Enhanced sodium-storage performances of crumpled MXene nanosheets via alkali treatment-induced active ammonium ions

Ti3C2Tx MXene demonstrates excellent potential as an anode material for sodium-ion capacitors. However, the narrow interlayer spacing and self-stacking phenomenon limit its applicability. In this study, we demonstrate an easy two-step method involving freezing and crumpling of MXene nanosheets to improve their Na-ion storage via the addition of ammonium ions (referred to as FCM nanosheets). Flat MXene particles aggregate and undergo folding in an alkaline solution. Ammonium ions can penetrate the gaps between MXene nanosheets, expanding interlayer spaces and inducing the formation of folds. Compared to MXene nanosheets, FCM nanosheets exhibit improved ion transfer kinetics and additional high capacity owing to the intercalated ammonium ions. The manufactured FCM anode exhibits remarkable electrochemical properties, including a high specific capacity of 313 mAhg-1 and stability over 15,000 cycles.

Two-dimensional molybdenum boride coordinating with ruthenium nanoparticles to boost hydrogen generation from hydrolytic dehydrogenation of ammonia borane

The coordination between carrier and active metal is critical to the catalytic efficiency of ammonia borane (AB) hydrolysis reaction. In the present study, we report a new type of catalytic support based on molybdenum boride (MBene) MoAl1-xB and demonstrate that the effective combination of MoAl1-xB with Ru nanoparticles can realize the significantly enhanced performance for hydrogen generation. Owing to the efficient activation and dissociation of reactants, the optimal Ru/MoAl1-xB catalyst achieves the large turnover frequency of 494 molH2 molRu-1 min-1, high hydrogen generation rate of 119817 mL min-1 gRu-1 and favorable apparent activation energy of 39.2 kJ mol-1 for the catalytic hydrolysis of AB under alkaline-free condition. The isotopic test suggests the cleavage of OH bond in H2O is the rate-determining step for hydrolysis reaction, while the fracture of B-H bond in AB is also well revealed by attenuated total reflectance (ATR)-Fourier transform infrared (FTIR) spectroscopy. Significantly, the flexible on-demand hydrogen generation is achieved by using chemical switches for on-off AB hydrolysis. This study provides a new support platform based on two-dimensional MBene to exploit efficient catalysts to boost AB dehydrogenation.

Enhancing electrochemiluminescence for chloramphenicol detection based on the synergistic effect of doped Ti3C2 with ultrasound

Chloramphenicol (CAP) is known to be harmful to the environment and food, posing a threat to human health. Developing an effective and convenient method for detecting CAP is crucial. An electrochemiluminescence (ECL) biosensor has been designed for sensitive detection of CAP. The improved ECL behavior was attributed to the synergistic effect of N and P co-doped Ti3C2-Apt1 (N, P-Ti3C2-Apt1) nanoprobes and high intensity focused ultrasound (HIFU) pretreatment. The doping of N and P could improve the electrochemical performance of Ti3C2. HIFU pretreatment generated more reactive oxygen species (ROS) in the luminol-O2 system. N, P-Ti3C2 could aggregate and catalyze ROS, causing an increase in ECL intensity. Furthermore, N, P-Ti3C2 as a carrier loaded more aptamer, which could recognize CAP with high specificity. The detection limit was 0.01 ng/mL. This biosensor has been successfully applied in milk and environmental water samples, highlighting its potential in the field of food and environmental analysis.

Stabilizing Ti3C2Tx MXene flakes in air by removing confined water

MXenes have demonstrated potential for various applications owing to their tunable surface chemistry and metallic conductivity. However, high temperatures can accelerate MXene film oxidation in air. Understanding the mechanisms of MXene oxidation at elevated temperatures, which is still limited, is critical in improving their thermal stability for high-temperature applications. Here, we demonstrate that Ti[Formula: see text]C[Formula: see text]T[Formula: see text] MXene monoflakes have exceptional thermal stability at temperatures up to 600[Formula: see text]C in air, while multiflakes readily oxidize in air at 300[Formula: see text]C. Density functional theory calculations indicate that confined water between Ti[Formula: see text]C[Formula: see text]T[Formula: see text] flakes has higher removal energy than surface water and can thus persist to higher temperatures, leading to oxidation. We demonstrate that the amount of confined water correlates with the degree of oxidation in stacked flakes. Confined water can be fully removed by vacuum annealing Ti[Formula: see text]C[Formula: see text]T[Formula: see text] films at 600[Formula: see text]C, resulting in substantial stability improvement in multiflake films (can withstand 600[Formula: see text]C in air). These findings provide fundamental insights into the kinetics of confined water and its role in Ti[Formula: see text]C[Formula: see text]T[Formula: see text] oxidation. This work enables the use of stable monoflake MXenes in high-temperature applications and provides guidelines for proper vacuum annealing of multiflake films to enhance their stability.

Self-Assembled MXene Supported on Carbonization-Free Wood for a Symmetrical All-Wood Eco-Supercapacitor

As an emerging two-dimensional (2D) material, MXene has garnered significant interest in advanced energy storage systems, yet the stackable structure, poor mechanical stability, and lack of moldability limit its large-scale applications. To address this challenge, herein, the self-assembly of MXene on carbonization-free wood was obtained to serve as high-performance electrodes for symmetrical all-wood eco-supercapacitors by a steam-driven self-assembly method. This method can be implemented in a low-temperature environment, significantly simplifying traditional high-temperature annealing processes and generating minimal impact on the environment, human health, and resource consumption. The environmentally friendly steam-driven self-assembly strategy can be further extended into various wood-based electrodes, regardless of the types and structures of wood. As a typical platform electrode, the optimized MXene@delignified balsa wood (MDBW) achieves high areal capacitance and specific capacitance values of 2.99 F cm-2 and 580.55 F g-1 at an extensive mass loading of 5.16 mg cm-2, respectively, with almost loss-free capacitance after 10,000 cycles at 50 mA cm-2. In addition, an all-solid-state symmetrical all-wood eco-supercapacitor was further assembled based on MDBW-20 as both positive and negative electrodes to achieve a high energy density of 19.22 μWh cm-2 at a power density of 0.58 mW cm-2. This work provides an effective strategy to optimize wood-based electrodes for the practical application of biomass eco-supercapacitors.

Ultrastrong MXene film induced by sequential bridging with liquid metal

Assembling titanium carbide (Ti3C2Tx) MXene nanosheets into macroscopic films presents challenges, including voids, low orientation degree, and weak interfacial interactions, which reduce mechanical performance. We demonstrate an ultrastrong macroscopic MXene film using liquid metal (LM) and bacterial cellulose (BC) to sequentially bridge MXene nanosheets (an LBM film), achieving a tensile strength of 908.4 megapascals. A layer-by-layer approach using repeated cycles of blade coating improves the orientation degree to 0.935 in the LBM film, while a LM with good deformability reduces voids into porosity of 5.4%. The interfacial interactions are enhanced by the hydrogen bonding from BC and the coordination bonding with LM, which improves the stress-transfer efficiency. Sequential bridging provides an avenue for assembling other two-dimensional nanosheets into high-performance materials.

Porous hybrid encapsulation enables high-rate lithium storage for a micron-sized SiO anode

Establishing a durable interfacial layer between an electrode and electrolyte to enable micron-sized silicon-based lithium-ion battery (LIB) anodes to achieve superior electrochemical performance is highly desired. Recent studies have shown that heterogeneous encapsulation with enhanced ion/electron transport is an effective strategy. However, the structural design of the existing hetero-coated interface lacks a reasonable ion/electron transport channel, resulting in high interfacial impedance. Herein, we designed a heterogenous MXene-mesoporous polypyrrole (mPPy) encapsulation layer onto micron-sized SiO particles. The MXene coating layer functions as a bridging interface that can build a strong chemical link to internal SiO via covalent bonding, thus reinforcing interfacial charge transfer rate. Meanwhile, it forms a dynamic connection with the outer mPPy through hydrogen bonding, which contributes to high interfacial Li+ concentration and ion/electron coupling transport rate. Accordingly, the as-prepared SiO@MXene@mPPy anode delivers a boosted specific capacity of 673.9 mA h g-1 at 2 A g-1 after 1000 cycles and high-rate capability of 777.4 mA h g-1 at 5 A g-1. Further, electrochemical kinetic analysis indicates that the MXene@mPPy coating layer shows a pseudocapacitance controlled Li storage mechanism, thereby displaying improved high-rate capability. This porous hybrid encapsulation strategy offers new possibilities for a micron-sized SiO anode to achieve an excellent performance.

Dual-Responsive MXene-Functionalized Wool Yarn Artificial Muscles

Fiber-based artificial muscles are promising for smart textiles capable of sensing, interacting, and adapting to environmental stimuli. However, the application of current artificial muscle-based textiles in wearable and engineering fields has largely remained a constraint due to the limited deformation, restrictive stimulation, and uncomfortable. Here, dual-responsive yarn muscles with high contractile actuation force are fabricated by incorporating a very small fraction (<1 wt.%) of Ti3C2Tx MXene/cellulose nanofibers (CNF) composites into self-plied and twisted wool yarns. They can lift and lower a load exceeding 3400 times their own weight when stimulated by moisture and photothermal. Furthermore, the yarn muscles are coiled homochirally or heterochirally to produce spring-like muscles, which generated over 550% elongation or 83% contraction under the photothermal stimulation. The actuation mechanism, involving photothermal/moisture-mechanical energy conversion, is clarified by a combination of experiments and finite element simulations. Specifically, MXene/CNF composites serve as both photothermal and hygroscopic agents to accelerate water evaporation under near-infrared (NIR) light and moisture absorption from ambient air. Due to their low-cost facile fabrication, large scalable dimensions, and robust strength coupled with dual responsiveness, these soft actuators are attractive for intelligent textiles and devices such as self-adaptive textiles, soft robotics, and wearable information encryption.

"Hard" Emulsion-Induced Interface Super-Assembly: A General Strategy for Two-Dimensional Hierarchically Porous Metal-Organic Framework Nanoarchitectures

Two-dimensional (2D) hierarchically porous metal-organic framework (MOF) nanoarchitectures with tailorable meso-/macropores hold great promise for enhancing mass transfer kinetics, augmenting accessible active sites, and thereby boosting performance in heterogeneous catalysis. However, achieving the general synthesis of 2D free-standing MOF nanosheets with controllable hierarchical porosity and thickness remains a challenging task. Herein, we present an ingenious "hard" emulsion-induced interface super-assembly strategy for preparing 2D hierarchically porous UiO-66-NH2 nanosheets with highly accessible pore channels, tunable meso-/macropore sizes, and adjustable thicknesses. The methodology relies on transforming the geometric shape of oil droplet templates within appropriate oil-in-water emulsions from conventional zero-dimensional (0D) "soft" liquid spheres to 2D "hard" solid sheets below the oil's melting/freezing point. Subsequent surfactant exchange on the surface of 2D "hard" emulsions facilitates the heterogeneous nucleation and interfacial super-assembly of in situ formed mesostructured MOF nanocomposites, serving as structural units, in a loosely packed manner to produce 2D MOF nanosheets with multimodal micro/meso-/macroporous systems. Importantly, this strategy can be extended to prepare other 2D hierarchically porous MOF nanosheets by altering metal-oxo clusters and organic ligands. Benefiting from fast mass transfer and highly accessible Lewis acidic sites, the resultant 2D hierarchically porous UiO-66-NH2 nanosheets deliver a fabulous catalytic yield of approximately 96% on the CO2 cycloaddition of glycidyl-2-methylphenyl ether, far exceeding the yield of approximately 29% achieved using conventional UiO-66-NH2 microporous crystals. This "hard" emulsion-induced interface super-assembly strategy paves a new path toward the rational construction of elaborate 2D nanoarchitecture of hierarchical MOFs with tailored physicochemical properties for diverse potential applications.

Aptamer-Modified Nb2C Multifunctional Nanomedicine for Targeted Photothermal/Chemotherapy Combined Therapy of Tumor

The poor delivery efficiency of nanotherapeutic drugs and their potential off-target toxicity significantly limit their effectiveness and extensive application. An active targeting system with high efficiency and few side effects is a promising strategy for tumor therapy. Herein, a multifunctional nanomedicine Nb2C-PAA-DOX@Apt-M (NDA-M) was constructed for targeted photothermal/chemotherapy (PTT/CHT) combined tumor therapy. The specific targeting ability of aptamer could effectively enhance the absorption of nanomedicine by the MCF-7 cell. By employing Apt-M, the NDA-M nanosheets demonstrated targeted delivery to MCF-7 cells, resulting in enhanced intracellular drug concentration. Under 1060 nm laser irradiation, a rapid temperature increase of the NDA-M was observed within the tumor region to achieve PTT. Meanwhile, CHT was triggered when DOX release was induced by photothermal/acid stimulation. The experimental results demonstrated that aptamer-mediated targeting achieved enhanced PTT/CHT efficacy both in vitro and in vivo. Notably, NDA-M induced complete ablation of solid tumors without any adverse side effects in mice. This study demonstrated new and promising tactics for the development of nanomaterials for targeted tumor therapy.

MXene-Stabilized VS2 Nanostructures for High-Performance Aqueous Zinc Ion Storage

Aqueous zinc-ion batteries (AZIBs) based on vanadium oxides or sulfides are promising candidates for large-scale rechargeable energy storage due to their ease of fabrication, low cost, and high safety. However, the commercial application of vanadium-based electrode materials has been hindered by challenging problems such as poor cyclability and low-rate performance. To this regard, sophisticated nanostructure engineering technology is used to adeptly incorporate VS2 nanosheets into the MXene interlayers to create a stable 2D heterogeneous layered structure. The MXene nanosheets exhibit stable interactions with VS2 nanosheets, while intercalation between nanosheets effectively increases the interlayer spacing, further enhancing their stability in AZIBs. Benefiting from the heterogeneous layered structure with high conductivity, excellent electron/ion transport, and abundant reactive sites, the free-standing VS2/Ti3C2Tz composite film can be used as both the cathode and the anode of AZIBs. Specifically, the VS2/Ti3C2Tz cathode presents a high specific capacity of 285 mAh g-1 at 0.2 A g-1. Furthermore, the flexible Zn-metal free in-plane VS2/Ti3C2Tz//MnO2/CNT AZIBs deliver high operation voltage (2.0 V) and impressive long-term cycling stability (with a capacity retention of 97% after 5000 cycles) which outperforms almost all reported Vanadium-based electrodes for AZIBs. The effective modulation of the material structure through nanocomposite engineering effectively enhances the stability of VS2, which shows great potential in Zn2+ storage. This work will hasten and stimulate further development of such composite material in the direction of energy storage.

Multifunctional SnO2 QDs/MXene Heterostructures as Laminar Interlayers for Improved Polysulfide Conversion and Lithium Plating Behavior

Poor cycling stability in lithium-sulfur (Li-S) batteries necessitates advanced electrode/electrolyte design and innovative interlayer architectures. Heterogeneous catalysis has emerged as a promising approach, leveraging the adsorption and catalytic performance on lithium polysulfides (LiPSs) to inhibit LiPSs shuttling and improve redox kinetics. In this study, we report an ultrathin and laminar SnO2@MXene heterostructure interlayer (SnO2@MX), where SnO2 quantum dots (QDs) are uniformly distributed across the MXene layer. The combined structure of SnO2 QDs and MXene, along with the creation of numerous active boundary sites with coordination electron environments, plays a critical role in manipulating the catalytic kinetics of sulfur species. The Li-S cell with the SnO2@MX-modified separator not only demonstrates superior electrochemical performance compared to cells with a bare separator but also induces homogeneous Li deposition during cycling. As a result, an areal capacity of 7.6 mAh cm-2 under a sulfur loading of 7.5 mg cm-2 and a high stability over 500 cycles are achieved. Our work demonstrates a feasible strategy of utilizing a laminar separator interlayer for advanced Li-S batteries awaiting commercialization and may shed light on the understanding of heterostructure catalysis with enhanced reaction kinetics.

Unlocking Ultrahigh Initial Coulombic Efficiency of MXene Anode via Presodiation and Electrolyte Optimization

The low initial Coulombic efficiency (ICE) greatly hinders the practical application of MXenes in sodium-ion batteries. Herein, theoretical calculations confirm that -F and -OH terminations as well as the tetramethylammonium ion (TMA+) intercalator in sediment Ti3C2Tx (s-Ti3C2Tx) MXene possess strong interaction with Na+, which impedes Na+ desorption during the charging process and results in low ICE. Consequently, Na+-intercalated sediment Ti3C2Tx (Na-s-Ti3C2Tx) is constructed through Na2S·9H2O treatment of s-Ti3C2Tx. Specifically, Na+ can first exchange with TMA+ of s-Ti3C2Tx and then combine with -F and -OH terminations, thus leading to the elimination of TMA+ and preshielding of -F and -OH. As expected, the resulting Na-s-Ti3C2Tx anode delivers considerably boosted ICE values of around 71% in carbonate-based electrolytes relative to s-Ti3C2Tx. Furthermore, electrolyte optimization is employed to improve ICE, and the results demonstrate that an ultrahigh ICE value of 94.0% is obtained for Na-s-Ti3C2Tx in the NaPF6-diglyme electrolyte. More importantly, Na-s-Ti3C2Tx exhibits a lower Na+ migration barrier and higher electronic conductivity compared with s-Ti3C2Tx based on theoretical calculations. In addition, the cyclic stability and rate performance of the Na-s-Ti3C2Tx anode in various electrolytes are comprehensively explored. The presented simple strategy in boosting ICE significantly enhances the commercialization prospect of MXenes in advanced batteries.

A Flexible Skin Bionic Thermally Comfortable Wearable for Machine Learning-Facilitated Ultrasensitive Sensing

Tremendous popularity is observed for multifunctional flexible electronics with appealing applications in intelligent electronic skins, human-machine interfaces, and healthcare sensing. However, the reported sensing electronics, mostly can hardly provide ultrasensitive sensing sensitivity, wider sensing range, and robust cycling stability simultaneously, and are limited of efficient heat conduction out from the contacted skin interface after wearing flexible electronics on human skin to satisfy thermal comfort of human skin. Inspired from the ultrasensitive tactile perception microstructure (epidermis/spinosum/signal transmission) of human skin, a flexible comfortably wearable ultrasensitive electronics is hereby prepared from thermal conductive boron nitride nanosheets-incorporated polyurethane elastomer matrix with MXene nanosheets-coated surface microdomes as epidermis/spinosum layers assembled with interdigitated electrode as sensing signal transmission layer. It demonstrates appealing sensing performance with ultrasensitive sensitivity (≈288.95 kPa-1), up to 300 kPa sensing range, and up to 20 000 sensing cycles from obvious contact area variation between microdome microstructures and the contact electrode under external compression. Furthermore, the bioinspired electronics present advanced thermal management by timely efficient thermal dissipation out from the contacted skin surface to meet human skin thermal comfort with the incorporated thermal conductive boron nitride nanosheets. Thus, it is vitally promising in wearable artificial electronic skins, intelligent human-interactive sensing, and personal health management.

All-MXene electronic tongue for neurotransmitters detection

Neurotransmitters (NTs) are molecules produced by neurons that act as the body's chemical messengers. Their abnormal levels in the human system have been associated with many disorders and neurodegenerative diseases, which makes the monitoring of NTs fundamentally important. Specifically for clinical analysis and understanding of brain behavior, simultaneous detection of NTs at low levels quickly and reliably is imperative for disease prevention and early diagnosis. However, the methods currently employed are usually invasive or inappropriate for multiple NTs detection. Herein, we developed a MXene-based impedimetric electronic tongue (e-tongue) for sensitive NT monitoring, using Nb2C, Nb4C3, Mo2C, and Mo2Ti2C3 MXenes as sensing units of the e-tongue, and Principal Component Analysis (PCA) as the data treatment method. The high specific surface area, distinct electrical properties, and chemical stability of the MXenes gave rise to high sensitivity and good reproducibility of the sensor array toward NT detection. Specifically, the e-tongue detected and differentiated multiple NTs (acetylcholine, dopamine, glycine, glutamate, histamine, and tyrosine) at concentrations as low as 1 nmol L-1 and quantified NTs present in a mixture. Besides, analyses performed with interferents and actual samples confirmed the system's potential to be used in clinical diagnostics. The results demonstrate that the MXene-based e-tongue is a suitable, rapid, and simple method for NT monitoring with high accuracy and sensitivity.

Construction of 2D/2D ZnIn2S4/Nb2CTx (MXene) hybrid with hole transport highway and active facet exposure boost photocatalytic hydrogen evolution

In this study, leveraging the tunable surface groups of MXene, the two-dimensional (2D) Nb2CTx with OH terminal (NC) was synthesized. 2D ZnIn2S4 (ZIS) nanosheets were prepared with the aid of sodium citrate, enhancing the exposure ratio of active (110) facet. On this basis, 2D/2D ZnIn2S4/Nb2CTx heterojunctions were fabricated to improve photocatalytic hydrogen evolution reaction (HER) performance. The optimized 6 wt%Nb2CTx/ZnIn2S4-450 (6NC/ZIS-450) photocatalyt exhibits a remarkable HER rate of 3603 μmol g-1h-1, which is 10 times superior to that of the original ZnIn2S4. Its apparent quantum efficiency (AQE) at 380 nm reaches 14.9 %. Meanwhile, even after 5 rounds of HER, the activity of 2D/2D ZnIn2S4/Nb2CTx heterojunction remained at 90 %, far superior to that of pure ZnIn2S4 (34 % and 31 %). Energy band structure analysis and density functional theory (DFT) calculation indicate that Nb2CTx adsorbed with OH exhibit a low work function. By serving as a hole cocatalyst, it effectively boosts the photocatalytic HER rate of ZnIn2S4/Nb2CTx heterojunction and inhibits the photocorrosion of ZnIn2S4. This unique insight, via hole transport highways and increased exposure of active facets, effectively enhances the activity and stability of sulfides photocatalysts.

Covalent Bonding of MXene/COF Heterojunction for Ultralong Cycling Li-Ion Battery Electrodes

Covalent organic frameworks (COFs) have emerged as promising renewable electrode materials for LIBs and gained significant attention, but their capacity has been limited by the densely packed 2D layer structures, low active site availability, and poor electronic conductivity. Combining COFs with high-conductivity MXenes is an effective strategy to enhance their electrochemical performance. Nevertheless, simply gluing them without conformal growth and covalent linkage restricts the number of redox-active sites and the structural stability of the composite. Therefore, in this study, a covalently assembled 3D COF on Ti3C2 MXenes (Ti3C2@COF) is synthesized and serves as an ultralong cycling electrode material for LIBs. Due to the covalent bonding between the COF and Ti3C2, the Ti3C2@COF composite exhibits excellent stability, good conductivity, and a unique 3D cavity structure that enables stable Li+ storage and rapid ion transport. As a result, the Ti3C2-supported 3D COF nanosheets deliver a high specific capacity of 490 mAh g-1 at 0.1 A g-1, along with an ultralong cyclability of 10,000 cycles at 1 A g-1. This work may inspire a wide range of 3D COF designs for high-performance electrode materials.

Beyond graphene: exploring the potential of MXene anodes for enhanced lithium-sulfur battery performance

The high theoretical energy density of Li-S batteries makes them a viable option for energy storage systems in the near future. Considering the challenges associated with sulfur's dielectric properties and the synthesis of soluble polysulfides during Li-S battery cycling, the exceptional ability of MXene materials to overcome these challenges has led to a recent surge in the usage of these materials as anodes in Li-S batteries. The methods for enhancing anode performance in Li-S batteries via the use of MXene interfaces are thoroughly investigated in this study. This study covers a wide range of techniques such as surface functionalization, heteroatom doping, and composite structure design for enhancing MXene interfaces. Examining challenges and potential downsides of MXene-based anodes offers a thorough overview of the current state of the field. This review encompasses recent findings and provides a thorough analysis of advantages and disadvantages of adding MXene interfaces to improve anode performance to assist researchers and practitioners working in this field. This review contributes significantly to ongoing efforts for the development of reliable and effective energy storage solutions for the future.

Recent Advances in Non-Ti MXenes: Synthesis, Properties, and Novel Applications

One of the most fascinating 2D nanomaterials (NMs) ever found is various members of MXene family. Among them, the titanium-based MXenes, with more than 70% of publication-related investigations, are comparatively well studied, producing fundamental foundation for the 2D MXene family members with flexible properties, familiar with a variety of advanced novel technological applications. Nonetheless, there are still more candidates among transitional metals (TMs) that can function as MXene NMs in ways that go well beyond those that are now recognized. Systematized details of the preparations, characteristics, limitations, significant discoveries, and uses of the novel M-based MXenes (M-MXenes), where M stands for non-Ti TMs (M = Sc, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, and Lu), are given. The exceptional qualities of the 2D non-Ti MXene outperform standard Ti-MXene in several applications. There is many advancement in top-down as well as bottom-up production of MXenes family members, which allows for exact control of the M-characteristics MXene NMs to contain cutting-edge applications. This study offers a systematic evaluation of existing research, covering everything in producing complex M-MXenes from primary limitations to the characterization and selection of their applications in accordance with their novel features. The development of double metal combinations, extension of additional metal candidates beyond group-(III-VI)B family, and subsequent development of the 2D TM carbide/TMs nitride/TM carbonitrides to 2D metal boride family are also included in this overview. The possibilities and further recommendations for the way of non-Ti MXene NMs are in the synthesis of NMs will discuss in detail in this critical evaluation.

Ultrastable Organic Anode Enabled by Electrochemically Active MXene Binder toward Advanced Potassium Ion Storage

Conjugated carbonyl compounds are regarded as promising organic anode materials for potassium ion batteries (PIBs) due to their rich redox sites, excellent reversibility, and structural tunability, but their low electrical conductivity and severe solubility in organic electrolytes have substantially restricted their practical application. Herein, 2D MXene is utilized as an electrochemically active binder to fabricate perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) electrodes for high-performance PIBs. MXene, coupled with Super-P particles, served as a binder and conductive matrix to facilitate rapid ion and electron transport, restrain the solubility of PTCDA, promote potassium adsorption, and alleviate the volume expansion of PTCDA during potassiation. Consequently, the PTCDA electrode bonded by the MXene/Super-P system delivers excellent potassium storage performance in terms of a high capacity of 462 mAh g-1 at 50 mA g-1, superior rate capability of 116.3 mAh g-1 at 2000 mA g-1, and stable cycle performance over 3000 cycles with a low capacity decay rate of ∼0.0033% per cycle. When configured with the PTCDA@450 cathode, an all-PTCDA potassium ion full cell delivers a maximum energy density of 179.5 Wh kg-1, indicating the superiority of MXene as an electrochemically active binder to promote the practical application of organic anodes for PIBs.

Discovery of Self-Assembled 2D Ru/Si Superlattices Boosting Hydrogen Evolution

2D heterostructuring is a versatile methodology for designing nanoarchitecture catalytic systems that allow for reconstruction and modulation of interfaces and electronic structures. However, catalysts with such structures are extremely scarce due to limited synthetic strategies. Here, a highly ordered 2D Ru/Si/Ru/Si… nano-heterostructures (RSHS) is reported by acid etching of the LaRuSi electride. RSHS shows a superior electrocatalytic activity for hydrogen evolution with an overpotential of 14 mV at 10 mA cm-2 in alkaline media. Both experimental analysis and first-principles calculations demonstrate that the electronic states of Ru can be tuned by strong interactions of the interfacial Ru-Si, leading to an optimized hydrogen adsorption energy. Moreover, due to the synergistic effect of Ru and Si, the energy barrier of water dissociation is significantly reduced. The well-organized superlattice structure will provide a paradigm for construction of efficient catalysts with tunable electronic states and dual active sites.

MXenes and MXene-Based Metal Hydrides for Solid-State Hydrogen Storage: A Review

Hydrogen-driven energy is fascinating among the everlasting energy sources, particularly for stationary and onboard transportation applications. Efficient hydrogen storage presents a key challenge to accomplishing the sustainability goals of hydrogen economy. In this regard, solid-state hydrogen storage in nanomaterials, either physically or chemically adsorbed, has been considered a safe path to establishing sustainability goals. Though metal hydrides have been extensively explored, they fail to comply with the set targets for practical utilization. Recently, MXenes, both in bare form and hybrid state with metal hydrides, have proven their flair in ascertaining the hydrides' theoretical and experimental hydrogen storage capabilities far beyond the fancy materials and current state-of-the-art technologies. This review encompasses the significant accomplishments achieved by MXenes (primarily in 2019-2024) for enhancing the hydrogen storage performance of various metal hydride materials such as MgH2, AlH3, Mg(BH4)2, LiBH4, alanates, and composite hydrides. It also discusses the bottlenecks of metal hydrides for hydrogen storage, the potential use of MXenes hybrids, and their challenges, such as reversibility, H2 losses, slow kinetics, and thermodynamic barriers. Finally, it concludes with a detailed roadmap and recommendations for mechanistic-driven future studies propelling toward a breakthrough in solid material-driven hydrogen storage using cost-effective, efficient, and long-lasting solutions.

Multifunctional MXene/Carbon Nanotube Janus Film for Electromagnetic Shielding and Infrared Shielding/Detection in Harsh Environments

Multifunctional, flexible, and robust thin films capable of operating in demanding harsh temperature environments are crucial for various cutting-edge applications. This study presents a multifunctional Janus film integrating highly-crystalline Ti3C2Tx MXene and mechanically-robust carbon nanotube (CNT) film through strong hydrogen bonding. The hybrid film not only exhibits high electrical conductivity (4250 S cm-1), but also demonstrates robust mechanical strength and durability in both extremely low and high temperature environments, showing exceptional resistance to thermal shock. This hybrid Janus film of 15 μm thickness reveals remarkable multifunctionality, including efficient electromagnetic shielding effectiveness of 72 dB in X band frequency range, excellent infrared (IR) shielding capability with an average emissivity of 0.09 (a minimal value of 0.02), superior thermal camouflage performance over a wide temperature range (- 1 to 300 °C) achieving a notable reduction in the radiated temperature by 243 °C against a background temperature of 300 °C, and outstanding IR detection capability characterized by a 44% increase in resistance when exposed to 250 W IR radiation. This multifunctional MXene/CNT Janus film offers a feasible solution for electromagnetic shielding and IR shielding/detection under challenging conditions.

M4X3 MXenes: Application in Energy Storage Devices

MXene has garnered widespread recognition in the scientific community due to its remarkable properties, including excellent thermal stability, high conductivity, good hydrophilicity and dispersibility, easy processability, tunable surface properties, and admirable flexibility. MXenes have been categorized into different families based on the number of M and X layers in Mn+1Xn, such as M2X, M3X2, M4X3, and, recently, M5X4. Among these families, M2X and M3X2, particularly Ti3C2, have been greatly explored while limited studies have been given to M5X4 MXene synthesis. Meanwhile, studies on the M4X3 MXene family have developed recently, hence, demanding a compilation of evaluated studies. Herein, this review provides a systematic overview of the latest advancements in M4X3 MXenes, focusing on their properties and applications in energy storage devices. The objective of this review is to provide guidance to researchers on fostering M4X3 MXene-based nanomaterials, not only for energy storage devices but also for broader applications.

Manganese Oxides with Different Morphologies In Situ Anchored onto Ti3C2Tx Nanosheets: Highly Effective Decontamination toward Sulfur Mustard Simulants

Manganese oxides with porous structure and abundant active sites show potential in degrading sulfur mustard (HD). However, there is an interface effect between the oily liquid HD and nano oxides, and the powder is prone to agglomeration, which leads to incomplete contact and limited degradation ability. Here, we demonstrate a simple hydrothermal method for preparing MnO2/Ti3C2 composites to address this problem. The influence of morphology and crystal structure on performance are examined. Herein, flower-like MnO2 is loaded onto the surface or interlayer of Ti3C2-MXene nanosheets during in situ formation, significantly expanding the specific surface area. It also provides abundant acid-base sites and oxygen vacancies for the degradation of simulants 2-chloro-ethyl-ethyl thioether (2-CEES) without external energy, resulting in a reaction half-life as fast as 12.5 min. The relationship between structure and performance is clearly elaborated through temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS) analyses. Based on in situ attenuated total reflection-Fourier transform infrared (ATR-FTIR) analysis, gas chromatography-mass spectrometry (GC-MS) analysis, and density functional theory (DFT) calculation, the proposed degradation pathway of the 2-CEES molecule is a synergistic effect of hydrolysis, elimination, and oxidation. Furthermore, the products are nontoxic or low toxic. Metal oxide/MXene composites are first illustrated for their potential use in degrading sulfur mustard, suggesting new insights into these materials as novel decontamination for decomposing chemical warfare agents.

Ultrasensitive electrochemical sensor based on synergistic effect of Ag@MXene and antifouling cyclic multifunctional peptide for PD-L1 detection in serum

A sensing interface co-constructed from the two-dimensional conductive material (Ag@MXene) and an antifouling cyclic multifunctional peptide (CP) is described. While the large surface area of Ag@MXene loads more CP probes, CP binds to Ag@MXene to form a fouling barrier and ensure the structural rigidity of the targeting sequence. This strategy synergistically enhances the biosensor's sensitivity and resistance to contamination. The SPR results showed that the binding affinity of the CP to the target was 6.23 times higher than that of the antifouling straight-chain multifunctional peptide (SP) to the target. In the 10 mg/mL BSA electrochemical fouling test, the fouling resistance of Ag@MXene + CP (composite sensing interface of CP combined with Ag@MXene) was 30 times higher than that of the bare electrode. The designed electrochemical sensor exhibited good selectivity and wide dynamic response range at PD-L1 concentrations from 0.1 to 50 ng/mL. The lowest detection limit was 24.54 pg/mL (S/N = 3). Antifouling 2D materials with a substantial specific surface area, coupled with non-straight chain antifouling multifunctional peptides, offer a wide scope for investigating the sensitivity and antifouling properties of electrochemical sensors.

MXenes with ordered triatomic-layer borate polyanion terminations

Surface terminations profoundly influence the intrinsic properties of MXenes, but existing terminations are limited to monoatomic layers or simple groups, showing disordered arrangements and inferior stability. Here we present the synthesis of MXenes with triatomic-layer borate polyanion terminations (OBO terminations) through a flux-assisted eutectic molten etching approach. During the synthesis, Lewis acidic salts act as the etching agent to obtain the MXene backbone, while borax generates BO2- species, which cap the MXene surface with an O-B-O configuration. In contrast to conventional chlorine/oxygen-terminated Nb2C with localized charge transport, OBO-terminated Nb2C features band transport described by the Drude model, exhibiting a 15-fold increase in electrical conductivity and a 10-fold improvement in charge mobility at the d.c. limit. This transition is attributed to surface ordering that effectively mitigates charge carrier backscattering and trapping. Additionally, OBO terminations provide Ti3C2 MXene with substantially enriched Li+-hosting sites and thereby a large charge-storage capacity of 420 mAh g-1. Our findings illustrate the potential of intricate termination configurations in MXenes and their applications for (opto)electronics and energy storage.

2D Materials-Based Thermal Interface Materials: Structure, Properties, and Applications

The challenges associated with heat dissipation in high-power electronic devices used in communication, new energy, and aerospace equipment have spurred an urgent need for high-performance thermal interface materials (TIMs) to establish efficient heat transfer pathways from the heater (chip) to heat sinks. Recently, emerging 2D materials, such as graphene and boron nitride, renowned for their ultrahigh basal-plane thermal conductivity and the capacity to facilitate cross-scale, multi-morphic structural design, have found widespread use as thermal fillers in the production of high-performance TIMs. To deepen the understanding of 2D material-based TIMs, this review focuses primarily on graphene and boron nitride-based TIMs, exploring their structures, properties, and applications. Building on this foundation, the developmental history of these TIMs is emphasized and a detailed analysis of critical challenges and potential solutions is provided. Additionally, the preparation and application of some other novel 2D materials-based TIMs are briefly introduced, aiming to offer constructive guidance for the future development of high-performance TIMs.

Additive-Free Anode with High Stability: Nb2CTx MXene Prepared by HCl-LiF Hydrothermal Etching for Lithium-Ion Batteries

MXenes, represented by Ti3C2Tx, have been widely studied in the electrochemical energy storage fields, including lithium-ion batteries, for their unique two-dimensional structure, tunable surface chemistry, and excellent electrical conductivity. Recently, Nb2CTx, as a new type of MXene, has attracted more and more attention due to its high theoretical specific capacity of 542 mAh g-1. However, the preparation of few-layer Nb2CTx nanosheets with high-quality remains a challenge, which limits their research and application. In this work, high-quality few-layer Nb2CTx nanosheets with a large lateral size and a high conductivity of up to 500 S cm-1 were prepared by a simple HCl-LiF hydrothermal etching method, which is 2 orders of magnitude higher than that of previously reported Nb2CTx. Furthermore, from its aqueous ink, the viscosity-tunable organic few-layer Nb2CTx ink was prepared by HCl-induced flocculation and N-methyl-2-pyrrolidone treatment. When using the organic few-layer Nb2CTx ink as an additive-free anode of lithium-ion batteries, it showed excellent cycling performance with a reversible specific capacity of 524.0 mAh g-1 after 500 cycles at 0.5 A g-1 and 444.0 mAh g-1 after 5000 cycles at 1 A g-1. For rate performance, a specific capacity of 159.8 mAh g-1 was obtained at a high current density of 5 A g-1, and an excellent capacity retention rate of about 95.65% was achieved when the current density returned to 0.5 A g-1. This work presents a simple and scalable process for the preparation of high-quality Nb2CTx and its aqueous/organic ink, which demonstrates important application potential as electrodes for electrochemical energy storage devices.

Recent Advances in Flexible Pressure Sensors Based on MXene Materials

In the past decade, with the rapid development of wearable electronics, medical health monitoring, the Internet of Things, and flexible intelligent robots, flexible pressure sensors have received unprecedented attention. As a very important kind of electronic component for information transmission and collection, flexible pressure sensors have gained a wide application prospect in the fields of aerospace, biomedical and health monitoring, electronic skin, and human-machine interface. In recent years, MXene has attracted extensive attention because of its unique 2D layered structure, high conductivity, rich surface terminal groups, and hydrophilicity, which has brought a new breakthrough for flexible sensing. Thus, it has become a revolutionary pressure-sensitive material with great potential. In this work, the recent advances of MXene-based flexible pressure sensors are reviewed from the aspects of sensing type, sensing mechanism, material selection, structural design, preparation strategy, and sensing application. The methods and strategies to improve the performance of MXene-based flexible pressure sensors are analyzed in details. Finally, the opportunities and challenges faced by MXene-based flexible pressure sensors are discussed. This review will bring the research and development of MXene-based flexible sensors to a new high level, promoting the wider research exploitation and practical application of MXene materials in flexible pressure sensors.

Nano-achiral complex composites for extreme polarization optics

Composites from 2D nanomaterials show uniquely high electrical, thermal and mechanical properties1,2. Pairing their robustness with polarization rotation is needed for hyperspectral optics in extreme conditions3,4. However, the rigid nanoplatelets have randomized achiral shapes, which scramble the circular polarization of photons with comparable wavelengths. Here we show that multilayer nanocomposites from 2D nanomaterials with complex textured surfaces strongly and controllably rotate light polarization, despite being nano-achiral and partially disordered. The intense circular dichroism (CD) in nanocomposite films originates from the diagonal patterns of wrinkles, grooves or ridges, leading to an angular offset between axes of linear birefringence (LB) and linear dichroism (LD). Stratification of the layer-by-layer (LBL) assembled nanocomposites affords precise engineering of the polarization-active materials from imprecise nanoplatelets with an optical asymmetry g-factor of 1.0, exceeding those of typical nanomaterials by about 500 times. High thermal resilience of the composite optics enables operating temperature as high as 250 °C and imaging of hot emitters in the near-infrared (NIR) part of the spectrum. Combining LBL engineered nanocomposites with achiral dyes results in anisotropic factors for circularly polarized emission approaching the theoretical limit. The generality of the observed phenomena is demonstrated by nanocomposite polarizers from molybdenum sulfide (MoS2), MXene and graphene oxide (GO) and by two manufacturing methods. A large family of LBL optical nanocomponents can be computationally designed and additively engineered for ruggedized optics.

Oxygen-Vacancy-Induced Formation of Pt-Based Intermetallics on MXene with Strong Metal-Support Interactions for Efficient Oxygen Reduction Reaction

The Pt-based alloys can moderate the binding energies of oxygenated species on the catalytic surface, endowing the superior catalytic performance towards oxygen reduction reaction (ORR). Nevertheless, it is still challenging to explore general methods to synthesize structurally ordered intermetallics with uniform distributions. Herein, the strong metal-support interaction is employed to facilitate the interdiffusion of Pt/M atoms by establishing a tunnel of oxygen vacancy on ultrathin Ti3C2Tx (MXene) sheets, synthesizing the ordered PtFe, PtCo, PtZn, PdFe, PdZn intermetallics loaded onto Ti3C2Tx. Furthermore, the in-situ generation of Ti-O from Ti3C2Tx could be bonded with Pt and forming Pt-O-Ti, resulting in charge redistribution through Pt-O-Ti structure. Theoretical calculations demonstrate that the valuable charge redistribution can be observed at the interface and extended even to at the distance of two nanometers from the interface, which can modulate the Pt-Pt distance, optimize Pt-O binding energy and enhance intrinsic activity towards ORR. The strong coupling interaction between PtFe and Ti3C2Tx containing the titanium oxide layer endows the high stability of the composites. This work not only presents a general synthesis strategy for intermetallics but also provides a new insight that metal-support interaction is essential for the structural evolution of intermetallics on materials with oxygen vacancies.

Augmented Electrochemical Oxygen Evolution by d-p Orbital Electron Coupling

While high-entropy alloys, high-entropy oxides, and high-entropy hydroxides, are advanced as a novel frontier in electrocatalytic oxygen evolution, their inherent activity deficiency poses a major challenge. To achieve the unlimited goal to tailor the structure-activity relationship in multicomponent systems, entropy-driven composition engineering presents substantial potential, by fabricating high-entropy anion-regulated transition metal compounds as sophisticated oxygen evolution reaction electrocatalysts. Herein, a versatile 2D high-entropy metal phosphorus trisulfide is developed as a promising and adjustable platform. Leveraging the multiple electron couplings and d-p orbital hybridizations induced by the cocktail effect, the exceptional oxygen evolution catalytic activity is disclosed upon van der Waals material (MnFeCoNiZn)PS3, exhibiting an impressively low overpotential of 240 mV at a current density of 10 mA cm-2, a minimal Tafel slope of 32 mV dec-1, and negligible degradation under varying current densities for over 96 h. Density functional theory calculations further offer insights into the correlation between orbital hybridization and catalytic performance within high-entropy systems, underscoring the contribution of active phosphorus centers on the substrate to performance enhancements. Moreover, by achieving electron redistribution to optimize the electron coordination environment, this work presents an effective strategy for advanced catalysts in energy-related applications.

Comprehensive synthesis of Ti3C2Tx from MAX phase to MXene

MXenes are a large family of two-dimensional materials that have attracted attention across many fields due to their desirable optoelectronic, biological, mechanical and chemical properties. There currently exist many synthesis procedures that lead to differences in flake size, defects and surface chemistry, which in turn affect their properties. Herein, we describe the steps to synthesize Ti3C2Tx-the most important and widely used MXene, from a Ti3AlC2 MAX phase precursor. The procedure contains three main sections: synthesis of Ti3AlC2 MAX, wet chemical etching of the MAX in hydrofluoric acid/HCl solution to yield multilayer Ti3C2Tx and its delamination into single-layer flakes. Three delamination options are described; these use LiCl, tertiary amines (tetramethyl ammonium hydroxide/ tetrabutyl ammonium hydroxide) and dimethylsulfoxide respectively. These procedures can be adapted for the synthesis of MXenes beyond Ti3C2Tx. The MAX phase synthesis takes about 1 week, with the etching and delamination each requiring 2 d. This protocol requires users to have experience working with hydrofluoric acid, and it is recommended that users have experience with wet chemistry and centrifugation; characterization techniques such as X-ray diffraction and particle size analysis are also essential for the success of the protocol. While alternative synthesis methods, such as minimally intensive layer delamination, are desirable for certain MXenes (such as Ti2CTx) or specific applications, this protocol aims to standardize the more commonly used hydrofluoric acid/HCl etching method, which produces Ti3C2Tx with minimal concentration of defects and the highest conductivity and serves as a guideline for those working with MXenes for the first time.

Reversible Constrained Dissociation and Reassembly of MXene Films

Enabling materials to undergo reversible dynamic transformations akin to the behaviors of living organisms represents a critical challenge in the field of material assembly. The pursuit of such capabilities using conventional materials has largely been met with limited success. Herein, the discovery of reversible constrained dissociation and reconfiguration in MXene films, offering an effective solution to overcome this obstacle is reported. Specifically, MXene films permit rapid intercalation of water molecules between their distinctive layers, resulting in a significant expansion and exhibiting confined dissociation within constrained spaces. Meanwhile, the process of capillary compression driven by water evaporation reinstates the dissociated MXene film to its original compact state. Further, the adhesive properties emerging from the confined disassociation of MXene films can spontaneously induce fusion between separate films. Utilizing this attribute, complex structures of MXene films can be effortlessly foamed and interlayer porosity precisely controlled, using only water as the inducer. Additionally, a parallel phenomenon has been identified in graphene oxide films. This work not only provides fresh insights into the microscopic mechanisms of 2D materials such as MXene but also paves a transformative path for their macroscopic assembly applications in the future.

Biocompatible Electronic Skins for Cardiovascular Health Monitoring

Cardiovascular diseases represent a significant threat to the overall well-being of the global population. Continuous monitoring of vital signs related to cardiovascular health is essential for improving daily health management. Currently, there has been remarkable proliferation of technology focused on collecting data related to cardiovascular diseases through daily electronic skin monitoring. However, concerns have arisen regarding potential skin irritation and inflammation due to the necessity for prolonged wear of wearable devices. To ensure comfortable and uninterrupted cardiovascular health monitoring, the concept of biocompatible electronic skin has gained substantial attention. In this review, biocompatible electronic skins for cardiovascular health monitoring are comprehensively summarized and discussed. The recent achievements of biocompatible electronic skin in cardiovascular health monitoring are introduced. Their working principles, fabrication processes, and performances in sensing technologies, materials, and integration systems are highlighted, and comparisons are made with other electronic skins used for cardiovascular monitoring. In addition, the significance of integrating sensing systems and the updating wireless communication for the development of the smart medical field is explored. Finally, the opportunities and challenges for wearable electronic skin are also examined.

Fabrication of innovative multifunctional dye using MXene nanosheets

The increasing demand for natural and safer alternatives to traditional hair dyes has led to the investigation of nanomaterials as potential candidates for hair coloring applications. MXene nanosheets have emerged as a promising alternative in this context due to their unique optical and electronic properties. In this study, we aimed to evaluate the potential of Ti3C2Tx (Tx = -O, -OH, -F, etc.) MXene nanosheets as a hair dye. MXene nanosheet-based dyes have been demonstrated to exhibit not only coloring capabilities but also additional properties such as antistatic properties, heat dissipation, and electromagnetic wave shielding. Additionally, surface modification of MXene using collagen reduces the surface roughness of hair and upregulates keratinocyte markers KRT5 and KRT14, demonstrating the potential for tuning its physicochemical and biological properties. This conceptual advancement highlights the potential of MXene nanosheets to go beyond simple cosmetic improvements and provide improved comfort and safety by preventing the presence of hazardous ingredients and solvents while providing versatility.

Surface-engineered Mo2B: a promising electrode material for constructing Ohmic contacts with blue phosphorene for electronic device applications

The Schottky barrier between a metal and a semiconductor plays an important role in determining the transport efficiency of carriers and improving the performance of devices. In this work, we systematically studied the structure and electronic properties of heterostructures of blue phosphorene (BP) in contact with Mo2B based on density functional theory. The semiconductor properties of BP are destroyed owing to strong interaction with bare Mo2B. The effect of modifying Mo2B with O and OH on the contact properties was investigated. A p-type Schottky contact can be obtained in BP/Mo2BO2. The height of the Schottky barrier can be modulated by interlayer distance to realize a transition from a p-type Schottky contact to a p-type Ohmic contact in BP/Mo2BO2. The BP/Mo2B(OH)2 forms robust Ohmic contacts, which are insensitive to interlayer distance and external electric fields due to the Fermi level pinning effect. Our work provides important clues for contact engineering and improvement of device performance based on BP.

Two-Dimensional Materials for Highly Efficient and Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) offer low costs and high power conversion efficiency. However, the lack of long-term stability, primarily stemming from the interfacial defects and the susceptible metal electrodes, hinders their practical application. In the past few years, two-dimensional (2D) materials (e.g., graphene and its derivatives, transitional metal dichalcogenides, MXenes, and black phosphorus) have been identified as a promising solution to solving these problems because of their dangling bond-free surfaces, layer-dependent electronic band structures, tunable functional groups, and inherent compactness. Here, recent progress of 2D material toward efficient and stable PSCs is summarized, including its role as both interface materials and electrodes. We discuss their beneficial effects on perovskite growth, energy level alignment, defect passivation, as well as blocking external stimulus. In particular, the unique properties of 2D materials to form van der Waals heterojunction at the bottom interface are emphasized. Finally, perspectives on the further development of PSCs using 2D materials are provided, such as designing high-quality van der Waals heterojunction, enhancing the uniformity and coverage of 2D nanosheets, and developing new 2D materials-based electrodes.

Thermally Activated Photoluminescence Induced by Tunable Interlayer Interactions in Naturally Occurring van der Waals Superlattice SnS/TiS2

van der Waals (vdW) superlattices, comprising different 2D materials aligned alternately by weak interlayer interactions, offer versatile structures for the fabrication of novel semiconductor devices. Despite their potential, the precise control of optoelectronic properties with interlayer interactions remains challenging. Here, we investigate the discrepancies between the SnS/TiS2 superlattice (SnTiS3) and its subsystems by comprehensive characterization and DFT calculations. The disappearance of certain Raman modes suggests that the interactions alter the SnS subsystem structure. Specifically, such structural changes transform the band structure from indirect to direct band gap, causing a strong PL emission (∼2.18 eV) in SnTiS3. In addition, the modulation of the optoelectronic properties ultimately leads to the unique phenomenon of thermally activated photoluminescence. This phenomenon is attributed to the inhibition of charge transfer induced by tunable intralayer strains. Our findings extend the understanding of the mechanism of interlayer interactions in van der Waals superlattices and provide insights into the design of high-temperature optoelectronic devices.

A mechanically robust spiral fiber with ionic-electronic coupling for multimodal energy harvesting

Wearable electronics are some of the most promising technologies with the potential to transform many aspects of human life such as smart healthcare and intelligent communication. The design of self-powered fabrics with the ability to efficiently harvest energy from the ambient environment would not only be beneficial for their integration with textiles, but would also reduce the environmental impact of wearable technologies by eliminating their need for disposable batteries. Herein, inspired by classical Archimedean spirals, we report a metastructured fiber fabricated by scrolling followed by cold drawing of a bilayer thin film of an MXene and a solid polymer electrolyte. The obtained composite fibers with a typical spiral metastructure (SMFs) exhibit high efficiency for dispersing external stress, resulting in simultaneously high specific mechanical strength and toughness. Furthermore, the alternating layers of the MXene and polymer electrolyte form a unique, tandem ionic-electronic coupling device, enabling SMFs to generate electricity from diverse environmental parameters, such as mechanical vibrations, moisture gradients, and temperature differences. This work presents a design rule for assembling planar architectures into robust fibrous metastructures, and introduces the concept of ionic-electronic coupling fibers for efficient multimodal energy harvesting, which have great potential in the field of self-powered wearable electronics.

Facilitating Atom Probe Tomography of 2D MXene Films by In Situ Sputtering

2D materials are emerging as promising nanomaterials for applications in energy storage and catalysis. In the wet chemical synthesis of MXenes, these 2D transition metal carbides and nitrides are terminated with a variety of functional groups, and cations such as Li+ are often used to intercalate into the structure to obtain exfoliated nanosheets. Given the various elements involved in their synthesis, it is crucial to determine the detailed chemical composition of the final product, in order to better assess and understand the relationships between composition and properties of these materials. To facilitate atom probe tomography analysis of these materials, a revised specimen preparation method is presented in this study. A colloidal Ti3C2Tz MXene solution was processed into an additive-free free-standing film and specimens were prepared using a dual beam scanning electron microscope/focused ion beam. To mechanically stabilize the fragile specimens, they were coated using an in situ sputtering technique. As various 2D material inks can be processed into such free-standing films, the presented approach is pivotal for enabling atom probe analysis of other 2D materials.

Photocatalytic Deposition of Au Nanoparticles on Ti3C2Tx MXene Substrates for Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) is a promising technique for sensitive detection. The design and optimization of plasma-enhanced structures for SERS applications is an interesting challenge. In this study, we found that the SERS activity of MXene (Ti3C2Tx) can be improved by adding Au nanoparticles (NPs) in a simple photoreduction process. Fluoride-salt-etched MXene was deposited by drop-casting on a glass slide, and Au NPs were formed by the photocatalytic growth of gold(III) chloride trihydrate solutions under ultraviolet (UV) irradiation. The Au-MXene substrate formed by Au NPs anchored on the Ti3C2Tx sheet produced significant SERS through the synergistic effect of chemical and electromagnetic mechanisms. The structure and size of the Au-decorated MXene depended on the reaction time. When the MXene films were irradiated with a large number of UV photons, the size of the Au NPs increased. Hot spots were formed in the nanoscale gaps between the Au NPs, and the abundant surface functional groups of the MXene effectively adsorbed and interacted with the probe molecules. Simultaneously, as a SERS substrate, the proposed Au-MXene composite exhibited a wider linear range of 10-4-10-9 mol/L for detecting carbendazim. In addition, the enhancement factor of the optimized SERS substrate Au-MXene was 1.39 × 106, and its relative standard deviation was less than 13%. This study provides a new concept for extending experimental strategies to further improve the performance of SERS.

Ion pair sites for efficient electrochemical extraction of uranium in real nuclear wastewater

Electrochemical uranium extraction from nuclear wastewater represents an emerging strategy for recycling uranium resources. However, in nuclear fuel production which generates the majority of uranium-containing nuclear wastewater, fluoride ion (F-) co-exists with uranyl (UO22+), resulting in the complex species of UO2Fx and thus decreasing extraction efficiency. Herein, we construct Tiδ+-PO43- ion pair extraction sites in Ti(OH)PO4 for efficient electrochemical uranium extraction in wastewater from nuclear fuel production. These sites selectively bind with UO2Fx through the combined Ti-F and multiple O-U-O bonds. In the uranium extraction, the uranium species undergo a crystalline transition from U3O7 to K3UO2F5. In real nuclear wastewater, the uranium is electrochemically extracted with a high efficiency of 99.6% and finally purified as uranium oxide powder, corresponding to an extraction capacity of 6829 mg g-1 without saturation. This work paves an efficient way for electrochemical uranium recycling in real wastewater of nuclear production.

Strong and Tough MXene Bridging-induced Conductive Nacre

Nacre is a classic model, providing an inspiration for fabricating high-performance bulk nanocomposites with the two-dimensional platelets. However, the "brick" of nacre, aragonite platelet, is an ideal building block for making high-performance bulk nanocomposites. Herein, we demonstrated a strong and tough conductive nacre through reassembling aragonite platelets with bridged by MXene nanosheets and hydrogen bonding, not only providing high mechanical properties but also excellent electrical conductivity. The flexural strength and fracture toughness of the obtained conductive nacre reach ~282 MPa and ~6.3 MPa m1/2, which is 1.6 and 1.6 times higher than that of natural nacre, respectively. These properties are attributed to densification and high orientation degree of the conductive nacre, which is effectively induced by the combined interactions of hydrogen bonding and MXene nanosheets bridging. The crack propagations in conductive nacre are effectively inhibited through crack deflection with hydrogen bonding, and MXene nanosheets bridging between aragonite platelets. In addition, our conductive nacre also provides a self-monitoring function for structural damage and offers exceptional electromagnetic interference shielding performance. Our strategy of reassembling the aragonite platelets exfoliated from waste nacre into high-performance artificial nacre, provides an avenue for fabricating high-performance bulk nanocomposites through the sustainable reutilization of shell resources.

Regulating Functional Groups Enhances the Performance of Flexible Microporous MXene/Bacterial Cellulose Electrodes in Supercapacitors

Ultrathin MXene-based films exhibit superior conductivity and high capacitance, showing promise as electrodes for flexible supercapacitors. This work describes a simple method to enhance the performance of MXene-based supercapacitors by expanding and stabilizing the interlayer space between MXene flakes while controlling the functional groups to improve the conductivity. Ti3C2Tx MXene flakes are treated with bacterial cellulose (BC) and NaOH to form a composite MXene/BC (A-M/BC) electrode with a microporous interlayer and high surface area (62.47 m2 g-1). Annealing the films at low temperature partially carbonizes BC, increasing the overall electrical conductivity of the films. Improvement in conductivity is also attributed to the reduction of -F, -Cl, and -OH functional groups, leaving -Na and -O functional groups on the surface. As a result, the A-M/BC electrode demonstrates a capacitance of 594 F g-1 at a current density of 1 A g-1 in 3 M H2SO4, which represents a ∼2× increase over similarly processed films without BC (309 F g-1) or pure MXene (298 F g-1). The corresponding device has an energy density of 9.63 Wh kg-1 at a power density of 250 W kg-1. BC is inexpensive and enhances the overall performance of MXene-based film electrodes in electronic devices. This method underscores the importance of functional group regulation in enhancing MXene-based materials for energy storage.

Interlayer manipulation of bio-inspired Ti3C2Tx nanocontainer through intercalation of amino acid molecules to dramatically boosting uranyl hijacking capability from seawater

More than 4.5 billion tons of unconventional uranium resources [UO2(CO3)3]4- are uniformly dissolved in seawater, providing a sustainable and abundant fuel source for the development of nuclear energy. Herein, we presented a rational design and development of Ti3C2Tx nanocontainer inspired by the exceptional selectivity and affinity exhibited by superb-uranyl proteins through amino acid intercalation. The amino acid intercalation of Ti3C2Tx demonstrated exceptional UO22+ capture capacity (Arg-Ti3C2Tx, His-Ti3C2Tx, and Lys-Ti3C2Tx with qmax values of 594.46, 846.04, and 1030.17 mg/g). Furthermore, these intercalated materials exhibited remarkable sequestration efficiency and selectivity (Uinitial = ∼45.2 ∼7636 μg/L; ∼84.45% ∼98.08%; and ∼2.72 ×104 ∼1.28 ×105 KdU value), despite the presence of an overwhelming surplus of Na+, Ca2+, Mg2+, and Co2+ ions. Significantly, even in the 0.3 M NaHCO3 solution and surpassing 103-fold of the Na3VO4 system, the adsorption efficiency of Lys-Ti3C2Tx still achieved a remarkable 63.73% and 65.05%. Moreover, the Lys-Ti3C2Tx can extract ∼30.23 ∼8664.03 μg/g uranium after 24 h contact in ∼13.3 ∼5000 μg/L concentration from uranium-spiked natural seawater. The mechanism analysis revealed that the high binding capability can be attributed to the chelation of carboxyl and amino groups with uranyl ions. This innovative state-of-the-art approach in regulating uranium harvesting capability through intercalation of amino acid molecules provides novel insights for extracting uranium from seawater.

Self-Thermal Management in Filtered Selenium-Terminated MXene Films for Flexible Safe Batteries

Li-ion batteries with superior interior thermal management are crucial to prevent thermal runaway and ensure safe, long-lasting operation at high temperatures or during rapid discharging and charging. Typically, such thermal management is achieved by focusing on the separator and electrolyte. Here, the study introduces a Se-terminated MXene free-standing electrode with exceptional electrical conductivity and low infrared emissivity, synergistically combining high-rate capacity with reduced heat radiation for safe, large, and fast Li+ storage. This is achieved through a one-step organic Lewis acid-assisted gas-phase reaction and vacuum filtration. The Se-terminated Nb2Se2C outperformed conventional disordered O/OH/F-terminated materials, enhancing Li+-storage capacity by ≈1.5 times in the fifth cycle (221 mAh·g-1 at 1 A·g-1) and improving mid-infrared adsorption with low thermal radiation. These benefits result from its superior electrical conductivity, excellent structural stability, and high permittivity in the infrared region. Calculations further reveal that increased permittivity and conductivity along the z-direction can reduce heat radiation from electrodes. This work highlights the potential of surface groups-terminated layered material-based free-standing flexible electrodes with self-thermal management ability for safe, fast energy storage.

Ultrahigh Nonlinear Responses from MXene Plasmons in the Short-Wave Infrared Range

Surface plasmons in 2D materials such as graphene exhibit exceptional field confinement. However, the low electron density of majority of 2D materials, which are semiconductors or semimetals, has limited their plasmons to mid-wave or long-wave infrared regime. This study demonstrates that a 2D Ti3C2Tx MXene with high electron density can not only support strong plasmon confinement with an acoustic plasmon mode in the short-wave infrared region, but also provide ultrahigh nonlinear responses. The acoustic MXene plasmons (AMPs) in the MXene (Ti3C2Tx)-insulator (SiO2)-metal (Au) nanostructure generate in the 1.5-6.0 µm wavelength range, exhibiting a two orders of magnitude reduction in wavelength compared to wavelength in free space. Furthermore, AMP resonators with patterned Au rods exhibit a record-high nonlinear absorption coefficient of 1.37 × 10-2 m W-1 at wavelength of 1.56 µm, ≈3 orders of magnitude greater than the highest value recorded for other 2D materials. These results indicate that MXenes can overcome fundamental plasmon wavelength limitations of previously studied 2D materials, providing groundbreaking opportunities in nonlinear optical applications, including all-optical processing and ultrafast optical switching.

Direct Ink Writing of Low-Concentration MXene/Aramid Nanofiber Inks for Tunable Electromagnetic Shielding and Infrared Anticounterfeiting Applications

MXene inks offer a promising avenue for the scalable production and customization of printing electronics. However, simultaneously achieving a low solid content and printability of MXene inks, as well as mechanical flexibility and environmental stability of printed objects, remains a challenge. In this study, we overcame these challenges by employing high-viscosity aramid nanofibers (ANFs) to optimize the rheology of low-concentration MXene inks. The abundant entangled networks and hydrogen bonds formed between MXene and ANF significantly increase the viscosity and yield stress up to 103 Pa·s and 200 Pa, respectively. This optimization allows the use of MXene/ANF (MA) inks at low concentrations in direct ink writing and other high-viscosity processing techniques. The printable MXene/ANF inks with a high conductivity of 883.5 S/cm were used to print shields with customized structures, achieving a tunable electromagnetic interference shielding effectiveness (EMI SE) in the 0.2-48.2 dB range. Furthermore, the MA inks exhibited adjustable infrared (IR) emissivity by changing the ANF ratio combined with printing design, demonstrating the application for infrared anticounterfeiting. Notably, the printed MXene/ANF objects possess outstanding mechanical flexibility and environmental stability, which are attributed to the reinforcement and protection of ANF. Therefore, these findings have significant practical implications as versatile MXene/ANF inks can be used for customizable, scalable, and cost-effective production of flexible printed electronics.