3D Seed-Germination-Like MXene with In Situ Growing CNTs/Ni Heterojunction for Enhanced Microwave Absorption via Polarization and Magnetization

Microwave-Infrared Compatible Camouflage by MXene-Based Composite Aerogels via Synergistic Electromagnetic, Emissivity, and Thermal Regulation

The advancement of multispectral surveillance technologies has rendered conventional single-band camouflage materials ineffective, driving an urgent demand for multispectral-compatible stealth materials. Herein, we report a multidimensional MXene-based composite aerogel engineered via cost-effective lyophilization for radar-infrared compatible camouflage. As building blocks, few-layer Ti3C2Tx MXene nanosheets functionalized with NiB alloy nanoparticles and thermoresponsive VO2 phase-change materials are cross-linked by poly(vinyl alcohol) to construct the MXene/NiB/VO2 composite aerogel through one-step cryo-assembly. The composite demonstrates a remarkable multispectral stealth performance. The thermal radiation temperature of a heated target is reduced from 180 to 55 °C. In addition, a minimum reflection loss (RLmin) of -54.7 dB with an effective absorption bandwidth of 7.1 GHz (8.8-15.9 GHz) at an ultralow low density of 19 mg·cm-3 has been achieved. These breakthroughs stem from synergistic mechanisms: low infrared emissivity, suppressed thermal conduction, dynamic temperature regulation via the VO2 phase transition, and multimodal electromagnetic dissipation. This work establishes a material design paradigm to reconcile infrared-microwave spectral incompatibilities through multidimensional heterostructure engineering, providing a roadmap for next-generation adaptive multispectral stealth technologies.

Multiple Charge Carriers Manipulation Toward Semiconductive Ceramic Nanocomposites for Corrosion-Resistant Electromagnetic Wave Absorption

The modulation of transport properties in ceramic-based semiconductors can be used to optimize the electromagnetic response mechanism and performance. A semiconductor ceramic foam interlayer wall (SCFW) is designed by a physical vapor deposition method. The interlayer structural SCFW is composed of semiconductor-insulator-semiconductor layers, incorporating a composite system of SiC, Al4.8Si1.2O9.6, and Al2O3. Moreover, the hierarchical network structure of the foam interlayer wall is controlled by the pyrolysis-deposition kinetic process. Electrons and holes are transported through the heterojunctions between SiC and Al4.8Si1.2O9.6, achieving effective charge relaxation. The Al2O3 matrix provides lightweight properties (density of 0.967 g cm-3), while the hierarchical network structure determines the excellent electromagnetic wave (EMW) absorption performance of the SCFW, with an effective bandwidth up to 14.8 GHz under electromagnetic response (minimum reflection loss RLmin = -50.6 dB). the SCFW has been proven to exhibit corrosion resistance and thermal insulation properties, with a thermal conductivity up to 0.025 W m-1 K-1. This study provides valuable insights into the structural design and dielectric property optimization of ceramic-based semiconductor nanocomposites, which leads to strong polarization loss, opening new avenues for the application of EMW absorbers, and the EMW absorption mechanism of ceramics.

Flexible graphene/PAM/PVA hydrogel composites with highly dispersed cobalt nanoparticles for enhanced microwave absorption

With the increasing demand for flexible microwave-absorbing materials (MAMs), it is necessary to ensure a continuous network of MAM fillers. However, it is still a great challenge to achieve uniform loading of magnetic nanoparticles because of the uncertain reaction sites of graphene. For this research, we adopted a high-pressure homogenization strategy to realize a uniform distribution of Co nanoparticles on the graphene surface via polyethyleneimine (PEI) modification. Transferring the Co reaction sites from the randomly distributed oxygen functional groups to the uniformly distributed PEI molecules, the homogeneous graphene oxide (GO)/PEI/Co (GP/Co) dispersion ensured to form the uniform reduced graphene oxide (RGO)/PEI/Co (RGP/Co) after reduction. RGP/Co-2 achieved an effective absorption of -51.9 dB in the C band and a microwave absorption bandwidth of 5.84 GHz. In addition, RGP/Co-2 was filled into polyacrylamide/polyvinyl alcohol (PAM/PVA) hydrogel to construct a uniform and continuous network structure, and RGP/Co-2/PAM/PVA flexible MAMs were prepared. The minimum reflection loss (RLmin) is -41.5 dB under the thickness of 2.5 mm and shows excellent mechanical flexibility. In addition, RGP/Co-2/PAM/PVA exhibited excellent sensing performance. This research supplied a new perspective for the development of MAMs in flexible electronics.

Few-Layered MXene Modulating In Situ Growth of Carbon Nanotubes for Enhanced Microwave Absorption

MXene is widely used in the fields of microwave absorption and electromagnetic shielding to balance electromagnetic pollution with the development of communication technologies and human health, due to its excellent surface functional groups and tunable electronic properties. Although pure multilayered MXene has an excellent accordion-like structure, the weak dielectric loss and lack of magnetic loss result in poor microwave absorption performance. Here, we propose a strategy for the catalytic growth of CNTs by the electrophoretic deposition of adsorbed metal ions, leading to the successful preparation of Ni-MWCNTs/Ti3C2Tx composites with a "layer-by-layer" structure, achieved through in situ regulated growth of CNTs. By introducing dielectric-magnetic synergy to improve the impedance matching conditions, and by regulating the diameter of the CNTs to alter the electromagnetic parameters of Ni-MWCNTs/Ti3C2Tx, the 2-Ni-MWCNTs/Ti3C2Tx composite achieves the best reflection loss (RL) value of -44.08 dB and an effective absorption bandwidth of 1.52 GHz at only 2.49 mm thickness. This unique layered structure and the regulation strategy provide new opportunities for the development of few-layered MXene composites.

Enhanced Microwave Absorption of Multi-Interface Core-Shell FeSiAl@MnOx@C Composites by Morphology Engineering

The rational manipulation of interfacial properties, composition, and morphology of materials has emerged as an effective strategy for enhancing their microwave absorption performance. The crystal phase composition, microstructure, and electromagnetic properties can be regulated by varying the thermal treatment temperature. The synergistic integration of heterogeneous interfaces, magnetic materials, microstructures, and defect engineering helps optimize impedance matching and enhance polarization and magnetic losses. Herein, multi-interface core-shell FeSiAl@MnOx@C composites with various morphologies demonstrated superior microwave absorption performance. A minimum reflection loss of -56.3 dB is achieved at an absorber thickness of 1.41 mm, and effective absorption bandwidth of 5.0 GHz is obtained at a thickness of 1.59 mm. The radar cross-section reduction value reached 19.448 at an incidence angle of 0°. The excellent microwave absorption performance is due to the synergistic effect of the significant magnetic and dielectric losses and improved impedance matching. This study establishes a foundation for designing next-generation high-performance microwave-absorbing materials with high magnetic losses.

Yolk-Shell CoNi@N-Doped Carbon-CoNi@CNTs for Enhanced Microwave Absorption, Photothermal, Anti-Corrosion, and Antimicrobial Properties

The previous studies mainly focused on improving microwave absorbing (MA) performances of MA materials. Even so, these designed MA materials were very difficult to be employed in complex and changing environments owing to their single-functionalities. Herein, a combined Prussian blue analogues derived and catalytical chemical vapor deposition strategy was proposed to produce hierarchical cubic sea urchin-like yolk-shell CoNi@N-doped carbon (NC)-CoNi@carbon nanotubes (CNTs) mixed-dimensional multicomponent nanocomposites (MCNCs), which were composed of zero-dimensional CoNi nanoparticles, three-dimensional NC nanocubes and one-dimensional CNTs. Because of good impedance matching and attenuation characteristics, the designed CoNi@NC-CoNi@CNTs mixed-dimensional MCNCs exhibited excellent MA performances, which achieved a minimum reflection loss (RLmin) of -71.70 dB at 2.78 mm and Radar Cross section value of -53.23 dB m2. More importantly, the acquired results demonstrated that CoNi@NC-CoNi@CNTs MCNCs presented excellent photothermal, antimicrobial and anti-corrosion properties owing to their hierarchical cubic sea urchin-like yolk-shell structure, highlighting their potential multifunctional applications. It could be seen that this finding not only presented a generalizable route to produce hierarchical cubic sea urchin-like yolk-shell magnetic NC-CNTs-based mixed-dimensional MCNCs, but also provided an effective strategy to develop multifunctional MCNCs and improve their environmental adaptabilities.

Nano-assisted delivery tools for plant genetic engineering: a review on recent developments

Conventional approaches like Agrobacterium-mediated transformation, viral transduction, biolistic particle bombardment, and polyethylene glycol (PEG)-facilitated delivery methods have been optimized for transporting specific genes to various plant cells. These conventional approaches in genetically modified crops are dependent on several factors like plant types, cell types, and genotype requirements, as well as numerous disadvantages such as time-consuming, untargeted distribution of genes, and high cost of cultivation. Therefore, it is suggested to develop novel techniques for the transportation of genes in crop plants using tailored nanoparticles (NPs) of manipulative and controlled high-performance features synthesized using green and chemical routes. It is observed that site-specific delivery of genes exhibits high efficacy in species-independent circumstances which leads to an increased level of productivity. Therefore, to achieve these outcomes, NPs can be utilized as gene nano-carriers for excellent delivery inside crops (i.e., cotton, tobacco, rice, wheat, okra, and maize) for desired genetic engineering modifications. As outcomes, this review provides an outline of the conventional techniques and current application of numerous nano-enabled gene delivery needed for crop gene manipulation, the benefits, and drawbacks associated with state-of-the-art techniques, which serve as a roadmap for the possible applicability of nanomaterials in plant genomic engineering as well as crop improvement in the future.

Constructing MXene-based mixed-dimensional structure with multiple interfaces to optimize dielectric-magnetic synergistic effect for effective electromagnetic wave absorption

Exploring efficient microwave absorbing materials (MAMs) which could convert electromagnetic (EM) energy into thermal energy represents an approbatory vision to reducing EM radiation and interference. Designing of mixed-dimensional structure with multiple interfaces represents the available target to investigate an ideal MAMs, which maximizes the superiority of mixed-dimensional structure in electromagnetic wave absorption (EMWA). Herein, we take full advantage of multiple interfaces engineering of MXene for optimizing the impedance matching to improve EMWA, MXene-based mixed-dimensional structure was designed by incorporating three-dimensional Fe3C@Carbon layers coated zero-dimensional Fe3O4 nanoparticles (NPs) supported two-dimensional MXene nanosheets (MXene/Fe3O4@Fe3C@Carbon, MFC). The Fe3O4@Fe3C@C with Core@shell structure arrests the essentially self-restacked of MXene and provides various attenuation mechanisms for the incident electromagnetic waves (EMWs). By regulating the carbonization temperature, the MFC exhibits enhanced EMWA property which is attributed to the characteristic structure and optimized dielectric-magnetic synergy effect. The minimum reflection loss (RLmin) value of MFC can reach to -64.3 dB with a matching thickness of 1.73 mm. Otherwise, the maximum effective absorption bandwidth (EAB) (RLmin < -10 dB) reaches 6.42 GHz at only 1.5 mm. Thus, our study refers a novel-fire enlighten to develop excellent mixed-dimensional microwave absorbent based on MXene.

High Absorption of Electromagnetic Waves Based on 3D PMMA@Mxene@Co3O4 Composite Microsphere

With the increasing demand for effective electromagnetic wave (EMW) absorbers due to the proliferation of electronic devices and 5G communication systems, traditional wave-absorbing materials can no longer meet the current requirements. Thus, this research introduces a three-dimensional (3D) composite material consisting of PMMA@Mxene@Co₃O₄ microspheres, prepared through in situ self-assembly and hydrothermal growth. The strong electrical conductivity of Mxene, combined with the magnetic loss of Co₃O₄, ensures enhanced dielectric-magnetic synergy, leading to excellent EMW absorption. The study investigates the influence of varying Co₃O₄ content on the electromagnetic properties of the composite. Experimental results show that the optimal sample, with a thickness of 2.5 mm, achieves a minimum reflection loss (RLmin) of -52.88 dB at 6.88 GHz and an effective absorption bandwidth (EAB) of 5.28 GHz. This work highlights the potential of 3D PMMA@Mxene@Co₃O₄ composites as high-performance microwave absorbers, providing a promising solution to EMW pollution. The findings offer valuable insights into material design strategies, demonstrate a promising pathway for developing lightweight, high-performance EMW absorbing materials by optimizing impedance matching and utilizing advanced microstructure design techniques.

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.

Multifunctional carbon aerogels loaded with pea-pod-like carbon nanotubes for outstanding electromagnetic wave absorption performance

Although ordered porous carbon materials (PCMs) have shown promising potential in the field of electromagnetic wave absorption (EWA), creating multifunctional PCMs with outstanding microwave absorption performance remains a significant challenge. Herein, ordered porous carbon aerogels loaded with pea-pod-like nitrogen-doped carbon nanotubes (CNTs) were fabricated via orientation freeze-drying followed by high-temperature pyrolysis. The optimized aerogel exhibits extraordinary EWA performance with a broad effective absorption bandwidth of 7.68 GHz and exceptionally strong absorption of -91.58 dB at a low filling ratio of only 3 wt%, which is the largest absorption strength among all known aerogels to date. The exceptional EWA performance is attributed to the synergistic effect of abundant loss mechanisms resulting from a unique pod-like structure in ordered porous carbon aerogel, where nitrogen-doped CNTs encapsulate magnetic alloy nanoparticles. Optimized aerogel exhibits superior compressive elasticity, thermal insulation, and light weight, laying the groundwork for designing practical next-generation EWA materials.

Multifunctional MoCx Hybrid Polyimide Aerogel with Modified Porous Defect Engineering for Highly Efficient Electromagnetic Wave Absorption

Traditional electromagnetic absorbing materials (EWAMs) are usually single functions and can easily affect their performance in diverse application scenarios. Effective integration of EWAMs into multiple function components is a valuable strategy to achieve maximum absorption and multifunction performance while maintaining their indispensable physical and chemical properties. In this work, the polyoxometalates (POMs) serving as "guests" are embedded within the Co-MOFs to construct 3d/4d-bimetallic based crystalline precursors of dielectric/magnetic synergistic system. The proper pyrolysis temperature induced the homogeneously distributed metallic Co and MoCx hetero-units into carbon matrix with modified porous defect engineering to enhance electromagnetic wave (EW). Owing to the brilliant synergistic effect of polarization, magnetic loss, and impedance matching, the superior RLmin of -47.72 dB at 11.76 GHz at the thickness of 2.0 mm and a wide adequate absorption bandwidth (EAB) of 4.58 GHz (7.44-12.02 GHz) covered the whole X-band at the thickness of 2.5 mm for η-MoC/Co@NC-800 are observed. More importantly, the resulting MoCx hybrid polyimide (MCP) aerogel exhibits desirable properties such as structural robustness, nonflammability, excellent thermal insulation, and self-cleaning capabilities that are comparable to those of commercially available products. This work offers inspiration and strategy for creating multipurpose microwave absorbers with intricate structural designs.

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.

Rapid and effective treatment of chronic osteomyelitis by conductive network-like MoS2/CNTs through multiple reflection and scattering enhanced synergistic therapy

Staphylococcus aureus (S. aureus)-infected chronic osteomyelitis (COM) is one of the most devastating infectious diseases with a high recurrence rate, often leading to amputation and even death. It is incurable by all the current strategies involving the clinical use of radical debridement and systemic intravenous antibiotics. Here, we reported on a microwave (MW)-assisted therapy for COM by constructing a heterojunction formed by flake nanoflower-shaped molybdenum disulfide (MoS2) and tubular carbon nanotubes (CNTs). This composite could achieve a combination of MW thermal therapy (MTT) and MW dynamic therapy (MDT) to accurately and rapidly treat COM with deep tissue infection. In vitro and in vivo experiments showed that MoS2/CNTs were effective in non-invasively treating S. aureus-induced COM due to the heat and reactive oxygen species (ROS) produced under MW irradiation. The mechanism of heat and ROS generation was explained by MW network vector analysis, density of states (DOS), oxygen adsorption energy, differential charge and finite element (FEM) under MW irradiation. Since the Fermi layer was mainly contributed by the Mo-4d and C-2P orbitals, MoS2/CNTs could store a large amount of charge and easily release more electrons. In addition, charge accumulation and dissipation motion were strong on the surface of and inside MoS2/CNTs because of electromagnetic hot spots, resulting in the spilling out of a great deal of high-energy electrons. Due to the low oxygen adsorption energy of MoS2/CNTs-O2, these high-energy electrons combined further with the adsorbed oxygen to produce ROS.

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.

Interfacial and Defect Polarization Enhanced Microwave Noninvasive Therapy for Staphylococcus aureus-Infected Chronic Osteomyelitis

Chronic osteomyelitis (COM), is a long-term, constant, and intractable disease mostly induced by infection from the invasion of Staphylococcus aureus (S. aureus) into bone cells. Here, we describe a highly effective microwave (MW) therapeutic strategy for S. aureus-induced COM based on the in situ growth of interfacial oxygen vacancy-rich molybdenum disulfide (MoS2)/titanium carbide (Ti3C2Tx) MXene with oxygen-deficient titanium dioxide (TiO2-x) on Ti3C2Tx (labeled as HU-MoS2/Ti3C2Tx) by producing reactive oxygen species (ROS) and heat. HU-MoS2/Ti3C2Tx produced heat and ROS, which could effectively treat S. aureus-induced COM under MW irradiation. The underlying mechanism determined by density functional theory (DFT) and MW vector network analysis was that HU-MoS2/Ti3C2Tx formed a high-energy local electric field under MW irradiation, consequently generating more high-energy free electrons to pass and move across the interface at a high speed and accelerate by the heterointerface, which enhanced the charge accumulation on both sides of the interface. Moreover, these charges were captured by the oxygen species adsorbed at the HU-MoS2/Ti3C2Tx interface to produce ROS. MoS2 facilitated multiple reflections and scattering of electromagnetic waves as well as enhanced impedance matching. Ti3C2Tx enhanced the conduction loss of electromagnetic waves, while functional groups induced dipole polarization to enhance attenuation of MW.

Multifunctional MXene/C Aerogels for Enhanced Microwave Absorption and Thermal Insulation

Two-dimensional transition metal carbides and nitrides (MXene) have emerged as promising candidates for microwave absorption (MA) materials. However, they also have some drawbacks, such as poor impedance matching, high self-stacking tendency, and high density. To tackle these challenges, MXene nanosheets were incorporated into polyacrylonitrile (PAN) nanofibers and subsequently assembled into a three-dimensional (3D) network structure through PAN carbonization, yielding MXene/C aerogels. The 3D network effectively extends the path of microcurrent transmission, leading to enhanced conductive loss of electromagnetic (EM) waves. Moreover, the aerogel's rich pore structure significantly improves the impedance matching while effectively reducing the density of the MXene-based absorbers. EM parameter analysis shows that the MXene/C aerogels exhibit a minimum reflection loss (RLmin) value of - 53.02 dB (f = 4.44 GHz, t = 3.8 mm), and an effective absorption bandwidth (EAB) of 5.3 GHz (t = 2.4 mm, 7.44-12.72 GHz). Radar cross-sectional (RCS) simulations were employed to assess the radar stealth effect of the aerogels, revealing that the maximum RCS reduction value of the perfect electric conductor covered by the MXene/C aerogel reaches 12.02 dB m2. In addition to the MA performance, the MXene/C aerogel also demonstrates good thermal insulation performance, and a 5-mm-thick aerogel can generate a temperature gradient of over 30 °C at 82 °C. This study provides a feasible design approach for creating lightweight, efficient, and multifunctional MXene-based MA materials.

Structural design and preparation of Ti3C2Tx MXene/polymer composites for absorption-dominated electromagnetic interference shielding

Electromagnetic interference (EMI) is a pervasive and harmful phenomenon in modern society that affects the functionality and reliability of electronic devices and poses a threat to human health. To address this issue, EMI-shielding materials with high absorption performance have attracted considerable attention. Among various candidates, two-dimensional MXenes are promising materials for EMI shielding due to their high conductivity and tunable surface chemistry. Moreover, by incorporating magnetic and conductive fillers into MXene/polymer composites, the EMI shielding performance can be further improved through structural design and impedance matching. Herein, we provide a comprehensive review of the recent progress in MXene/polymer composites for absorption-dominated EMI shielding applications. We summarize the fabrication methods and EMI shielding mechanisms of different composite structures, such as homogeneous, multilayer, segregated, porous, and hybrid structures. We also analyze the advantages and disadvantages of these structures in terms of EMI shielding effectiveness and the absorption ratio. Furthermore, we discuss the roles of magnetic and conductive fillers in modulating the electrical properties and EMI shielding performance of the composites. We also introduce the methods for evaluating the EMI shielding performance of the materials and emphasize the electromagnetic parameters and challenges. Finally, we provide insights and suggestions for the future development of MXene/polymer composites for EMI shielding applications.

Manipulation of Impedance Matching toward 3D-Printed Lightweight and Stiff MXene-Based Aerogels for Consecutive Multiband Tunable Electromagnetic Wave Absorption

Highly conductive MXene material exhibits outstanding dissipation capability of electromagnetic (EM) waves. However, the interfacial impedance mismatch due to high reflectivity restricts the application of MXene-based EM wave absorbing materials. Herein, a direct ink writing (DIW) 3D printing strategy to construct lightweight and stiff MXene/graphene oxide aerogels (SMGAs) with controllable fret architecture is demonstrated, exhibiting tunable EM wave absorption properties by manipulating impedance matching. Noteworthy, the maximum reflection loss variation value (ΔRL) of SMGAs is -61.2 dB by accurately modulating the width of the fret architecture. The effective absorption region (f_E) of SMGAs exhibits consecutive multiband tunability, and the broadest tunable f_E (Δf) is 14.05 GHz, which could be continuously tuned in the whole C- (4-8 GHz), X- (8-12 GHz), and Ku-bands (12-18 GHz). Importantly, the hierarchical structures and the orderly stacking of filaments endow lightweight SMGAs (0.024 g cm^-3) with a surprising compression resistance, which can withstand 36 000 times its own weight without obvious deformation. Finite element analysis (FEA) further indicates that the hierarchical structure facilitates stress dispersion. The strategy developed here provides a method for fabricating tunable MXene-based EM wave absorbers that are lightweight and stiff.

Regulation of Impedance Matching and Dielectric Loss Properties of N-Doped Carbon Hollow Nanospheres Modified With Atomically Dispersed Cobalt Sites for Microwave Energy Attenuation

The rational design of lightweight, broad-band, and high-performance microwave absorbers is urgently required for addressing electromagnetic pollution issue. Metal single atoms (M-SAs) absorbers receive considerable interest in the field of microwave absorption due to the unique electronic structures of M-SAs. However, the simultaneous engineering of the morphology and electronic structure of M-SAs based absorbers remains challenging. Herein, a template-assisted method is utilized to fabricate isolated Co-SAs on N-doped hollow carbon spheres (NHCS@Co-SAs) for high-performance microwave absorption. The combination of atomically dispersed Co sites and hollow supports endows NHCS@Co-SAs with excellent microwave absorption properties. Typically, at an ultralow filler content of 8 wt%, the minimum reflection loss and effective absorption bandwidth of the NHCS@Co-SAs are up to -44.96 dB and 5.25 GHz, respectively, while the absorbing thickness is only 2 mm. Theoretical calculations and experimental results indicate that the impedance matching characteristic and dielectric loss of the NHCSs can be tuned via the introduction of M-SAs, which are responsible for the excellent microwave absorption properties of NHCS@Co-SAs. This work provides an atomic-level insight into the relationship between the electronic states of absorbers and their microwave absorption properties for developing advanced microwave absorbers.

Recent Advances and Perspectives of Lewis Acidic Etching Route: An Emerging Preparation Strategy for MXenes

Since the discovery in 2011, MXenes have become the rising star in the field of two-dimensional materials. Benefiting from the metallic-level conductivity, large and adjustable gallery spacing, low ion diffusion barrier, rich surface chemistry, superior mechanical strength, MXenes exhibit great application prospects in energy storage and conversion, sensors, optoelectronics, electromagnetic interference shielding and biomedicine. Nevertheless, two issues seriously deteriorate the further development of MXenes. One is the high experimental risk of common preparation methods such as HF etching, and the other is the difficulty in obtaining MXenes with controllable surface groups. Recently, Lewis acidic etching, as a brand-new preparation strategy for MXenes, has attracted intensive attention due to its high safety and the ability to endow MXenes with uniform terminations. However, a comprehensive review of Lewis acidic etching method has not been reported yet. Herein, we first introduce the Lewis acidic etching from the following four aspects: etching mechanism, terminations regulation, in-situ formed metals and delamination of multi-layered MXenes. Further, the applications of MXenes and MXene-based hybrids obtained by Lewis acidic etching route in energy storage and conversion, sensors and microwave absorption are carefully summarized. Finally, some challenges and opportunities of Lewis acidic etching strategy are also presented.

Induced Crystallization-Controllable Nanoarchitectonics of 3D-Ordered Hierarchical Macroporous Co@N-Doped Carbon Frameworks for Enhanced Microwave Absorption

The construction of ordered hierarchical porous structures in metal-organic frameworks (MOFs) and their derivatives is highly promising to meet the low-density and high-performance demands of microwave absorption materials. However, traditional methods based on sacrificial templates or corrosive agents inevitably suffer from the collapse of the microporous framework and the accumulation of nanoparticles during the carbonization transformation, resulting in the deteriorating impedance match, which greatly limits the incident and attenuation of microwaves. Herein, an induced crystallization and controllable nanoarchitectonics strategy is employed to replace traditional growing-etching methods and successfully synthesize carbonized 3D-ordered macroporous Co@N-doped carbon (3DOM Co@NDC) based on the 3D-ordered template. The obtained 3D-ordered macroporous structure ensures the stable growth of hybrid carbon frameworks and CoC nanoparticles without collapse, preserves abundant interfaces for both the incident and attenuation performance, so as to significantly improve the impedance matching and absorption properties compared to conventional MOFs derivatives. The minimum reflection loss of 3DOM Co@NDC is -57.36 dB at the thickness of 1.9 mm, and the effective bandwidth is 7.36 GHz at 1.6 mm. Moreover, the innovative strategy to prepare 3D-ordered hierarchical macroporous structures opens up a new avenue for advanced MOFs-derived absorbers with excellent performance.

In Situ Synthesis of C-N@NiFe2O4@MXene/Ni Nanocomposites for Efficient Electromagnetic Wave Absorption at an Ultralow Thickness Level

Recently, the development of composite materials composed of magnetic materials and MXene has attracted significant attention. However, the thickness and microwave absorption performance of the composite is still barely satisfactory. In this work, the C-N@NiFe₂O₄@MXene/Ni nanocomposites were successfully synthesized in situ by hydrothermal and calcination methods. Benefiting from the introduction of the carbon-nitrogen(C-N) network structure, the overall dielectric properties are improved effectively, consequently reducing the thickness of the composite while maintaining excellent absorption performance. As a result, the minimum reflection loss of C-N@NiFe₂O₄@MXene/Ni can reach -50.51 dB at 17.3 GHz at an ultralow thickness of 1.5 mm, with an effective absorption bandwidth of 4.95 GHz (13.02-18 GHz). This research provides a novel strategy for materials to maintain good absorption performance at an ultralow thickness level.

Carbon-encapsulated core-shell structure ZnFe2O4 sphere composites coupled with excellent microwave absorption and corrosion resistance

Microwave absorbing materials (MAMs) have been identified as an efficient means to solve major electromagnetic pollution problems. Current core-shell composite MAMs are fabricated as single magnetic cores with dielectric shells, yielding decreased magnetic couplings and impedance mismatches. Herein, carbon shell encapsulated core-shell structured zinc ferrate (ZnFe₂O₄) sphere composites (CSZF@C) were fabricated using a hydrothermal method and subsequent carbonisation process. The complex permittivity and complex permeability of CSZF@C can be effectively adjusted by varying the parameters of the outer carbon shell. The synergistic effect of carbon shell and inner core-shell structured ZnFe₂O₄ (CSZF) not only meets impedance matching but also improves electromagnetic energy loss, a result of the unique microstructure. CSZF@C-1 exhibited a considerable reflection loss (RL) of -53.5 dB and an effective absorption bandwidth (EAB) of up to 6.56 GHz, the thickness is only 2.94 mm. Meanwhile, the epoxy resin coating of CSZF@C-1 substantially increases the corrosion resistance of the metal substrate owing to carbon encapsulation. This study presents new ideas for designing efficient multifunctional nanocomposites with high microwave absorption and corrosion resistance.

High-temperature stability in air of Ti3C2Tx MXene-based composite with extracted bentonite

Although Ti₃C₂T_x MXene is a promising material for many applications such as catalysis, energy storage, electromagnetic interference shielding due to its metallic conductivity and high processability, it’s poor resistance to oxidation at high temperatures makes its application under harsh environments challenging. Here, we report an air-stable Ti₃C₂T_x based composite with extracted bentonite (EB) nanosheets. In this case, oxygen molecules are shown to be preferentially adsorbed on EB. The saturated adsorption of oxygen on EB further inhibits more oxygen molecules to be adsorbed on the surface of Ti₃C₂T_x due to the weakened p-d orbital hybridization between adsorbed O₂ and Ti₃C₂T_x, which is induced by the Ti₃C₂T_x/EB interface coupling. As a result, the composite is capable of tolerating high annealing temperatures (above 400 °C for several hours) both in air or humid environment, indicating highly improved antioxidation properties in harsh condition. The above finding is shown to be independent on the termination ratio of Ti₃C₂T_x obtained through different synthesis routes. Utilized as terahertz shielding materials, the composite retains its shielding ability after high-temperature treatment even up to 600 °C, while pristine Ti₃C₂T_x is completely oxidized with no terahertz shielding ability. Joule heating and thermal cycling performance are also demonstrated.

A major challenge for the effective use of Ti-based MXenes in applications with harsh environmental conditions is their poor resistance to oxidation. Here, authors report an air-stable Ti₃C₂T_x composite with extracted bentonite able to endure high-temperature annealing in air by an oxygen adsorption competition mechanism.

Achieving Ultra-Wideband and Elevated Temperature Electromagnetic Wave Absorption via Constructing Lightweight Porous Rigid Structure

Realizing ultra-wideband absorption, desirable attenuation capability at high temperature and mechanical requirements for real-life applications remains a great challenge for microwave absorbing materials. Herein, we have constructed a porous carbon fiber/polymethacrylimide (CP) structure for acquiring promising microwave absorption performance and withstanding both elevated temperature and high strength in a low density. Given the ability of porous structure to induce desirable impedance matching and multiple reflection, the absorption bandwidth of CP composite can reach ultra-wideband absorption of 14 GHz at room temperature and even cover the whole X-band at 473 K. Additionally, the presence of imide ring group in polymethacrylimide and hard bubble wall endows the composite with excellent heat and compressive behaviors. Besides, the lightweight of the CP composite with a density of only 110 mg cm^-3 coupled with high compressive strength of 1.05 MPa even at 453 K also satisfies the requirements in engineering applications. Compared with soft and compressible aerogel materials, we envision that the rigid porous foam absorbing material is particularly suitable for environmental extremes.

One-Dimensional Magnetic FeCoNi Alloy Toward Low-Frequency Electromagnetic Wave Absorption

Rational designing of one-dimensional (1D) magnetic alloy to facilitate electromagnetic (EM) wave attenuation capability in low-frequency (2-6 GHz) microwave absorption field is highly desired but remains a significant challenge. In this study, a composite EM wave absorber made of a FeCoNi medium-entropy alloy embedded in a 1D carbon matrix framework is rationally designed through an improved electrospinning method. The 1D-shaped FeCoNi alloy embedded composite demonstrates the high-density and continuous magnetic network using off-axis electronic holography technique, indicating the excellent magnetic loss ability under an external EM field. Then, the in-depth analysis shows that many factors, including 1D anisotropy and intrinsic physical features of the magnetic medium-entropy alloy, primarily contribute to the enhanced EM wave absorption performance. Therefore, the fabricated EM wave absorber shows an increasing effective absorption band of 1.3 GHz in the low-frequency electromagnetic field at an ultrathin thickness of 2 mm. Thus, this study opens up a new method for the design and preparation of high-performance 1D magnetic EM absorbers.

In Situ Fabrication of Magnetic and Hierarchically Porous Carbon Films for Efficient Electromagnetic Wave Shielding and Absorption

Carbon-based materials have been recognized as a promising method to eliminate electromagnetic interference (EMI) shielding and electromagnetic (EM) wave absorption. However, developing lightweight, ultrathin, and efficient EM wave-shielding and wave-absorbing materials remains a challenge. Herein, a series of magnetic porous carbon composite films with a hierarchical network structure were fabricated via pyrolysis of porous polyimide (PI) films containing magnetic metallic salts of Fe(acac)3 and Ni(acac)2. After pyrolysis, the obtained uniform porous carbon films (CFs) possess a favorable EMI-shielding efficiency (SE) of 46 dB in the X-band with a thickness of ∼0.3 mm. In addition, a higher EMI SE of 58 dB can be achieved by increasing the thickness of the porous CF-20Ni to 0.53 mm. Moreover, the CF-20Ni composites also present effective EM wave-absorbing performance of RLmin = - 30.2 dB with a loading amount of 20 wt % at 13.0 GHz owing to the hierarchically conductive carbon skeleton, magnetic Ni nanoparticles, and dielectric interlaced carbon nanotube cluster within the micropores. These novel lightweight and ultrathin porous CFs are expected to be attractive candidates for efficient EM wave absorption and EMI shielding.

Bio-inspired, bimetal ZIF-derived hollow carbon/MXene microstructure aim for superior microwave absorption

Electromagnetic pollution has become an increasingly important problem which has drawbacks to both the accurate operation of the electronic facilities and the safety of human beings. To alleviate and eliminate electromagnetic irradiation, it is inevitable to design microwave absorption materials with desirable absorption intensity and broad effective frequency bandwidth. The combination of carbon-based materials and magnetic materials is an adoptable strategy to perform remarkable microwave absorption performance, while the microstructure should not be ignored. Inspired by the electromagnetic response behaviors of the microstructure from the leafhopper, the hetero-microstructure with hollow void is constructed by adopting bimetal ZIF as the precursor, followed by an interfacial tailoring strategy through electrostatic assembling and calcinating process, which enhances the microwave absorption performance by integrating the merits between the components and the micro-structure. The minimum value of reflection loss achieved -76.40 dB at 7.50 GHz under filler loading of 20% with the thickness of 2.92 mm. Besides, the effective absorption bandwidth could be tailored from 3.55 to 18 GHz among different thicknesses as required. The bio-inspired strategy is validated as a promising method, exhibiting great potential in the designing of the next-generation microwave absorber.

High-Performance Ferroelectric Electromagnetic Attenuation Materials with Multiple Polar Units Based on Nanodomain Engineering

The multirelaxation behavior is promising for high-performance dielectric materials based on polarization-controllable high-efficiency electromagnetic attenuation. However, a single polar unit is the main problem that restricts the development of dielectric materials in the field. Herein, by constructing multiple polar units based on nanodomain engineering, enhanced electromagnetic attenuation properties are achieved in La doping BiFeO₃ ferroelectric ceramics. A dual-band attenuation with a maximum reflection loss of -43.4 dB together with a wide effective bandwidth (<-10 dB) of 3.3 GHz in X-band, is acquired in Bi_0.85 La_0.15 FeO₃ which just has a thickness of 1.54 mm. A systematic experimental analysis coupled with potential well modeling suggests that the miniaturization of the ferroelectric domain, from micron to nanoscale, induces an additional interface polarization that is capable of responding to microwave frequency, leading to the formation of dual dielectric relaxation. The way that intrinsic polar unit induces another polar unit through size effect to obtain multiple contributions of electromagnetic loss provides a feasible and universal strategy to design high-performance electromagnetic attenuation materials based on the ferroelectric family.

Dimensional Design and Core-Shell Engineering of Nanomaterials for Electromagnetic Wave Absorption

Electromagnetic (EM) wave absorption materials possess exceptionally high EM energy loss efficiency. With vigorous developments in nanotechnology, such materials have exhibited numerous advanced EM functions, including radiation prevention and antiradar stealth. To achieve improved EM performance and multifunctionality, the elaborate control of microstructures has become an attractive research direction. By designing them as core-shell structures with different dimensions, the combined effects, such as interfacial polarization, conduction networks, magnetic coupling, and magnetic-dielectric synergy, can significantly enhance the EM wave absorption performance. Herein, the advances in low-dimensional core-shell EM wave absorption materials are outlined and a selection of the most remarkable examples is discussed. The derived key information regarding dimensional design, structural engineering, performance, and structure-function relationship are comprehensively summarized. Moreover, the investigation of the cutting-edge mechanisms is given particular attention. Additional applications, such as oxidation resistance and self-cleaning functions, are also introduced. Finally, insight into what may be expected from this rapidly expanding field and future challenges are presented.

State of the Art and Prospects in Metal-Organic Framework-Derived Microwave Absorption Materials

Microwave has been widely used in many fields, including communication, medical treatment and military industry; however, the corresponding generated radiations have been novel hazardous sources of pollution threating human's daily life. Therefore, designing high-performance microwave absorption materials (MAMs) has become an indispensable requirement. Recently, metal-organic frameworks (MOFs) have been considered as one of the most ideal precursor candidates of MAMs because of their tunable structure, high porosity and large specific surface area. Usually, MOF-derived MAMs exhibit excellent electrical conductivity, good magnetism and sufficient defects and interfaces, providing obvious merits in both impedance matching and microwave loss. In this review, the recent research progresses on MOF-derived MAMs were profoundly reviewed, including the categories of MOFs and MOF composites precursors, design principles, preparation methods and the relationship between mechanisms of microwave absorption and microstructures of MAMs. Finally, the current challenges and prospects for future opportunities of MOF-derived MAMs are also discussed.

High-Density Anisotropy Magnetism Enhanced Microwave Absorption Performance in Ti3C2Tx MXene@Ni Microspheres

Two-dimensional materials, especially the newly emerging MXene, have attracted numerous interests in the fields of energy conversion/storage and electromagnetic shielding/absorption. However, the inherently inevitable aggregation and absence of magnetic loss of MXene considerably limit its electromagnetic absorption application. The introduction of magnetic component and favorable structural engineering are the alternatives to improve the microwave absorption (MA) performance. Herein, we report a spheroidization strategy to assemble double-shell MXene@Ni microspheres, where the commonly lamellar MXene are reshaped into three-dimensional microspheres that provide the substrate for oriented growth of Ni nanospikes. Whereas this structural feature offers massive accessible active surfaces that effectively promote the dielectric loss ability, the introduction of magnetic Ni nanospikes enables the additional magnetic loss capacity. Benefiting from these merits, the synthesized 3D MXene@Ni microspheres exhibit superior MA performance with the minimum reflection loss value of -59.6 dB at an ultrathin thickness (∼1.5 mm) and effective absorption bandwidth of 4.48 GHz. Moreover, the electron holography results reveal that the high-density anisotropy magnetism plays an important role in the improvement of MA performance, which provides an insight for the design of MXene-based materials as high-efficient microwave absorbers.

Bio-Inspired Microwave Modulator for High-Temperature Electromagnetic Protection, Infrared Stealth and Operating Temperature Monitoring

High-temperature electromagnetic (EM) protection materials integrated of multiple EM protection mechanisms and functions are regarded as desirable candidates for solving EM interference over a wide temperature range. In this work, a novel microwave modulator is fabricated by introducing carbonyl iron particles (CIP)/resin into channels of carbonized wood (C-wood). Innovatively, the spaced arrangement of two microwave absorbents not only achieves a synergistic enhancement of magnetic and dielectric losses, but also breaks the translational invariance of EM characteristics in the horizontal direction to obtain multiple phase discontinuities in the frequency range of 8.2-18.0 GHz achieving modulation of reflected wave radiation direction. Accordingly, CIP/C-wood microwave modulator demonstrates the maximum effective bandwidth of 5.2 GHz and the maximum EM protection efficiency over 97% with a thickness of only 1.5 mm in the temperature range 298-673 K. Besides, CIP/C-wood microwave modulator shows stable and low thermal conductivities, as well as monotonic electrical conductivity-temperature characteristics, therefore it can also achieve thermal infrared stealth and working temperature monitoring in wide temperature ranges. This work provides an inspiration for the design of high-temperature EM protection materials with multiple EM protection mechanisms and functions.

Identification of the Intrinsic Dielectric Properties of Metal Single Atoms for Electromagnetic Wave Absorption

Atomically dispersed metals on N-doped carbon supports (M-N_xCs) have great potential applications in various fields. However, a precise understanding of the definitive relationship between the configuration of metal single atoms and the dielectric loss properties of M-N_xCs at the atomic-level is still lacking. Herein, we report a general approach to synthesize a series of three-dimensional (3D) honeycomb-like M-N_xC (M = Mn, Fe, Co, Cu, or Ni) containing metal single atoms. Experimental results indicate that 3D M-N_xCs exhibit a greatly enhanced dielectric loss compared with that of the NC matrix. Theoretical calculations demonstrate that the density of states of the d orbitals near the Fermi level is significantly increased and additional electrical dipoles are induced due to the destruction of the symmetry of the local microstructure, which enhances conductive loss and dipolar polarization loss of 3D M-N_xCs, respectively. Consequently, these 3D M-N_xCs exhibit excellent electromagnetic wave absorption properties, outperforming the most commonly reported absorbers. This study systematically explains the mechanism of dielectric loss at the atomic level for the first time and is of significance to the rational design of high-efficiency electromagnetic wave absorbing materials containing metal single atoms.

MXene/Carbon Nanotube Hybrids: Synthesis, Structures, Properties, and Applications

Since the successful preparation of few-layer transition metal carbides from three-dimensional MAX phases in 2011, MXenes (known as a family of layered transition metal carbides, nitrides, and carbonitrides) have been intensively studied. Though MXenes have been adopted as active materials in many applications, issues including aggregation and restacking are likely to hamper their potential applications. In order to address these prevailing challenges, the concept of MXene/carbon nanotube (CNT) hybrids was proposed initially in 2015, where CNTs were incorporated as the spacers and conductive additives. Ever since, MXene/CNT hybrids with different architectures have been synthesized by a number of methods and applied in numerous fields. Herein, after the discussion about general synthesis approaches, architectures, and properties of the hybrids, this Review summarized the recent advances in the application of MXene/CNT hybrids in energy storage devices, sensors, electrocatalysis, electromagnetic interference shielding, and water treatment, in which the function of individual components was clarified. In the end, the current research trend in this field were discussed and several technical issues were highlighted along with some suggestions on future research directions.

Nitrogen-Doped Ti3C2Tx MXene Induced by Plasma Treatment with Enhanced Microwave Absorption Properties

Ti₃C₂T_x has microwave absorption (MA) properties due to its dielectric loss, but the absence of magnetic loss capability of pure Ti₃C₂T_x causes unmatched impedance and unsatisfied MA performance. Modification of Ti₃C₂T_x with magnetic particles is an effective way to introduce the magnetic loss mechanism. However, these modified Ti₃C₂T_x particles have higher density and require complicated fabrication processes, restricting the industrial production and functional applications. Here, a low-temperature and simple method of radio-frequency N₂ plasma treatment was adopted to modify Ti₃C₂T_x with N. More interestingly, the N-doped Ti₃C₂T_x flakes demonstrated magnetic properties and thus exhibited drastically enhanced MA properties. The minimum reflection loss (RL_min) of -59.20 dB at 10.56 GHz was achieved in N-doped Ti₃C₂T_x products after only 3 min of plasma treatment, remarkably higher than RL_min of -11.07 dB at 7.92 GHz for the pristine Ti₃C₂T_x. The main mechanism is due to the combination of dielectric loss, magnetic loss, and the good impedance matching in the N-doped Ti₃C₂T_x. Further prolonging the nitriding time induces much desorption of -F and the formation of TiO₂, thus deteriorating the impedance matching and the MA properties.