Ultrathin and Flexible CNTs/MXene/Cellulose Nanofibrils Composite Paper for Electromagnetic Interference Shielding

Supertough MXene/Sodium Alginate Composite Fiber Felts Integrated with Outstanding Electromagnetic Interference Shielding and Heating Properties

The development of multifunctional MXene-based fabrics for smart textiles and portable devices has garnered significant attention. However, very limited studies have focused on their structure design and associated mechanical properties. Here, the supertough MXene fiber felts composed of MXene/sodium alginate (SA) fibers were fabricated. The fracture strength and bending stiffness of felts can be up to 97.8 MPa and 1.04 N mm2, respectively. Besides, the fracture toughness of felts was evaluated using the classic Griffith theory, yielding to a critical stress intensity factor of 1.79 M P a m . In addition, this kind of felt presents outstanding electrothermal conversion performance (up to 119 °C at a voltage of 2.5 V), high cryogenic and high-temperature tolerance of photothermal conversion performance (-196 to 160 °C), and excellent electromagnetic interference (EMI) shielding effectiveness (54.4 dB in the X-band). This work provides new structural design concepts for high-performance MXene-based textiles, broadening their future applications.

In Situ Synthesis of Liquid Metal Conductive Fibers toward Smart Cloth

To meet the diverse needs of humans, smart cloth has become a potential research hotspot to replace traditional cloth. However, it is challenging to manufacture a flexible fabric with multiple functions. Here, we introduce a smart cloth based on liquid metal (LM) conductive fibers. Ga2O3 nanoparticles are obtained through ultrasonic pretreatment. Furthermore, a coordination bond is formed between thiol groups on the surface of protein fibers and Ga2O3 through a scraping method, allowing Ga2O3 particles to be grafted onto the surface of protein fibers in situ. Finally, LM conductive fibers are encapsulated using a photocuring adhesive. In addition, a wearable smart cloth integrated with multiple sensors has been developed based on LM conductive fibers. Users can not only monitor their movement trajectory and the surrounding environment in real time but also have their data supervised by family members through a client, achieving remote and continuous monitoring. The development of this wearable smart cloth provides strong support for future wearable, flexible electronic devices.

Creation of Wood-Based Hierarchical Superstructures via In Situ Growth of ZIF-8 for Enhancing Mechanical Strength and Electromagnetic Shielding Performance

Given the escalating prevalence of electromagnetic pollution, there is an urgent need for the development of high-performance electromagnetic interference (EMI) shielding materials. Herein, wood-based electromagnetic shielding materials have gained significant popularity due to their exceptional performance as building materials. In this study, a novel wood-based composite with electromagnetic shielding properties is developed. Through the in situ growth of zeolitic imidazolate framework-8 (ZIF-8) crystals on wood fibers, coupled with uniform integration of carbon nanotubes (CNTs), a multifunctional composite named ZIF-8/Poplar-CNT composite is synthesized via a one-step thermoforming process. The incorporation of CNTs endows the composites with excellent EMI shielding effectiveness (EMI SE). Among these elements, despite ZIF-8 crystals not possessing intrinsic electromagnetic shielding functionality, their distinctive dodecahedral structure proves adept at scattering and reflecting electromagnetic waves within the composites, further improving the electromagnetic shielding effect. Hence, the ZIF-8/Poplar-CNT composite (56.95 dB) has ≈10 dB higher EMI SE compared to that of the composites without ZIF-8 crystals. Meanwhile, ZIF-8 crystals endow the materials with excellent tensile strength (54.84 MPa, enhanced by 4 times). Moreover, the introduction of Zn2+ provides superior antibacterial properties. The potential applications of ZIF-8/Poplar-CNT composites extend to diverse areas such as building decoration, electronic products, and medical equipment.

Sandwich-Structured Mxene/Waste Polyurethane Foam Composites For Highly Efficient Electromagnetic Interference, Infrared Shielding and Joule Heating

Electromagnetic interference (EMI) shielding and infrared (IR) stealth materials have attracted increasing attention owing to the rapid development of modern communication and military surveillance technologies. However, to realize excellent EMI shielding and IR stealth performance simultaneously remains a great challenge. Herein, a facile strategy is demonstrated to prepare high-efficiency EMI shielding and IR stealth materials of sandwich-structured MXene-based thin foam composites (M-W-M) via filtration and hot-pressing. In this composite, the conductive Ti3C2Tx MXene/cellulose nanofiber (MXene/CNF) film serves as the outer layer, which reflects electromagnetic waves and reduces the IR emissivity. Meanwhile, the middle layer is composed of a porous waste polyurethane foam (WPUF), which not only improves thermal insulation capacity but also extends electromagnetic wave propagation paths. Owing to the unique sandwich structure of "film-foam-film", the M-W-M composite exhibits a high EMI shielding effectiveness of 83.37 dB, and in the meantime extremely low emissivity (22.17%) in the wavelength range of 7-14 µm and thermal conductivity (0.19 W m-1 K-1), giving rise to impressive IR stealth performance at various surrounding temperatures. Remarkably, the M-W-M composite also shows excellent Joule heating properties, capable of maintaining the IR stealth function during Joule heating.

Ultrasonication Influence on the Morphological Characteristics of Graphene Nanoplatelet Nanocomposites and Their Electrical and Electromagnetic Interference Shielding Behavior

Graphene nanoplatelets (GNPs)/epoxy composites have been fabricated via gravity molding. The electrical and thermal properties of the composites have been studied with variable GNP type (C300, C500, and C750, whose surface areas are ~300, 500, and 750 m2/g, respectively), GNP loading (5, 10, 12, and 15 wt.%), and dispersion time via ultrasonication (0, 30, 60, and 120 min). By increasing the time of sonication of the GNP into the epoxy matrix, the electrical conductivity decreases, which is an effect of GNP fragmentation. The best results were observed with 10-12% loading and a higher surface area (C750), as they provide higher electrical conductivity, thereby preserving thermal conductivity. The influence of sonication over electrical conductivity was further analyzed via the study of the composite morphology by means of Raman spectroscopy and X-ray diffraction (XRD), providing information about the aspect ratio of GNPs. Moreover, electromagnetic shielding (EMI) has been studied up to 4 GHz. Composites with C750 and 120 min ultrasonication show the best performance in EMI shielding, influenced by their higher electrical conductivity.

Hollow Metal-Organic Framework/MXene/Nanocellulose Composite Films for Giga/Terahertz Electromagnetic Shielding and Photothermal Conversion

With the continuous advancement of communication technology, the escalating demand for electromagnetic shielding interference (EMI) materials with multifunctional and wideband EMI performance has become urgent. Controlling the electrical and magnetic components and designing the EMI material structure have attracted extensive interest, but remain a huge challenge. Herein, we reported the alternating electromagnetic structure composite films composed of hollow metal-organic frameworks/layered MXene/nanocellulose (HMN) by alternating vacuum-assisted filtration process. The HMN composite films exhibit excellent EMI shielding effectiveness performance in the GHz frequency (66.8 dB at Ka-band) and THz frequency (114.6 dB at 0.1-4.0 THz). Besides, the HMN composite films also exhibit a high reflection loss of 39.7 dB at 0.7 THz with an effective absorption bandwidth up to 2.1 THz. Moreover, HMN composite films show remarkable photothermal conversion performance, which can reach 104.6 °C under 2.0 Sun and 235.4 °C under 0.8 W cm-2, respectively. The unique micro- and macro-structural design structures will absorb more incident electromagnetic waves via interfacial polarization/multiple scattering and produce more heat energy via the local surface plasmon resonance effect. These features make the HMN composite film a promising candidate for advanced EMI devices for future 6G communication and the protection of electronic equipment in cold environments.

Heat-triggered shape recovery, EMI shielding and flame retardant: A novel cellulose/M(OH)(OCH3)@dopamine@Ag (M=Co, Ni) nanopaper for early fire alarm

Fire alarm systems are essential for protecting lives and properties from fire hazards. However, most of the existing fire alarm nanopapers rely on the resistance reduction after heating, which requires direct contact with the flame. In this study, we present a novel fire alarm nanopaper (CMPA) based on heat-triggered shape recovery. The CMPA is composed of hydroxypropyl methyl cellulose (HPMC) as the matrix and 2D nanomaterials M(OH)(OCH3) as fillers. When the temperature of CMPA exceeded the glass transition, the thrice-folded CMPA-1.0 flattened in 30s and connected to the alarm circuit based on its conductive surface. According to the results, the CMPA-1.0 with a thickness of about 0.2 mm had an efficient electromagnetic shielding of 42.1 dB. Moreover, the CMPA-1.0 self-extinguished rapidly after being ignited with its original shape preserved. The peak heat release rate of CMPA-1.0 was 108.9 W/g, which was 61.9 % lower than that of HPMC. Furthermore, the thermal conductivity of CMPA-1.0 reached to 0.317 W m-1 K-1, which was 40.8 % higher than that of HPMC, reducing the heat accumulation effectively. This work shows that CMPA is an ideal material for sensitive and safe early fire alarm, and the strategy based on heat-triggered shape recovery is promising in fire alarm application.

Recent advances in nanocellulose-based two-dimensional nanostructured membranes for sustainable water purification: A review

Nanocellulose (NC), a one-dimensional nanomaterial, is considered a sustainable material for water and wastewater purification because of its promising hydrophilic surface and mechanical characteristics. In this regard, nanostructured membranes comprising NC and two-dimensional (2D) nanomaterials emerged as advanced membranes for efficient and sustainable water purification. This article critically reviews the recent progress on NC-2D nanostructured membranes for water and wastewater treatment. The review highlights the main techniques employed to fabricate NC-2D nanostructured membranes. The physicochemical properties, including hydrophilicity, percent porosity, surface roughness, structure, and mechanical and thermal stability, are summarized. The key performance indicators such as permeability, rejection, long operation stability, antifouling, and interaction mechanisms are thoroughly discussed to evaluate the role of NC and 2D nanomaterials. Finally, summary points and future development work are highlighted to overcome the challenges for potential practical applications. This review contributes to the design and development of advanced membranes to solve growing water pollution concerns in a sustainable manner.

Multifunctional MXene/PEDOT:PSS-Based Phase Change Organohydrogels for Electromagnetic Interference Shielding and Medium-Low Temperature Infrared Stealth

Electromagnetic interference (EMI) shielding and infrared stealth technologies are essential for military and civilian applications. However, it remains a significant challenge to integrate various functions efficiently into a material efficiently. Herein, a minimalist strategy to fabricate multifunctional phase change organohydrogels (PCOHs) was proposed, which were fabricated from polyacrylamide (PAM) organohydrogels, MXene/PEDOT:PSS hybrid fillers, and sodium sulfate decahydrate (Na2SO4·10H2O, SSD) via one-step photoinitiation strategies. PCOHs with a high enthalpy value (130.7 J/g) and encapsulation rate (98%) could adjust the temperature by triggering a phase change of SSD, which can hide infrared radiation to achieve medium-low temperature infrared stealth. In addition, the PCOH-based sensor has good strain sensing ability due to the incorporation of MXene/PEDOT:PSS and can precisely monitor human movement. Remarkably, benefiting from the electron conduction of the three-dimensional conductive network and the ion conduction of the hydrogel, the EMI shielding efficiency (k) of PCOHs can reach 99.99% even the filler content as low as 1.8 wt %. Additionally, EMI shielding, infrared stealth, and sensing-integrated PCOHs can be adhered to arbitrary targets due to their excellent flexibility and adaptability. This work offers a promising pathway for fabricating multifunctional phase change materials, which show great application prospects in military and civilian fields.

New Carbon Materials for Multifunctional Soft Electronics

Soft electronics are garnering significant attention due to their wide-ranging applications in artificial skin, health monitoring, human-machine interaction, artificial intelligence, and the Internet of Things. Various soft physical sensors such as mechanical sensors, temperature sensors, and humidity sensors are the fundamental building blocks for soft electronics. While the fast growth and widespread utilization of electronic devices have elevated life quality, the consequential electromagnetic interference (EMI) and radiation pose potential threats to device precision and human health. Another substantial concern pertains to overheating issues that occur during prolonged operation. Therefore, the design of multifunctional soft electronics exhibiting excellent capabilities in sensing, EMI shielding, and thermal management is of paramount importance. Because of the prominent advantages in chemical stability, electrical and thermal conductivity, and easy functionalization, new carbon materials including carbon nanotubes, graphene and its derivatives, graphdiyne, and sustainable natural-biomass-derived carbon are particularly promising candidates for multifunctional soft electronics. This review summarizes the latest advancements in multifunctional soft electronics based on new carbon materials across a range of performance aspects, mainly focusing on the structure or composite design, and fabrication method on the physical signals monitoring, EMI shielding, and thermal management. Furthermore, the device integration strategies and corresponding intriguing applications are highlighted. Finally, this review presents prospects aimed at overcoming current barriers and advancing the development of state-of-the-art multifunctional soft electronics.

Robust, ultrathin and flexible electromagnetic interference shielding paper designed with all-polysaccharide hydrogel and MXene

An effective strategy was demonstrated to design an electromagnetic interference (EMI) shielding paper via a facile surface treatment on paper. TEMPO-oxidized cellulose nanofibers (TOCN) were first integrated with Ti3C2Tx MXene, and subsequently cast onto a filter paper with cationic guar gum (CGG) in a sequential way. TOCN and CGG generated a self-assembling hydrogel and formed a MXene-containing hydrogel film on top of the filter paper. The hydrogel film enhanced the tensile strength (9.49 MPa) of composite paper, and resulted in a 17 % increase as compared to the control. The composite paper containing 80 mg MXene (namely, 2.07 mg·cm-2) showed a conductivity of 3843 S·m-1 and EMI shielding effectiveness (EMI SE) of 49.37 dB. Furthermore, the 2-layer assembled TC-M 80 hydrogel composite paper achieved an EMI SE of 73.99 dB. Importantly, this composite paper showed higher EMI SE and lower thickness than a lot of reported materials. The presence of TOCN and CGG also protected MXene against several solvents and the incorporation of polydimethylsiloxane (PDMS) further improved the durability of the composite paper. This work provides a novel and simple strategy to design robust, ultrathin and flexible EMI shielding materials, and it might also inspire other work in paper-based functional materials.

Review on design strategies and applications of flexible cellulose‑carbon nanotube functional composites

Combining the excellent biocompatibility and mechanical flexibility of cellulose with the outstanding electrical, mechanical, optical and stability properties of carbon nanotubes (CNTs), cellulose-CNT composites have been extensively studied and applied to many flexible functional materials. In this review, we present advances in structural design strategies and various applications of cellulose-CNT composites. Firstly, the structural characteristics and corresponding treatments of cellulose and CNTs are analyzed, as are the potential interactions between the two to facilitate the formation of cellulose-CNT composites. Then, the design strategies and processing techniques of cellulose-CNT composites are discussed from the perspectives of cellulose fibers at the macroscopic scale (natural cotton, hemp, and other fibers; recycled cellulose fibers); nanocellulose at the micron scale (nanofibers, nanocrystals, etc.); and macromolecular chains at the molecular scale (cellulose solutions). Further, the applications of cellulose-CNT composites in various fields, such as flexible energy harvesting and storage devices, strain and humidity sensors, electrothermal devices, magnetic shielding, and photothermal conversion, are introduced. This review will help readers understand the design strategies of cellulose-CNT composites and develop potential high-performance applications.

Diverse Structural Design Strategies of MXene-Based Macrostructure for High-Performance Electromagnetic Interference Shielding

There is an urgent demand for flexible, lightweight, mechanically robust, excellent electromagnetic interference (EMI) shielding materials. Two-dimensional (2D) transition metal carbides/nitrides (MXenes) have been potential candidates for the construction of excellent EMI shielding materials due to their great electrical electroconductibility, favorable mechanical nature such as flexibility, large aspect ratios, and simple processability in aqueous media. The applicability of MXenes for EMI shielding has been intensively explored; thus, reviewing the relevant research is beneficial for advancing the design of high-performance MXene-based EMI shields. Herein, recent progress in MXene-based macrostructure development is reviewed, including the associated EMI shielding mechanisms. In particular, various structural design strategies for MXene-based EMI shielding materials are highlighted and explored. In the end, the difficulties and views for the future growth of MXene-based EMI shields are proposed. This review aims to drive the growth of high-performance MXene-based EMI shielding macrostructures on basis of rational structural design and the future high-efficiency utilization of MXene.

Ultrastrong Ionotronic Films Showing Electrochemical Osmotic Actuation

A multifunctional soft material with high ionic and electrical conductivity, combined with high mechanical properties and the ability to change shape can enable bioinspired responsive devices and systems. The incorporation of all these characteristics in a single material is very challenging, as the improvement of one property tends to reduce other properties. Here, a nanocomposite film based on charged, high-aspect-ratio 1D flexible nanocellulose fibrils, and 2D Ti3 C2 Tx MXene is presented. The self-assembly process results in a stratified structure with the nanoparticles aligned in-plane, providing high ionotronic conductivity and mechanical strength, as well as large water uptake. In hydrogel form with 20 wt% liquid, the electrical conductivity is over 200 S cm-1 and the in-plane tensile strength is close to 100 MPa. This multifunctional performance results from the uniquely layered composite structure at nano- and mesoscales. A new type of electrical soft actuator is assembled where voltage as low as ±1 V resulted in osmotic effects and giant reversible out-of-plane swelling, reaching 85% strain.

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.

Research progress and future perspectives on electromagnetic wave absorption of fibrous materials

Electromagnetic waves have caused great harm to military safety, high-frequency electronic components, and precision instruments, and so forth, which urgently requires the development of lightweight, high-efficiency, broadband electromagnetic waves (EMW) absorbing materials for protection. As the basic fibrous materials, carbon fibers (CFs) and SiC fibers (SiCf) have been widely applied in EMW absorption due to their intrinsic characteristics of low density, high mechanical properties, high conductivity, and dielectric loss mechanism. Nevertheless, it has remained a great challenge to develop lightweight EMW-absorbing fibrous materials with strong absorption capability and broad frequency range. In this review, the fundamental electromagnetic attenuation mechanisms are firstly introduced. Furthermore, the preparation, structure, morphology, and absorbing performance of CFs and SiCf-based EMW absorbing composites are summarized. In addition, prospective research opportunities are highlighted toward the development of fibrous absorbing materials with the excellent absorption performance.

Synthesis, Properties, and Applications of Nanocomposite Materials Based on Bacterial Cellulose and MXene

MXene exhibits impressive characteristics, including flexibility, mechanical robustness, the capacity to cleanse liquids like water through MXene membranes, water-attracting nature, and effectiveness against bacteria. Additionally, bacterial cellulose (BC) exhibits remarkable qualities, including mechanical strength, water absorption, porosity, and biodegradability. The central hypothesis posits that the incorporation of both MXene and bacterial cellulose into the material will result in a remarkable synthesis of the attributes inherent to MXene and BC. In layered MXene/BC coatings, the presence of BC serves to separate the MXene layers and enhance the material's integrity through hydrogen bond interactions. This interaction contributes to achieving a high mechanical strength of this film. Introducing cellulose into one layer of multilayer MXene can increase the interlayer space and more efficient use of MXene. Composite materials utilizing MXene and BC have gained significant traction in sensor electronics due to the heightened sensitivity exhibited by these sensors compared to usual ones. Hydrogel wound healing bandages are also fabricated using composite materials based on MXene/BC. It is worth mentioning that MXene/BC composites are used to store energy in supercapacitors. And finally, MXene/BC-based composites have demonstrated high electromagnetic interference (EMI) shielding efficiency.

Flexible MXene/Nanocellulose Composite Aerogel Film with Cellular Structure for Electromagnetic Interference Shielding and Photothermal Conversion

With the rapid development of wearable devices and integrated systems, protection against electromagnetic waves is an issue. For solving the problems of poor flexibility and a tendency to corrode traditional electromagnetic interference (EMI) shielding materials, two-dimensional (2D) nanomaterial MXene was employed to manufacture next-generation EMI shielding materials. Vacuum-assisted filtration combined with the liquid nitrogen prefreezing strategy was adopted to prepare flexible MXene/cellulose nanofibers (CNFs) composite aerogel film with unique cellular structure. Here, CNFs were employed as the reinforcement, and such a cellular structure design can effectively improve the shielding effectiveness (SE). In particular, the composite shows an outstanding EMI SE of 54 dB. Furthermore, the MXene/CNFs composite aerogel film exhibited prominent and steady photothermal conversion ability, which could obtain the maximum equilibrium temperature of 89.4 °C under an 808 nm NIR laser. Thus, our flexible composite aerogel film with appealing cellular construction holds great promise for wearable EMI shielding materials and heating applications in a cold and complex practical environment.

Emerging Two-Dimensional Materials for Electromagnetic Interference Shielding Application

Graphene is the first two-dimensional material that becomes the center material in various research areas of material science, chemistry, condensed matter, and engineering due to its advantageous properties, including larger specific area, lower density, outstanding electrical conductivity, and ease of processability. These properties attracted the attention of material researchers that resulted in a large number of publications on EMI shielding in a short time and play a central role in addressing the problems and challenges faced in this modern era of electronics by electromagnetic interference. After the popularity of graphene, the community of material researchers investigated other two-dimensional materials like MXenes, hexagonal boron nitride, black phosphorous, transition metal dichalcogenides, and layered double hydroxides, to additionally enhance the EMI shielding response of materials. The present article conscientiously reviews the current progress in EMI shielding materials in reference to two-dimensional materials and addresses the future challenges and research directions to achieve the goals.

Effective assessment of biopolymer-based multifunctional sorbents for the remediation of environmentally hazardous contaminants from aqueous solutions

Persistent contaminants in wastewater effluent pose a significant threat to aquatic life and are one of the most significant environmental concerns of our time. Although there are a variety of traditional methods available in wastewater treatment, including adsorption, coagulation, flocculation, ion exchange, membrane filtration, co-precipitation and solvent extraction, none of these have been found to be significantly cost-effective in removing toxic pollutants from the water environment. The upfront costs of these treatment methods are extremely high, and they require the use of harmful synthetic chemicals. For this reason, the development of new technologies for the treatment and recycling of wastewater is an absolute necessity. Our way of life can be made more sustainable by the synthesis of adsorbents based on biomass, making the process less harmful to the environment. Biopolymers offer a sustainable alternative to synthetic polymers, which are manufactured by joining monomer units through covalent bonding. This review presents a detailed classification of biopolymers such as pectin, alginate, chitosan, lignin, cellulose, chitin, carrageen, certain proteins, and other microbial biomass compounds and composites, with a focus on their sources, methods of synthesis, and prospective applications in wastewater treatment. A concise summary of the extensive body of knowledge on the fate of biopolymers after adsorption is also provided. Finally, consideration is given to open questions about future developments leading to environmentally friendly and economically beneficial applications of biopolymers.

Construction of Hollow Carbon Nanofibers with Graphene Nanorods as Nano-Antennas for Lower-Frequency Microwave Absorption

Electromagnetic (EM) wave absorbers at a lower-frequency region (2-8 GHz) require higher attenuation ability to achieve efficient absorption. However, the impedance match condition and attenuation ability are usually inversely related. Herein, one-dimensional hollow carbon nanofibers with graphene nanorods are prepared based on coaxial electrospinning technology. The morphology of graphene nanorods can be controlled by the annealing process. As the annealing time increased from 2 to 8 h, graphene nanospheres grew into graphene nanorods, which were catalyzed by Co catalysts derived from ZIF-67 nanoparticles. These nanorods can play the role of nano-antennas, which can guide EM waves into materials to enhance impedance match conditions. As a result, the carbon nanofibers with graphene nanorods possess a larger impedance match area with higher attenuation ability. The minimum reflection loss reaches -57.1 dB at a thickness of 4.6 mm, and the effective absorption bandwidth can cover almost both the S and C bands (2.4-8 GHz). This work contributes a meaningful perspective into the modulation of microwave absorption performance in the lower-frequency range.

MXene/bacterial cellulose/Fe3O4/methyltrimethoxylsilane flexible film with hydrophobic for effective electromagnetic shielding

Electromagnetic (EM) pollution has become a serious problem in modern society as it affects human lives. The fabrication of strong and highly flexible materials for electromagnetic interference (EMI) shielding applications is extremely urgent. Herein, a MXene Ti₃C₂T_x/Fe₃O₄ & bacterial cellulose (BC)/Fe₃O₄&Methyltrimethoxysilane (MTMS) flexible hydrophobic electromagnetic shielding film (SBTF_X-Y, X and Y were the number of layers of BC/Fe₃O₄ and the layers of Ti₃C₂T_x/Fe₃O₄), was fabricated. In the prepared film, MXene Ti₃C₂T_x absorbs a large amount of radio waves through polarization relaxation and conduction loss. Because of its extremely low reflectance of electromagnetic waves, BC@Fe₃O₄, as the outermost layer of the material, allows more electromagnetic waves to incident inside the material. The maximum electromagnetic interference (EMI) shielding efficiency (SE) of 68 dB was achieved for the composite film at 45 μm thickness. What's more, the SBTF_X-Y films show excellent mechanical properties, hydrophobicity and flexibility. The unique stratified structure of the film provides a new strategy for designing high-performance EMI shielding films with excellent surface and mechanical properties.

Structure Design and Processing Strategies of MXene-Based Materials for Electromagnetic Interference Shielding

The development of new materials for electromagnetic interference (EMI) shielding is an important area of research, as it allows for the creation of more effective and high-efficient shielding solutions. In this sense, MXenes, a class of 2D transition metal carbides and nitrides have exhibited promising performances as EMI shielding materials. Electric conductivity, low density, and flexibility are some of the properties given by MXene materials, which make them very attractive in the field. Different processing techniques have been employed to produce MXene-based materials with EMI shielding properties. This review summarizes processes and the role of key parameters like the content of fillers and thickness in the desired EMI shielding performance. It also discusses the determination of power coefficients in defining the EMI shielding mechanism and the concept of green shielding materials, as well as their influence on the real application of a produced material. The review concludes with a summary of current challenges and prospects in the production of MXene materials as EMI shields.

3D Janus structure MXene/cellulose nanofibers/luffa aerogels with superb mechanical strength and high-efficiency desalination for solar-driven interfacial evaporation

Interfacial solar steam generation (ISSG) is considered to be an attractive technique to address the water shortage. However, developing a sustainable thermal management, salt rejection, and excellent mechanical strength ISSG device for long-term stability desalination is still a challenge. Herein, a biomass ISSG device with superb mechanical properties was prepared by introducing a luffa sponge as the skeleton and constructing the MXene/cellulose nanofibers (CNFs) aerogels via freeze-drying. The Janus MXene-decorated CNFs/luffa (JMCL) aerogels integrated the multifunction of fast water transport, good thermal management, and efficient photothermal conversion in a single module, to achieve high-efficiency desalination. 3D Janus structure endowed the JMCL aerogel with opposite wettability, which is feasible to construct the localized photothermal generation and self-floating. The mechanical strength of JMCL aerogels is 437 times that of MXene/CNFs aerogels. The JMCL aerogels delivered a water evaporation rate of 1.40 kg m^-2h^-1 and an efficiency of 91.20% under 1 sun illumination. The excellent salt resistance during 24 h working and long-term solar vapor generation of up to 28 days were achieved. The multifunctional JMCL aerogels with 3D Janus structure offer new insights for developing good durability and eco-friendly biopolymer-based steam generators.

Self-Healing MXene- and Graphene-Based Composites: Properties and Applications

Today, self-healing graphene- and MXene-based composites have attracted researchers due to the increase in durability as well as the cost reduction in long-time applications. Different studies have focused on designing novel self-healing graphene- and MXene-based composites with enhanced sensitivity, stretchability, and flexibility as well as improved electrical conductivity, healing efficacy, mechanical properties, and energy conversion efficacy. These composites with self-healing properties can be employed in the field of wearable sensors, supercapacitors, anticorrosive coatings, electromagnetic interference shielding, electronic-skin, soft robotics, etc. However, it appears that more explorations are still needed to achieve composites with excellent arbitrary shape adaptability, suitable adhesiveness, ideal durability, high stretchability, immediate self-healing responsibility, and outstanding electromagnetic features. Besides, optimizing reaction/synthesis conditions and finding suitable strategies for functionalization/modification are crucial aspects that should be comprehensively investigated. MXenes and graphene exhibited superior electrochemical properties with abundant surface terminations and great surface area, which are important to evolve biomedical and sensing applications. However, flexibility and stretchability are important criteria that need to be improved for their future applications. Herein, the most recent advancements pertaining to the applications and properties of self-healing graphene- and MXene-based composites are deliberated, focusing on crucial challenges and future perspectives.

A Single Electronic Tattoo for Multisensory Integration

Wearable electronics are garnering growing interest in various emerging fields including intelligent sensors, artificial limbs, and human-machine interfaces. A remaining challenge is to develop multisensory devices that can conformally adhere to the skin even during dynamic-moving environments. Here, a single electronic tattoo (E-tattoo) based on a mixed-dimensional matrix network, which integrates two-dimensional  MXene nanosheets and one-dimensional cellulose nanofibers/Ag nanowires, is presented for multisensory integration. The multidimensional configurations endow the E-tattoo with excellent multifunctional sensing capabilities including temperature, humidity, in-plane strain, proximity, and material identification. In addition, benefiting from the satisfactory rheology of hybrid inks, the E-tattoos are able to be fabricated through multiple facile strategies including direct writing, stamping, screen printing, and three-dimensional printing on various hard/soft substrates. Especially, the E-tattoo with excellent triboelectric properties also can serve as a power source for activating small electronic devices. It is believed that these skin-conformal E-tattoo systems can provide a promising platform for next-generation wearable and epidermal electronics.

Progress of high performance Ti3C2Tx MXene nanocomposite films for electromagnetic interference shielding

With the rapid growth of 5G communication technology, it is imperative to produce electromagnetic interference (EMI) shielding materials to combat the growing electromagnetic radiation pollution. For new shielding applications, EMI shielding materials with high flexibility, light weight and good mechanical strength are in high demand. Due to their light weight, high flexibility, excellent EMI shielding performance, high mechanical properties, and multifunctionality, Ti₃C₂T_x MXene nanocomposite films have shown absolute benefits in EMI shielding in recent years. Consequently, numerous lightweight and flexible high-performance Ti₃C₂T_x MXene nanocomposite films have been generated quickly. In this article, we discuss not only the present state of EMI shielding material research, but also the synthesis and electromagnetic properties of Ti₃C₂T_x MXene. In addition, the loss mechanism of EMI shielding is described, with an emphasis on the analysis and summary of the research progress of diverse layer structured Ti₃C₂T_x MXene nanocomposite films for EMI shielding. Finally, the current issues of design and fabrication for Ti₃C₂T_x MXene nanocomposite films that need to be addressed are proposed, as well as the future research direction for Ti₃C₂T_x MXene nanocomposite films.

Multilayer Ultrathin MXene@AgNW@MoS2 Composite Film for High-Efficiency Electromagnetic Shielding

Structure and material composition is crucial in realizing high electromagnetic interference (EMI) shielding effectiveness (SE). Herein, an ultrathin MXene@AgNW@MoS₂ (MAM) composite film that resembles the structure of a pork belly and exhibits superior EMI shielding performance was fabricated via the vacuum-assisted suction filtration process and atomic layer deposition (ALD). The staggered AgNWs form skeletons and intersperse in MXene sheets to build a doped layer with three-dimensional network structures, which improves the electrical conductivity of the film. Based on the optimal dispersion concentration of Ag in doped and single layers, the MXene/AgNW doped layer and AgNW single layer are alternately vacuum-assisted-filtered to obtain laminated structures with multiple heterogeneous interfaces. These interfaces generate interface polarization and increase multiple reflection and scattering, resulting in the increased electromagnetic (EM) wave losses. On the other hand, MoS₂ outer nanolayers fabricated precisely by ALD effectively increases the absorption proportion of electromagnetic waves, reduces the secondary reflection, and improves the stability of EMI shielding properties. Ultimately, an ultrathin MAM film (a thickness of 0.03 mm) with five alternating internal layers and MoS₂ outer layers exhibits an excellent EMI SE of 86.3 dB in the X-band.

Enhanced Electromagnetic Shielding and Thermal Management Properties in MXene/Aramid Nanofiber Films Fabricated by Intermittent Filtration

High-efficiency electromagnetic interference (EMI) shielding and heat dissipation synergy materials with flexible, robust, and environmental stability are urgently demanded in next-generation integration electronic devices. In this work, we report the lamellar MXene/Aramid nanofiber (ANF) composite films, which establish a nacre-like structure for EMI shielding and heat dissipation by using the intermittent filtration strategy. The MXene/ANF composite film filled with 50 wt % MXene demonstrates enhanced mechanical properties with a strength of 230.5 MPa, an elongation at break of 6.2%, and a toughness of 11.8 MJ·m³ (50 wt % MXene). These remarkable properties are attributed to the hydrogen bonding and highly oriented structure. Furthermore, due to the formation of the MXene conductive network, the MXene/ANF composite film shows an outstanding conductivity of 624.6 S/cm, an EMI shielding effectiveness (EMI SE) of 44.0 dB, and a superior specific SE value (SSE/t) of 18847.6 dB·cm²/g, which is better than the vacuum filtration film. Moreover, the MXene/ANF composite film also shows a great thermal conductivity of 0.43 W/m·K. The multifunctional MXene/ANF composite films with high-performance EMI shielding, heat dissipation, and joule heating show great potential in the field of aerospace, military, microelectronics, microcircuit, and smart wearable electronics.

Development of Electromagnetic-Wave-Shielding Polyvinylidene Fluoride-Ti3C2Tx MXene-Carbon Nanotube Composites by Improving Impedance Matching and Conductivity

Absorption-dominated electromagnetic interference (EMI) shielding is attained by improving impedance matching and conductivity through structural design. Polyvinylidene fluoride (PVDF)-Ti₃C₂T_x MXene-single-walled carbon nanotubes (SWCNTs) composites with layered heterogeneous conductive fillers and segregated structures were prepared through electrostatic flocculation and hot pressing of the PVDF composite microsphere-coated MXene and SWCNTs in a layer-by-layer fashion. Results suggest that the heterogeneous fillers improve impedance matching and layered coating, and hot compression allows the MXene and SWCNTs to form a continuous conducting network at the PVDF interface, thereby conferring excellent conductivity to the composite. The PVDF-MXene-SWCNTs composite showed a conductivity of 2.75 S cm^-1 at 2.5% MXene and 1% SWCNTs. The EMI shielding efficiency (SE) and contribution from absorption loss to the total EMI SE of PVDF-MXene-SWCNTs were 46.1 dB and 85.7%, respectively. Furthermore, the PVDF-MXene-SWCNTs composite exhibited excellent dielectric losses and impedance matching. Therefore, the layered heteroconductive fillers in a segregated structure optimize impedance matching, provide excellent conductivity, and improve absorption-dominated electromagnetic shielding.

MXene-Carbon Nanotube Composites: Properties and Applications

Today, MXenes and their composites have shown attractive capabilities in numerous fields of electronics, co-catalysis/photocatalysis, sensing/imaging, batteries/supercapacitors, electromagnetic interference (EMI) shielding, tissue engineering/regenerative medicine, drug delivery, cancer theranostics, and soft robotics. In this aspect, MXene-carbon nanotube (CNT) composites have been widely constructed with improved environmental stability, excellent electrical conductivity, and robust mechanical properties, providing great opportunities for designing modern and intelligent systems with diagnostic/therapeutic, electronic, and environmental applications. MXenes with unique architectures, large specific surface areas, ease of functionalization, and high electrical conductivity have been employed for hybridization with CNTs with superb heat conductivity, electrical conductivity, and fascinating mechanical features. However, most of the studies have centered around their electronic, EMI shielding, catalytic, and sensing applications; thus, the need for research on biomedical and diagnostic/therapeutic applications of these materials ought to be given more attention. The photothermal conversion efficiency, selectivity/sensitivity, environmental stability/recyclability, biocompatibility/toxicity, long-term biosafety, stimuli-responsiveness features, and clinical translation studies are among the most crucial research aspects that still need to be comprehensively investigated. Although limited explorations have focused on MXene-CNT composites, future studies should be planned on the optimization of reaction/synthesis conditions, surface functionalization, and toxicological evaluations. Herein, most recent advancements pertaining to the applications of MXene-CNT composites in sensing, catalysis, supercapacitors/batteries, EMI shielding, water treatment/pollutants removal are highlighted, focusing on current trends, challenges, and future outlooks.

High-strength, low infrared-emission nonmetallic films for highly efficient Joule/solar heating, electromagnetic interference shielding and thermal camouflage

High-strength nonmetallic materials with low infrared (IR) emission are rare in nature, yet highly anticipated especially in military and aerospace fields for thermal camouflage, IR stealth, energy-saving heating. Here, we reported a high-strength (422 MPa) nonmetallic film with very low IR emissivity (12%), realized by constructing alternating multilayered structures consisting of successive MXene functionalized outer layers and continuous GO reinforced inner layers. This nonmetallic film is capable of competing with typical stainless steel (415 MPa, 15.5%), and exhibits remarkable thermal camouflage performance (ΔT = 335 °C), ultrahigh Joule heating capability (350 °C at 2 V), excellent solar-to-thermal conversion efficiency (70.2%), and ultrahigh specific electromagnetic interference shielding effectiveness (83 429 dB cm^-1). Impressively, these functionalities can be maintained well after prolonged outdoor aging, and even after undergoing harsh application conditions including strong acid/alkali and boiling water immersion, and cryogenic (-196 °C) temperature.

Significantly Enhanced Electromagnetic Interference Shielding Performances of Epoxy Nanocomposites with Long-Range Aligned Lamellar Structures

High‑efficiency electromagnetic interference (EMI) shielding materials are of great importance for electronic equipment reliability, information security and human health. In this work, bidirectional aligned Ti₃C₂T_x@Fe₃O₄/CNF aerogels (BTFCA) were firstly assembled by bidirectional freezing and freeze-drying technique, and the BTFCA/epoxy nanocomposites with long-range aligned lamellar structures were then prepared by vacuum-assisted impregnation of epoxy resins. Benefitting from the successful construction of bidirectional aligned three-dimensional conductive networks and electromagnetic synergistic effect, when the mass fraction of Ti₃C₂T_x and Fe₃O₄ are 2.96 and 1.48 wt%, BTFCA/epoxy nanocomposites show outstanding EMI shielding effectiveness of 79 dB, about 10 times of that of blended Ti₃C₂T_x@Fe₃O₄/epoxy (8 dB) nanocomposites with the same loadings of Ti₃C₂T_x and Fe₃O₄. Meantime, the corresponding BTFCA/epoxy nanocomposites also present excellent thermal stability (T_{heat-resistance index} of 198.7 °C) and mechanical properties (storage modulus of 9902.1 MPa, Young's modulus of 4.51 GPa and hardness of 0.34 GPa). Our fabricated BTFCA/epoxy nanocomposites would greatly expand the applications of MXene and epoxy resins in the fields of information security, aerospace and weapon manufacturing, etc.

Ultrahigh Energy and Power Densities of d-MXene-Based Symmetric Supercapacitors

Here, rational design electrodes are fabricated by mixing MXene with an aqueous solution of chloroauric acid (HAuCl₄). In order to prevent MXene from self-restacking, the groups of -OH on the surface of Ti₃C₂T_x nanosheets underwent a one-step simultaneous self-reduction from AuCl₄-, generating spaces for rapid ion transit. Additionally, by using this procedure, MXene's surface oxidation can be decreased while preserving its physio-chemical properties. The interlayered MX/Au NPs that have been obtained are combined into a conducting network structure that offers more active electrochemical sites and improved mass transfer at the electrode-electrolyte interface, both of which promote quick electron transfer during electrochemical reactions and excellent structural durability. The Ti₃C₂T_x-AuNPs film thus demonstrated a rate performance that was preferable to that of pure Ti₃C₂T_x film. According to the results of the characterization, the AuNPs effectively adorn the MXene nanosheets. Due to the renowned pseudocapacitance charge storage mechanism, MXene-based electrode materials also work well as supercapacitors in sulfuric acid, which is why MXene AuNPs electrodes have been tested in 3 M and 1 M H₂SO₄. The symmetric supercapacitors made of MXene and AuNPs have shown exceptional specific capacitance of 696.67 Fg^-1 at 5 mVs^-1 in 3 M H₂SO₄ electrolyte, and they can sustain 90% of their original capacitance for 5000 cycles. The highest energy and power density of this device, which operates within a 1.2 V potential window, are 138.4 Wh kg^-1 and 2076 W kg^-1, respectively. These findings offer a productive method for creating high-performance metal oxide-based symmetric capacitors and a straightforward, workable approach for improving MXene-based electrode designs, which can be applied to other electro-chemical systems that are ion transport-restricted, such as metal ion batteries and catalysis.

Recent progress in use of MXene in perovskite solar cells: for interfacial modification, work-function tuning and additive engineering

The use of perovskites in photovoltaic and related industries has achieved tremendous success over the last decade. However, there are still obstacles to overcome in terms of boosting their performance and resolving stability issues for future commercialization. The introduction of a new 2D material of halide perovskites is now the key advancement in boosting the solar energy conversion efficiency. The implication of a new 2D material (MXene) in perovskite solar cells has been initiated since its first report in 2018, showing excellent transparency, electrical conductivity, carrier mobility, superior mechanical strength, and tunable work function. Based on distinctive features at the hetero-interface, halide perovskite and MXene heterostructures (HPs/Mx) have recently exhibited exceptional improvements in both the performance and stability of perovskite solar cells. Furthermore, the wide families of HPs and MXene materials allow playing with the composition and functionalities of HP/Mx interfaces by applying rational designing and alterations. In this review a comprehensive study of implementing MXenes in perovskite solar cells is presented. First, the implementation of MXenes in perovskites as an additive, and then in charge extraction layers (HTL/ETL), is described in detail. It is worth noting that still only Ti₃C₂T_x, Nb₂CT_x,V₂CT_x MXene is being incorporated into perovskite photovoltaics. Finally, the present obstacles in the use of MXenes in PSCS are discussed, along with the future research potential. This review is expected to provide a complete and in-depth description of the current state of research and to open up new opportunities for the study of other MXenes in PSCs.

Multifunctional MXene/Aramid Nanofiber Composite Films for Efficient Electromagnetic Interference Shielding and Repeatable Early Fire Detection

Rapid development of highly integrated electronic and telecommunication devices has led to urgent demands for electromagnetic interference (EMI) shielding materials that incorporate flame retardancy, and more desirably the early fire detection ability, due to the potential fire hazards caused by heat propagation and thermal failure of the devices during operation. Here, multifunctional flexible films having the main dual functions of high EMI shielding performance and repeatable fire detection ability are fabricated by vacuum filtration of the mixture of MXene and aramid nanofiber (ANF) suspensions. ANFs serve to reinforce MXene films via the formation of hydrogen bonding between the carbonyl groups of ANFs and the hydroxyl groups of MXene. When the ANF content is 20 wt %, the tensile strength of the film is increased from 24.6 MPa for a pure MXene film to 79.5 MPa, and such a composite film (9 μm thickness) exhibits a high EMI shielding effectiveness (SE) value of ∼40 dB and a specific SE (SSE) value of 4361.1 dB/mm. Upon fire exposure, the composite films can trigger the fire detection system within 10 s owing to the thermoelectric property of MXene. The self-extinguishing feature of ANFs ensures the structural integrity of the films during burning, thus allowing for continuous alarm signals. Moreover, the films also exhibit excellent Joule heating and photothermal conversion performances with rapid response and sufficient heating reliability.

A flexible, robust and multifunctional montmorillonite/aramid nanofibers@MXene electromagnetic shielding nanocomposite with an alternating structure for enhanced Joule heating and fire-resistant protective performance

With the rapidly increasing development of portable devices and flexible electronic devices, multifunctional composites with excellent mechanical strength, great electromagnetic interference shielding, great Joule heating performance and strong fire-resistant protective performance are noticeably required. Herein, inspired by the sandwich structure, we have designed a montmorillonite/aramid nanofibers@MXene (MMT/ANFs@MXene) nanocomposite with an alternating multilayered structure via a simple AVF process. In this nanocomposite, the ANFs/MMT (AT) layer acts as a mechanically reinforced and insulation protection layer, while the MXene layer maintains a complete conductive network. The superior alternating multilayered structure endows the nanocomposite with outstanding mechanical properties (154.66 MPa, 14.22%) and excellent EMI shielding effectiveness values (58.4 dB). In addition, the fire-resistant protective performance of the nanocomposite improves its safety and reliability, especially, the EMI shielding effectiveness is maintained at ∼34 dB after burning for 30 s. Besides, the MMT/ANFs@MXene nanocomposite shows excellent Joule heating performance with a fast thermal response, low driving voltage and long-time temperature stability, which could reach 110.2 °C at only 3 V applied voltage within 10 s. As a result, this work presents a novel strategy for constructing multifunctional composites with outstanding overall performance, which will broaden application areas and prospects in thermal management and EMI shielding in wearable products.

Rheology-Guided Assembly of a Highly Aligned MXene/Cellulose Nanofiber Composite Film for High-Performance Electromagnetic Interference Shielding and Infrared Stealth

Delicately aligned structures of two-dimensional (2D) MXene nanosheets have demonstrated positive effects on applications, especially in electromagnetic interference (EMI) shielding and infrared (IR) stealth. However, precise regulation of structural assembly by theory-guided solution processing is still a great challenge. Herein, one-dimensional (1D) cellulose nanofibers (CNFs) with a high aspect ratio are applied as a reinforcing agent and a rheological modifier for MXene/CNF colloids to fabricate aligned MXene-based materials for EMI shielding and IR stealth. Notably, a systematical rheological study of the MXene/CNF colloids is proposed to determine the optimal solution-processing conditions for finely oriented component arrangement requirements and provides in-depth information on the interactions between the components. The delicately regulated orientation structure assembled by shear inducement is convincingly demonstrated through micro-CT and wide-angle X-ray diffraction/small-angle X-ray scattering (WAXD/SAXS), which endows the MXene/CNF film with a significantly enhanced electrical conductivity of 46 685 S m^-1, a tensile strength of 281.7 MPa, and Young's modulus of 14.8 GPa. Furthermore, the highly aligned structure of the ultrathin film possesses a great enhancement in EMI shielding effectiveness (50.2 dB) and IR stealth (0.562 emissivity). These findings provide a fruitful understanding of the optimized fabrication in solution processing of high-performance MXene-based functional composite films and open up a great opportunity for the development of multifunctional stealth materials.

MXene based nanocomposite films

Since the first report in 2011, two-dimensional transition metal carbide/nitride MXenes have aroused widespread attention owing to the particular structure and physiochemical properties. In the last few years, MXene-based nanocomposite films have been widely investigated, showing promising applications in many fields. However, poor mechanical properties and thermal/electrical conductivities of MXene-based nanocomposite films still limited their practical applications. Herein, we summarize the fabrication approach of MXene-based nanocomposite films and discuss the mechanical properties and other applications, including electromagnetic interference shielding, thermal conductivity, and supercapacitors. Then, several vital factors for fabricating high performance MXene based nanocomposite films have been refined. To further fabricate high performance MXene-based nanocomposite films, some effective sequential bridging strategies are also discussed. Lastly, a conclusion of the challenges and opportunities of MXene-based nanocomposite films is provided to facilitate their development and application for various purposes in the future of scientific research.

Bridging Sheet Size Controls Densification of MXene Films for Robust Electromagnetic Interference Shielding

Numerous voids among the incompact layer-structure of MXene films result in their low ambient stability and poor innate conductivity for electromagnetic interference (EMI) shielding. Herein, we report a bridging-sheet-size-controlled densification process of MXene films by applying graphene oxide (GO) as a bridging agent. Specifically, the sheet size of GO is tailored to quantify a negative correlation of sheet size with densification for directing the preparation of most compact MXene-GO films. Benefiting from the shortest electron-transport-distance in the most compact structure, the conductivity of the MXene-GO film achieves 1.7 times (∼1.6 × 10⁵ S/m) that of MXene film. The EMI shielding performance (5.2 × 10⁶ dB/m) reaches the record-value among reported MXene films at 10 μm-scale thickness. Moreover, the compact structure boosts the ambient stability of MXene-GO films where the conductivity and EMI shielding performance remain 88.7% and 90.0% after 15 days, respectively. The findings rationale the structure-activity relationship of compact MXene films for flexible electronics.

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Densification of MXene films is controlled by a bridging-sheet-size strategy

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Shortening electron-transport-distance in compact structure improves conductivity

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Control of densification delivers high EMI shielding performance and air stability

Ultrastrong and Hydrophobic Sandwich-Structured MXene-Based Composite Films for High-Efficiency Electromagnetic Interference Shielding

Electromagnetic interference (EMI) shielding materials are highly necessary to solve the problem of electromagnetic radiation. Transition-metal carbide/nitride (MXene) materials offer great potential for the construction of high-performance EMI shields because of their high electrical conductivity and versatile surface chemistry. However, MXene generally suffers from poor mechanical and oxidation-resistant properties, which hinders its practical applications. Herein, flexible, strong, and hydrophobic sandwich-structured composite films (H-S-MXene), consisting of a conductive MXene layer and supporting aramid nanofiber layer, were fabricated using step-by-step vacuum-assisted filtration and dip coating. Given the unique sandwich structure, hydrogen bonding interactions, and covalent cross-linking of the MXene sheets, the H-S-MXene composite films demonstrated simultaneously excellent EMI shielding and mechanical properties. The EMI shielding effectiveness of the H-S-MXene composite film with 20 wt % MXene content reached 46.1 dB at thickness of 23.2 ± 0.5 μm, and the tensile strength of the film reached 302.1 MPa, which outperformed other reported EMI shielding materials. The excellent mechanical flexibility and hydrophobicity of the H-S-MXene composite films ensured a stable EMI shielding performance, which could withstand cycled bending, torsion, and exposure to aqueous environments. These impressive features made the H-S-MXene composite films promising candidates for electronic devices and aerospace. This study provides important guidance for the rational design of stable MXene-based composites with advanced properties.

Bioinspired MXene-Based User-Interactive Electronic Skin for Digital and Visual Dual-Channel Sensing

User-interactive electronic skin (e-skin) that could convert mechanical stimuli into distinguishable outputs displays tremendous potential for wearable devices and health care applications. However, the existing devices have the disadvantages such as complex integration procedure and lack of the intuitive signal display function. Here, we present a bioinspired user-interactive e-skin, which is simple in structure and can synchronously achieve digital electrical response and optical visualization upon external mechanical stimulus. The e-skin comprises a conductive layer with a carbon nanotubes/cellulose nanofibers/MXene nanohybrid network featuring remarkable electromechanical behaviors, and a stretchable elastomer layer, which is composed of silicone rubber and thermochromic pigments. Furthermore, the conductive nanohybrid network with outstanding Joule heating performance can generate controllable thermal energy under voltage input and then achieve the dynamic coloration of silicone-based elastomer. Especially, such an innovative fusion strategy of digital data and visual images enables the e-skin to monitor human activities with evermore intuition and accuracy. The simple design philosophy and reliable operation of the demonstrated e-skin are expected to provide an ideal platform for next-generation flexible electronics.

Gelation-Assisted Assembly of Large-Area, Highly Aligned, and Environmentally Stable MXene Films with an Excellent Trade-Off between Mechanical and Electrical Properties

Layered MXene films have shown enormous potential for wide applications due to their high electrical conductivity and unique laminated microstructure. However, the intrinsic susceptibility to oxidation and the mechanical fragility of MXene films are the two major bottlenecks that prevent their widespread industrial applications. Here, a facile yet efficient assembly strategy is proposed to address these issues by increasing the alignment and compactness of MXene layers as well as strengthening the interlayer interactions. This method involves the gelation of MXene flakes with a multifunctional inorganic "mortar" polymer (ammonium polyphosphate, APP) followed by quasi-solid-state assembly enabled by a mechanical rolling process, by which the 3D gel network is transformed into 2D freestanding MXene films with unprecedented flake alignment and compactness. Besides, due to the multiple molecular-level interactions (hydrogen bonding, coordination bonding, and electrostatic force) between APP and MXene flakes, the resultant MXene-APP film (MAF) displays high mechanical strength (286.4 ± 20.3 MPa) and excellent electrical conductivity (8012.4 ± 325.6 S cm^-1 ), along with remarkable environmental stability. As an application demonstration, MAF exhibits outstanding electromagnetic interference shielding effectiveness with long-term durability, highlighting the great potential of this gelation-assisted assembly strategy in fabricating large-area, high-performance MXene films for diverse real-world applications.

Bioinspired, High-Strength, and Flexible MXene/Aramid Fiber for Electromagnetic Interference Shielding Papers with Joule Heating Performance

High-strength, flexible, and multifunctional characteristics are highly desirable for electromagnetic interference (EMI) shielding materials in the field of electric devices. In this work, inspired by natural nacre, we fabricated large-scale, layered MXene/amarid nanofiber (ANF) nanocomposite papers by blade-coating process plus sol-gel conversion step. The as-synthesized papers possess excellent mechanical performance, that is, exceptional tensile strength (198.80 ± 5.35 MPa), large strain (15.30 ± 1.01%), and good flexibility (folded into various models without fracture), which are ascribed to synergetic interactions of the interconnected three-dimensional network frame and hydrogen bonds between MXene and ANF. More importantly, the papers with extensive continuous conductive paths formed by MXene nanosheets present a high EMI shielding effectiveness of 13188.2 dB cm² g^-1 in the frequency range of 8.2-12.4 GHz. More interestingly, the papers show excellent Joule heating performance with a fast thermal response (<10 s) and a low driving voltage (≤4 V). As such, the large-scale MXene/ANF papers are considered as promising alternatives in a wide range of applications in electromagnetic shielding and thermal management.