2D Higher-Metal Nitride Nanosheets for Solar Steam Generation.

Higher-metal (HM) nitrides are a fascinating family of materials being increasingly researched due to their unique physical and chemical properties. However, few focus on investigating their application in a solar steam generation because the controllable and large-scale synthesis of these materials remains a significant challenge. Herein, it is reported that higher-metal molybdenum nitride nanosheets (HM-Mo5 N6 ) can be produced at the gram-scale using amine-functionalized MoS2 as precursor. The first-principles calculation confirms amine-functionalized MoS2 nanosheet effectively lengthens the bonds of MoS leading to a lower bond binding energy, promoting the formation of MoN bonds and production of HM-Mo5 N6 . Using this strategy, other HM nitride nanosheets, such as W2 N3 , Ta3 N5 , and Nb4 N5 , can also be synthesized. Specifically, under one simulated sunlight irradiation (1 kW m-2 ), the HM-Mo5 N6 nanosheets are heated to 80 °C within only ≈24 s (0.4 min), which is around 78 s faster than the MoS2 samples (102 s/1.7 min). More importantly, HM-Mo5 N6 nanosheets exhibit excellent solar evaporation rate (2.48 kg m-2  h-1 ) and efficiency (114.6%), which are 1.5 times higher than the solar devices of MoS2 /MF.

Tough and Fatigue Resistant Cellulose Nanocrystal Stitched Ti3 C2 Tx MXene Films.

Ti3 C2 Tx MXene (or "MXene" for simplicity) has gained noteworthy attention for its metal-like electrical conductivity and high electrochemical capacitance-a unique blend of properties attractive toward a wide range of applications such as energy storage, healthcare monitoring, and electromagnetic interference shielding. However, processing MXene architectures using conventional methods often deals with the presence of defects, voids, and isotropic flake arrangements, resulting in a trade-off in properties. Here, a sequential bridging (SB) strategy is reported to fabricate dense, freestanding MXene films of interconnected flakes with minimal defects, significantly enhancing its mechanical properties, specifically tensile strength (≈285 MPa) and breaking energy (≈16.1 MJ m-3 ), while retaining substantial values of electrical conductivity (≈3050 S cm-1 ) and electrochemical capacitance (≈920 F cm-3 ). This SB method first involves forming a cellulose nanocrystal-stitched MXene framework, followed by infiltration with structure-densifying calcium cations (Ca2+ ), resulting in tough and fatigue resistant films with anisotropic, evenly spaced, and strongly interconnected flakes - properties essential for developing high-performance energy-storage devices. It is anticipated that the knowledge gained in this work will be extended toward improving the robustness and retaining the electronic properties of 2D nanomaterial-based macroarchitectures.

Toughening Wet-Spun Silk Fibers by Silk Nanofiber Templating.

Regenerated silk fibers typically fall short of silkworm cocoon fibers in mechanical properties due to reduced fiber crystal structure and alignment. One approach to address this has been to employ inorganic materials as reinforcing agents. The present study avoids the need for synthetic additives, demonstrating the first use of exfoliated silk nanofibers to control silk solution crystallization, resulting in all-silk pseudocomposite fibers with remarkable mechanical properties. Incorporating only 0.06 wt% silk nanofibers led to a ≈44% increase in tensile strength (over 600 MPa) and ≈33% increase in toughness (over 200 kJ kg-1 ) compared with fibers without silk nanofibers. These remarkable properties can be attributed to nanofiber crystal seeding in conjunction with fiber draw. The crystallinity nearly doubled from ≈17% for fiber spun from pure silk solution to ≈30% for the silk nanofiber reinforced sample. The latter fiber also shows a high degree of crystal orientation with a Herman's orientation factor of 0.93, a value which approaches that of natural degummed B. mori silk cocoon fiber (0.96). This study provides a strong foundation to guide the development of simple, eco-friendly methods to spin regenerated silk with excellent properties and a hierarchical structure that mimics natural silk.

Spinning Regenerated Silk Fibers with Improved Toughness by Plasticizing with Low Molecular Weight Silk.

Low-molecular weight (LMW) silk was utilized as a LMW silk plasticizer for regenerated silk, generating weak physical crosslinks between high-molecular weight (HMW) silk chains in the amorphous regions of a mixed solution of HMW/LMW silk. The plasticization effect of LMW silk was investigated using mechanical testing, Raman spectroscopy, and wide-angle X-ray scattering (WAXS). Small amounts (10%) of LMW silk resulted in a 19.4% enhancement in fiber extensibility and 37.8% increase in toughness. The addition of the LMW silk facilitated the movement of HMW silk chains during drawing, resulting in an increase in molecular chain orientation when compared with silk spun from 100% HMW silk solution. The best regenerated silk fibers produced in this work had an orientation factor of 0.94 and crystallinity of 47.82%, close to the values of natural degummedBombyx mori silk fiber. The approach and mechanism elucidated here can facilitate artificial silk systems with enhanced properties.

Interfacial Modification of Lithium Metal Anode by Boron Nitride Nanosheets.

Metallic lithium (Li) is the most attractive anode for Li batteries because it holds the highest theoretical specific capacity (3860 mA h g-1) and the lowest redox potential (-3.040 V vs SHE). However, the poor interface stability of the Li anode, which is caused by the high reactivity and dendrite formation of metallic Li upon cycling, leads to undesired electrochemical performance and safety issues. While two-dimensional boron nitride (BN) nanosheets have been utilized as an interfacial layer, the mechanism on how they stabilize the Li-electrolyte interface remains elusive. Here, we show how BN nanosheet interlayers suppress Li dendrite formation, enhance Li ion transport kinetics, facilitate Li deposition, and reduce electrolyte decomposition. We show through both simulation and experimental data that the desolvation process of a solvated Li ion within the interlayer nanochannels kinetically favors Li deposition. This process enables long cycling stability, reduced voltage polarization, improved interface stability, and negligible volume expansion. Their application as an interfacial layer in symmetric cells and full cells that display significantly improved electrochemical properties is also demonstrated. The knowledge gained in this study provides both critical insights and practical guidelines for designing a Li metal anode with significantly improved performance.

Applications of X-Ray-Based Characterization in MXene Research.

X-rays are a penetrating form of high-energy electromagnetic radiation with wavelengths ranging from 10 pm to 10 nm. Similar to visible light, X-rays provide a powerful tool to study the atoms and elemental information of objects. Different characterization methods based on X-rays are established, such as X-ray diffraction, small- and wide-angle X-ray scattering, and X-ray-based spectroscopies, to explore the structural and elemental information of varied materials including low-dimensional nanomaterials. This review summarizes the recent progress of using X-ray related characterization methods in MXenes, a new family of 2D nanomaterials. These methods provide key information on the nanomaterials, covering synthesis, elemental composition, and the assembly of MXene sheets and their composites. Additionally, new characterization methods are proposed as future research directions in the outlook section to enhance understanding of MXene surface and chemical properties. This review is expected to provide a guideline for characterization method selection and aid in precise interpretation of the experimental data in MXene research.

Environmentally stable MXene ink for direct writing flexible electronics.

MXene inks are promising candidates for fabricating conductive circuits and flexible devices. Here, MXene inks prepared from solvent mixtures demonstrate long-term stability and can be employed in commercial rollerball pens to write electronic circuits on flexible substrates. Such circuits exhibit a fast and accurate capacitive response for touch-boards and water level measurement, indicating the excellent potential of these MXene inks in electrical device fabrication.

Highly stable lithium anodes from recycled hemp textile.

Three-dimensional lithium (Li) hosts have been shown to suppress the growth of Li dendrites for next generation Li metal batteries. Here, we report a cost-effective and scalable approach to produce highly stable Li composite anodes from industrial hemp textile waste. The hemp@Li composite anodes demonstrate stable cycling both in half and full cells.

Ti3C2Tx MXene: from dispersions to multifunctional architectures for diverse applications.

The exciting combination of high electrical conductivity, high specific capacitance and colloidal stability of two-dimensional Ti3C2Tx MXene (referred to as MXene) has shown great potential in a wide range of applications including wearable electronics, energy storage, sensors, and electromagnetic interference shielding. To realize its full potential, recent literature has reported a variety of solution-based processing methodologies to develop MXenes into multifunctional architectures, such as fibres, films and aerogels. In response to these recent critical advances, this review provides a comprehensive analysis of the diverse solution-based processing methodologies currently being used for MXene-architecture fabrication. A critical evaluation of the processing challenges directly affecting macroscale material properties and ultimately, the performance of the resulting prototype devices is also provided. Opportunities arising from the observed and foreseen challenges regarding their use are discussed to provide avenues for new designs and realise practical use in high performance applications.

Scalable Fabrication of Ti3C2Tx MXene/RGO/Carbon Hybrid Aerogel for Organics Absorption and Energy Conversion.

High aspect ratio two-dimensional Ti3C2Tx MXene flakes with extraordinary mechanical, electrical, and thermal properties are ideal candidates for assembling elastic and conductive aerogels. However, the scalable fabrication of large MXene-based aerogels remains a challenge because the traditional preparation method relies on supercritical drying techniques such as freeze drying, resulting in poor scalability and high cost. Herein, the use of porous melamine foam as a robust template for MXene/reduced graphene oxide aerogel circumvents the volume shrinkage during its natural drying process. Through this approach, we were able to produce large size (up to 600 cm3) MXene-based aerogel with controllable shape. In addition, the aerogels possess an interconnected cellular structure and display resilience up to 70% of compressive strain. Some key features also include high solvent absorption capacity (∼50-90 g g-1), good photothermal conversion ability (an average evaporation rate of 1.48 kg m-2 h-1 for steam generation), and an excellent electrothermal conversion rate (1.8 kg m-2 h-1 at 1 V). More importantly, this passive drying process provides a scalable, convenient, and cost-effective approach to produce high-performance MXene-based aerogels, demonstrating the feasibility of commercial production of MXene-based aerogels toward practical applications.

Development and Applications of MXene-Based Functional Fibers.

The increasing interest toward wearable and portable electronic devices calls for multifunctional materials and fibers/yarns capable of seamless integration with everyday textiles. To date, one particular gap inhibiting the development of such devices is the production of robust functional fibers with improved electronic conductivity and electrochemical energy storage capability. Recent efforts have been made to produce functional fibers with 2D carbides known as MXenes to address these demands. Ti3C2Tx MXene, in particular, is known for its metallic conductivity and high volumetric capacitance, and has shown promise for fibers and textile-based devices when used either as an additive, coating or the main fiber component. In this spotlight article, we highlight the recent exciting developments in our diverse efforts to fabricate MXene functionalized fibers, along with a critical evaluation of the challenges in processing, which directly affect macroscale material properties and the performance of the subsequent prototype devices. We also provide our assessment of observed and foreseen challenges of the current manufacturing methods and the opportunities arising from recent advances in the development of MXene fibers and paving future avenues for textile design and practical use in advanced applications.

Superelastic Ti3C2Tx MXene-Based Hybrid Aerogels for Compression-Resilient Devices.

Superelastic aerogels with excellent electrical conductivity, reversible compressibility, and high durability hold great potential for varied emerging applications, ranging from wearable electronics to multifunctional scaffolds. In the present work, superelastic MXene/reduced graphene oxide (rGO) aerogels are fabricated by mixing MXene and GO flakes, followed by a multistep reduction of GO, freeze-casting, and finally an annealing process. By optimizing both the composition and reducing conditions, the resultant aerogel shows a reversible compressive strain of 95%, surpassing all current reported values. The conducting MXene/rGO network provides fast electron transfer and stable structural integrity under compression/release cycles. When assembled into compressible supercapacitors, 97.2% of the capacitance was retained after 1000 compression/release cycles. Moreover, the high conductivity and porous structure also enabled the fabrication of a piezoresistive sensor with high sensitivity (0.28 kPa-1), wide detection range (up to 66.98 kPa), and ultralow detection limit (∼60 Pa). It is envisaged that the superelasticity of MXene/rGO aerogels offers a versatile platform for utilizing MXene-based materials in a wide array of applications including wearable electronics, electromagnetic interference shielding, and flexible energy storage devices.

Freezing Titanium Carbide Aqueous Dispersions for Ultra-long-term Storage.

Two-dimensional titanium carbide (Ti3C2Tx), or MXene, is a new nanomaterial that has attracted increasing interest due to its metallic conductivity, good solution processability, and excellent energy storage performance. However, Ti3C2Tx MXene flakes suffer from degradation through oxidation due to prolonged exposure to oxygenated water. Preventing the occurrence of oxidation, i.e., the formation of TiO2 particles, was found to be crucial in maintaining MXene quality. In the present work, we found that freezing aqueous MXene dispersions at a low temperature can effectively prevent the formation of TiO2 nanoparticles at the flake edge, which is known as the early stage of oxidation. The Ti3C2Tx flakes in frozen dispersion remain consistent in morphology and elemental composition for over 650 days, compared with freshly synthesized MXene, which in contrast exhibits flake edge degradation within two days when stored at room temperature. This result suggests that freezing a MXene dispersion dramatically postpones the oxidation of MXene flakes and that the stored MXene dispersion can be treated as freshly prepared MXene. This work not only fundamentally fulfilled the study on temperature dependence of MXene oxidation but has also demonstrated a simple method to extend the shelf life of MXene aqueous dispersion to years, which will be a cornerstone for large-scale production of MXene and ultimately benefit the research on MXenes.

Improving the Tensile Properties of Wet Spun Silk Fibers Using Rapid Bayesian Algorithm.

Wet spinning of silkworm silk has the potential to overcome the limitations of the natural spinning process, producing fibers with exceptional mechanical properties. However, the complexity of the extraction and spinning processes have meant that this potential has so far not been realized. The choice of silk processing parameters, including fiber degumming, dissolving, and concentration, are critical in producing a sufficiently viscous dope, while avoiding silk's natural tendency to gel via self-assembly. This study utilized recently developed rapid Bayesian optimization to explore the impact of these variables on dope viscosity. By following the dope preparation conditions recommended by the algorithm, a 13% (w/v) silk dope was produced with a viscosity of 0.46 Pa·s, approximately five times higher than the dope obtained using traditional experimental design. The tensile strength, modulus, and toughness of fibers spun from this dope also improved by a factor of 2.20×, 2.16×, and 2.75×, respectively. These results represent the outcome of just five sets of experimental trials focusing on just dope preparation. Given the number of parameters in the spinning and post spinning processes, the use of Bayesian optimization represents an exciting opportunity to explore the multivariate wet spinning process to unlock the potential to produce wet spun fibers with truly exceptional mechanical properties.

1-Tetra-decyl-pyridinium bromide monohydrate.

In the title compound, C(19)H(34)N(+)·Br(-)·H(2)O, the dihedral angle between the trans-planar alkyl side chain and the pyridinium ring is 52.73 (7)°. In the crystal structure, O-H⋯Br, C-H⋯Br and C-H⋯O hydrogen bonds form a network, while the hydro-phobic alkyl chains inter-digitate, forming bilayers.