Ni Flower/MXene-Melamine Foam Derived 3D Magnetic/Conductive Networks for Ultra-Efficient Microwave Absorption and Infrared Stealth

Challenges and future prospects of the 2D material-based composites for microwave absorption

The widespread use of electronic devices inevitably brings about the problem of electromagnetic pollution. As a result, it is important and urgent to develop efficient absorbing materials to alleviate increasing pollution issues. Recently, two-dimensional (2D) material-based microwave absorbers have attracted wide attention in microwave absorption due to their unique lamellar structure, large specific surface area, low density, good thermal and chemical stability. Through various modulation strategies such as structure configuration, pore/defect engineering, heteroatom doping and coupling of functional materials, 2D materials or 2D material-based composites exhibit excellent microwave absorption performance. In this review, the absorption mechanism is firstly introduced and then the latest progress in 2D material-based microwave absorbers is reviewed in depth. The challenges and future prospects for graphene, h-BN, and MXene-based microwave absorbers are discussed in the final part. This timely review aims to provide guidance or stimulation to develop advanced multifunctional 2D material-based microwave absorbers in this rapidly blossoming field.

Advanced Multiphysics Camouflage Based on Low-Emissivity Meta-surface Coupled with Wave-Absorbing and Thermal-Insulating Aerogel

The irreconcilable camouflage mechanisms of radar and infrared spectroscopy present substantial challenges to integrating multi-physics field cloaking technology. Although aerogels possess both microwave dissipation and thermal insulation, higher infrared emissivity restrict further amelioration in compatible stealth field. Herein, we propose a bilayer configuration comprised of aramid nanofiber (ANF) aerogel and infrared shielding meta-surface (ISM). The top ISM with low-pass filtering capabilities is engineered to regulate emissivity while remaining transparent to microwaves. While the bottom quaternary ANF aerogels with radar dissipation and thermal insulation are synthesized by multi-scale design strategy and heterogeneous surface engineering. Through theoretical and experimental optimization, the assembled compatible stealth composite achieves a near-perfect absorption in X-band, while the synergy of low emissivity and thermal insulation facilitates concealment in infrared windows. Specifically, the minimum reflection loss (RL) reaches -32.44 dB, effective absorption bandwidth (EAB) expands to 3.69 GHz (8.71-12.40 GHz), and the integration of effective reflection loss value (ΔH) increases to 9.92 dB GHz mm-1. Additionally, low thermal conductivity (0.0288 W (m K)-1) and average infrared emissivity (0.23 in 3-5 µm and 0.25 in 8-14 µm) can reduce infrared radiation energy by 68.1%. This research provides a new thought for the design of multispectral camouflage and demonstrates enormous potential in stealth technologies.

Enhancing strategies of MOFs-derived materials for microwave absorption: review and perspective

Microwave absorption materials (MAMs) gradually exhibit crucial applications in reducing electromagnetic wave (EMW) pollution, avoiding EMW information leakage, and solving radar stealth. Metal-organic frameworks (MOFs)-derived materials are flourishing in the domain of EMW absorption attributed to their especial structures, heteroatom doping and controllable components. Herein, various strategies to enhance the EMW absorption ability of MOFs-derived materials are outlined, covering structural design and compositional regulation. Additionally, the applications of MOFs-derived composites in EMW absorption domains are introduced in detail, with emphasis on recent progress in MOFs-derived composites materials like foams, films and aerogels. Finally, existent opportunities, challenges and future orientations of MOFs-derived MAMs are proposed.

Switchable Multi-Spectral Electromagnetic Defense in the Ultraviolet, Visible, Infrared, Gigahertz, and Terahertz Bands Using a Magnetically-Controllable Soft Actuator

Traditional passive single-spectrum electromagnetic defense materials are inadequate to defend against complex multispectral electromagnetic threats. Herein, a bilayer heterofilm (BLH film)-based magnetically controllable soft actuator (MCSA), comprising a defense unit and a drive unit, is constructed. The defense unit offers multispectral electromagnetic protection, while the drive unit enables active defense via magnetic actuation. The synergy allows the MCSA to provide intelligent, switchable electromagnetic defense from ultraviolet to terahertz spectra. The BLH film exhibits the lowest infrared emissivity of 0.04 at 14 μm and an average of 0.16 at 8-14 μm, outperforming comparable composites while integrating radiation energy management for enhanced overall protection. It also demonstrates complete blocking of ultraviolet and visible light (320-780 nm), demonstrating zero transmission. Furthermore, the MCSA can be modulated between open and closed states by applying a magnetic field, facilitating a seamless transition between full-band transparency and full-band defense modes. To expand electromagnetic defense applications, a multilayer gradient impedance matching (M-BLH-300) absorber based on the BLH film is fabricated for stealth in microwave bands, achieving a strong reflection loss of -26.7 dB with an effective absorption bandwidth of 4.85 GHz. Notably, the M-BLH-300 absorber retains excellent performance when extended to the terahertz frequency range and further demonstrates its suitability for multispectrum (from ultraviolet to terahertz) defense. In short, this innovative design concept of combining multispectral defense with intelligent switches will guide the development of next-generation advanced electromagnetic defense systems.

High-Temperature Stealth Across Multi-Infrared and Microwave Bands with Efficient Radiative Thermal Management

High-temperature stealth is vital for enhancing the concealment, survivability, and longevity of critical assets. However, achieving stealth across multiple infrared bands-particularly in the short-wave infrared (SWIR) band-along with microwave stealth and efficient thermal management at high temperatures, remains a significant challenge. Here, we propose a strategy that integrates an IR-selective emitter (Mo/Si multilayer films) and a microwave metasurface (TiB2-Al2O3-TiB2) to enable multi-infrared band stealth, encompassing mid-wave infrared (MWIR), long-wave infrared (LWIR), and SWIR bands, and microwave (X-band) stealth at 700 °C, with simultaneous radiative cooling in non-atmospheric window (5-8 μm). At 700 °C, the device exhibits low emissivity of 0.38/0.44/0.60 in the MWIR/LWIR/SWIR bands, reflection loss below - 3 dB in the X-band (9.6-12 GHz), and high emissivity of 0.82 in 5-8 μm range-corresponding to a cooling power of 9.57 kW m-2. Moreover, under an input power of 17.3 kW m-2-equivalent to the aerodynamic heating at Mach 2.2-the device demonstrates a temperature reduction of 72.4 °C compared to a conventional low-emissivity molybdenum surface at high temperatures. This work provides comprehensive guidance on high-temperature stealth design, with far-reaching implications for multispectral information processing and thermal management in extreme high-temperature environments.

Dimensional Design of Cellulose Aerogels with Schottky Contact for Efficient Microwave Absorption

Cellulose aerogels, as a novel class of carbon-based materials, exhibit immense potential in the field of microwave absorption (MWA) due to their biocompatibility, low density, unique porous structure, and tunable architecture. However, the development of multi-dimensional components with specialized heterogeneous structures, which are based on cellulose aerogels, remains a significant challenge. This 0D/1D/3D structural configuration facilitates tunable electromagnetic properties and favorable impedance matching. The Schottky contact at the ZnO/Ni interface, in particular, induces a strong interfacial polarization, and the multi-dimensional structural design results in multiple heterointerfaces. Density functional theory (DFT) calculations reveal that the unique Schottky contact induces a Schottky barrier that causes band bending, facilitating the directed migration of electrons at the interface and the formation of an internal electric field, thus significantly accelerating the multipolar relaxation process. As anticipated, the CCMC/ZnO@Ni aerogel exhibits a minimum reflection loss (RLmin) value of -64.0 dB at 13.9 GHz at a thickness of 2.0 mm, and its effective absorption bandwidth (EAB) reaches 4.9 GHz. This work gives valuable guidance and inspiration for the design of multi-dimensional materials that are composed of dimensional gradient structures, which holds great application potential for electromagnetic wave (EMW) attenuation.

Ultra-Bandwidth Microwave Absorption and Low Angle Sensitivity in Dual-Network Aerogels with Dual-Scale Pores

Aerogels with porous structures offer an attractive approach to modulating electromagnetic parameters and enhancing electromagnetic wave (EMW) absorption performance. However, conventional aerogels are limited by their single-scale pore size and fixed orientation, which constrain their EMW absorption capabilities. This study introduces aerogels with dual-scale pores and dual-network structure constructed via constant-temperature freezing and secondary-infusion freezing method. Multiscale aerogels with both micrometer- and submillimeter-scale pores are constructed when the Ti3C2Tx MXene and thermoplastic polyurethane solution is frozen and dried at a specific temperature, leading to an ultra-wide effective absorption bandwidth (EAB) reaching 10.41 GHz in the vertical direction. Furthermore, to address the poor EMW absorption in the parallel direction, a secondary infusion freezing method is applied to form an aerogel with a dual-network structure, which forms reflective interfaces perpendicular to the incident EMW in various directions. This adjustment enhances the EAB in the parallel direction from 1.58 to 5.93 GHz, marking a 275.32% enhancement, while the EAB in the vertical incident direction reaches 8.08 GHz. This design strategy overcomes the limitations of structural scale and arrangement direction, enriching the attenuation mechanisms of the absorber, while effectively reducing sensitivity to the direction of incoming EMW, offering new insights for designing efficient EMW absorbers.

Research Progress on High-Temperature-Resistant Electromagnetic Wave Absorbers Based on Ceramic Materials: A Review

Ceramic materials have the merits of an adjustable dielectric constant, high strength, high temperature resistance, and oxidation resistance, and are thus being used as the protection matrix for carbon series, metal oxides, and other wave-absorbing materials at high temperatures. Here, progress on high-temperature-resistant wave-absorbing ceramic materials is introduced through the aspects of their composition and structure. In addition, metamaterials used for such purposes, which are mainly produced through 3D printing, are also highlighted. The pros and cons of high-temperature-resistant electromagnetic wave absorbers based on ceramic materials are systematically analyzed, and possible development directions are proposed. This work may assist in the design and manufacture of a new generation of radars, ships, and aircraft.

Boosting Thermal Generation in Cation-Exchanged Transparent MXene Composite Films with Hierarchical Wrinkled Structure

Efficient thermal generation from solar/electric energy in transparent films remains challenging due to the limited toolbox of high-performance thermal generation materials and methods for microstructure engineering. Here, we proposed a two-step strategy to introduce hierarchical wrinkles to the MXene composite films with high transparency, leading to upgraded photo/electrothermal conversion efficiency. Specifically, the thin film contains protic acid-treated MXene layers assembled with Ag nanowires (H-MXene/Ag NWs). The hydrogen-bonding interaction between MXene and Ag NWs in a MXene-based thin film forms the first-level wrinkles, while the cation-exchanged method is then developed to enhance conductivity and form the second-level wrinkles. The H-MXene/Ag NWs composite transparent film is observed to achieve a surface temperature rise of 40 °C relative to an ambient environment under 1.0 sun illumination and 70 °C at 1 V voltage in the dark, along with notable photo/electrothermal production stability under ambient conditions. Moreover, experimental and theoretical results show that the improved heat production capability is mainly due to low reflectivity led by the wrinkles and high conductivity led by the cation-exchange process. On the basis of the excellent photothermal generation capability of the H-MXene/Ag NWs composite transparent film, we applied it to biomimetic soft robots and flexible wearable devices. This work paves a novel strategy for the generation of thermal production devices that achieve high-performance photo/electroconversion.

Advancements in 2D Titanium Carbide (MXene) for Electromagnetic Wave Absorption: Mechanisms, Methods, Enhancements, and Applications

With the advent of the 5G era, there has been a marked increase in research interest concerning electromagnetic wave-absorbing materials. A critical challenge remains in improving the wave-absorbing properties of these materials while satisfying diverse application demands. MXenes, identified as prominent "emerging" 2D materials for wave absorption, offer unique advantages that are expected to drive advancements and innovations in this field. This review emphasizes the synthesis benefits provided by the unique structural characteristics of MXenes and the performance enhancements achieved through their combination with other absorbing materials. Material requirements, synthesis approaches, and conceptual frameworks are integrated to underscore these advantages. The study provides a thorough analysis of MXene-absorbing composites, going beyond basic classification to address preparation and modification processes affecting the absorption properties of MXenes and their composites. Attention is directed to synthesis techniques, structural design principles, and their influence on composite performance. Additionally, the potential applications of MXenes in electromagnetic wave absorbing devices are summarized. The review concludes by addressing the challenges currently confronting MXene materials and outlining expected developmental trends, aiming to offer guidance for subsequent research in this domain.

Carbon nanofiber coated ionic crystal architecture withconfinement effect for high-performance microwave absorption along with high-efficiency water harvesting from air

Water is considered an effective microwave absorber due to its high transmittance and frequency-dispersive dielectric constant, yet it is challenging to form it into a stable state as an absorber. Herein, we developed a water-containing microwave absorber using chemical vapor deposition (CVD), namely, the bifunctional carbon/NaCl multi-interfaces hybrid with excellent water harvesting and microwave absorption performance. Carbon/NaCl exhibits remarkable water harvesting abilities from air, exceeding 210 % of its weight in 12 h. The development of the hydrophilic/hydrophobic heterojunction interface is responsible for this outstanding performance. Additionally, the interfacial polarization provided by carbon/NaCl, along with the dipole polarization induced by the internally captured water and defects, enhances its microwave absorption. The carbon/NaCl hybrid achieved a minimum reflection loss (RLmin) of -69.62 dB at 17.1 GHz with a thickness of 2.13 mm, and a maximum effective absorption bandwidth (EABmax) of 6.74 GHz at a thickness of 2.5 mm. Compared with raw NaCl (RLmin of -24.5 dB, EABmax of 3.88 GHz), the RLmin and EABmax values of the absorber increased by approximately 2.85 and 1.74 times. These results highlight the potential for bifunctional carbon/NaCl hybrid in applications within extreme environments, presenting a promising avenue for further research and development.

Hierarchically Porous Polypyrrole Foams Contained Ordered Polypyrrole Nanowire Arrays for Multifunctional Electromagnetic Interference Shielding and Dynamic Infrared Stealth

As modern communication and detection technologies advance at a swift pace, multifunctional electromagnetic interference (EMI) shielding materials with active/positive infrared stealth, hydrophobicity, and electric-thermal conversion ability have received extensive attention. Meeting the aforesaid requirements simultaneously remains a huge challenge. In this research, the melamine foam (MF)/polypyrrole (PPy) nanowire arrays (MF@PPy) were fabricated via one-step electrochemical polymerization. The hierarchical MF@PPy foam was composed of three-dimensional PPy micro-skeleton and ordered PPy nanowire arrays. Due to the upwardly grown PPy nanowire arrays, the MF@PPy foam possessed good hydrophobicity ability with a water contact angle of 142.00° and outstanding stability under various harsh environments. Meanwhile, the MF@PPy foam showed excellent thermal insulation property on account of the low thermal conductivity and elongated ligament characteristic of PPy nanowire arrays. Furthermore, taking advantage of the high conductivity (128.2 S m-1), the MF@PPy foam exhibited rapid Joule heating under 3 V, resulting in dynamic infrared stealth and thermal camouflage effects. More importantly, the MF@PPy foam exhibited remarkable EMI shielding effectiveness values of 55.77 dB and 19,928.57 dB cm2 g-1. Strong EMI shielding was put down to the hierarchically porous PPy structure, which offered outstanding impedance matching, conduction loss, and multiple attenuations. This innovative approach provides significant insights to the development of advanced multifunctional EMI shielding foams by constructing PPy nanowire arrays, showing great applications in both military and civilian fields.

Multifunctional microwave absorption materials: construction strategies and functional applications

The widespread adoption of wireless communication technology, especially with the introduction of artificial intelligence and the Internet of Things, has greatly improved our quality of life. However, this progress has led to increased electromagnetic (EM) interference and pollution issues. The development of advanced microwave absorbing materials (MAMs) is one of the most feasible solutions to solve these problems, and has therefore received widespread attention. However, MAMs still face many limitations in practical applications and are not yet widely used. This paper presents a comprehensive review of the current status and future prospects of MAMs, and identifies the various challenges from practical application scenarios. Furthermore, strategies and principles for the construction of multifunctional MAMs are discussed in order to address the possible problems that are faced. This article also presents the potential applications of MAMs in other fields including environmental science, energy conversion, and medicine. Finally, an analysis of the potential outcomes and future challenges of multifunctional MAMs are presented.

A Direct Current Self-Sustained Moisture-Electric Generator with 1D/2D Hierarchical Nanostructure for Continuous Operation of Off-Grid Electronics

Ubiquitous moisture is a colossal reservoir of clean energy, and the emergence of moisture-electric generators (MEGs) is expected to provide direct power support for off-grid electronic devices anytime and anywhere. However, most MEGs rely on auxiliary energy storage devices and rectifier circuits to drive small electronic devices, which hinder scalability and widespread deployment, and the development of direct current (DC) MEGs with high power output that can directly drive off-grid electronic devices is highly promising but challenging. Herein, a self-sustained moisture-electric generator (SMEG) with a hierarchical nanostructure based on one-dimensional (1D) negatively charged nanofibers and two-dimensional (2D) conductive nanosheets was demonstrated to generate continuous DC electricity from atmospheric humidity. Sulfation of bacterial cellulose nanofibers lowers the surface potential and increases the surface charge energy, and reduced graphene oxide (rGO) provides a conduction pathway for electrons. The hierarchical nanostructures constructed by the combination of 1D nanofibers and 2D nanosheets endow the SMEG with self-sustained moisture gradients and structural anisotropy, which force the generation of a pseudocurrent. This combination also constructs microcapacitors that further enhance the moisture-electric power output. The SMEG can generate a continuous voltage in excess of 0.54 V for over 2160 h, with a power density of about 822 μW cm-3, demonstrating excellent operational durability. This research provides a feasible solution for the development of sustainable, versatile, and efficient power supplies for off-grid self-powered devices.

Graphene-Wrapped Magnetic Multichamber Ti3C2Tx Spheres for Stable Broadband Microwave Absorption

Two-dimensional transition metal carbides/nitrides (MXenes) have aroused widespread interest in the field of microwave absorption because of their unique layered structures. However, the inherent aggregation, poor impedance matching, and low chemical stability of MXenes inevitably obstruct their practical applications. Herein, a multichamber Fe3O4/Ti3C2Tx@reduced graphene oxide (FT@RGO) hierarchical structure was constructed through self-assembly and sacrificial template strategies where the Ti3C2Tx nanosheets were assembled into hollow microspheres that were decorated with Fe3O4 nanospheres and wrapped by RGO nanosheets. The massive heterointerfaces and interior cavities favor enhanced microwave absorption performance via interfacial polarization, multiple scattering/reflections, and dielectric-magnetic synergistic effects. Consequently, the synthesized ultralight FT@RGO foam (0.009 g/cm3) presents superior microwave absorption ability with the minimum reflection loss of -50.5 dB at the matching thickness of 2.5 mm and effective absorption bandwidth of 8.0 GHz covering the frequency range of 10.0-18.0 GHz at the thickness of 2 mm. Furthermore, the encapsulation of hollow Ti3C2Tx spheres by RGO nanosheets avoids direct contact with external air, which considerably improves the stability of Ti3C2Tx and ensures the long-term application of FT@RGO foam in a conventional environment. This work provides a reference for the structural design of MXene-based materials as broadband and durable microwave absorbers.

MXene Based Flame Retardant and Electrically Conductive Polymer Coatings

Modern polymer coatings possess tremendous multifunctionalities and have attracted immense research interest in recent decades. However, with the expeditious development of technologies and industries, there is a vast demand for the flame retardancy and electrical conductivity of engineered polymer coatings. Traditional functional materials that render the polymer coatings with these properties require a sophisticated fabrication process, and their high mass gains can be a critical issue for weight-sensitive applications. In recent years, massive research has been conducted on a newly emerged two-dimensional (2D) nanosize material family, MXene. Due to the excellent electrical conductivity, flame retardancy, and lightweightness, investigations have been launched to synthesise MXene-based polymer coatings. Consequently, we performed a step-by-step review of MXene-involved polymer coatings, from solely attaching MXene to the substrate surface to the multilayered coating of modified MXene with other components. This review examines the performances of the fire safety enhancement and electrical conductivity as well as the feasibility of the manufacturing procedures of the as-prepared polymer composites. Additionally, the fabricated polymer coatings' dual property mechanisms are well-demonstrated. Finally, the prospect of MXene participating in polymer coatings to render flame retardancy and electrical conductivity is forecasted.

Multi-Scale MXene/Silver Nanowire Composite Foams with Double Conductive Networks for Multifunctional Integration

With the onset of the 5G era, wearable flexible electronic devices have developed rapidly and gradually entered the daily life of people. However, the vast majority of research focuses on the integration of functions and performance improvement, while ignoring electromagnetic hazards caused by devices. Herein, the 3D double conductive networks are constructed through a repetitive vacuum-assisted dip-coating technique to decorate the 2D MXene and 1D silver nanowires on the melamine foam. Benefiting from the unique porous structure and multi-scale interconnected frame, the resultant composite foam exhibited high electrical conductivity, low density, superb electromagnetic interference shielding (48.32 dB), and Joule heating performance (up to 90.8 °C under 0.8 V). Furthermore, a single-electrode triboelectric nanogenerator (TENG) with powerful energy harvesting capability is assembled by combining the composite foam with an ultra-thin Ecoflex film and a polyvinylidene fluoride film. Simultaneously, the foam-based TENG can also be considered a reliable wearable sensor for monitoring activity patterns in different parts of the human body. The versatility and scalable manufacturing of high-performance composite foams will provide new design ideas for the development of next-generation flexible wearable devices.

An Ultra-Wideband Frequency Selective Rasorber with Low Infrared Emissivity

The paper proposes an ultra-wideband frequency selective rasorber (FSR) with low infrared emissivity for the composite detection threat of both radars and infrared sensors. Firstly, the equivalent circuit (EC) method based on transmission line (TL) theory is utilized to analyze the absorption/transmission conditions. Then, based on the analysis above, sinusoidal microstrip lines with non-frequency-varying characteristics are adopted in the design, which significantly enhances the transmission bandwidth of FSR. The FSR demonstrates an absorption band ranging from 2.65 GHz to 8.80 GHz and a transmission band ranging from 9.15 GHz to 17.71 GHz. Furthermore, an infrared shielding layer (IRSL) exhibiting low emissivity in the infrared band and high transmittance in the microwave band is applied to the FSR. The simulation and experiment results verify that the IRSL-FSR demonstrates an ultra-wide transmission band ranging from 9.16 GHz to 17.94 GHz and an ultra-wide absorption band ranging from 2.66 GHz to 8.01 GHz. Additionally, it exhibits a low emissivity value (0.23) in 8-14 μm, providing a viable solution to the formidable challenge of radar-infrared bistealth for satellites and other communication-enabled flying platforms.

Coral-Inspired Terahertz-Infrared Bi-Stealth Electronic Skin

The development of electronic skin with dual stealth functionality is crucial for enabling devices to operate effectively in dynamic electromagnetic environments, thereby facilitating intelligent electromagnetic protection for autonomous perception. However, achieving compatibility between terahertz (THz) and infrared (IR) stealth technologies remains largely unexplored due to their inherent contradictions. Herein, inspired by natural corals, a novel coral-like multi-scale composite foam (CMSF) was proposed that ingeniously reconciles these contradictions. The design capitalizes on the conductive network and heat insulation properties of the foam skeleton, the loss effects and low infrared emission of metal particles, and the infrared transparency of magneto-optical materials. This approach leads to the realization of a THz-IR bi-stealth electronic skin concept. The CMSF exhibits a maximum reflection loss of 84.8 dB in the terahertz band, while its infrared stealth capability ensures environmental adaptability under varying temperatures. Furthermore, the electronic skin exhibits exceptional sensitivity and reliability as a wearable device for perceiving environmental changes. This advanced material, combining multispectral stealth with sensing capabilities, holds immense potential for applications ranging from camouflage technology to smart wearables.

Lightweight Dual-Functional Segregated Nanocomposite Foams for Integrated Infrared Stealth and Absorption-Dominant Electromagnetic Interference Shielding

Lightweight infrared stealth and absorption-dominant electromagnetic interference (EMI) shielding materials are highly desirable in areas of aerospace, weapons, military and wearable electronics. Herein, lightweight and high-efficiency dual-functional segregated nanocomposite foams with microcellular structures are developed for integrated infrared stealth and absorption-dominant EMI shielding via the efficient and scalable supercritical CO2 (SC-CO2) foaming combined with hydrogen bonding assembly and compression molding strategy. The obtained lightweight segregated nanocomposite foams exhibit superior infrared stealth performances benefitting from the synergistic effect of highly effective thermal insulation and low infrared emissivity, and outstanding absorption-dominant EMI shielding performances attributed to the synchronous construction of microcellular structures and segregated structures. Particularly, the segregated nanocomposite foams present a large radiation temperature reduction of 70.2 °C at the object temperature of 100 °C, and a significantly improved EM wave absorptivity/reflectivity (A/R) ratio of 2.15 at an ultralow Ti3C2Tx content of 1.7 vol%. Moreover, the segregated nanocomposite foams exhibit outstanding working reliability and stability upon dynamic compression cycles. The results demonstrate that the lightweight and high-efficiency dual-functional segregated nanocomposite foams have excellent potentials for infrared stealth and absorption-dominant EMI shielding applications in aerospace, weapons, military and wearable electronics.

Mixed-Dimensional Assembly Strategy to Construct Reduced Graphene Oxide/Carbon Foams Heterostructures for Microwave Absorption, Anti-Corrosion and Thermal Insulation

Considering the serious electromagnetic wave (EMW) pollution problems and complex application condition, there is a pressing need to amalgamate multiple functionalities within a single substance. However, the effective integration of diverse functions into designed EMW absorption materials still faces the huge challenges. Herein, reduced graphene oxide/carbon foams (RGO/CFs) with two-dimensional/three-dimensional (2D/3D) van der Waals (vdWs) heterostructures were meticulously engineered and synthesized utilizing an efficient methodology involving freeze-drying, immersing absorption, secondary freeze-drying, followed by carbonization treatment. Thanks to their excellent linkage effect of amplified dielectric loss and optimized impedance matching, the designed 2D/3D RGO/CFs vdWs heterostructures demonstrated commendable EMW absorption performances, achieving a broad absorption bandwidth of 6.2 GHz and a reflection loss of - 50.58 dB with the low matching thicknesses. Furthermore, the obtained 2D/3D RGO/CFs vdWs heterostructures also displayed the significant radar stealth properties, good corrosion resistance performances as well as outstanding thermal insulation capabilities, displaying the great potential in complex and variable environments. Accordingly, this work not only demonstrated a straightforward method for fabricating 2D/3D vdWs heterostructures, but also outlined a powerful mixed-dimensional assembly strategy for engineering multifunctional foams for electromagnetic protection, aerospace and other complex conditions.

Multi-interfaced Ni/C@RGO/PTFE composites for electromagnetic protection applications with high environmental stability and durability

To efficiently address the growing electromagnetic pollution problem, it is urgently required to research high-performance electromagnetic materials that can effectively absorb or shield electromagnetic waves. In addition, the stability and durability of electromagnetic materials in complex practical environments is also an issue that needs to be noticed. Therefore, the starting point for our problem-solving is how to endow magnetic/dielectric multi-interfaced composite materials with excellent electromagnetic protection capability and environmental stability. In this study, magnetic/dielectric multi-interfaced Ni/carbon@reduced graphene oxide/polytetrafluoroethylene (Ni/C@RGO/PTFE) composites were developed to utilize as excellent EWA (electromagnetic wave absorption) and EMI (electromagnetic interference) shielding materials. Due to their diverse heterogeneous interfaces, rich conductive networks, and multiple loss mechanisms, the Ni/C@RGO/PTFE composite exhibits an optimal reflection loss of -61.48 dB and an effective absorption bandwidth of 7.20 GHz, with a filler loading of 5 wt%. Furthermore, Ni/C@RGO/PTFE composite films have an optimal absorption effectiveness value of 9.50 dB and an absorption coefficient of 0.49. Moreover, Ni/C@RGO/PTFE can hold high EWA performance in various corrosive media and maintain more than 90% of EMI shielding effectiveness, which can be attributed to the carbon coating and PTFE matrix acting as dual protective barriers for the susceptible metal Ni, thus obviously improving the stability and durability of composites. Overall, this work presents an effective strategy for the growth of high-performance EWA and EMI shielding materials with outstanding environmental stability and durability, which have wide application prospects in the future.

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.

3D Lightweight Interconnected Melamine Foam Modified with Hollow CoFe2O4/MXene toward Efficient Microwave Absorption

Considering the increasing severity of electromagnetic wave pollution, the development of high-performance low-filler-content microwave absorbers possessing wide frequency bands and strong absorption for practical applications is a demanding research hotspot. In this study, from the perspectives of the electromagnetic component coordination and structural design, a three-dimensional (3D) interconnected CoFe2O4/MXene-melamine foam (MF) was constructed via simple impregnation and a single freeze-drying step. By changing the absorber (CoFe2O4/MXene) concentration, the pore opening and electromagnetic properties of the 3D foams can be effectively adjusted. When the absorber concentration is sufficiently high to clog the internal pores, the microwave absorption is hindered. When the filler (CoFe2O4/MXene-MF) content is just ∼5.8 wt % (at a density of ∼33.3 mg cm-3), a minimum reflection loss (RLmin) of -72.1 dB is achieved at a matching thickness of 3.32 mm, and an effective absorption bandwidth (4.54 GHz) covering the whole X band is achieved at a thickness of 3 mm. CoFe2O4/MXene-MF, which possesses a 3D porous electromagnetic network structure, optimizes impedance matching and enhances multiple polarization relaxations and reflections/scattering, resulting in superior absorption capabilities. In particular, the continuous network structure ensures the uniform distribution of electromagnetic fields in the microstructure, achieving high absorption at low filler contents. This work provides a reference for subsequent 3D absorber concentration studies and a novel engineering strategy for preparing a low-filler-content, lightweight, and efficient electromagnetic wave absorber, which could be applied in the fields of radar security and information communications.

MXene Hollow Spheres Supported by a C-Co Exoskeleton Grow MWCNTs for Efficient Microwave Absorption

High-performance microwave absorption (MA) materials must be studied immediately since electromagnetic pollution has become a problem that cannot be disregarded. A straightforward composite material, comprising hollow MXene spheres loaded with C-Co frameworks, was prepared to develop multiwalled carbon nanotubes (MWCNTs). A high impedance and suitable morphology were guaranteed by the C-Co exoskeleton, the attenuation ability was provided by the MWCNTs endoskeleton, and the material performance was greatly enhanced by the layered core-shell structure. When the thickness was only 2.04 mm, the effective absorption bandwidth was 5.67 GHz, and the minimum reflection loss (RLmin) was - 70.70 dB. At a thickness of 1.861 mm, the sample calcined at 700 °C had a RLmin of - 63.25 dB. All samples performed well with a reduced filler ratio of 15 wt%. This paper provides a method for making lightweight core-shell composite MA materials with magnetoelectric synergy.

Ultra-flexible silver/iron nanowire decorated melamine composite foams for high-efficiency electromagnetic wave absorption and thermal management

Nowadays, functional electronic devices with excellent flexibility and thermal management capability for effective electromagnetic wave absorption are urgently in demand. Herein, a novel and highly flexible silver nanowire (AgNW)/iron nanowire (FeNW) decorated melamine composite foam (AgFe-MF) was prepared via simple dip-coating process. Owing to optimal impedance matching, synergistic dielectric and magnetic losses as well as three-dimensional porous structure, the AgFe-MF with an ultra-low filler content (0.22 vol%) exhibited an outstanding minimum reflection loss of -69.61 dB, and the best effective absorption bandwidth (EAB) could reach up to 6.37 GHz. Importantly, the EAB of long-time working AgFe-MF was enhanced to 7.01 GHz after 1000 compress-release cycles under 40 % strain. Besides, it also featured considerate Joule heating capacity and achieved a saturation temperature of over 85.7 ℃ under 2.6 V voltage. The impressive thermal isolation and long-term stability ensured the safety used as portable heater. Therefore, this work will provide a vital slight for fabricating smart wearable electronic devices with integrated anti-electromagnetic radiation and personalized thermal management performances towards potential thermal and health threats.

Advancements in Microwave Absorption Motivated by Interdisciplinary Research

Microwave absorption materials (MAMs) are originally developed for military purposes, but have since evolved into versatile materials with promising applications in modern technologies, including household use. Despite significant progress in bench-side research over the past decade, MAMs remain limited in their scope and have yet to be widely adopted. This review explores the history of MAMs from first-generation coatings to second-generation functional absorbers, identifies bottlenecks hindering their maturation. It also presents potential solutions such as exploring broader spatial scales, advanced characterization, introducing liquid media, utilizing novel toolbox (machine learning, ML), and proximity of lab to end-user. Additionally, it meticulously presents compelling applications of MAMs in medicine, mechanics, energy, optics, and sensing, which go beyond absorption efficiency, along with their current development status and prospects. This interdisciplinary research direction differs from previous research which primarily focused on meeting traditional requirements (i.e., thin, lightweight, wide, and strong), and can be defined as the next generation of smart absorbers. Ultimately, the effective utilization of ubiquitous electromagnetic (EM) waves, aided by third-generation MAMs, should be better aligned with future expectations.

Graphene-like structure of bio-carbon with CoFe Prussian blue derivative composites for enhanced microwave absorption

Traditional carbon materials such as graphene are often applied in the field of electromagnetic wave (EMW) absorption but they have unbalanced impedance matching and high conductivity. Bio-carbon with graphene-like structure derived from apples has many advantages over graphene: it can be prepared in large quantities and the abundant heteroatoms present in the lattice can provide many polarization phenomena. Herein, Prussian blue analogue (PBA) as a source of magnetic component was combined with bio-carbon or reduced graphene oxide (rGO) to study the EMW absorption properties. The fabricated BC/CFC-12-7 displayed performance with a minimum reflection loss (RLmin) of -72.57 dB and a wide effective absorption bandwidth (EAB) of 5.25 GHz with an ultra-thin and nearly equal matching thickness at 1.61 mm. The results show that the good EMW absorption property of bio-carbon composites comes from good conduction loss, large relaxation polarization loss especially from pyridinic-N, and better impedance matching. The optimized radar cross section is found to be -33.55 dB m2 in the far-field condition using CST. This work explored the advantages of bio-carbon as a novel EMW absorbing material compared with graphene and provided ideas for realizing high-performance EMW absorbing materials in the future.

An Optically Transparent Metamaterial Absorber with Tunable Absorption Bandwidth and Low Infrared Emissivity

A transparent metamaterial absorber (MMA) with both tunable absorption bandwidth and low infrared (IR) emissivity is proposed in this paper. The MMA is hierarchical, which consists of an infrared shielding layer (IRSL), two radar-absorption layers (RALs), an air/water layer, and an indium-tin-oxide (ITO) backplane from the top downwards. The IRSL and the RALs are made of ITO patterns etched on polyethylene terephthalate (PET) substrates. By changing the thickness of the water, the 90% absorption bandwidth can be tuned from 6.4-11.3 GHz to 12.7-20.6 GHz, while retaining good polarization and angular stability. An equivalent circuit model (ECM) is present, to reveal the physical mechanism of absorption. The proposed MMA has a low theoretical IR emissivity of about 0.24. A sample was fabricated and measured, and the experimental results are consistent with the simulation results, showing its potential applications in stealth glass and multifunctional radome.

Efficient Electromagnetic Wave Absorption and Thermal Infrared Stealth in PVTMS@MWCNT Nano-Aerogel via Abundant Nano-Sized Cavities and Attenuation Interfaces

Pre-polymerized vinyl trimethoxy silane (PVTMS)@MWCNT nano-aerogel system was constructed via radical polymerization, sol-gel transition and supercritical CO2 drying. The fabricated organic-inorganic hybrid PVTMS@MWCNT aerogel structure shows nano-pore size (30-40 nm), high specific surface area (559 m2 g-1), high void fraction (91.7%) and enhanced mechanical property: (1) the nano-pore size is beneficial for efficiently blocking thermal conduction and thermal convection via Knudsen effect (beneficial for infrared (IR) stealth); (2) the heterogeneous interface was beneficial for IR reflection (beneficial for IR stealth) and MWCNT polarization loss (beneficial for electromagnetic wave (EMW) attenuation); (3) the high void fraction was beneficial for enhancing thermal insulation (beneficial for IR stealth) and EMW impedance match (beneficial for EMW attenuation). Guided by the above theoretical design strategy, PVTMS@MWCNT nano-aerogel shows superior EMW absorption property (cover all Ku-band) and thermal IR stealth property (ΔT reached 60.7 °C). Followed by a facial combination of the above nano-aerogel with graphene film of high electrical conductivity, an extremely high electromagnetic interference shielding material (66.5 dB, 2.06 mm thickness) with superior absorption performance of an average absorption-to-reflection (A/R) coefficient ratio of 25.4 and a low reflection bandwidth of 4.1 GHz (A/R ratio more than 10) was experimentally obtained in this work.

Multi-interfacial engineering in the hierarchical self-assembled micro-nano dielectric aerogel for wide-band absorption and low infrared emissivity

Radar-infrared (IR) compatible stealth can satisfy the characteristics of excellent electromagnetic wave attenuation property and low infrared emissivity. However, concurrently satisfying these demands is still a great challenge at present. Herein, multi-interfacial engineering strategy was proposed for the preparation of radar-IR compatible stealth materials. ZnO has a high electron binding energy and a large band gap at room temperature, and doping with sulphide can increase the concentration of unconstrained carriers. Therefore, bimetallic sulphide aerogels loaded with ZnO were prepared by means of carbonization and vulcanization, combined with freeze-drying method. When the filling ratio is 20 %, an absorption bandwidth (fe) of 6.62 GHz at a matching thickness of 2.0 mm and a reduction in IR emissivity from 0.920 to 0.539 in the 8-14 μm band are achieved. This work provides a guidance to design and synthesize high-performance absorbers by multi-interfacial engineering for IR-radar compatible stealth application.

Commonly Neglected Ester Groups Enhanced Microwave Absorption

Oxygen-containing functional groups have high potential to excite polarization loss. The nature and mechanism of the polarization loss brought on by oxygen-containing functional groups, however, remain unclear. In this study, metal-organic framework precursors are in situ pyrolyzed to produce ultrathin carbon nanosheets (UCS) that are abundant in oxygen functional groups. By altering the pyrolysis temperature, the type and concentration of functional groups are altered to produce good microwave absorption capabilities. It is demonstrated that the main processes of electromagnetic loss are polarization caused by "field effects and induced effects" brought on by strongly polar ester functional groups. Moreover, links between various oxygen functional groups and structural flaws are established, and their respective contributions to polarization are sharply separated. The sample with the highest ester group content ultimately achieves an effective absorption bandwidth of 6.47 GHz at a pyrolysis temperature of 800°C. This research fills a theoretical hole in the frequently overlooked polarization mechanism in the microwave band by defining the key polarization parameters in chaotic multiple dipole systems and, in particular, redefining the significance of ester groups.

Defect-Free Few-Layer M4 C3 Tx (M = V, Nb, Ta) MXene Nanosheets: Synthesis, Characterization, and Physicochemical Properties

High-quality few-layer M4 C3 Tx (M = V, Nb, Ta) MXenes are very important for applications and are necessary for clarifying their physicochemical properties. However, the difficulty in etching for themselves and the existence of MC/MC1-δ and M-Al alloy impurities in their M4 AlC3 precursors seriously hinder the achievement of defect-free few-layer M4 C3 Tx (M = V, Nb, Ta) MXenes nanosheets. Herein, three different defect-free few-layer M4 C3 Tx (M = V, Nb, Ta) nanosheets are obtained by using a universal synthesis strategy of calcination, selective etching, intercalation, and exfoliation. Comprehensive characterizations confirm their defect-free few-layer structure feature, large interlayer spacing (1.702-1.955 nm), types of functional groups (-OH, -F, -O), and abundant valance states (M5+ , M4+ , M3+ , M2+ , M0 ). M4 C3 Tx (M = V, Nb, Ta) free-standing films obtained by vacuum filtration of few-layer M4 C3 Tx inks show good hydrophilia, high thermostability, and conductivity. A roadmap on synthesis of defect-free few-layer M4 C3 Tx (M = V, Nb, Ta) nanosheets are proposed and three key points are summarized. This work provides detailed guidelines for the synthesis of other defect-free few-layer MXenes nanosheets, but also will stimulate extensive functional explorations for M4 C3 Tx (M = V, Nb, Ta) MXenes nanosheets in the future.

Hierarchical and Orderly Surface Conductive Networks in Yolk-Shell Fe3 O4 @C@Co/N-Doped C Microspheres for Enhanced Microwave Absorption

Constructing the adjustable surface conductive networks is an innovation that can achieve a balance between enhanced attenuation and impedance mismatch according to the microwave absorption mechanism. However, the traditional design strategies remain significant challenges in terms of rational selection and controlled growth of conductive components. Herein, a hierarchical construction strategy and quantitative construction technique are employed to introduce conductive metal-organic frameworks (MOFs) derivatives in the classic yolk-shell structure composed of electromagnetic components and the cavity for remarkable optimized performance. Specifically, the surface conductive networks obtained by carbonized ZIF-67 quantitative construction, together with the Fe3 O4 magnetic core and dielectric carbon layer linked by the cavity, achieve the cooperative enhancement of impedance matching optimization and synergistic attenuation in the Fe3 O4 @C@Co/N-Doped C (FCCNC) absorber. This interesting design is further verified by experimental results and simulation calculations. The products FCCNC-2 yield a distinguished minimum reflection loss of -66.39 dB and an exceptional effective absorption bandwidth of 6.49 GHz, indicating that moderate conduction excited via hierarchical and quantitative design can maximize the absorption capability. Furthermore, the proposed versatile methodology of surface assembly paves a new avenue to maximize beneficial conduction effect and manipulate microwave attenuation in MOFs derivatives.

Micro-Nano Water Film Enabled High-Performance Interfacial Solar Evaporation

Interfacial solar evaporation holds great promise to address the freshwater shortage. However, most interfacial solar evaporators are always filled with water throughout the evaporation process, thus bringing unavoidable heat loss. Herein, we propose a novel interfacial evaporation structure based on the micro-nano water film, which demonstrates significantly improved evaporation performance, as experimentally verified by polypyrrole- and polydopamine-coated polydimethylsiloxane sponge. The 2D evaporator based on the as-prepared sponge realizes an enhanced evaporation rate of 2.18 kg m-2 h-1 under 1 sun by fine-tuning the interfacial micro-nano water film. Then, a homemade device with an enhanced condensation function is engineered for outdoor clean water production. Throughout a continuous test for 40 days, this device demonstrates a high water production rate (WPR) of 15.9-19.4 kg kW-1 h-1 m-2. Based on the outdoor outcomes, we further establish a multi-objective model to assess the global WPR. It is predicted that a 1 m2 device can produce at most 7.8 kg of clean water per day, which could meet the daily drinking water needs of 3 people. Finally, this technology could greatly alleviate the current water and energy crisis through further large-scale applications.

Polyvinylpyrrolidone induced uniform coating of nickel nanoparticles on carbon nanotubes for efficient microwave absorption

The impedance matching performance of carbon nanotubes (CNTs) can be effectively enhanced by developing a uniform magnetic impedance matching layer, which can take on critical significance in achieving the desirable microwave absorption (MA) performance. To obtain a uniform coating of Nickel (Ni) nanoparticles on CNTs, several methods have been developed (e.g., the γ-irradiation technique, electroless deposition, as well as microwave welding method). However, the intricate and complicated conditions of the above-mentioned methods limit their wide application. Therefore, controlling the distribution of Ni nanoparticles with the aid of a concise and effective method remains a great challenge. Herein, in view of the uniform dispersion effect of polyvinylpyrrolidone (PVP) on CNTs and its complexation with Ni ions, uniform coating of Ni nanoparticles on CNTs is well developed after it is introduced in the hydrothermal process. The prepared Ni/CNTs composites exhibited excellent MA performance in comparison with those of reported Ni/CNTs composites for the ideal impedance matching performance and microwave attenuation ability. When the filler content was only 15 wt%, the minimum reflection loss (RL_min) reached -39.5 dB, and the effective bandwidth (EB) with RL < -10 dB reached 5.2 GHz at the thickness of 1.15 mm. A scalable strategy of regulating the distribution of Ni nanoparticles and preparing a lightweight microwave absorber based on CNTs was developed in this study, which can serve as a vital guideline for preparing novel MA composite materials.

An efficient Pt@MXene platform for the analysis of small-molecule natural products

Small-molecule (m/z<500) natural products have rich biological activity and significant application value thus need to be effectively detected. Surface-assisted laser desorption/ionization mass spectrometry (SALDI MS) has become a powerful detection tool for small-molecule analysis. However, more efficient substrates need to be developed to improve the efficiency of SALDI MS. Thus, platinum nanoparticle-decorated Ti₃C₂ MXene (Pt@MXene) was synthesized in this study as an ideal substrate for SALDI MS in positive ion mode and exhibited excellent performance for the high-throughput detection of small molecules. Compared with using MXene, GO, and CHCA matrix, a stronger signal peak intensity and wider molecular coverage was obtained using Pt@MXene in the detection of small-molecule natural products, with a lower background, excellent salt and protein tolerance, good repeatability, and high detection sensitivity. The Pt@MXene substrate was also successfully used to quantify target molecules in medicinal plants. The proposed method has potentially wide application.

Wideband RCS Reduction Based on Hybrid Checkerboard Metasurface

Traditional stealth technologies all have their problems such as high cost and large thickness. To solve the problems, we used novelty checkerboard metasurface in stealth technology. Checkerboard metasurface does not have as high conversion efficiency as radiation converters, but it has many advantages such as small thickness and low cost. So it is expected to overcome the problems of traditional stealth technologies. Unlike other checkerboard metasurfaces, we improved it further by using two types of polarization converter units to be arranged in turn to form a hybrid checkerboard metasurface. Because the checkerboard metasurface composed of one type of polarization converter units can have a relatively wide radar cross-section (RCS) reduction in bandwidth when two types of polarization converter units are arranged in turn to form a hybrid checkerboard metasurface and mutual compensation of the two polarization converter units can broaden RCS reduction band further. Therefore, by designing the metasurface to be independent from the polarization, the effect of RCS reduction can be insensitive to the polarization of the incoming EM waves. The experiment and simulation results showed the value of this proposed hybrid checkerboard metasurface for RCS reduction. Mutual compensation of the units is a new attempt in the field of checkerboard metasurfaces for stealth technology and proved to be effective.

Multi-Scale Design of Ultra-Broadband Microwave Metamaterial Absorber Based on Hollow Carbon/MXene/Mo2 C Microtube

Developing various nanocomposite microwave absorbers is a crucial means to address the issue of electromagnetic pollution, but remains a challenge in satisfying broadband absorption at low thickness with dielectric loss materials. Herein, an ultra-broadband microwave metamaterial absorber (MMA) based on hollow carbon/MXene/Mo₂ C (HCMM) is fabricated by a multi-scale design strategy. The microscopic 1D hierarchical microtube structure of HCMM contributes to break through the limit of thickness, exhibiting a strong reflection loss of -66.30 dB (99.99997 wave absorption) at the thinnest matching thickness of 1.0 mm. Meanwhile, the strongest reflection loss of -87.28 dB is reached at 1.4 mm, superior to most MXene-based and Mo₂ C-based microwave absorbers. Then, the macroscopic 3D structural metasurface based on the HCMM is simulated, optimized, and finally manufactured. The as-prepared flexible HCMM-based MMA realizes an ultra-broadband effective absorption in the range of 3.7-40.0 GHz at a thickness of 5.0 mm, revealing its potential for practical application in the electromagnetic compatibility field.

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.

Macroscopic Electromagnetic Cooperative Network-Enhanced MXene/Ni Chains Aerogel-Based Microwave Absorber with Ultra-Low Matching Thickness

Electromagnetic cooperative strategy has been presented as a mainstream approach that can effectively optimize the matching thickness of dielectric loss dominant system. However, it is still challenging for dielectric-magnetic loss coexisting-type absorber to develop electromagnetic wave (EMW) performance with ultra-low matching thickness (≤ 1 mm). Breaking the limitation of traditional electromagnetic response at microscopic/mesoscopic scale, a ficus microcarpa-like magnetic aerogel with macroscopical electromagnetic cooperative effect was fabricated through highly oriented self-assembly engineering. The highly oriented Ni chains with unique macroscopic morphology (~ 1 cm in length) were achieved via a special magnetic field-induced growth. Strong magnetic coupling was observed in the Ni chains confirmed by the micromagnetic simulation. The deductive calculation validates that maintaining high value of electromagnetic parameters at high frequencies is the prerequisites of ultrathin absorber. The electromagnetic cooperative networks with uninterrupted and dual pathways spread through the entire aerogel skeleton, resulting in the impressive permittivity even at high frequencies. Consequently, the aerogel exhibits a remarkable EMW performance at an ultrathin thickness of 1 mm. Thus, based on the modulation of electromagnetic parameters, this work proposed a macroscopic ordered structure with the electromagnetic cooperative effect useful to develop a suitable strategy for achieving ultrathin EMW absorbers.

Digital Light Processing 3D-Printed Ceramic Metamaterials for Electromagnetic Wave Absorption

Combining 3D printing with precursor-derived ceramic for fabricating electromagnetic (EM) wave-absorbing metamaterials has attracted great attention. This study presents a novel ultraviolet-curable polysiloxane precursor for digital light processing (DLP) 3D printing to fabricate ceramic parts with complex geometry, no cracks and linear shrinkage. Guiding with the principles of impedance matching, attenuation, and effective-medium theory, we design a cross-helix-array metamaterial model based on the complex permittivity constant of precursor-derived ceramics. The corresponding ceramic metamaterials can be successfully prepared by DLP printing and subsequent pyrolysis process, achieving a low reflection coefficient and a wide effective absorption bandwidth in the X-band even under high temperature. This is a general method that can be extended to other bands, which can be realized by merely adjusting the unit structure of metamaterials. This strategy provides a novel and effective avenue to achieve "target-design-fabricating" ceramic metamaterials, and it exposes the downstream applications of highly efficient and broad EM wave-absorbing materials and structures with great potential applications.