MXene-Based Pressure Sensor with a Self-Healing Property for Joule Heating and Friction Sliding

As a kind of flexible electronic device, flexible pressure sensor has attracted wide attention in medical monitoring and human-machine interaction. With the continuous deepening of research, high-sensitivity sensor is developing from single function to multi-function. However, Current multifunctional sensors lack the ability to integrate joule heating, detect sliding friction, and self-healing. Herein, a MXene/polyurethane (PU) flexible pressure sensor with a self-healing property for joule heating and friction sliding is fabricated. The MXene/PU sensitive layer with special spinosum structure is prepared by a simple spraying method. After face-to-face assembly of the sensitive layers, the MXene/PU flexible pressure sensor is obtained and showed excellent sensitivity (150.65 kPa-1), fast response/recovery speed (75.5/63.9 ms), and good stability (10 000 cycles). Based on the self-healing property of PU, the sensor also has the ability to heal after mechanical damage. In addition, the sensor realizes the joule heating function under low voltage, and has the real-time monitoring ability of sliding objects. Combined with low cost and simple manufacturing method, the multi-functional MXene/PU flexible sensor shows a wide range of application potential in human activity monitoring, thermal management, and slip recognition.

High-Throughput Screening of Sulfur Reduction Reaction Catalysts Utilizing Electronic Fingerprint Similarity

The catalytic performance is determined by the electronic structure near the Fermi level. This study presents an effective and simple screening descriptor, i.e., the one-dimensional density of states (1D-DOS) fingerprint similarity, to identify potential catalysts for the sulfur reduction reaction (SRR) in lithium-sulfur batteries. The Δ1D-DOS in relation to the benchmark W2CS2 was calculated. This method effectively distinguishes and identifies 30 potential candidates for the SRR from 420 types of MXenes. Further analysis of the Gibbs free energy profiles reveals that MXene candidates exhibit promising thermodynamic properties for SRR, with the protocol achieving an accuracy rate exceeding 93%. Based on the crystal orbital Hamilton population (COHP) and differential charge analysis, it is confirmed that the Δ1D-DOS could effectively differentiate the interaction between MXenes and lithium polysulfide (LiPS) intermediates. This study underscores the importance of the electronic fingerprint in catalytic performance and thus may pave a new way for future high-throughput material screening for energy storage applications.

Design of MXene-Based Multiporous Nanosheet Stacking Structures Integrating Multiple Synergistic SERS Enhancements for Ultrasensitive Detection of Chloramphenicol

Motivated by the desire for more sensitivity and stable surface-enhanced Raman scattering (SERS) substrates to trace detect chloramphenicol due to its high toxicity and ubiquity, MXene has attracted increasing attention and is encountering the high-priority task of further observably improving detection sensitivity. Herein, a universal SERS optimization strategy that incorporates NH4VO3 to induce few-layer MXenes assembling into multiporous nanosheet stacking structures was innovatively proposed. The synthesized Nb2C-based multiporous nanosheet stacking structure can achieve a low limit of detection of 10-10 M and a high enhancement factor of 2.6 × 109 for MeB molecules, whose detection sensitivity is improved by 3 orders of magnitude relative to few-layer Nb2C MXenes. Such remarkably enhanced SERS sensitivity mainly originates from the multiple synergistic contributions of the developed physical adsorption, the chemical enhancement, and the conspicuously improved electromagnetic enhancement arising from the intersecting MXenes. Furthermore, the improved SERS sensitivity endows Nb2C-based multiporous structures with the capability to achieve ultrasensitive detection of chloramphenicol with a wide linear range from 100 μg/mL to 1 ng/mL. We believe it is of great significance in conspicuously developing the SERS sensitivity of other MXenes with surficial negative charges and has a great promising perspective for the trace detection of other antibiotics in microsystems.

MXene-Integrated Silk Fibroin-Based Self-Assembly-Driven 3D-Printed Theragenerative Scaffolds for Remotely Photothermal Anti-Osteosarcoma Ablation and Bone Regeneration

Aiming to address the bone regeneration and cancer therapy functionalities in one single material, in this study, we developed a dual-functional theragenerative three-dimensional (3D) aerogel-based composite scaffold from hybridization of photo-cross-linked silk fibroin (SF) biopolymer with MXene (Ti3C2) two-dimensional (2D) nanosheets. To fabricate the scaffold, we first develop a dual-cross-linked SF-based aerogel scaffold through 3D printing and photo-cross-linking of the self-assembly-driven methacrylate-modified SF (SF-MA) gel with controlled pore size, macroscopic geometry, and mechanical stability. In the next step, to endow a remotely controlled photothermal antiosteosarcoma ablation function to fabricated aerogel scaffold, MXene 2D nanosheets with strong near-infrared (NIR) photon absorption properties were integrated into the 3D-printed scaffolds. While 3D-printed MXene-modified dual-cross-linked SF composite scaffolds can mediate the in vitro growth and proliferation of preosteoblastic cell lines, they also endow a strong photothermal effect upon remote irradiation with NIR laser but also significantly stimulate bone mineral deposition on the scaffold surface. Additionally, besides the local release of the anticancer model drug, the generated heat (45-53 °C) mediated the photothermal ablation of cancer cells. The developed aerogel-based composites and chosen therapeutic techniques are thought to render a significant breakthrough in biomaterials' future clinical applications.

Preparation of High Conductive Medium and Establishment of Laege Capacity Conductive Channel

The preparation of highly conductive media and the construction of conducting channels play a crucial role in improving the electrical conductivity of electrically conductive adhesives. Therefore, a new MXene structure is reported in this paper, and the improved structure is rationally designed by computational modeling, which greatly prevents the buildup of MXene nanosheets, improves the stability of the structure, and creates a wide electron transfer channel, and the capacitance contribution of this structure is up to 86.3%. By mixing MXene modified with Ag-plated copper powder in a quantitative relationship to form high conductive media, the electrical conductivity is largely improved and the defect of low electron transfer rate of conventional conductive fillers is broken. The potential value of high conductive media is largely exploited using high throughput and machine learning methods, and here we show that the resistivity has reached 9.668 × 10-7 Ω m. The first principles investigate the conductive channels and electron transfer pathways of high-conductive media at the atomic level, further revealing the mechanism of action of high-conductive media. This study is also the first report on the application of MXene to high-conductive media.

Low Temperature Chemoresistive Oxygen Sensors Based on Titanium-Containing Ti2CTx and Ti3C2Tx MXenes

The chemoresistive properties of multilayer titanium-containing Ti₂CT_x and Ti₃C₂T_x MXenes, synthesized by etching the corresponding MAX phases with NaF solution in hydrochloric acid, and the composites based on them, obtained by partial oxidation directly in a sensor cell in an air flow at 150 °C, were studied. Significant differences were observed for the initial MXenes, both in microstructure and in the composition of surface functional groups, as well as in gas sensitivity. For single Ti₂CT_x and Ti₃C₂T_x MXenes, significant responses to oxygen and ammonia were observed. For their partial oxidation at a moderate temperature of 150 °C, a high humidity sensitivity (T, RH = 55%) is observed for Ti₂CT_x and a high and selective response to oxygen for Ti₃C₂T_x at 125 °C (RH = 0%). Overall, these titanium-containing MXenes and composites based on them are considered promising as receptor materials for low temperature oxygen sensors.

Ice-Crystal-Templated "Accordion-Like" Cellulose Nanofiber/MXene Composite Aerogels for Sensitive Wearable Pressure Sensors

Exfoliated MXene nanosheets are integrated with cellulose nanofibers (CNFs) to form composite aerogels with high electric conductivity. The combination of CNFs and MXene nanosheets forms a unique "accordion-like" hierarchical architecture with MXene-CNF pillared layers through ice-crystal templating. Benefiting from the special "layer-strut" structure, the MXene/CNF composite aerogels have low density (50 mg/cm³), excellent compressibility and recoverability, as well as superior fatigue resistance (up to 1000 cycles). When being used as a piezoresistive sensor, the composite aerogel exhibits high sensitivity upon different strains, stable sensing performance with various compressive frequencies, broad detection range, and quick responsiveness (0.48 s). Moreover, the piezoresistive sensors are shown to have an excellent real-time sensing ability for human motions such as swallowing, arm bending, walking, and running. The composite aerogels also have a low environmental impact with the natural biodegradability of CNFs. The designed composite aerogels can serve as a promising sensing material for developing next-generation sustainable and wearable electronic devices.

Emerging approaches for sensing and modulating neural activity enabled by nanocarbons and carbides

Devices that can record or modulate neural activity are essential tools in clinical diagnostics and monitoring, basic research, and consumer electronics. Realizing stable functional interfaces between manmade electronics and biological tissues is a longstanding challenge that requires device and material innovations to meet stringent safety and longevity requirements and to improve functionality. Compared to conventional materials, nanocarbons and carbides offer a number of specific advantages for neuroelectronics that can enable advances in functionality and performance. Here, we review the latest emerging trends in neuroelectronic interfaces based on nanocarbons and carbides, with a specific emphasis on technologies developed for use in vivo. We highlight specific applications where the ability to tune fundamental material properties at the nanoscale enables interfaces that can safely and precisely interact with neural circuits at unprecedented spatial and temporal scales, ranging from single synapses to the whole human body.

V2C Nanosheets as Dual-Functional Antibacterial Agents

Antibiotic-resistant bacterial strains have been continuously increasing and becoming a supreme threat to public health globally. The nanoparticle-based photothermal treatment has emerged as a powerful tool to combat toxic bacteria. Photothermal agents (PTAs) with cost-effective and high photothermal conversion efficiency are highly desirable. Herein, we unite the green process for delamination of V2AlC to produce a high yield mass of two-dimensional (2D) V2C nanosheets (NSs) by using algae extracts and demonstrate their high antibacterial efficiency. The resultant V2C NSs present decent structural reliability and intrinsic antibacterial ability. Powerful near-infrared (NIR) absorption and extraordinary photothermal conversion proficiency make it a good PTA for the photothermal treatment of bacteria. The antibacterial efficiency evaluation indicated that V2C NSs could effectively kill both Gram-positive S. aureus and Gram-negative E. coli. About 99.5% of both types of bacteria could be killed with low-dose of V2C NSs suspension (40 μg/mL) with 5 min NIR irradiation due to the intrinsic antibacterial ability and photothermal effect of V2C NSs, which is much higher than previous reports on Ta4C3, Ti3C2, MoSe2, and Nb2C. This work expands the application of MXene V2C NSs for rapid bacteria-killing and would gain promising attention for applications in the sterilization industry.

Flexible, Ultralight, and Mechanically Robust Waterborne Polyurethane/Ti3C2Tx MXene/Nickel Ferrite Hybrid Aerogels for High-Performance Electromagnetic Interference Shielding

Flexible, ultralight, and mechanically robust electromagnetic interference (EMI) shielding materials are urgently demanded to manage the increasing electromagnetic radiation pollution, but it remains a great challenge to simultaneously achieve ultralight yet mechanically robust properties while retaining high-efficiency EMI shielding performance. Herein, we fabricate a novel waterborne polyurethane/Ti₃C₂T_x MXene/nickel ferrite (WPU/MXene/NiFe₂O₄) hybrid aerogel by constructing a strong chemical bonding interaction between an NCO-terminated WPU prepolymer and hydroxyl functionalized MXene nanosheets. The resultant aerogels exhibit remarkable lightweight and mechanical properties, particularly high compressive stress far exceeding that of other MXene-based and WPU-based porous materials. Furthermore, synergistic effects of the oriented porous architecture and the multiphase skeleton endow the hybrid aerogels with a high X-band EMI shielding effectiveness (SE) of 64.7 dB at a low density of ∼38.2 mg/cm³. The corresponding specific SE value achieves 1694-3124 dB·cm³/g, and the SSE/d is up to 15,620 dB·cm²/g, surpassing that of most reported EMI shielding materials. Importantly, this aerogel, with excellent electromagnetic radiation protection effects and shielding reliability, is highly promising for long-term and effective EMI shielding service in various application environments.