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Cost analysis of MXene for low-cost production, and pinpointing of its economic footprint
... This environmentally efficient method reduces the environmental impact by utilizing waste materials. By realizing this importance, a review work of providing detailed cost analysis of MXenes that includes raw materials, synthesizing process, validation test, storage condition, etc. has been conducted to assist the scientific community in optimizing a large-scale production cost of these emerging 2D materials in the near future [65]. Some strategies, including critical parameters related to synthesis methods, precursor materials, post-synthesis characterizations, and innovations in scaling up MXene production, have been discussed in another review work [66]. ...
... Meanwhile, Shuck et al. have used a selective wet-chemistry method to synthesize MXenes dispersion in a large amount by using a custom-designed chemical reactor [45]. The work has proven experimentally that the production yield is readily scaled with the reactor volume [17,45,[61][62][63][64][65][66]. Another work has successfully produced large-area, highly conductive, and strong MXene films on a scalable basis by using a scalable blade coating process [69]. ...
... J Mater Sci processes and materials to reduce costs while maintaining the product quality [65]. Numerous scientists are diligently working to reduce processing time and costs. ...
MXenes, a class of two-dimensional material with exceptional properties, have garnered significant attention for their potential applications in various industries. However, the high production costs associated with MXene synthesis present a substantial barrier to its widespread use. The synthesis methods, risk factors, environmental factors, and most importantly, expensive precursors create a barrier to MXene applications. Numerous review articles on MXene materials have been published. However, this review article aims to provide a comprehensive analysis of potential ways to reduce the cost of these potential materials, which indicates the novelty of this work. The current article aims to provide a review of the synthesis method, risk factors, environmental factors, and, most importantly, how to convert recycled materials as precursors into MXenes and enhance the cost-effectiveness of MXene production. This review found that modified acid etching is the most convenient route for MXene synthesis, preserving the MXene properties while being concerned with risks and environmental factors. Recycled materials (e.g., tires, aluminum scrap, biochar, and activated carbon) can be used to synthesize high-quality MXenes by fine-tuning their contents. We propose a comprehensive approach to reduce the cost of MXenes. This article includes technical challenges and future recommendations for further research on this topic.
Graphical abstract
Two emerging materials, MXenes and MBenes, have garnered significant attention as promising candidates for CCS applications. Both materials possess unique properties that make them well-suited for CO 2 adsorption, such as high surface area, porosity, and tunable chemical functionality. This perspective article presents a comparative evaluation of MXenes and MBenes for CO 2 capture, leveraging advanced computational simulations and experimental data to elucidate their respective adsorption capacities, kinetic performance, and stability. The simulations reveal that both materials exhibit superior CO 2 adsorption performance compared to conventional CCS materials, with MXenes demonstrating a slight edge in adsorption capacity and selectivity. Furthermore, the potential of MXenes and MBenes for CCS applications is discussed, including their layer thickness, selective affinity to CO 2 , advantages over conventional sorbents, regeneration, stability, and durability. The findings provide valuable insights into the structure–property relationships of MXenes and MBenes in the context of CO 2 capture and shed light on the technology readiness of these materials for specific CCS applications. Finally, this perspective article aims to advance the fundamental understanding of these novel 2D materials for CCS, paving the way for future developments in sustainable CO 2 capture technologies.
Graphical abstract
Highlights
MXenes and MBenes are two-dimensional layered materials with the potential to revolutionize carbon capture and storage (CCS). MXenes have several advantages over other CCS materials, such as greater porosity, higher CO2 adsorption capacity, and easier and less expensive production. MBenes are more stable in humid environments and have higher oxidation resistance and thermal conductivity than MXenes, making them a better choice for CCS applications where the CO2 stream is humid, hot, and/or corrosive. MXenes and MBenes have the potential to make CCS more efficient, cost-effective, and versatile.
Discussion
Why are MXenes and MBenes ideal for carbon capture applications?
In terms of carbon capture efficiency, how do MXenes and MBenes stack up against other materials such as MOFs, zeolites, and activated carbons?
Which are better, MXenes or MBenes, for carbon capture?
Why do MXenes and MBenes have a selective affinity to CO2 compared to other gases such as N2 and O2?
What is the optimal number of layers for MXenes/MBenes for carbon capture, and does interlayer spacing affect performance?
What is the best surface termination for CO2 capture?
What happens to the CO2 after it is absorbed onto MXene and MBene surfaces, and how can one remove CO2 that has been adsorbed?
What are the major challenges, besides scalability, that need to be overcome for these materials to be practical?
How durable and stable are MXenes and MBenes?
The remarkable versatility of MXene materials has propelled them into the forefront of advanced material science, with applications spanning energy storage, catalysis, water treatment, and electronics. Bulk production of MXene materials is essential to meet the demands of applications, enhance commercial viability, support research efforts, integrate MXene into industries, and drive technological advancements. It is a key step in realizing the full potential of MXene materials and ensuring their widespread use in diverse fields. However, the problem is that MXene synthesis methods, especially those developed at the laboratory scale, face challenges when transitioning to large-scale production. Maintaining the quality, consistency, and yield of MXene materials on a large scale can be complex. The paper provides a comprehensive overview of current synthesis methods, critical parameters that influence bulk production, precursor materials and post-synthesis characterizations, and innovations in scaling up MXene production. The necessary environmental and safety measures were also reviewed. This comprehensive review work is critical for developing the area of MXene bulk manufacturing and has major implications for the larger community. By thoroughly addressing problems, investigating crucial factors, and emphasising breakthroughs in large-scale synthesis, the study serves as a road map for researchers, industry experts, and maybe policymakers.
The development of new materials for electromagnetic interference (EMI) shielding is an important area of research, as it allows for the creation of more effective and high‐efficient shielding solutions. In this sense, MXenes, a class of 2D transition metal carbides and nitrides have exhibited promising performances as EMI shielding materials. Electric conductivity, low density, and flexibility are some of the properties given by MXene materials, which make them very attractive in the field. Different processing techniques have been employed to produce MXene‐based materials with EMI shielding properties. This review summarizes processes and the role of key parameters like the content of fillers and thickness in the desired EMI shielding performance. It also discusses the determination of power coefficients in defining the EMI shielding mechanism and the concept of green shielding materials, as well as their influence on the real application of a produced material. The review concludes with a summary of current challenges and prospects in the production of MXene materials as EMI shields.
The large and rapidly growing family of 2D early transition metal carbides, nitrides, and carbonitrides (MXenes) raises significant interest in the materials science and chemistry of materials communities. Discovered a little more than a decade ago, MXenes have already demonstrated outstanding potential in various applications ranging from energy storage to biology and medicine. The past two years have witnessed increased experimental and theoretical efforts toward studying MXenes’ mechanical and tribological properties when used as lubricant additives, reinforcement phases in composites, or solid lubricant coatings. Although research on the understanding of the friction and wear performance of MXenes under dry and lubricated conditions is still in its early stages, it has experienced rapid growth due to the excellent mechanical properties and chemical reactivities offered by MXenes that make them adaptable to being combined with other materials, thus boosting their tribological performance. In this perspective, the most promising results in the area of MXene tribology are summarized, future important problems to be pursued further are outlined, and methodological recommendations that could be useful for experts as well as newcomers to MXenes research, in particular, to the emerging area of MXene tribology, are provided.
Liquid phase exfoliation of Ti 3 C 2 T x MXene using LiF/HCl mix, forming HF in situ , has been modified by the addition of NH 4 OH. The base assisted dilution and extraction of MXene enables a quick control over pH and improves the structural, morphological and optical properties of the compound. The formation of a buffer compound NH 4 F, reduces the oxidation on the surface of MXene and etches off the residual MAX phase, by attacking Al. The structural features of the prepared NH 4 OH added Ti 3 C 2 T x MXene are remarkably better than the HF etched samples, with the characteristic MXene peak in XRD being emphasized in the former. The addition of ammonia solution improves the milder in situ HF etching technique, by giving the characteristic open accordion structure to the compound, making the compound easy to delaminate and more stable against oxidation in ambient atmosphere.
2D transition metal carbides, nitrides, and carbonitrides, also known as MXenes, are versatile materials due to their adjustable structure and rich surface chemistry. The physical and chemical diversity has recognized MXenes as a potential 2D material with a wide spectrum of application domains. Since the discovery of MXenes in 2011, a wide variety of synthetic routes has been proposed with advancement toward large-scale preparing methods for MXene nanosheets and derivative products. Herein, the critical synthesis aspects and the operating conditions that influence the physical and chemical characteristics of MXenes are discussed in detail. The emerging etching methods including HF etching methods, in situ HF-forming etching methods, electrochemical etching methods, alkali etching methods, and molten salt etching methods, as well as delamination strategies are discussed. Considering the future developments and practical applications, the large-scale synthesis routes and the antioxidation strategies of MXenes are also summarized. In summary, a generalized overview of MXenes synthesis protocols with an outlook for the current challenges and promising technologies for large-scale preparation and stable storage is provided.
Since their discovery in 2011, the number of 2D transition metal carbides and nitrides (MXenes) has steadily increased. Currently more than 40 MXene compositions exist. The ultimate number is far greater and in time they may develop into the largest family of 2D materials known. MXenes’ unique properties, such as their metal‐like electrical conductivity reaching ≈20 000 S cm−1, render them quite useful in a large number of applications, including energy storage, optoelectronic, biomedical, communications, and environmental. The number of MXene papers and patents published has been growing quickly. The first MXene generation is synthesized using selective etching of metal layers from the MAX phases, layered transition metal carbides and carbonitrides using hydrofluoric acid. Since then, multiple synthesis approaches have been developed, including selective etching in a mixture of fluoride salts and various acids, non‐aqueous etchants, halogens, and molten salts, allowing for the synthesis of new MXenes with better control over their surface chemistries. Herein, a brief historical overview of the first 10 years of MXene research and a perspective on their synthesis and future development are provided. The fact that their production is readily scalable in aqueous environments, with high yields bodes well for their commercialization. The transition metal carbides and nitrides (MXenes) are among the largest 2D material families. MXenes’ unique properties, such as their metal‐like electrical conductivity, render them quite useful in a large number of applications including energy storage, optoelectronic, biomedical, communications, and environmental. A brief historical overview of the first 10 years of MXene research and a perspective on their synthesis and future development are provided.
MXene is a recently emerged multifaceted two-dimensional (2D) material that is made up of surface-modified carbide, providing its flexibility and variable composition. They consist of layers of early transition metals (M), interleaved with n layers of carbon or nitrogen (denoted as X) and terminated with surface functional groups (denoted as T x /T z ) with a general formula of M n+1 X n T x , where n = 1–3. In general, MXenes possess an exclusive combination of properties, which include, high electrical conductivity, good mechanical stability, and excellent optical properties. MXenes also exhibit good biological properties, with high surface area for drug loading/delivery, good hydrophilicity for biocompatibility, and other electronic-related properties for computed tomography (CT) scans and magnetic resonance imaging (MRI). Due to the attractive physicochemical and biocompatibility properties, the novel 2D materials have enticed an uprising research interest for application in biomedicine and biotechnology. Although some potential applications of MXenes in biomedicine have been explored recently, the types of MXene applied in the perspective of biomedical engineering and biomedicine are limited to a few, titanium carbide and tantalum carbide families of MXenes. This review paper aims to provide an overview of the structural organization of MXenes, different top-down and bottom-up approaches for synthesis of MXenes, whether they are fluorine-based or fluorine-free etching methods to produce biocompatible MXenes. MXenes can be further modified to enhance the biodegradability and reduce the cytotoxicity of the material for biosensing, cancer theranostics, drug delivery and bio-imaging applications. The antimicrobial activity of MXene and the mechanism of MXenes in damaging the cell membrane were also discussed. Some challenges for in vivo applications, pitfalls, and future outlooks for the deployment of MXene in biomedical devices were demystified. Overall, this review puts into perspective the current advancements and prospects of MXenes in realizing this 2D nanomaterial as a versatile biological tool.
The considerable amount of Cr(VI) pollutants in the aqueous environment is a significant environmental concern that cannot be ignored. A series of novel Mxene–CS inorganic–organic composite nanomaterials synthesized by using the solution reaction method was applied to treat the Cr(VI) contaminated water. The Mxene–CS composites were characterized through SEM (scanning electron microscope), XRD (X–ray diffraction), XPS (X–ray photoelectron spectroscopy), and FTIR (Fourier transform infrared). The XRD patterns (observed at 2θ of 18.1°, 35.8°, 41.5°, and 60.1°) and the FT–IR spectra (-NH2 group for 1635 and 1517 cm−1, and -OH group for 3482 cm−1) illustrated that CS was successfully loaded on the Mxene. The effects of solution pH, the dosage of Mxene–CS, and duration time on the adsorption of Cr(VI) by synthesized Mxene–CS were investigated. The removal efficiency of Cr(VI) was increased from 12.9% to 40.5% with Mxene–CS dosage ranging from 0.02 to 0.12 g/L. The adsorption process could be well fitted by the pseudo–second–order kinetics model, indicating chemisorption occurred. The Langmuir isotherm model could be better to describe the process with a maximum adsorption capacity of 43.1 mg/g. The prepared novel Mxene–CS composite was considered as an alternative for adsorption of heavy metals from wastewater.
MXene (e.g., Ti3C2) represents an important class of two‐dimensional (2D) materials owing to its unique metallic conductivity and tunable surface chemistry. However, the mainstream synthetic methods rely on the chemical etching of MAX powders (e.g., Ti3AlC2) using hazardous HF or alike, leading to MXene sheets with fluorine termination and poor ambient stability in colloidal dispersions. Here, we demonstrate a fluoride‐free, iodine (I2) assisted etching route for preparing 2D MXene (Ti3C2Tx, T=O, OH) with oxygen‐rich terminal groups and intact lattice structure. More than 71 % of sheets are thinner than 5 nm with an average size of 1.8 μm. They present excellent thin‐film conductivity of 1250 S cm⁻¹ and great ambient stability in water for at least 2 weeks. 2D MXene sheets with abundant oxygen surface groups are excellent electrode materials for supercapacitors, delivering a high gravimetric capacitance of 293 F g⁻¹ at a scan rate of 1 mV s⁻¹, superior to those made from fluoride‐based etchants (<290 F g⁻¹ at 1 mV s⁻¹). Our strategy provides a promising pathway for the facile and sustainable production of highly stable MXene materials.
Recently, a new class of two-dimensional (2D) materials, called MXene, consisting of layers of transition-metal carbides and nitrides/carbonitrides has been introduced. MXene, a multifunctional material with hydrophilic nature and excellent electrical conductivity and chemical stabilities, can be applied in diverse research areas such as energy harvesting and its storage, water purification, thermal dissipation, and gas sensing. To achieve the best quality of MXene, optimization of some important synthetic parameters is highly required such as an optimized etchant concentration to remove an "A" element from the MAX phase and sonication time for the efficient exfoliation of MXene flakes. Besides, there is a need to disclose that particular solvent through which intercalation can easily be achieved. In this work, we optimized the abovementioned critical parameters for the synthesis of good-quality MXene. Our results clearly explain the variations in the quality of MXene under applied etchant concentrations, solvents for better intercalation, and optimization of sonication time for better exfoliation. The obtained results suggest that 30% HF as an etchant, dimethyl sulfoxide (DMSO) as a solvent, and 135 min as the sonication time are effective parameters for the synthesis of good-quality MXene. We expect that this report will be helpful for the young research community to synthesize good-quality MXene with the required properties.
The chemical stability of 2D MXene nanosheets in aqueous dispersions must be maintained to foster their widespread application. MXene nanosheets react with water, which results in the degradation of their 2D structure into oxides and carbon residues. The latter detrimentally restricts the shelf life of MXene dispersions and devices. However, the mechanism of MXene degradation in aqueous environment has yet to be fully understood. In this work, the oxidation kinetics is investigated of Ti3C2Tx and Ti2CTx in aqueous media as a function of initial pH values, ionic strengths, and nanosheet concentrations. The pH value of the dispersion is found to change with time as a result of MXene oxidation. Specifically, MXene oxidation is accelerated in basic media by their reaction with hydroxyl anions. It is also demonstrated that oxidation kinetics are strongly dependent on nanosheet dispersion concentration, in which oxidation is accelerated for lower MXene concentrations. Ionic strength does not strongly affect MXene oxidation. The authors also report that citric acid acts as an effective antioxidant and mitigates the oxidation of both Ti3C2Tx and Ti2CTx MXenes. Reactive molecular dynamic simulations suggest that citric acid associates with the nanosheet edge to hinder the initiation of oxidation. Oxidation kinetics of Ti3C2Tx and Ti2CTx MXene nanosheets in aqueous media are accelerated at high pH and at low MXene concentrations. However, this degradation process can be mitigated; citric acid acts as an effective MXene antioxidant for both Ti3C2Tx and Ti2CTx.
Polymer composites with enhanced thermal and dielectric properties can be widely used in electric and energy related applications. In this work, epoxy composites have been prepared with Ti3C2Tx, one of the most studied MXene materials that can be massively produced by direct etching using hydrofluoric acid. The addition of conductive two dimensional Ti3C2Tx platelet fillers leads to improved but anisotropic thermal conductivity of the composites. The through-plane thermal conductivity reaches 0.583 Wm−1K−1 and the in-plane thermal conductivity reaches 1.29 Wm−1K−1 when filler content is 40 wt% (21.3 vol%), achieving enhancements of 2.92 times and 10.65 times respectively, as compared with epoxy matrix. The dielectric permittivity of epoxy composite is enhanced by a factor of ~2.25 with 40 wt% fillers, and the dielectric losses are within a small value of 0.02. The results prove the effectiveness of Ti3C2Tx in simultaneously improving thermal and dielectric performance of epoxy composites, and it is deduced that further improvements may be obtained by using Ti3C2Tx nanoflake fillers.
In 2017, a new family of in‐plane, chemically‐ordered quaternary MAX phases, coined i‐MAX, has been reported since 2017. The first i‐MAX phase, (Mo2/3Sc1/3)2AlC, garnered significant research attention due to the presence of chemically ordered Sc within the Mo‐dominated M layer, and the facilitated removal of both Al and Sc upon etching, resulting in 2D i‐MXene, Mo1.33C, with ordered divacancies. The i‐MXene renders an exceptionally low resistivity of 33.2 µΩ m⁻¹ and a high volumetric capacitance of ≈1150 F cm⁻³. This discovery has been followed by the synthesis of, to date, 32 i‐MAX phases and 5 i‐MXenes, where the latter have shown potential for applications including, but not limited to, energy storage and catalysis. Herein, fundamental investigations of i‐MAX phases and i‐MXenes, along with their applicability in supercapacitive and catalytic applications, are reviewed. Moreover, recent results on ion intercalation and post‐etching treatment of Mo1.33C are presented. The charge storage performance can also be tuned by forming MXene hydrogel and through inert atmosphere annealing, where the latter renders a superior volumetric capacitance of ≈1635 F cm⁻³. This report demonstrates the potential of the i‐MXene family for catalytic and energy storage applications, and highlights novel research directions for further development and successful employment in practical applications.
Scaling the production of synthetic 2D materials to industrial quantities has faced significant challenges due to synthesis bottlenecks whereby few have been produced in large volumes. These challenges typically stem from bottom‐up approaches limiting the production to the substrate size or precursor availability for chemical synthesis and/or exfoliation. In contrast, MXenes, a large class of 2D transition metal carbides and/or nitrides, are produced via a top‐down synthesis approach. The selective wet etching process does not have similar synthesis constraints as some other 2D materials. The reaction occurs in the whole volume; therefore, the process can be readily scaled with reactor volume. Herein, the synthesis of 2D titanium carbide MXene (Ti3C2Tx) is studied in two batch sizes, 1 and 50 g, to determine if large‐volume synthesis affects the resultant structure or composition of MXene flakes. Characterization of the morphology and properties of the produced MXene using scanning electron microscopy, X‐ray diffraction, dynamic light scattering, Raman spectroscopy, X‐ray photoelectron spectroscopy, UV–visible spectroscopy, and conductivity measurements show that the materials produced in both batch sizes are essentially identical. This illustrates that MXenes experience no change in structure or properties when scaling synthesis, making them viable for further scale‐up and commercialization.
MXenes, generally referring to two-dimensional (2D) transition-metal carbides, nitrides, and carbonitrides, have received tremendous attention since the first report in 2011. Extensive experimental and theoretical studies have unveiled their enormous potential for applications in optoelectronics, photonics, catalysis, and many other areas. Because of their intriguing mechanical and electronic properties, together with the richness of elemental composition and chemical decoration, MXenes are poised to provide a new 2D nanoplatform for advanced optoelectronics. This comprehensive review, intended for a broad multidisciplinary readership, highlights the state-of-the-art progress on MXene theory, materials synthesis techniques, morphology modifications, opto-electro-magnetic properties, and their applications. The efforts exploring the device performance limits, steric configurations, physical mechanisms, and novel application boundaries are comprehensively discussed. The review is concluded with a compelling perspective, outlook as well as non-trivial challenges in future investigation of MXene-based nano-optoelectronics.
The high specific surface area of multilayered two-dimensional carbides called MXenes, is a critical feature for their use in energy storage systems, especially supercapacitors. Therefore, the possibility of controlling this parameter is highly desired. This work presents the results of the influence of oxygen concentration during Ti3AlC2 ternary carbide—MAX phase preparation on α-Al2O3 particles content, and thus the porosity and specific surface area of the Ti3C2Tx MXenes. In this research, three different Ti3AlC2 samples were prepared, based on TiC-Ti2AlC powder mixtures, which were conditioned and cold pressed in argon, air and oxygen filled glove-boxes. As-prepared pellets were sintered, ground, sieved and etched using hydrofluoric acid. The MAX phase and MXene samples were analyzed using scanning electron microscopy and X-ray diffraction. The influence of the oxygen concentration on the MXene structures was confirmed by Brunauer-Emmett-Teller surface area determination. It was found that oxygen concentration plays an important role in the formation of α-Al2O3 inclusions between MAX phase layers. The mortar grinding of the MAX phase powder and subsequent MXene fabrication process released the α-Al2O3 impurities, which led to the formation of the porous MXene structures. However, some non-porous α-Al2O3 particles remained inside the MXene structures. Those particles were found ingrown and irremovable, and thus decreased the MXene specific surface area.
Two‐dimensional (2D) titanium carbide (Ti3C2) is emerging as an important member of the MXene family. However, fluoride‐based synthetic procedures remain an impediment to the practical applications of this promising class of materials. Here we demonstrate an efficient fluoride‐free etching method based on the anodic corrosion of titanium aluminium carbide (Ti3AlC2) in a binary aqueous electrolyte. The dissolution of aluminium followed by in‐situ intercalation of ammonium hydroxide results in the extraction of carbide flakes (Ti3C2Tx, T=O, OH) with sizes up to 18.6 µm and high yield (over 90 %) of mono‐ and bilayers. All‐solid‐state supercapacitor based on exfoliated sheets exhibits high areal and volumetric capacitances of 220 mF cm‐2 and 439 F cm‐3, respectively, at a scan rate of 10 mV s‐1, superior to those of LiF/HCl‐etched MXenes. Our strategy paves a safe way to the scalable synthesis and application of MXene 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.
This study reports on the first experimental evidence of the existence of the Zr2AlC MAX phase, synthesised by means of reactive hot pressing of a ZrH2, Al and C powder mixture. The crystal structure of this compound was investigated by X-ray and neutron diffraction. The lattice parameters were determined and confirmed by high-resolution transmission electron microscopy. The effect of varying the synthesis temperature was investigated, indicating a relatively narrow temperature window for the synthesis of Zr2AlC. ZrC was always present as a secondary phase by hot pressing in the 1475–1575 °C range.
In the present work, ultrasound was introduced throughout the synthesis of Ti3C2Tx MXene, the synthesis efficiency and energy storage performance of the MXenes were significantly improved under the aid of ultrasound. It was verified that intercalation of Li⁺ between the adjacent layers of Ti3C2Tx MXene was greatly promoted by the ultrasound. Under the impact of ultrasound, the 8 h sonicated etched showed a specific capacitance of 270.5 F/g, which is a 16-fold enhancement compared with the sample without the aid of ultrasound. Monolayered samples with and without sonication treatment were synthesized, and the sample prepared in presence of ultrasound showed a specific capacitance of 420.66 F/g. The specific capacitance retention of the 8 h ultrasonically etched multiple layered samples after 10,000 cycles at 5 A/g was 95.52%, 4.27% higher than the corresponding value of the monolayered sample.
In this rapidly developing society, it is always crucial to exploit new materials with suitable properties to meet specific application demands. Two-dimensional (2D) transition metal carbon/nitrides (MXenes) are a novel graphene-like material with exciting research potential in recent years. Among them, Ti3C2 debuts in a central position due to its relatively longer research history, mature synthetic process, and incredibly rich store of merits, such as good flexibility, large specific surface area, abundant termination groups, excellent electrical conductivity, and light-to-heat conversion ability. In this review, recent research progress on Ti3C2 MXene and its composites was updated mainly from three aspects, including their fundamentals, synthesis, and applications. It has been found that diverse applications of Ti3C2-based composites are inseparable and correlated with each other, which were linked by their unique physicochemical properties. In the end, a summary and a perspective on future opportunities and challenges of Ti3C2 were given to offer theoretical and technical guidelines for further investigation on MXene family.
This work describes a novel and rapid strategy to produce delaminated MXene sheets from the MAX phase. The current method uses a novel microwave-assisted hydrothermal method to etch aluminium (Al) from the MAX phase (as well as delaminate) within 2 h of processing which has remarkably reduced time from up to 48 h to 30 min and temperature from 180 to 40 °C. A range of characterizations was carried out to evaluate the properties of the MXene. The X-ray photoelectron spectroscopy and X-ray diffraction patterns exhibited the spectra typical of Ti3C2Tx extracted from Ti3AlC2 after rapid etching of Al. These results were complemented by scanning and transmission electron microscopies, UV–visible absorption spectrum, and BET absorption-desorption curves. The results depicted the formation of high-quality MXene with negligible Al traces, which confirms the efficacy of the current method. This work not only establishes a comprehensive methodology for rapidly synthesizing high-quality MXene in bulk quantities but also opens up new avenues for its commercial applications.
Identification of the intrinsic active sites and understanding of the kinetics processes on electrocatalysts is essential in the rational design of highly efficient electrochemical nitrogen fixation electrocatalysts. In this work, 3D N-doped-TiV-Ti3-xC2Ty-1.2 MXene was fabricated for ENRR. The intrinsic active-site, as well as the activated mechanism of 3D porous N-doped Ti3-xC2Ty MXene, were elucidated by in situ electrochemical Raman spectrum and DFT simulation. It was demonstrated that the Ti³⁺ species were the intrinsic active sites for electrocatalytic nitrogen reduction reaction (ENRR), and the electronic state of the active Ti³⁺ species in 3D porous N-doped Ti3-xC2Ty MXene can be adjusted by surface atomic engineerings, such as vacancy creation and heteroatom doping. The introduction of Ti vacancies can trap the electrons that inject into an antibonding orbital of adsorbed N2, which facilitates the activation of N2. Besides, the N-dopant species in the MXene can not only act as steady active sites for ENRR but also promote the desorption of NH3 by minimize the orbits overlap between Ti³⁺ and N2, which was confirmed by a bidirectional isotopic exchange labeling method and DFT simulation. This finding paves a valuable strategy for the surface engineering design of efficient catalysts in ENRR.
Multi-layered Ti3C2TXMXene with F⁻/OH⁻ termination was synthesized from high purity Ti3AlC2 MAX-phase powders by selectively etching away Al atoms using hydrochloride (HCl)+lithium fluoride (LiF). Single and few atomic layerMXene flakes were prepared by delaminating multi-layered MXene powders by sonication under flowing Argon gas. A characteristic peak of Ti3AlC2 MAX-phase ceramics at 9.5 observed in XRD patterns is shifted to lower value of 8.1 which confirms the conversion of Ti3AlC2 to Ti3C2TxMXene. The field emission scanning electron microscopy (FE-SEM) image also shows a typical lamellar structure of few nanometer widths. Raman spectra obtained from MXene shows three broad peaks centred on 210, 397, and 610 cm ⁻¹ atypicalcharacteristic arising from Ti-C-Txatoms vibrationpresent in Ti3C2Tx MXene. The value of Electromagnetic interference shielding effectiveness (EMI SE) of Ti3C2TxMXene powder is of the order of 25 dB which makes it a promising candidate for EMI shielding applications.
Industrial use of heavy metals and dyes critically depends on the effective handling of industrial effluents. Effective remediation of industrial effluents using various adsorbent materials has thus become critical. In this paper, we study two-dimensional MXenes as an adsorbent for removing Cr(VI) and methyl orange (MO) in waters. The physico-chemical performance of MXenes was studied using X-ray diffraction, Fourier transform infrared spectroscopy, Brunauer−Emmett−Teller, scanning electron microscopy, high resolution-transmission electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy techniques. The adsorption system, including influence of contact time, pH of solutions, co-ions, and desorption experiments were performed for effective Cr(VI) and MO removal. The Cr(VI) and MO removal rate of the MXenes was very fast, and the kinetic system was driven by pseudo-second-order kinetics. The sorption isotherm closely well-tailored with the Langmuir isotherm, and the maximum removal efficiencies were 104 and 94.8 mg/g for Cr(VI) and MO, respectively. The MXenes was successfully regenerated by 0.1 M NaOH aqueous solution and can be repeatedly recycled. The uptake of Cr(VI) and MO by the MXenes was mainly due to chemical adsorption, namely electrostatic adsorption, complexation, surface interactions, and ion exchange mechanisms. This investigation demonstrates the selectivity and feasibility of the MXenes as a real adsorbent for eliminating Cr(VI) and MO from the aqueous environment.
Discovered in 2011, MXene becomes a most recent and active member of two-dimensional materials. Since then, the landscape of MXene grows significantly and now more than 30 different MXenes were obtained experimentally. Though most of the efforts are contributed to Ti-MXenes which have the highest level of maturity of the synthetic technology and productivity, in recent years, new-MXene systems with Molybdenum (Mo), Vanadium (V), and Niobium (Nb) as the transition metals demonstrated their unique properties and applications. The development of new-MXenes not only expands the synthetic methods and applications of MXenes but also faces new challenges. Therefore, a timely summary of Mo-, V- and Nb-MXenes will be extremely beneficial. Here, the synthetic methods of the selected new-MXenes are summarized and their most recent applications are highlighted to provide an outlook for the future development of MXenes.
We present a novel strategy to prepare Nb2CTx by etching Nb2AlC powders with a mixed solution of lithium fluoride and hydrochloric acid. The Nb2CTx exhibits a layered structure with excellent crystalline degree and structural order. Meanwhile, the electrochemical performance of Nb2CTx in aqueous electrolyte was examined for the first time. The Nb2CTx shows good electrochemical capacitance performance, and the addition of carbon nanotubes (CNT) as a conductive agent can significantly improve the rate performance of the electrode. This may provide an idea to improve the performance for the M2C-type MXenes electrodes with lower conductivity than Ti3C2Tx. The asymmetric supercapacitor was assembled by using Nb2CTx/CNT as negative electrode and activated carbon as positive electrode, which can deliver a high energy density of 154.1 μWh/cm² and a maximum power density of 74843.1 μW/cm² under the high mass loading. The power density is higher than most of the reported MXene-based supercapacitors.
The two-dimensional (2D) MXene has attracted great interest in the field of biomedical applications. Here, we synthesized for the first time, polycaprolactone-MXene (PCL-MXene) composite electrospun fibers and evaluated its possible applications in biomedical areas. The composite fibers were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis/differential scanning calorimetry, mechanical strength, and contact angle. Additionally, biocompatibility evaluation of the as-synthesized composite fibers was carried out on fibroblasts (NIH-3T3) and preosteoblasts (MC3T3-E1) cell lines, as a model. Besides these, possible biomineralization activity of the composites fibers was also determined for the harden tissues formation. The results showed that PCL-MXene composite electrospun fibers were cell friendly for both cell lines. However, pre-osteoblast cells exhibited higher cell viability compared to fibroblasts. Considering auspicious results, this work is expected to open the possible pathway for the expanded applications of MXene based composites in biomedical applications.
Due to highly tunable metallic compositions and surface functional groups, MXenes have attracted significant interests for a wide range of applications, such as energy storage, electromagnetic interference shielding, sensors, and biomedicine. With the introduction of porous structures, which have unique advantages in tuning the conductivity and dielectric constant, adjusting the ion/guest and even electromagnetic wave transport, and also directing the loading and distribution of other functional materials, porous MXenes hold great potential in profoundly enhancing their properties. We have surveyed rapidly increasing efforts in the design and synthesis of porous MXenes with advantageous structures for diverse applications, especially in the last three years. Here we classify Porous MXenes into four categories according to their formation routes, including (i) assembly by MXenes, (ii) depositing or inserting MXenes into porous substrates, (iii) loading or coating functional porous materials on the surface of MXenes, and (iv) creating in-plane pores within MXenes. Then we summarize the primary synthetic methods for each kind of porous MXenes and discuss their applications for pseudo-capacitors, lithium/sodium batteries, lithium-sulfur batteries, electromagnetic interference shielding and adsorption, piezoresistive sensors, and cancer therapy. A particular emphasis is on the formation mechanisms of different porous structures and the detailed composition-structure-property relationships in related applications. We lastly conclude with a brief perspective on future opportunities and challenges.
Two dimensional (2D) materials have attracted significant attention in the past decade for their high application potential to address some of society’s most pressing issues such as energy storage and the scarcity of potable water. One of the latest, and relatively large, family of 2D materials is transition-metal carbides and nitrides, called MXenes. Since the initial synthesis of Ti3C2 in hydrofluoric acid in 2011, almost 30 other new compositions and at least eight different synthesis pathways have been reported. In this review, we overview the structure, synthesis, and chemistry of MXenes, with examples of their properties and potential applications that partially explain why these materials have become so popular.
Solution processable two-dimensional transition metal carbides, commonly known as MXenes, have drawn much interest due to their diverse optoelectronic, electrochemical and other useful properties. These properties have been exploited to develop thin and optically transparent microsupercapacitors. However, color changing MXene-based microsupercapacitors have not been explored. In this study, we developed titanium carbide-poly(3,4-ethylenedioxythiophene) (PEDOT) heterostructures by electrochemical deposition using a non-aqueous monomeric electrolytic bath. Planar electrodes of such hybrid films were carved directly using an automated scalpel technique. Hybrid microsupercapacitors showed five-fold areal capacitance and higher rate capabilities (2.4 mF cm ⁻² at 10 mV s ⁻¹ , retaining 1.4 mF cm ⁻² at 1000 mV s ⁻¹ ) over the pristine MXene microsupercapacitors (455 μF cm ⁻² at 10 mV s ⁻¹ , 120 μF cm ⁻² at 1000 mV s ⁻¹ ). Furthermore, the electrochromic behavior of PEDOT/Ti 3 C 2 T x microsupercapacitors was investigated using in-situ UV–vis and resonant Raman spectroscopies. A high-rate color switch between a deep blue and colorless state is achieved on both electrodes in the voltage range of −0.6 to 0.6 V, with switching times of 6.4 and 5.5 s for bleaching and coloration, respectively. This study opens new avenues for developing electrochromic energy storage devices based on MXene heterostructures.
The present work describes a synthesis route for bulk Ta4AlC3 MAX phase ceramics with high phase purity. Pressure-assisted densification was achieved by both hot pressing and spark plasma sintering of Ta2H, Al and C powder mixtures in the 1200–1650 °C range. The phases present and microstructures were characterized as a function of the sintering temperature by X-ray diffraction and scanning electron microscopy. High-purity α-Ta4AlC3 was obtained by hot pressing at 1500 °C for 30 min at 30 MPa. The β-Ta4AlC3 allotrope was observed in the samples produced by SPS. The Young’s modulus, Vickers hardness, flexural strength and single-edge V-notch beam fracture toughness of the high-purity bulk sample were determined. The thermal decomposition of Ta4AlC3 into TaCx and Al vapour in high (˜10−5 mbar) vacuum at 1200 °C and 1250 °C was also investigated, as a possible processing route to produce porous TaCx components.
Nanolaminated materials are important because of their exceptional properties and wide range of applications. Here, we demonstrate a general approach to synthesize a series of Zn-based MAX phases and Cl-terminated MXenes originating from the replacement reaction between the MAX phase and the late transition metal halides. The approach is a top-down route that enables the late transitional element atom (Zn in the present case) to occupy the A site in the pre-existing MAX phase structure. Using this replacement reaction between Zn element from molten ZnCl2 and Al element in MAX phase precursors (Ti3AlC2, Ti2AlC, Ti2AlN, and V2AlC), novel MAX phases Ti3ZnC2, Ti2ZnC, Ti2ZnN, and V2ZnC were synthesized. When employing excess ZnCl2, Cl terminated MXenes (such as Ti3C2Cl2 and Ti2CCl2) were derived by a subsequent exfoliation of Ti3ZnC2 and Ti2ZnC due to the strong Lewis acidity of molten ZnCl2. These results indicate that A-site element replacement in traditional MAX phases by late transition metal halides opens the door to explore MAX phases that are not thermodynamically stable at high temperature and would be difficult to synthesize through the commonly employed powder metallurgy approach. In addition, this is the first time that exclusively Cl-terminated MXenes were obtained, and the etching effect of Lewis acid in molten salts provides a green and viable route to prepare MXenes through an HF-free chemical approach.
MXenes are two-dimensional metal carbides with promising applications in energy storage and sensors. Guidelines for safe, scalable MXene synthesis are important due to ongoing efforts to scale-up production of these novel nanomaterials. Here we investigate hazards associated with MXene production, including MAX phase synthesis from raw materials, etching of MAX phase to MXene clay, exfoliation to MXene nanosheets, and post-processing of MXenes with Ti3C2Tx as a model species. The major hazards in MXene synthesis are potential for dust ignition, runaway reactions, and toxic chemical exposure. Because the synthesis of MXenes is a multi-step process, safety guidelines for each step are evaluated, including preventive and mitigating measures, best practices, and emergency procedures and responses. This includes handling of combustible powders, exothermic reactions, and harsh chemical etchants. This study is intended to facilitate safer MXene synthesis across various levels of scale-up, from large laboratory batches to commercial production.
Of all the MXenes, Ti3C2Tz is the most studied and has shown promise in many different applications by virtue of its metal-like conductivity, hydrophilicity and ease by which aqueous stable colloids can be processed. Apart from appreciating that this high stability was due to relatively high negative surface charges on individual flakes, there has been very little other systematic work on colloidal stability. In this work, we systematically study the stability of Ti3C2Tz colloidal suspensions as a function of pH and sodium chloride concentrations and show that indeed while the negative surface charges are important, the fact that the edges of Ti3C2Tz sheets are positively charged, around neutral pH, also plays an important role in the aggregation. The positive charges on the edges at neutral pH, as evidenced in transmission electron microscope micrographs that show the aggregation of negative gold nanoparticles at the flake edges - open opportunities for direct edge or face specific organic functionalization, similar to the work done on other 2D materials
Two‐dimensional (2D) titanium carbide (Ti3C2) is emerging as an important member of the MXene family. However, fluoride‐based synthetic procedures remain an impediment to the practical applications of this promising class of materials. Here we demonstrate an efficient fluoride‐free etching method based on the anodic corrosion of titanium aluminium carbide (Ti3AlC2) in a binary aqueous electrolyte. The dissolution of aluminium followed by in‐situ intercalation of ammonium hydroxide results in the extraction of carbide flakes (Ti3C2Tx, T=O, OH) with sizes up to 18.6 µm and high yield (over 90 %) of mono‐ and bilayers. All‐solid‐state supercapacitor based on exfoliated sheets exhibits high areal and volumetric capacitances of 220 mF cm‐2 and 439 F cm‐3, respectively, at a scan rate of 10 mV s‐1, superior to those of LiF/HCl‐etched MXenes. Our strategy paves a safe way to the scalable synthesis and application of MXene materials.
Two-dimensional Ti3C2 MXene is prepared by a combination of ball milling and HF etching of Ti3AlC2 powder. Effects of etching temperature and ball milling duration on the preparation and electrochemical performance of as-prepared Ti3C2 MXene are investigated in detail. It is found that higher etching temperature and longer ball milling duration lead to faster transformation from Ti3AlC2 to Ti3C2 MXene. The ball milling treatment can improve the capacitive of Ti3C2 MXene. This improvement in the performance is attributed to higher carbon content for better conductivity and faster transportation of electrons, and the larger surface area for more access of aqueous electrolyte to the electrode.
Structural design on the atomic level can provide novel chemistries of hybrid MAX phases and their MXenes. Herein, density functional theory is used to predict phase stability of quaternary i‐MAX phases with in‐plane chemical order and a general chemistry (W2/3M²1/3)2AC, where M² = Sc, Y (W), and A = Al, Si, Ga, Ge, In, and Sn. Of over 18 compositions probed, only two—with a monoclinic C2/c structure—are predicted to be stable: (W2/3Sc1/3)2AlC and (W2/3Y1/3)2AlC and indeed found to exist. Selectively etching the Al and Sc/Y atoms from these 3D laminates results in W1.33C‐based MXene sheets with ordered metal divacancies. Using electrochemical experiments, this MXene is shown to be a new, promising catalyst for the hydrogen evolution reaction. The addition of yet one more element, W, to the stable of M elements known to form MAX phases, and the synthesis of a pure W‐based MXene establishes that the etching of i‐MAX phases is a fruitful path for creating new MXene chemistries that has hitherto been not possible, a fact that perforce increases the potential of tuning MXene properties for myriad applications.
Aerogel-like, porous Ti3C2Tx MXene architecture electrode displayed a high electroadsorption capacity for capacitive deionization of saline water. A vacuum freeze-drying process was employed to prevent the restacking of MXene nanosheets due to van der Waals forces, leading to the formation of a porous structure with a large specific surface area. When applied as electrode materials for capacitive deionization, porous MXene demonstrated a high specific capacitance of 156 F/g and a volumetric capacitance of 410 F/cm³ in 1 M sodium chloride (NaCl) electrolyte. The porous Ti3C2Tx MXene electrodes can deliver a high electroadsorption capacity of 118 mg/cm³ (45 mg/g) in 10,000 mg/L NaCl solution (applied voltage: 1.2 V) and excellent cycling stability (up to 60 cycles) in comparison with the restacked MXene and activated carbon electrodes, indicating its promising potential for desalination applications.
Here we reported the preparation of Ti3C2 MXene and Ti2C MXene by etching Ti3AlC2 and Ti2AlC with various fluoride salts in hydrochloric acid (HCl), including lithium fluoride (LiF), sodium fluoride (NaF), potassium fluoride (KF), and ammonium fluoride (NH4F). As-prepared Ti2C was further delaminated by urea, dimethylsulfoxide or ammonium hydroxide. Based on theoretical calculation and XPS results, the type of positive ions (Li⁺, Na⁺, K⁺, or NH4⁺) in etchant solution affect the surface structure of prepared MXene, which, in turn, affects the methane adsorption properties of MXene. The highest methane adsorption capacity is 8.5 cm³/g for Ti3C2 and 11.6 cm³/g for Ti2C. MXenes made from LiF and NH4F can absorb methane under high pressure and can keep methane under normal pressure, these MXenes may have important application on capturing methane or other hazardous gas molecules. MXenes made from NaF and KF can absorb methane under high pressure and release methane under low pressure. They can have important application in the adsorb storage of nature gas.
MXene, a new family of 2D transition metal carbides and carbonitrides, has been proved to possess excellent electrical conductivity and hydrophilicity. In this work, a single-step method to produce the larger interplanar spacing 2D MXene Ti3C2 by etching Ti3AlC2 with NH4HF2 was demonstrated, and the optimal reaction conditions between Ti3AlC2 and NH4HF2 were systematically researched. The morphology and microstructure of samples were characterized by scanning electron smicroscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD). The thermal stability of Ti3C2 was investigated by the thermogravimetry (TG) and differential thermal analyzer (DTA). It was found that the lattice parameter c of obtained Ti3C2 was up to 24.9 Å, and the larger interplanar spacing Ti3C2 was more stable than the sample exfoliated by HF. The transition temperature in air from NH4HF2-etched Ti3C2 to anatase TiO2 thoroughly is more than 500℃, and the multilayered structure of Ti3C2 could be well retained even afer 900℃ heat treatment, while the value of HF-etched Ti3C2 is less than 350℃. This work is important for exploring a safe synthesis method and well understanding the thermal stability of 2D MXene materials.
We present theoretical prediction and experimental evidence of a new MAX phase alloy, Mo2ScAlC2, with out-of-plane chemical order. Evaluation of phase stability was performed by ab initio calculations based on Density Functional Theory, suggesting that chemical order in the alloy promotes a stable phase, with a formation enthalpy of −24 meV/atom, as opposed to the predicted unstable Mo3AlC2 and Sc3AlC2. Bulk synthesis of Mo2ScAlC2 is achieved by mixing elemental powders of Mo, Sc, Al and graphite which are heated to 1700 °C. High resolution transmission electron microscopy reveals a chemically ordered structure consistent with theoretical predictions with one Sc layer sandwiched between two MoC layers. The two-dimensional derivative, the MXene, is produced by selective etching of the Al-layers in hydrofluoric acid, resulting in the corresponding chemically ordered Mo2ScC2, i.e. the first Sc-containing MXene. The here presented results expands the attainable range of MXene compositions and widens the prospects for property tuning.
Herein, enhanced exfoliation and large-scale delamination of two-dimensional (2D) Ti3C2Tx MXene using etchant of HCl + LiF, instead of HF, in which both etching and intercalation were achieved in exfoliation process, were thoroughly investigated with the focus on the effects of two critical factors, reaction temperature and washing solution. Increasing etching temperature promotes the exfoliation process, i.e., the transformation from Ti3AlC2 to multilayer Ti3C2Tx MXene, whereas simultaneously results in an aggravated surface oxidation of MXene layers formed after the extraction of Al. As a result, delamination ratio increases firstly and then decreases, and the samples etched at 35 °C show the highest delamination ratio. Compared with the distilled water, washing the exfoliation products using ethanol significantly improves the delamination ratio of Ti3C2Tx MXene by co-intercalation of larger alcohol molecule and more impurity ions and a large scale delamination of Ti3C2Tx MXene with a delamination ratio as high as 29.2% was obtained by simple sonication for 1 h, without additional intercalation step required, after washing using ethanol. The possible exfoliation reactions by HCl + LiF solution were proposed. Using the as-fabricated stable suspensions of delaminated Ti3C2Tx flakes, flexible, free-standing Ti3C2Tx papers with tailored thickness, hydrophilic surface and excellent conductivity, typically 2 × 10⁵ S/m at 5 μm in thickness, were prepared. As anode for lithium ion batteries, the delaminated Ti3C2Tx MXene obtained reversible capacities of 226.3 mAh g⁻¹, 137.9 mAh g⁻¹,102.0 mAh g⁻¹ and 47.9 mAh g⁻¹ respectively at the current density of 100, 300, 1000 and 3000 mA g⁻¹, which are superior to those of the Ti3C2 MXene prepared by conventional HF process.
Magnetic properties of Mn2CT2 (T = F, Cl, OH, O, and H) MXenes are reported based on a computational investigation. While other two dimensional Mn2CT2 MXenes become non-magnetic upon symmetrical functionalization of their surfaces, the Mn2C MXene functionalized with a functional group bearing formal charge -1 (F, Cl, and OH) retains the ferromagnetic ground state upon functionalization. Based on density functional theory calculations and Monte Carlo simulations the Mn2CF2 MXene is predicted to be an intrinsic half-metal with high Curie temperature (520 K), wide half-metallic gap (0.9 eV) and a sizable magnetic anisotropy (24 μeV). These magnetic properties make the Mn2CF2 MXene an optimal material for applications in spintronics. Different surface functional groups lead to either quantitative (Cl and OH) or qualitative (O and H) changes in Mn2CT2 magnetic properties. It is proposed that Mn2CT2 MXenes can be prepared experimentally from the already existing parent Mn2GaC MAX phase by exfoliation techniques.
MXene, a new family of 2D materials, possesses excellent electrical conductivity and hydrophilicity. To date, the majority of MXenes are only successfully produced by exfoliating the MAX phases with high concentration hydrofluoric acid (HF). In this study, the 2D MXene Ti3C2 with larger interplanar spacing was successfully obtained by etching Ti3AlC2 with bifluoride (NaHF2, KHF2, NH4HF2) in single-stage process. The morphology, structure and element composition of prepared Ti3C2 samples were characterized by scanning electron smicroscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS). The synthesis mechanism of Ti3C2 was elaborately demonstrated. The possible reaction equations between Ti3AlC2 and different bifluorides were generalized, indicating the formation of hydrosoluble by-products of Na3AlF6, K3AlF6 and (NH4)3AlF6. This work presents a safely effective method to synthesize the 2D nanocrystals MXene.
For the first time, MAX phases in the Hf-Al-C system were experimentally synthesized using reactive hot pressing. HfC was observed as the main competing phase. The lattice parameters of Hf2AlC and Hf3AlC2 were determined by Rietveld refinement based on the X-ray diffraction data. The atomic stacking sequence was revealed by high-resolution scanning transmission electron microscopy. Mixtures of 211 and 312 stacking were observed within the same grain, including 523 layers. This transition in atomic structure is discussed.
