Showing papers on "MXenes published in 2019"

Applications of 2D MXenes in energy conversion and storage systems

Abstract: Transition metal carbides and nitrides (MXenes), a family of two-dimensional (2D) inorganic compounds, are materials composed of a few atomic layers of transition metal carbides, nitrides, or carbonitrides. Ti3C2, the first 2D layered MXene, was isolated in 2011. This material, which is a layered bulk material analogous to graphite, was derived from its 3D phase, Ti3AlC2 MAX. Since then, material scientists have either determined or predicted the stable phases of >200 different MXenes based on combinations of various transition metals such as Ti, Mo, V, Cr, and their alloys with C and N. Extensive experimental and theoretical studies have shown their exciting potential for energy conversion and electrochemical storage. To this end, we comprehensively summarize the current advances in MXene research. We begin by reviewing the structure types and morphologies and their fabrication routes. The review then discusses the mechanical, electrical, optical, and electrochemical properties of MXenes. The focus then turns to their exciting potential in energy storage and conversion. Energy storage applications include electrodes in rechargeable lithium- and sodium-ion batteries, lithium-sulfur batteries, and supercapacitors. In terms of energy conversion, photocatalytic fuel production, such as hydrogen evolution from water splitting, and carbon dioxide reduction are presented. The potential of MXenes for the photocatalytic degradation of organic pollutants in water, such as dye waste, is also addressed, along with their promise as catalysts for ammonium synthesis from nitrogen. Finally, their application potential is summarized.

Control of MXenes' electronic properties through termination and intercalation.

Abstract: MXenes are an emerging family of highly-conductive 2D materials which have demonstrated state-of-the-art performance in electromagnetic interference shielding, chemical sensing, and energy storage. To further improve performance, there is a need to increase MXenes' electronic conductivity. Tailoring the MXene surface chemistry could achieve this goal, as density functional theory predicts that surface terminations strongly influence MXenes' Fermi level density of states and thereby MXenes' electronic conductivity. Here, we directly correlate MXene surface de-functionalization with increased electronic conductivity through in situ vacuum annealing, electrical biasing, and spectroscopic analysis within the transmission electron microscope. Furthermore, we show that intercalation can induce transitions between metallic and semiconductor-like transport (transitions from a positive to negative temperature-dependence of resistance) through inter-flake effects. These findings lay the groundwork for intercalation- and termination-engineered MXenes, which promise improved electronic conductivity and could lead to the realization of semiconducting, magnetic, and topologically insulating MXenes.

Element Replacement Approach by Reaction with Lewis Acidic Molten Salts to Synthesize Nanolaminated MAX Phases and MXenes

Abstract: Nanolaminated materials are important because of their exceptional properties and wide range of applications. Here, we demonstrate a general approach to synthesizing 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 the Zn element from molten ZnCl2 and the 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 preparing MXenes through an HF-free chemical approach.

A general Lewis acidic etching route for preparing MXenes with enhanced electrochemical performance in non-aqueous electrolyte

Abstract: Two-dimensional carbides and nitrides of transition metals, known as MXenes, are a fast-growing family of 2D materials that draw attention as energy storage materials. So far, MXenes are mainly prepared from Al-containing MAX phases (where A = Al) by Al dissolution in F-containing solution, but most other MAX phases have not been explored. Here, a redox-controlled A-site-etching of MAX phases in Lewis acidic melts is proposed and validated by the synthesis of various MXenes from unconventional MAX phase precursors with A elements Si, Zn, and Ga. A negative electrode of Ti3C2 MXene material obtained through this molten salt synthesis method delivers a Li+ storage capacity up to 738 C g-1 (205 mAh g-1) with high-rate performance and pseudocapacitive-like electrochemical signature in 1M LiPF6 carbonate-based electrolyte. MXene prepared from this molten salt synthesis route offer opportunities as high-rate negative electrode material for electrochemical energy storage applications.

On the Chemical Diversity of the MAX Phases

Abstract: The Mn+1AXn, or MAX, phases are nanolayered, hexagonal, machinable, early transition-metal carbides and nitrides, where n = 1, 2, or 3, M is an early transition metal, A is an A-group element (mostly groups 13 and 14), and X is C and/or N. These phases are characterized by a unique combination of both metallic and ceramic properties. The fact that these phases are precursors for MXenes and the dramatic increase in interest in the latter for a large host of applications render the former even more valuable. Herein we describe the structure of most, if not all, MAX phases known to date. This review covers ≈155 MAX compositions. Currently, 16 A elements and 14 M elements have been incorporated in these phases. The recent discovery of both quaternary in- and out-of-plane ordered MAX phases opens the door to the discovery of many more. The chemical diversity of the MAX phases holds the key to eventually optimizing properties for prospective applications. Since many of the newer quaternary (and higher) phases have yet to be characterized, much work remains to be done.

Titanium-carbide MXenes for work function and interface engineering in perovskite solar cells.

Abstract: To improve the efficiency of perovskite solar cells, careful device design and tailored interface engineering are needed to enhance optoelectronic properties and the charge extraction process at the selective electrodes. Here, we use two-dimensional transition metal carbides (MXene Ti3C2Tx) with various termination groups (Tx) to tune the work function (WF) of the perovskite absorber and the TiO2 electron transport layer (ETL), and to engineer the perovskite/ETL interface. Ultraviolet photoemission spectroscopy measurements and density functional theory calculations show that the addition of Ti3C2Tx to halide perovskite and TiO2 layers permits the tuning of the materials’ WFs without affecting other electronic properties. Moreover, the dipole induced by the Ti3C2Tx at the perovskite/ETL interface can be used to change the band alignment between these layers. The combined action of WF tuning and interface engineering can lead to substantial performance improvements in MXene-modified perovskite solar cells, as shown by the 26% increase of power conversion efficiency and hysteresis reduction with respect to reference cells without MXene. Addition of MXenes in the halide perovskite film, in the electron transport layer and at the interface between these layers is shown to enhance the efficiency of and reduce hysteresis in perovskite solar cells.

Review of MXenes as new nanomaterials for energy storage/delivery and selected environmental applications

Abstract: Energy and environmental issues presently attract a great deal of scientific attention. Recently, two-dimensional MXenes and MXene-based nanomaterials have attracted increasing interest because of their unique properties (e.g., remarkable safety, a very large interlayer spacing, environmental flexibility, a large surface area, and thermal conductivity). In 2011, multilayered MXenes (Ti3C2Tx, a new family of two-dimensional (2D) materials) produced by etching an A layer from a MAX phase of Ti3AlC2, were first described by researchers at Drexel University. The term “MXene” was coined to distinguish this new family of 2D materials from graphene, and applies to both the original MAX phases and MXenes fabricated from them. We present a comprehensive review of recent studies on energy and environmental applications of MXene and MXene-based nanomaterials, including energy conversion and storage, adsorption, membrane, photocatalysis, and antimicrobial. Future research needs are discussed briefly with current challenges that must be overcome before we completely understand the extraordinary properties of MXene and MXene-based nanomaterials.

Universal Strategy for HF-Free Facile and Rapid Synthesis of Two-dimensional MXenes as Multifunctional Energy Materials.

Abstract: Two-dimensional MXenes are promising for various energy-related applications such as energy storage devices and electrocatalysis of water-splitting. MXenes prepared from hydrofluoric (HF) acid etching have been widely reported. Nonetheless, the acute toxicity of HF acid impedes the large-scale fabrication of MXenes and their wide utilization in energy-related applications. It is thus greatly encouraging to explore a more innocuous protocol for MXenes synthesis. Thereby, a universal strategy based on thermal-assisted electrochemical etching route is developed to synthesize MXenes (e.g., Ti2CT x, Cr2CT x, and V2CT x). Furthermore, the cobalt ion doped MXenes show an exceptionally enhanced capability of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity, demonstrating their multifunctionalities, which is comparable to the commercialized catalysts. Moreover, we successfully exploited our MXenes as cathodes for the novel aqueous rechargeable battery, with proficient retention and excellent electrical output performance. This work paves a nontoxic and HF-free route to prepare various MXenes and demonstrates practical applications of the materials.

Influences from solvents on charge storage in titanium carbide MXenes

Abstract: Pseudocapacitive energy storage in supercapacitor electrodes differs significantly from the electrical double-layer mechanism of porous carbon materials, which requires a change from conventional thinking when choosing appropriate electrolytes. Here we show how simply changing the solvent of an electrolyte system can drastically influence the pseudocapacitive charge storage of the two-dimensional titanium carbide, Ti3C2 (a representative member of the MXene family). Measurements of the charge stored by Ti3C2 in lithium-containing electrolytes with nitrile-, carbonate- and sulfoxide-based solvents show that the use of a carbonate solvent doubles the charge stored by Ti3C2 when compared with the other solvent systems. We find that the chemical nature of the electrolyte solvent has a profound effect on the arrangement of molecules/ions in Ti3C2, which correlates directly to the total charge being stored. Having nearly completely desolvated lithium ions in Ti3C2 for the carbonate-based electrolyte leads to high volumetric capacitance at high charge–discharge rates, demonstrating the importance of considering all aspects of an electrochemical system during development.

Fast Gelation of Ti 3 C 2 T x MXene Initiated by Metal Ions

Abstract: Gelation is an effective way to realize the self-assembly of nanomaterials into different macrostructures, and in a typical use, the gelation of graphene oxide (GO) produces various graphene-based carbon materials with different applications. However, the gelation of MXenes, another important type of 2D materials that have different surface chemistry from GO, is difficult to achieve. Here, the first gelation of MXenes in an aqueous dispersion that is initiated by divalent metal ions is reported, where the strong interaction between these ions and OH groups on the MXene surface plays a key role. Typically, Fe2+ ions are introduced in the MXene dispersion which destroys the electrostatic repulsion force between the MXene nanosheets in the dispersion and acts as linkers to bond the nanosheets together, forming a 3D MXene network. The obtained hydrogel effectively avoids the restacking of the MXene nanosheets and greatly improves their surface utilization, resulting in a high rate performance when used as a supercapacitor electrode (≈226 F g-1 at 1 V s-1 ). It is believed that the gelation of MXenes indicates a new way to build various tunable MXene-based structures and develop different applications.

Surface Termination Dependent Work Function and Electronic Properties of Ti3C2Tx MXene

Abstract: MXenes, an emerging family of 2D transition metal carbides and nitrides, have shown promise in various applications, such as energy storage, electromagnetic interference shielding, conductive thin films, photonics, and photothermal therapy. Their metallic nature, wide range of optical absorption, and tunable surface chemistry are the key to their success in those applications. The physical properties of MXenes are known to be strongly dependent on their surface terminations. In this study, we investigated the electronic properties of Ti3C2Tx for different surface terminations, as achieved by different annealing temperatures, with the help of photoelectron spectroscopy, inverse photoelectron spectroscopy, and density functional theory calculations. We find that fluorine occupies solely the face-centered cubic adsorption site, whereas oxygen initially occupies at least two different adsorption sites, followed by a rearrangement after fluorine desorption at high annealing temperatures. The measured electroni...

Overview of the synthesis of MXenes and other ultrathin 2D transition metal carbides and nitrides

Abstract: 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 Ti3C2 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.

Oxidation stability of Ti 3 C 2 T x MXene nanosheets in solvents and composite films

Abstract: Ti3C2Tx belongs to the family of MXenes, 2D materials with an attractive combination of functional properties suitable for applications such as batteries, supercapacitors, and strain sensors. However, the fabrication of devices and functional coatings based on Ti3C2Tx remains challenging as they are prone to chemical degradation by their oxidation to TiO2. In this paper, we examine the oxidation of Ti3C2Tx in air, liquid, and solid media via conductivity measurements to assess the shelf life of Ti3C2Tx MXenes. The oxidation of Ti3C2Tx was observed in all the media used in this study, but it is fastest in liquid media and slowest in solid media (including polymer matrices). We also show that the conventional indicators of MXene oxidation, such as changes in color and colloidal stability, are not always reliable. Finally, we demonstrate the acceleration of oxidation under exposure to UV light. The storage and dispersion of MXene films in media influence their oxidation behavior. A team led by Miladin Radovic and Micah Green at Texas AM the oxidation was the slowest in solid media and the fastest in liquid media. In aqueous dispersions, Ti3C2Tx oxidized in 2 weeks, along with a sharp decrease in electrical conductivity; however, the dispersion retained its dark color and colloidal stability. Ti3C2Tx could be well preserved in ice, whereas its polymers were not effective barriers to decrease oxidation.

2D/2D heterojunction of Ti 3 C 2 /g-C 3 N 4 nanosheets for enhanced photocatalytic hydrogen evolution.

Abstract: Photocatalytic hydrogen evolution from water has received enormous attention due to its ability to address a number of global environmental and energy-related issues. Here, we synthesize 2D/2D Ti3C2/g-C3N4 composites by electrostatic self-assembly technique and demonstrate their use as photocatalysts for hydrogen evolution under visible light irradiation. The optimized Ti3C2/g-C3N4 composite exhibited a 10 times higher photocatalytic hydrogen evolution performance (72.3 μmol h-1 gcat-1) than that of pristine g-C3N4 (7.1 μmol h-1 gcat-1). Such enhanced photocatalytic performance was due to the formation of 2D/2D heterojunctions in the Ti3C2/g-C3N4 composites. The intimate contact between the monolayer Ti3C2 and g-C3N4 nanosheets promotes the separation of photogenerated charge carriers at the Ti3C2/g-C3N4 interface. Furthermore, the ultrahigh conductivity of Ti3C2 and the Schottky junction formed between g-C3N4/MXene interfaces facilitate the photoinduced electron transfer and suppress the recombination with photogenerated holes. This work demonstrates that the 2D/2D Ti3C2/g-C3N4 composites are promising photocatalysts thanks to the ultrathin MXenes as efficient co-catalysts for photocatalytic hydrogen production.

Assembling 2D MXenes into Highly Stable Pseudocapacitive Electrodes with High Power and Energy Densities.

Abstract: Electrochemical capacitors (ECs) that store charge based on the pseudocapacitive mechanism combine high energy densities with high power densities and rate capabilities. 2D transition metal carbides (MXenes) have been recently introduced as high-rate pseudocapacitive materials with ultrahigh areal and volumetric capacitances. So far, 20 different MXene compositions have been synthesized and many more are theoretically predicted. However, since most MXenes are chemically unstable in their 2D forms, to date only one MXene composition, Ti3 C2 Tx , has shown stable pseudocapacitive charge storage. Here, a cation-driven assembly process is demonstrated to fabricate highly stable and flexible multilayered films of V2 CTx and Ti2 CTx MXenes from their chemically unstable delaminated single-layer flakes. The electrochemical performance of electrodes fabricated using assembled V2 CTx flakes surpasses Ti3 C2 Tx in various aqueous electrolytes. These electrodes show specific capacitances as high as 1315 F cm-3 and retain ≈77% of their initial capacitance after one million charge/discharge cycles, an unprecedented performance for pseudocapacitive materials. This work opens a new venue for future development of high-performance supercapacitor electrodes using a variety of 2D materials as building blocks.

High-Temperature Behavior and Surface Chemistry of Carbide MXenes Studied by Thermal Analysis

Abstract: Two-dimensional (2D) transition-metal carbides and nitrides (MXenes) have attracted significant attention due to their electronic, electrochemical, chemical, and optical properties. However, understanding of their thermal stability is still lacking. To date, MXenes are synthesized via top-down wet chemical etching, which intrinsically results in surface terminations. Here, we provide detailed insight into the surface terminations of three carbide MXenes (Ti3C2Tx, Mo2CTx, and Nb2CTx) by performing thermal gravimetric analysis with mass spectrometry analysis (TA–MS) up to 1500 °C under a He atmosphere. This specific technique enables probing surface terminations including hydroxyl (−OH), oxy (═O), and fluoride (−F) and intercalated species, such as salts and structural water. The MXene hydrophilicity depends on the type of etching (hydrofluoric acid concentration and/or mixed acid composition) and subsequent delamination conditions. We show that the amount of structural water in Ti3C2Tx increases with decre...

Multifunctional Nanocomposites with High Strength and Capacitance Using 2D MXene and 1D Nanocellulose.

Abstract: The family of two-dimensional (2D) metal carbides and nitrides, known as MXenes, are among the most promising electrode materials for supercapacitors thanks to their high metal-like electrical conductivity and surface-functional-group-enabled pseudocapacitance. A major drawback of these materials is, however, the low mechanical strength, which prevents their applications in lightweight, flexible electronics. A strategy of assembling freestanding and mechanically robust MXene (Ti3 C2 Tx ) nanocomposites with one-dimensional (1D) cellulose nanofibrils (CNFs) from their stable colloidal dispersions is reported. The high aspect ratio of CNF (width of ≈3.5 nm and length reaching tens of micrometers) and their special interactions with MXene enable nanocomposites with high mechanical strength without sacrificing electrochemical performance. CNF loading up to 20%, for example, shows a remarkably high mechanical strength of 341 MPa (an order of magnitude higher than pristine MXene films of 29 MPa) while still maintaining a high capacitance of 298 F g-1 and a high conductivity of 295 S cm-1 . It is also demonstrated that MXene/CNF hybrid dispersions can be used as inks to print flexible micro-supercapacitors with precise dimensions. This work paves the way for fabrication of robust multifunctional MXene nanocomposites for printed and lightweight structural devices.

MXenes: An Introduction of Their Synthesis, Select Properties, and Applications

Abstract: 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.

High capacity silicon anodes enabled by MXene viscous aqueous ink

Abstract: The ever-increasing demands for advanced lithium-ion batteries have greatly stimulated the quest for robust electrodes with a high areal capacity. Producing thick electrodes from a high-performance active material would maximize this parameter. However, above a critical thickness, solution-processed films typically encounter electrical/mechanical problems, limiting the achievable areal capacity and rate performance as a result. Herein, we show that two-dimensional titanium carbide or carbonitride nanosheets, known as MXenes, can be used as a conductive binder for silicon electrodes produced by a simple and scalable slurry-casting technique without the need of any other additives. The nanosheets form a continuous metallic network, enable fast charge transport and provide good mechanical reinforcement for the thick electrode (up to 450 µm). Consequently, very high areal capacity anodes (up to 23.3 mAh cm−2) have been demonstrated.

Emerging 2D materials beyond graphene for ultrashort pulse generation in fiber lasers.

Abstract: Ultrafast fiber lasers have significant applications in ultra-precision manufacturing, medical diagnostics, medical treatment, precision measurement and astronomical detection, owing to their ultra-short pulse width and ultra-high peak-power. Since graphene was first explored as an optical saturable absorber for passively mode-locked lasers in 2009, many other 2D materials beyond graphene, including phosphorene, antimonene, bismuthene, transition metal dichalcogenides (TMDs), topological insulators (TIs), metal–organic frameworks (MOFs) and MXenes, have been successively explored, resulting in rapid development of novel 2D materials-based saturable absorbers. Herein, we review the latest progress of the emerging 2D materials beyond graphene for passively mode-locked fiber laser application. These 2D materials are classified into mono-elemental, dual-elemental and multi-elemental 2D materials. The atomic structure, band structure, nonlinear optical properties, and preparation methods of 2D materials are summarized. Diverse integration strategies for applying 2D materials into fiber laser systems are introduced, and the mode-locking performance of the 2D materials-based fiber lasers working at 1–3 μm are discussed. Finally, the perspectives and challenges facing 2D materials-based mode-locked fiber lasers are highlighted.

Hydrolysis of 2D Transition-Metal Carbides (MXenes)in Colloidal Solutions

Abstract: Although oxidation was deemed as the main factor responsible for the instability of MXenes in aqueous colloids, here we put forward and test a hypothesis about the central role of water as the prim...

2D Early Transition Metal Carbides (MXenes) for Catalysis.

Abstract: MXenes, a bourgeoning class of 2D transition metal carbides, are of considerable interest in catalysis due to their rich surface chemistry, tunable electronic structures, and thermal stability. Here, recent conceptual advances in applying MXenes and their nanocomposites in (photo)electrocatalysis and conventional heterogeneous catalysis are highlighted. In addition, the nature of active sites in the MXene-based catalysts are discussed and the significance and challenges in the future development of catalysts using MXenes as the platforms are summarized.

An investigation into the factors governing the oxidation of two-dimensional Ti3C2 MXene

Abstract: Two-dimensional (2D) transition metal carbides (MXenes) exhibit outstanding performances in many applications, such as energy storage, optoelectronics, and electrocatalysts. However, colloidal solutions of Ti3C2Tx MXene flakes deteriorate rapidly under ambient conditions due to the conversion of the titanium carbide to titanium dioxide. Here, we discuss the dominant factors influencing the rate of oxidation of Ti3C2Tx MXene flakes, and present guidelines for their storage with the aim of maintaining the intrinsic properties of the as-prepared material. The oxidation stability of the Ti3C2Tx flakes is dramatically improved in a system where water molecules and temperature were well-controlled. It was found that aqueous solutions of Ti3C2Tx MXene can be chemically stable for more than 39 weeks when the storage temperature (−80 °C) is sufficiently low to cease the oxidation processes. It was also found that if the Ti3C2Tx flakes are dispersed in ethanol, the degradation process can be significantly delayed even at 5 °C. Moreover, the oxidation stability of the Ti3C2Tx flakes is dramatically improved in both cases, even in the presence of oxygen-containing atmosphere. We demonstrate practical applications of our approach by employing Ti3C2Tx in a gas sensor showing that when oxidation is inhibited, the device can retain the original electrical properties after 5 weeks of storage.

Promoting Role of MXene Nanosheets in Biomedical Sciences: Therapeutic and Biosensing Innovations.

Abstract: MXene nanosheets have emerged as biocompatible transition metal structures, which illustrate desirable performance for various applications due to their unique structural, physicochemical, and compositional features. MXenes are currently expanding their usage territory from mechanical, optical, chemical, and electronic fields toward biomedical areas. This is mainly originated from their large surface area and strong absorbance in near-infrared region, which in combination with their facile surface functionalization with various polymers or nanoparticles, make them promising nanoplatforms for drug delivery, cancer therapy, precise biosensing and bioimaging. The facile surface modification of the MXenes can mediate the better in vivo performance of them through reduced toxicity, enhanced colloidal stability, and extended circulation within the body. Herein, the synthesis and state-of-the-art progresses of MXene nanosheets designed for biomedical applications, including structural- and dose-dependent antimicrobial activity, photothermal therapy, drug delivery, and implants are emphasized. Furthermore, biosensing applications are highlighted and a comprehensive discussion on photoacoustic imaging, magnetic resonance imaging, computed tomography imaging, and optical imaging of MXenes is presented. The challenges and future opportunities of applying MXene nanomaterials in the area of biomedicine are also discussed.