Ultra-efficient electromagnetic wave absorption with ethanol-thermally treated two-dimensional Nb2CTx nanosheets

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.

State-of-the-art in carbides/carbon composites for electromagnetic wave absorption

Electromagnetic wave absorbing materials (EWAMs) have made great progress in the past decades, and are playing an increasingly important role in radiation prevention and antiradar detection due to their essential attenuation toward incident EM wave. With the flourish of nanotechnology, the design of high-performance EWAMs is not just dependent on the intrinsic characteristics of single-component medium, but pays more attention to the synergistic effects from different components to generate rich loss mechanisms. Among various candidates, carbides and carbon materials are usually labeled with the features of chemical stability, low density, tunable dielectric property, and diversified morphology/microstructure, and thus the combination of carbides and carbon materials will be a promising way to acquire new EWAMs with good practical application prospects. In this review, we introduce EM loss mechanisms related to dielectric composites, and then highlight the state-of-the-art progress in carbides/carbon composites as high-performance EWAMs, including silicon carbide/carbon, MXene/carbon, molybdenum carbide/carbon, as well as some uncommon carbides/carbon composites and multicomponent composites. The critical information regarding composition optimization, structural engineering, performance reinforcement, and structure-function relationship are discussed in detail. In addition, some challenges and perspectives for the development of carbides/carbon composites are also proposed after comparing the performance of some representative composites.

Preparation of MoS2/MXene/NC Porous Composite Microspheres with Wrinkled Surface and Their Microwave Absorption Performances

In this paper, a MoS2/MXene/N-doped carbon (NC) porous composite microsphere with a wrinkled surface was designed and constructed. Lithium fluoride exfoliation and lithium-ion etching fabricated two types of 2D assembly elements, MXene (Ti3C2Tx) and MoS2 nanosheets. The two nanosheets were self-assembled by an ultrasonic spray technique with high-temperature reduction, and MoS2/MXene microspheres with 3Dwrinkled shapes were obtained. The coating of the surface NC layer was achieved by the carbonization of a polydopamine (PDA) precursor formed by the self-polymerization of dopamine. The amount of PDA coating and raw material ratio significantly affect the microstructure and electromagnetic wave absorption performance. The optimal MXene to MoS2 mass ratio is 5:1, and the optimal coating time and filler amount are 8 h and 40%. MoS2/MXene/NC composite microspheres exhibit excellent absorption performance with low reflection losses (RLmin) of -52.9 dB at 6.4 GHz and high adequate absorption bandwidths of 5.2 GHz. By adjusting the thickness of the absorber, the full coverage of the C-Ku band (4-18 GHz) can be achieved. As a new composite absorber, it has significant potential applications.

One-pot in-situ hydrothermal synthesis of ternary In2S3/Nb2O5/Nb2C Schottky/S-scheme integrated heterojunction for efficient photocatalytic hydrogen production

MXene-derived photocatalysts continue to fascinate the research community in developing photo-driven green and sustainable fuel production. However, the efficiency of MXene-derived photocatalyst is still low due to the wide bandgap and high recombination rate of photo-excited charge carriers. Here, we have synthesized the Nb₂C MXene-derived ternary photocatalyst via one-pot in-situ hydrothermal method for photocatalytic hydrogen (H₂) evolution. The partial oxidation of Nb₂C MXene into Nb₂O₅ nanorods and coupling with In₂S₃ nanoparticles via in-situ chemical anchoring were the key factors toward high efficiency and long-term stability during photocatalytic H₂ evolution. The optimized ternary photocatalyst composite manifested the highest H₂ evolution efficiency at 68.8 µmol g^-1 h^-1, which was 11 and 7.5 times higher than the Nb₂O₅/Nb₂C (NNC) and pure In₂S₃ photocatalyst, respectively. Moreover, the photocatalytic stability of the optimized ternary photocatalyst composite was analyzed for five consecutive cycles, and above 87% activity retention was observed even after the fifth cycle without any obvious decline. The separation efficiency of photoexcited charge carriers could be attributed to the synergic effect of the In₂S₃/Nb₂O₅ heterojunction and the redox reactions at different sites of the composite. More importantly, the participation of Schottky junction and S-scheme heterojunction charge transfer for the obtained novel ternary photocatalyst was evaluated via ultraviolet photoelectron spectroscopy (UPS) and electron paramagnetic resonance (EPR). This research will provide additional insight into the extended potential of MXene-derived ternary photocatalysts towards efficient H₂ production to meet future global energy demands.

Developing MXenes from Wireless Communication to Electromagnetic Attenuation

There is an urgent global need for wireless communication utilizing materials that can provide simultaneous flexibility and high conductivity. Avoiding the harmful effects of electromagnetic (EM) radiation from wireless communication is a persistent research hot spot. Two-dimensional (2D) materials are the preferred choice as wireless communication and EM attenuation materials as they are lightweight with high aspect ratios and possess distinguished electronic properties. MXenes, as a novel family of 2D materials, have shown excellent properties in various fields, owing to their excellent electrical conductivity, mechanical stability, high flexibility, and ease of processability. To date, research on the utility of MXenes for wireless communication has been actively pursued. Moreover, MXenes have become the leading materials for EM attenuation. Herein, we systematically review the recent advances in MXene-based materials with different structural designs for wireless communication, electromagnetic interference (EMI) shielding, and EM wave absorption. The relationship governing the structural design and the effectiveness for wireless communication, EMI shielding, and EM wave absorption is clearly revealed. Furthermore, our review mainly focuses on future challenges and guidelines for designing MXene-based materials for industrial application and foundational research.

Facile hydrothermal synthesis of rod-like Nb2O5/Nb2CTx composites for visible-light driven photocatalytic degradation of organic pollutants

The MXene-based transition metal oxide composite is a potential candidate for photocatalysts. Rod-like pseudohexagonal phase Nb₂O₅/Nb₂CT_x composites were synthesized by a simple hydrothermal oxidation of 2D layered Nb₂CT_x. The Nb₂O₅/Nb₂CT_x composites show superior photocatalytic activity for 98.5% of degradation of Rhodamine B (RhB) for 120 min and 91.2% of tetracycline hydrochloride (TC-HCl) for 180 min under visible light irradiation. The Schottky junction is formed between Nb₂O₅ nanorods and Nb₂CT_x and the photo-generated carriers are effectively separated, enhancing the photocatalytic activity of the Nb₂O₅/Nb₂CT_x. High photoactivity and cycle stability of Nb₂O₅/Nb₂CT_x composites indicate that hydrothermal oxidation of 2D layered Nb₂CT_x is an alternative to prepare efficient photocatalyst for degradation of organic pollutants.

Efficient Energy Conversion and Storage Based on Robust Fluoride-Free Self-Assembled 1D Niobium Carbide in 3D Nanowire Network

Owing to their high robustness and conductivity, 2D transition metal carbides and nitrides known as MXenes are considered as a promising material class for electrochemical catalysis, energy conversion, and storage applications. Nevertheless, conventional hazardous fluoride-based synthesis routes and the intense intralayer bonding restrict the development of MXenes. Herein, a fluoride-free, facile, and rapid method for synthesizing self-assembled 1D architecture from an MXene-based compound is reported. The MXene nanowire (NW) not only provides a robust connection to the flexible substrate but also effectively increases the electrochemically active surface area. The kinetics-favorable structure yields a boosted performance for the hydrogen/oxygen evolution reaction and the intake of the zinc ion. The 1D NW based on MXene compound maintains high stability in a quite low overpotential of 236 mV for 24 h without detachment from the substrate and manifests an exceptional high-power density of 420 W kg-1 over 150 cycles as a flexible aqueous zinc ion battery. This work paves a novel and non-toxic synthesis method for the 1D nanofiber structure from MXene composition and demonstrates its multifunctional applications for energy conversion and storage.

Ti3C2Tx MXene-derived TiO2/C-QDs as oxidase mimics for the efficient diagnosis of glutathione in human serum

A Ti₃C₂T_x MXene-derived TiO₂/C-QD oxidase mimic was developed and used for the efficient diagnosis of glutathione in human serum.

Bacteria-derived fluorescent carbon dots for highly selective detection ofp-nitrophenol and bioimaging

Schematic of the synthetic route for fluorescent CDs-BC and their applications in the detection ofp-NP and bioimaging.

Two-dimensional transition metal carbide (Ti3C2Tx) as an efficient adsorbent to remove cesium (Cs+)

Industrial utilization of nuclear resources greatly depends on the effective treatment of nuclear waste.