various magnetic orders, and large spin−orbit coupling, MXenes can truly be considered as multifunctional materials that can be used to realize highly correlated phenomena. In addition, owing to their large surface area, hydrophilicity, adsorption ability, and high surface reactivity, MXenes have attracted attention for many applications, e.g., catalysts, ion batteries, gas storage media, and sensors. Given the fast progress of MXene-based science and technology, it is timely to update our current knowledge on various properties and possible applications. Since many theoretical predictions remain to be experimentally proven, here we mainly emphasize the physics and chemistry that can be observed in MXenes and discuss how these properties can be tuned or used for different applications.
The exploration of two-dimensional solids is an active area of materials discovery. Research in this area has given us structures spanning graphene to dichalcogenides, and more recently 2D transition metal carbides (MXenes). One of the challenges now is to master ordering within the atomic sheets. Herein, we present a top-down, high-yield, facile route for the controlled introduction of ordered divacancies in MXenes. By designing a parent 3D atomic laminate, (Mo 2/3 Sc 1/3) 2 AlC, with in-plane chemical ordering, and by selectively etching the Al and Sc atoms, we show evidence for 2D Mo 1.33 C sheets with ordered metal divacancies and high electrical conductivities. At B1,100 F cm À 3 , this 2D material exhibits a 65% higher volumetric capacitance than its counterpart, Mo 2 C, with no vacancies, and one of the highest volumetric capacitance values ever reported, to the best of our knowledge. This structural design on the atomic scale may alter and expand the concept of property-tailoring of 2D materials.
The family of 2D transition metal carbides, carbonitrides and nitrides (collectively referred to as MXenes) has expanded rapidly since the discovery of Ti3C2 in 2011. The materials reported so far always have surface terminations, such as hydroxyl, oxygen or fluorine, which impart hydrophilicity to their surfaces. About 20 different MXenes have been synthesized, and the structures and properties of dozens more have been theoretically predicted. The availability of solid solutions, the control of surface terminations and a recent discovery of multi-transition-metal layered MXenes offer the potential for synthesis of many new structures. The versatile chemistry of MXenes allows the tuning of properties for applications including energy storage, electromagnetic interference shielding, reinforcement for composites, water purification, gas- and biosensors, lubrication, and photo-, electro- and chemical catalysis. Attractive electronic, optical, plasmonic and thermoelectric properties have also been shown. In this Review, we present the synthesis, structure and properties of MXenes, as well as their energy storage and related applications, and an outlook for future research.
MXenes are a recently discovered family of two-dimensional (2D) early transition metal carbides and carbonitrides, which have already shown many attractive properties and great promise in energy storage and many other applications. However, a complex surface chemistry and small coherence length have been obstacles in some applications of MXenes, also limiting the accuracy of predictions of their properties. In this study, we describe and benchmark a novel way of modeling layered materials with real interfaces (diverse surface functional groups and stacking order between the adjacent monolayers) against experimental data. The structures of three kinds of Ti3C2Tx MXenes (T stands for surface terminating species, including O, OH, and F) produced under different synthesis conditions were resolved for the first time using atomic pair distribution function obtained by high-quality neutron total scattering. The true nature of the material can be easily captured with the sensitivity of neutron scattering to the surface species of interest and the detailed "third-generation" structure model we present. The modeling approach leads to new understanding of MXene structural properties and can replace the currently used idealized models in predictions of a variety of physical, chemical, and functional properties of Ti3C2-based MXenes. The developed models can be employed to guide the design of new MXene materials with selected surface termination and controlled contact angle, catalytic, optical, electrochemical, and other properties. We suggest that the multilevel structural modeling should form the basis for a generalized methodology on modeling diffraction and pair distribution function data for 2D and layered materials.
The ability to disperse different clay materials in aqueous suspensions into fundamental particles 1–10 nm thick and combine them in various combinations and proportions has stimulated research into the more effective use of the unique properties of these materials. These properties include high surface area (up to 800 m2/g). cation exchange capacity (up to 120 meq./100 g) and anion exchange capacity (up to 25 meq./100 g) which can be utilized in a variety of industrial processes and other commerical applications. The products of such combinations are synthetic, randomly interstratified clays whose adsorption/desorption characteristics, micro-porosity, permeability, and interlayer chemistry can be modified to optimize their performance as chemical supports and heterogeneous catalysts. Thin films (10–100 nm) can be formed from these materials with a wide range of compositions and properties with possible applications in the medical treatment of burns and wounds, as release agents and coatings in pharmaceuticals and agricultural products, for the immobilization of bacteria and as enzyme supports in biotechnology. The coatings and films can be fired at temperatures of 1000°C to produce micro-ceramic products which could lead to applications such as electrical insulators and semiconductors and as protective coatings and bonding intermediates in the material sciences. This report outlines the methods of preparation and properties of these clay materials and presents analytical and experimental results demonstrating the promise of this technology.
MXenes constitute a family of two-dimensional transition metal carbides, carbonitrides and nitrides. Discovered in 2011, the number of MXenes has expanded significantly and more than 20 different MXenes have been synthesized, with many more predicted from theoretical calculations. MXenes constitute an exceptional family of materials based on their availability for elemental alloying and control of surface terminations, which enables synthesis of a range of structures and chemistries. Consequently, the MXenes exhibit an unparalleled potential for tuning of the materials properties for a wide range of applications. At present, MXenes have emerged with astonishing electronic, optical, plasmonic and thermoelectric properties. This has resulted in a global surge of research around a wide variety of applications, including but not limited to energy storage, carbon capture, electromagnetic interference shielding, reinforcement for composites, water filtering, sensors, and photo-, electro- and chemical catalysis etc. In this review, we present the available state of the art tailoring of the MXene properties owing to recent advances in structural ordering and tuning of surface terminations.
The 2D transition metal carbides (MXenes) are increasingly considered among of the most promising 2D nanomaterials, because of their unique properties such as hydrophilic nature, metallic conductivity, large surface-area-to-volume ratio, and active surface functionalities. This has led to their growing utilization in water/wastewater treatment and environmental remediation applications, including water purification membranes, heavy metal removal, capacitive deionization, and bactericidal agents. This account will focus on the key characteristic properties of MXenes such as high metallic/electronic conductivity, and catalytic activity, and their utilization for the electrocatalytic and photocatalytic-based environmental remediation applications. We will also address the key challenges facing MXene-based materials in aqueous media and possible mitigation routs.
MXenes, a relatively new class of two-dimensional (2D) transition-metal carbides, carbonitrides, and nitrides, exhibit unique properties such as high electronic conductivity, a wide range of optical characteristics, hydro-philicity, and mechanical stability. Because of the high electronic conductivity, MXenes have shown promise in many applications, such as energy storage, electromagnetic interference shielding, antennas, and transparent coatings. 2D titanium carbide (Ti 3 C 2 T x , where T x represents surface terminations), the first discovered and most studied MXene, has the highest electronic conductivity exceeding 10 000 S cm −1. There have been several efforts to alter the conductivity of MXenes, such as manipulation of the transition-metal layer and control of surface terminations. However, the impact of the C and N site composition on electronic transport has not been explored. In this study, the effects of synthesis methods on optoelectronic properties of 2D titanium carbonitride, Ti 3 CNT x , were systematically investigated. We show that Ti 3 CNT x , which hosts a mix of carbon and nitrogen atoms in the X layer, has lower electronic conductivity and a blue shift of the main absorption feature within the UV−visible spectrum, compared to Ti 3 C 2 T x. Moreover, intercalants such as water and tetraalkylammonium hydroxides decrease the electronic conductivity of MXene due to increased interflake resistance, leading to an increase in resistivity with decreasing temperature as observed in ensemble transport measurements. When the intercalants are removed, Ti 3 CNT x exhibits its intrinsic metallic behavior in good agreement with Hall measurements and transport properties measured on single-flake field-effect transistor devices. The dependence of conductivity of Ti 3 CNT x on the presence of intercalants opens wide opportunities for creating MXene-based materials with tunable electronic properties.
In 2011, a new family of two dimensional (2D) carbides, carbonitrides and nitrides – labeled MXenes – was discovered. Since then the number of papers on these materials has increased exponentially for several reasons amongst them: their hydrophilic nature, excellent electronic conductivities and ease of synthesizing large quantities in water. This unique combination of properties and ease of processing has positioned them as enabling materials for a large, and quite varied, host of applications from energy storage to electromagnetic shielding, transparent conductive electrodes, electrocatalysis, to name a few. Since the initial synthesis of Ti 3 C 2 in hydrofluoric acid, many more compositions were discovered, and different synthesis pathways were explored. Most of the work done so far has been conducted on top-down synthesis where a layered parent compound is etched and then exfoliated. Three bottom-up synthesis methods, chemical vapor deposition, a template method and plasma enhanced pulsed laser deposition have been reported. The latter methods enable the synthesis of not only high-quality ultrathin 2D transition metal carbide and nitride films, but also those that could not be synthesized by selective etching. This article reviews and summarizes the most important breakthroughs in the synthesis of MXenes and high-quality ultrathin 2D transition metal carbide and nitride films.
The room-temperature synthesis of a new two-dimensional (2D) zirconium-containing carbide, Zr3 C2 Tz MXene is presented. In contrast to traditional preparation of MXene, the layered ternary Zr3 Al3 C5 material instead of MAX phases is used as source under hydrofluoric acid treatment. The structural, mechanical, and electronic properties of the synthesized 2D carbide are investigated, combined with first-principles density functional calculations. A comparative study on the structrual stability of our obtained 2D Zr3 C2 Tz and Ti3 C2 Tz MXenes at elevated temperatures is performed. The obtained 2D Zr3 C2 Tz exhibits relatively better ability to maintain 2D nature and strucural integrity compared to Ti-based Mxene. The difference in structural stability under high temperature condition is explained by a theoretical investigation on binding energy.
The room-temperature synthesis of a new two-dimensional (2D) zirconium-containing carbide, Zr3C2Tz MXene is presented. In contrast to traditional preparation of MXene, the layered ternary Zr3Al3C5 material instead of MAX phases is used as source under hydrofluoric acid treatment. The structural, mechanical, and electronic properties of the synthesized 2D carbide are investigated, combined with first-principles density functional calculations. A comparative study on the structrual stability of our obtained 2D Zr3C2Tz and Ti3C2Tz MXenes at elevated temperatures is performed. The obtained 2D Zr3C2Tz exhibits relatively better ability to maintain 2D nature and strucural integrity compared to Ti-based Mxene. The difference in structural stability under high temperature condition is explained by a theoretical investigation on binding energy.
The higher the chemical diversity and structural complexity of two-dimensional (2D) materials the higher the likelihood they possess unique and useful properties. Herein, density functional theory (DFT) is used to predict the existence of two new families of 2D ordered, carbides (MXenes) - M'2M"C2 and M'2M"2C3 - where M' and M" are two different early transition metals. In these solids, M' layers sandwich M" carbide layers. By synthesizing Mo2TiC2Tx, Mo2Ti2C3Tx and Cr2TiC2Tx (where T is a surface termination) we validated the DFT predictions. Since the Mo and Cr atoms are on the outside, they control the 2D flakes' chemical and electrochemical properties. The latter was proven by showing quite different electrochemical behavior of Mo2TiC2Tx and Ti3C2Tx. This work further expands the family of 2D materials, offering new choices of structures, chemistries and ultimately useful properties.
Two-dimensional (2D) materials have attracted much attention in the past decade. They offer high specific surface area, as well as electronic structure and properties that differ from their bulk counterparts due to the low dimensionality. Graphene is the best known and the most studied 2D material, but metal oxides and hydroxides (including clays), dichalcogenides, boron nitride (BN), and other materials that are one or several atoms thick are receiving increasing attention. They may deliver a combination of properties that cannot be provided by other materials.
Two new MAX compounds, (Cr2/3Ti1/3)3AlC2 and (Cr5/8Ti3/8)4AlC3, were successfully synthesized by hot-pressing elemental powders at 1500°C for 1 h under 30 MPa in a flowing argon atmosphere. Their crystal structures were indentified and characterized by X-ray diffraction and transmission electron microscopy analysis. (Cr2/3Ti1/3)3AlC2 and (Cr5/8Ti3/8)4AlC3 have the same crystal structures with the well-characterized Ti3AlC2 and Ti4AlN3, respectively.
MoS2 has been exfoliated into monolayers by intercalation with lithium followed by reaction with water. X-ray diffraction analysis has shown that the exfoliated MoS2 in suspension is in the form of one-molecule-thick sheets. X-ray patterns from dried and re-stacked films of exfoliated MoS2 indicate that the layers are randomly stacked. Exfoliated MoS2 has been deposited on alumina particles in aqueous suspension, enabling recovery of dry exfoliated MoS2 supported on alumina.
Herein we report on the synthesis of two-dimensional transition metal carbides and carbonitrides by immersing select MAX phase powders in hydrofluoric acid, HF. The MAX phases represent a large (>60 members) family of ternary, layered, machinable transition metal carbides, nitrides, and carbonitrides. Herein we present evidence for the exfoliation of the following MAX phases: Ti(2)AlC, Ta(4)AlC(3), (Ti(0.5),Nb(0.5))(2)AlC, (V(0.5),Cr(0.5))(3)AlC(2), and Ti(3)AlCN by the simple immersion of their powders, at room temperature, in HF of varying concentrations for times varying between 10 and 72 h followed by sonication. The removal of the "A" group layer from the MAX phases results in 2-D layers that we are labeling MXenes to denote the loss of the A element and emphasize their structural similarities with graphene. The sheet resistances of the MXenes were found to be comparable to multilayer graphene. Contact angle measurements with water on pressed MXene surfaces showed hydrophilic behavior.
Unilamellar colloids of graphite oxide (GO) were prepared from natural graphite and were grown as monolayer and multilayer thin films on cationic surfaces by electrostatic self-assembly. The multilayer films were grown by alternate adsorption of anionic GO sheets and cationic poly(allylamine hydrochloride) (PAH). The monolayer films consisted of 11?14 Å thick GO sheets, with lateral dimensions between 150 nm and 9 ?m. Silicon substrates primed with amine monolayers gave partial GO monolayers, but surfaces primed with Al13O4(OH)24(H2O)127+ ions gave densely tiled films that covered approximately 90% of the surface. When alkaline GO colloids were used, the monolayer assembly process selected the largest sheets (from 900 nm to 9 ?m) from the suspension. In this case, many of the flexible sheets appeared folded in AFM images. Multilayer (GO/PAH)n films were invariably thicker than expected from the individual thicknesses of the sheets and the polymer monolayers, and this behavior is also attributed to folding of the sheets. Multilayer (GO/PAH)n and (GO/polyaniline)n films grown between indium?tin oxide and Pt electrodes show diodelike behavior, and higher currents are observed with the conductive polyaniline-containing films. The resisitivity of these films is decreased, as expected, by partial reduction of GO to carbon.
2D Ti 3C 2 nanosheets, multilayer structures, and conical scrolls produced by room temperature exfoliation of Ti 3AlC 2 in HF are reported. Since Ti 3AlC 2 is a member of a 60+ group of layered ternary carbides and nitrides, this discovery opens a door to the synthesis of a large number of other 2D crystals.
We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions,
metallic, and of remarkably high quality. The films are found to be a two-dimensional semimetal with a tiny overlap between
valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in
concentrations up to 1013 per square centimeter and with room-temperature mobilities of ∼10,000 square centimeters per volt-second can be induced by
applying gate voltage.
- M Naguib
- V N Mochalin
- M W Barsoum
- Y Gogotsi
M. Naguib, V.N. Mochalin, M.W. Barsoum, Y. Gogotsi, 25th anniversary article:
MXenes: a new family of two-dimensional materials, Adv. Mater. 26 (7) (2014)
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AlC 3 : new MAX-phase compounds in Ti-Cr-Al-C system
AlC 3 : new MAX-phase compounds in Ti-Cr-Al-C system, J. Am. Ceram. Soc. 97
(1) (2014) 67-69.