Atomic Layer Tailoring Titanium Carbide MXene To Tune Transport and Polarization for Utilization of Electromagnetic Energy beyond Solar and Chemical Energy

Recent achievements and performance of nanomaterials in microwave absorption and electromagnetic shielding

Due to the swift advancement of the electronic industry and information technology, electromagnetic wave absorption materials are gaining significance in the field of intelligent equipment and weaponry. Nanomaterials were developed to investigate wave absorbing materials that can achieve both impedance matching and attenuation balance. Nanomaterials possess the properties of being thin, lightweight, and capable of absorbing microwave radiation across a wide range of frequencies. This work aims to present a systematic overview of the recent advancements in core-shell materials, specifically carbon, oxide, and sulfide nanomaterials, with regards to their applications in electromagnetic absorption and electromagnetic shielding. This review intends to emphasize the core principles of electromagnetic interference (EMI) shielding and microwave absorption in different systems documented in the literature, along with diverse methods of synthesis and fabrication for creating effective wideband electromagnetic absorbers/shields. Lastly, we also endeavor to offer a comprehensive view and insight into the areas where future research will thrive. This study provides a comprehensive assessment of the current advancements in the field of microwave absorption and electromagnetic shielding of nanomaterials.

Kirkendall Effect-Induced Ternary Heterointerfaces Engineering for High Polarization Loss MOF-LDH-MXene Absorbers

Heterogeneous interfacial engineering has garnered widespread attention for optimizing polarization loss and enhancing the performance of electromagnetic wave absorption. A novel Kirkendall effect-assisted electrostatic self-assembly method is employed to construct a metal-organic framework (MOF, MIL-88A) decorated with Ni-Fe layered double hydroxide (LDH), forming a multilayer nano-cage coated with Ti3C2Tx. By modulating the surface adsorption of Ti3C2Tx on LDH, the heterointerfaces in MOF-LDH-MXene ternary composites exhibit excellent interfacial polarization loss. Additionally, the Ni-Fe LDH@Ti3C2Tx nano-cage exhibits a large specific surface area, abundant defects, and a large number of heterojunction structures, resulting in excellent electromagnetic wave absorption performance. The MIL-88A@Ni-Fe LDH@Ti3C2Tx-1.0 nano-cage achieves a reflection loss value of -46.7 dB at a thickness of 1.4 mm and an effective absorption bandwidth of 5.12 GHz at a thickness of 1.8 mm. The heterojunction interface composed of Ni-Fe LDH and Ti3C2Tx helps to enhance polarization loss. Additionally, Ti3C2Tx forms a conductive network on the surface, while the cavity between the MIL-88A core and the Ni-Fe LDH shell facilitates multiple attenuations by increasing the transmission path of internal incident waves. This work may reveal a new structural design of multi-component composites by heterointerfaces engineering for electromagnetic wave absorption.

Pressure-Induced Molding of Black Phosphorus@Ti3C2Tx Composite Electrode and Its Implications on the Lithium Storage

For the first time, an innovative pressure quenching technique is used to create the integrated electrode of the black phosphorus (BP) @Ti3C2Tx composite material, doing away with the requirement for adhesive additives and simplifying time-consuming processes. Through the formation of Ti-O-P bonds with BP, Ti3C2Tx MXenes can function as conductive additives and affect the interlayer gap. Additionally, we have found that there is a critical synthetic pressure threshold (300 kN) at which the performance of BP@Ti3C2Tx-integrated electrodes can be improved: too high of a pressure prevents lithium-ion transport because of mesopore reduction; too low of a pressure prevents Ti-O-P chemical bond formation between the two components; and suboptimal pressure does not allow for density enhancement for better electron conduction. The integrated electrode produced at 300 kN shows a discharge capacity of about 724.9 mA h/g at 0.1 A/g current density after 100 cycles, which is much larger than that obtained at 50 kN (270.2 mA h/g). Furthermore, the capacity can remain steady at 560.74 mA h/g even after 500 lengthy cycles at the high current density of 0.5 A/g. Significantly lower resistance (1.10 × 102 Ω at 300 kN; 2.02 × 103 Ω at 50 kN) and faster reaction kinetics are responsible for this improvement. This study offers a new, straightforward, and broadly useful technique for creating integrated electrodes and BP-based composite materials.

Charge Dynamics Engineering Sparks Hetero-Interfacial Polarization for an Ultra-Efficient Microwave Absorber with Mechanical Robustness

Microwave absorbers with high efficiency and mechanical robustness are urgently desired to cope with more complex and harsh application scenarios. However, manipulating the trade-off between microwave absorption performance and mechanical properties is seldom realized in microwave absorbers. Here, a chemistry-tailored charge dynamic engineering strategy is proposed for sparking hetero-interfacial polarization and thus coordinating microwave attenuation ability with the interfacial bonding, endowing polymer-based composites with microwave absorption efficiency and mechanical toughness. The absorber designed by this new conceptual approach exhibits remarkable Ku-band microwave absorption efficiency (-55.3 dB at a thickness of 1.5 mm) and satisfactory effective absorption bandwidth (5.0 GHz) as well as desirable interfacial shear strength (97.5 MPa). The calculated differential charge density depicts the uneven distribution of space charge and the intense hetero-interfacial polarization, clarifying the structure-performance relationship from a theoretical perspective. This work breaks through traditional single performance-oriented design methods and ushers a new direction for next-generation microwave absorbers.

Facile constructing Ti3C2Tx/TiO2@C heterostructures for excellent microwave absorption properties

Optimizing and enhancing the performance of electromagnetic wave (EMW) absorption materials relies on the modification of their composition and structure through heterogeneous interface engineering. Ti3C2Tx's high conductivity results in an impedance mismatch, which hinders efficient EMW absorption. Herein, a one-step catalytic chemical vapor deposition (CCVD) method is used to construct the Ti3C2Tx/TiO2@C heterogeneous structure. Upon annealing at 500 °C, amorphous carbon is uniformly deposited on the Ti3C2Tx surface, thereby incorporating the scale-like TiO2 generated during the process. The inclusion of the amorphous carbon layer and TiO2 reduces the substrate's conductivity, achieving optimized impedance matching. Additionally, building heterogeneous interfaces between Ti3C2Tx, TiO2, and C enriches multiple loss mechanisms involving dipole and interfacial polarization, ultimately enabling optimal EMW absorption performance. The minimum reflection loss (RLmin) value of Ti3C2Tx/TiO2@C-500 is -53.12 dB when its thickness and frequency are 1.15 mm and 13.80 GHz, respectively. Moreover, thermal infrared imaging confirms that coatings fabricated using Ti3C2Tx/TiO2@C-500 demonstrate a favorable heat dissipation rate, validating its effectiveness in addressing the challenge of efficient heat dissipation in electronic devices. This study significantly contributes to the progress of two-dimensional (2D) materials, enabling high-performance EMW absorption and expanding their applications in complex scenarios.

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.

Construction of MoS2-ReS2 Hybrid on Ti3C2Tx MXene for Enhanced Microwave Absorption

Utilizing interface engineering to construct abundant heterogeneous interfaces is an important means to improve the absorbing performance of microwave absorbers. Here, we have prepared the MXene/MoS2-ReS2 (MMR) composite with rich heterogeneous interfaces composed of two-dimensional Ti3C2Tx MXene and two-dimensional transition metal disulfides through a facile hydrothermal process. The surface of MXene is completely covered by nanosheets of MoS2 and ReS2, forming a hybrid structure. MRR exhibits excellent absorption performance, with its strongest reflection loss reaching -51.15 dB at 2.0 mm when the filling ratio is only 10 wt%. Meanwhile, the effective absorption bandwidth covers the range of 5.5-18 GHz. Compared to MXene/MoS2 composites, MRR with a MoS2-ReS2 heterogeneous interface exhibits stronger polarization loss ability and superior absorption efficiency at the same thickness. This study provides a reference for the design of transition metal disulfides-based absorbing materials.

Thermally Derived Hierarchical Nanoplates for Electromagnetic Protection and Waste Energy Recovery Device

With the advent of intelligent society and the popularity of electronic equipment, the protection and treatment of electromagnetic (EM) radiation have become hot research topics all over the world. Herein, novel 2D carbon-based nanoplates with uniformly embedded Co nanoparticles are prepared, with unique hierarchical structure and integrated magnetic-dielectric components. The obtained hierarchical nanoplates exhibit a wide range of tunable EM properties (ε' for 3.38 to 34.67 and ε″ for 0.13 to 31.45) by manipulating the dispersed states inside wax system, which can achieve an effective switch from microwave absorption to EM interference shielding performance. The optimal reflection loss reaches -55.6 dB, and the shielding efficiency is 93.5%. Meanwhile, the hierarchical nanoplates also exhibit impressive capacitive performance, with a specific capacitance of 1654 F g-1 at 1 A g-1 . Based on this, a creative device is constructed with the nanoplates, which can convert harmful EM radiation to useful electric energy for recycling. This work offers a new idea for the development of EM materials and functional devices, powerfully promoting the advance of energy and environmental fields.

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.

Microwave-Excited, Antibacterial Core-Shell BaSO4/BaTi5O11@PPy Heterostructures for Rapid Treatment of S. aureus-Infected Osteomyelitis

Owing to its deep penetration capability, microwave (MW) therapy has emerged as a promising method to eradicate deep-seated acute bone infection diseases such as osteomyelitis. However, the MW thermal effect still needs to be enhanced to achieve rapid and efficient treatment of deep focal infected areas. In this work, the multi-interfacial core-shell structure barium sulfate/barium polytitanates@polypyrrole (BaSO₄/BaTi₅O₁₁@PPy) was prepared, which exhibited enhanced MW thermal response via the well-designed multi-interfacial structure. To be specific, BaSO₄/BaTi₅O₁₁@PPy achieved rapid temperature increases in a short period and efficient clearance of Staphylococcus aureus (S. aureus) infections under MW irradiation. After 15 min MW irradiation, the antibacterial efficacy of BaSO₄/BaTi₅O₁₁@PPy can reach up to 99.61 ± 0.22%. Their desirable thermal production capabilities originated from enhanced dielectric loss including multiple interfacial polarization and conductivity loss. Additionally, in vitro analysis illuminated that the underlying antimicrobial mechanism was attributed to the noticeable MW thermal effect and changes in energy metabolic pathways on bacterial membrane instigated by BaSO₄/BaTi₅O₁₁@PPy under MW irradiation. Considering remarkable antibacterial efficiency and acceptable biosafety, we envision that it has significant value in broadening the pool of desirable candidates to fight against S. aureus-infected osteomyelitis. STATEMENT OF SIGNIFICANCE: : The treatment of deep bacterial infection remains challenging due to the ineffectiveness of antibiotic treatment and the susceptibility to bacterial resistance. Microwave (MW) thermal therapy (MTT) is a promising approach with remarkable penetration to centrally heat up the infected area. This study proposes to utilize the core-shell structure BaSO₄/BaTi₅O₁₁@PPy as an MW absorber to achieve localized heating under MW radiation for MTT. In vitro experiments demonstrated that the disrupted bacterial membrane is primarily due to the localized high temperature and interrupted electron transfer chain. As a consequence, its antibacterial rate is as high as 99.61% under MW irradiation. It is shown that the BaSO₄/BaTi₅O₁₁@PPy is a promising candidate for eliminating bacterial infection in deep-seated tissues.

Progress and challenges of emerging MXene based materials for thermoelectric applications

To realize sustainable development, more and more countries forwarded carbon neutrality goal. Accordingly, improving the utilization efficiency of traditional fossil fuel is an effective strategy for this great goal. Keeping this in mind, developing thermoelectric devices to recover waste heat energy resulted in the consumption process of fuel is demonstrated to be promising. High performance thermoelectric devices require advanced materials. MXenes are a kind of 2D materials with a layered structure, which demonstrate excellent thermoelectric performance owing to their unique physical, mechanical, and chemical properties. Also, substantial achievement has been gained during the past few years in synthesizing MXene based materials for thermoelectric devices. In this review, the mainstream synthetic routes of MXene from etching MAX were summarized. Significantly, the current state and challenges of research on improving the performance of MXene based thermoelectrics are explored, including pristine MXene and MXene based composites.

Upgrading Electricity Generation and Electromagnetic Interference Shielding Efficiency via Phase-Change Feedback and Simple Origami Strategy

Developing ultimate electromagnetic interference (EMI) shielding materials that can simultaneously upgrade the quality of generated electricity and the light-thermal-electric conversion efficiency based on traditional thermoelectric devices is crucially desired. Herein, a series of flexible multilayered phase change films (PCFs) is developed by a simple and novel origami strategy. The PCFs are first reported to improve the light-thermal-electric conversion efficiency by as high as 11.3%. Simultaneously, the PCFs could significantly upgrade the generated electricity on average voltage (27.3%), average current (23.8%), and lasting power outputs by 2010 times from microwatts to milliwatts. Besides, the EMI shielding efficiency of PCFs could be tuned from 39.2 to 71.9 dB by the origami process, the wide-range EMI shielding performance could be suitable for varying occasions. Overall, this work provides a promising solution for both the preparation of multifunctional materials, high-efficiency solar energy harvesting and upgrading electricity generation, which shows broad application prospects in EMI shielding, energy storage, and conversion.

Controllable Architecture of ZnO/FeNi Composites Derived from Trimetallic ZnFeNi Layered Double Hydroxides for High-Performance Electromagnetic Wave Absorbers

The optimization design of micro-structure and composition is an important strategy to obtain high-performance metal-based electromagnetic (EM) wave absorption materials. In this work, ZnO/FeNi composites derived from ZnFeNi layered double hydroxides are prepared by a one-step hydrothermal method and subsequent pyrolysis process, and can be employed as an effective alternative for high-performance EM wave absorber. A series of ZnO/FeNi composites with different structures are obtained by varying the molar ratios of Zn²⁺ /Fe³⁺ /Ni²⁺ , and the ZnO/FeNi composites with a Zn²⁺ /Fe³⁺ /Ni²⁺ molar ratio of 6:1:3 show a hierarchical flower-like structure. Owing to the strong synergistic loss mechanism of dielectric-magnetic components and favorable structural features, this hierarchical flower-like ZnO/FeNi sample supplies the optimal EM wave absorption performance with the highest reflection loss of -52.08 dB and the widest effective absorption bandwidth of 6.56 GHz. The EM simulation further demonstrates that impedance matching plays a determining role in EM wave absorption performance. This work provides a new way for the fabrication of a high-performance metal-based EM wave absorber.

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

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

Synergistic Effect of Fe Single-Atom Catalyst for Highly Efficient Microwave-Stimulated Remediation of Chloramphenicol-Contaminated Soil

Chloramphenicol (CAP) has long been used extensively in agriculture and is severely toxic to the biological environment. Microwave catalysis appears a promising method for soil remediation due to its fast and effective heat transfer, but it is challenging to prepare catalysts with good electromagnetic wave absorption and robust catalytic activity. In this study, atomically dispersed Fe on three-dimensional N-doped carbon supports (3D Fe-NC) is firstly used for microwave remediation of soil. Thanks to the synergistic effect of microwave "hot spots" and reactive oxygen species (•OH, •O₂ ^- ), 3D Fe-NC can completely remove 99.9% of CAP in 5 min. The removal rate constant is nearly twice that of commercial activated carbon. Significantly, the germination rate of lettuce seeds in microwave-repaired soil contaminated by CAP reaches 70%. This work demonstrates the application of Fe single-atom catalyst in microwave remediation of contaminated soil, providing a novel insight for agricultural soil remediation.

Constructing Active Sites on Self-Supporting Ti3C2Tx (T = OH) Nanosheets for Enhanced Photocatalytic CO2 Reduction into Alcohols

Ti3C2Tx (T = OH) was first prepared from Ti3AlC2 by HF etching and applied into a photocatalytic CO2 reduction. Then, the Ti3C2Tx nanosheets present interbedded a self-supporting structure and extended interlayer spacing. Meanwhile, the Ti3C2Tx nanosheets are decorated with abundant oxygen-containing functional groups in the process of etching, which not only serve as active sites but also show efficient charge migration and separation. Among Ti3C2Tx materials prepared by etching for different times, Ti3C2Tx-36 (Etching time: 36 h) showed the best performance for photoreduction of CO2 into alcohols (methanol and ethanol), giving total yield of 61 μmol g catal.−1, which is 2.8 times than that of Ti3AlC2. Moreover, excellent cycling stability for CO2 reduction is beneficial from the stable morphology and crystalline structure. This work provided novel sights into constructing surface active sites controllably.

A Robust, Flexible, Hydrophobic, and Multifunctional Pressure Sensor Based on an MXene/Aramid Nanofiber (ANF) Aerogel Film

Pressure sensors with desirable flexibility, robustness, and versatility are urgently needed for complicated smart wearable devices. However, developing an ideal multifunctional flexible sensor is still challenging. In this work, a composite aerogel film sensor with an internal three-dimensional (3D) microporous and hierarchical structure is successfully fabricated by the self-assembly of aramid nanofiber (ANF) and conductive MXene by vacuum-assisted filtration and ice crystal growth. The resultant MXene/ANF aerogel film with a mass ratio of 3/7 (30% MAAF) presents high robustness with an outstanding tensile strength of 14.1 MPa and a modulus of 455 MPa while retaining appealing flexibility and sensitive characteristics due to the 3D microstructure. Accompanied by superior electric conductivity, the MAAF sensor performs noticeably in human motion and microexpression detection with a fast response time of 100 ms and a high sensitivity of 37.4 kPa^-1. In addition, MAAF exhibits considerable thermal shielding performance based on the excellent thermostability. Moreover, it possesses prominent electrothermal property with a wide heating temperature range (32.7-242 °C) in a fast thermal response time (5 s) due to the Joule effect. Additionally, a hydrophobic SiO₂ coating is introduced on the surface of MAAF to further broaden the sensing application, and the obtained MAAF@SiO₂ sensor shows distinguished sensing capability underwater, which can be accurately applied to swimming monitoring. Therefore, this work provides a highly flexible, lightweight, robust, and multifunctional aerogel film sensor, showing promising potential in smart wearable sensing and healthcare devices, intelligent robots, and underwater detection.

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

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

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

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Shortening electron-transport-distance in compact structure improves conductivity

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Control of densification delivers high EMI shielding performance and air stability

Thermal Properties of MXenes and Relevant Applications

The properties and applications of MXenes (a family of layered transition metal carbides, nitrides, and carbonitrides) have aroused enormous research interests for a decade since the successful synthesis of few-layer transition metal carbides in 2011. Though MXenes, as the building blocks, have already been applied in various fields (such as wearable electronics) owing to the distinctive optical, mechanical and electrical properties, their thermal stability and intrinsic thermal properties were less thoroughly investigated compared to other characteristics in early reports. The pioneering theoretical prediction of the thermoelectric nature of MXenes was performed in 2013 while the first experiment-based report concerning the degradation behavior of the 2D structure at elevated temperatures in a controlled atmosphere was published in 2015, followed by numerous discoveries regarding the thermal properties of MXenes. Herein, after a brief description of the synthesis, this Review summarized the latest insights into the thermal stability and thermophysical properties of MXenes, and further associated these unique properties with relevant applications by multiple examples. Finally, current hurdles and challenges in this field were provided along with some advices on potential research directions in the future.

A General Way to Fabricate Chain-like Ferrite with Ultralow Conductive Percolation Threshold and Wideband Absorbing Ability

The magnetic nanochain-like material has been regards as one of the most promising electromagnetic (EM) absorbing material but remains a challenging. Herein, magnetic chain-like ferrite (included Fe3O4, CoFe2O4 and NiFe2O4) are successfully produced through a general solvothermal method, using PVP as the structural-liking agent. Experimental results confirm the ultimate sample possess a 3-dimensional chain-like structure which are constructed by numerous ferrite's nanoparticles with ~60 nm in diameter. Their electromagnetic parameters can be also manipulated by such a chain structure, especially the dielectric loss, where a sharply increases can be observed on within a lower filling ratio. It greatly benefits to the EM absorbing property. In this article, the electromagnetic absorption layer made with a lower content of ferrite possess the excellent electromagnetic absorption ability, where the optimized effective absorption band was nearly 6.4 GHz under a thickness of 1.8 mm. Moreover, the filling ratio is only 30 wt%. Our method for designing of chain-like magnetic material can be helpful for producing wideband electromagnetic absorption in a low filling ratio.

Dielectric Loss Mechanism in Electromagnetic Wave Absorbing Materials

Electromagnetic (EM) wave absorbing materials play an increasingly important role in modern society for their multi-functional in military stealth and incoming 5G smart era. Dielectric loss EM wave absorbers and underlying loss mechanism investigation are of great significance to unveil EM wave attenuation behaviors of materials and guide novel dielectric loss materials design. However, current researches focus more on materials synthesis rather than in-depth mechanism study. Herein, comprehensive views toward dielectric loss mechanisms including interfacial polarization, dipolar polarization, conductive loss, and defect-induced polarization are provided. Particularly, some misunderstandings and ambiguous concepts for each mechanism are highlighted. Besides, in-depth dielectric loss study and novel dielectric loss mechanisms are emphasized. Moreover, new dielectric loss mechanism regulation strategies instead of regular components compositing are summarized to provide inspiring thoughts toward simple and effective EM wave attenuation behavior modulation.

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.

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

The development of multifunctional and efficient electromagnetic wave absorbing materials is a challenging research hotspot. Here, the magnetized Ni flower/MXene hybrids are successfully assembled on the surface of melamine foam (MF) through electrostatic self-assembly and dip-coating adsorption process, realizing the integration of microwave absorption, infrared stealth, and flame retardant. Remarkably, the Ni/MXene-MF achieves a minimum reflection loss (RL_min) of - 62.7 dB with a corresponding effective absorption bandwidth (EAB) of 6.24 GHz at 2 mm and an EAB of 6.88 GHz at 1.8 mm. Strong electromagnetic wave absorption is attributed to the three-dimensional magnetic/conductive networks, which provided excellent impedance matching, dielectric loss, magnetic loss, interface polarization, and multiple attenuations. In addition, the Ni/MXene-MF endows low density, excellent heat insulation, infrared stealth, and flame-retardant functions. This work provided a new development strategy for the design of multifunctional and efficient electromagnetic wave absorbing materials.

Sensitive Micro-Breathing Sensing and Highly-Effective Photothermal Antibacterial Cinnamomum camphora Bark Micro-Structural Cotton Fabric via Electrostatic Self-Assembly of MXene/HACC

Natural fabrics are gradually becoming the ideal substrate for flexible smart wearable devices due to their excellent moisture absorption, softness, and skin-friendliness. However, the bonding fastness of the conductive layer and the corresponding durability during service have not yet been well satisfied. In this report, we successfully prepared a smart wearable multifunctional protective cotton fabric with microbreathing monitoring and rapid-photothermal antibacterial abilities of Cinnamomum camphora bark microstructure, by combining chitosan quaternary ammonium salt (HACC) with MXene nanosheets through electrostatic self-assembly. Impressively, MXene nanosheets and HACC established a strong interaction using the electrostatic attraction, endowing the fiber surface with ordered nanosheets. Meanwhile, the fabric decorated with MXene/HACC retains its original characteristics of outstanding breathability and softness, and its conductivity exhibits noticeable stability in terms of resistances to oxidation, washing, various solvents, and long-term bending cycles. On the basis of the principle of adsorption and release of water molecules in the MXene multilayer structures, the MXene/HACC fabric could accurately monitor the physiological health activities of users according to their breathing frequency and depth. Benefiting from the local surface plasmon resonance (LSPR) effect, the MXene/HACC shows encouraging photothermal conversion ability, photothermal stability under long time irradiation, washing resistance, and cycle stability. In addition, the fabric achieved an antibacterial efficiency of nearly 100% against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus within 5 min under an irradiation intensity of 400 mW/cm². More importantly, after 10 washes, the antibacterial efficiency against the two bacteria could still reach 99.975% and 99.98%, respectively. This multifunctional protective MXene/HACC cotton fabric is expected to play a unique role in the new generation of smart wearable microbreathing sensing and against to bacterial attack, and shows a broad application prospect.

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.

Fabrication of clay soil/CuFe2O4 nanocomposite toward improving energy and shielding efficiency of buildings

In this research, the energy and shielding efficiency of brick, fabricated by clay soil, as a practical building material was reinforced using CuFe₂O₄ nanoparticles. Initially, the nanoparticles were fabricated using the sol-gel method and then loaded in the brick matrix as a guest. The architected samples were characterized by X-ray powder diffraction (XRD), Fourier transform infrared (FTIR), diffuse reflection spectroscopy (DRS), field emission scanning electron microscopy (FE-SEM), High-resolution transmission electron microscopy (HRTEM), vibrating-sample magnetometer (VSM), differential scanning calorimetry (DSC) thermograms, and vector network analyzer (VNA) analyses. IR absorption of the tailored samples was monitored under an IR source using an IR thermometer. IR absorption and energy band gap attested that inserting the nanoparticles in brick medium led to the acceleration of a warming brick, desirable for energy efficiency in cold climates. It is worth noting that the brick/CuFe₂O₄ nanocomposite achieved a strong reflection loss (RL) of 58.54 dB and gained an efficient bandwidth as wide as 4.22 GHz (RL > 10 dB) with a thickness of 2.50 mm, meanwhile it shielded more than 58% of the electromagnetic waves at X-band by only a filler loading of 10 wt%. The microwave absorbing and shielding characteristics of the composite are mainly originated from conductive loss, electron hopping, natural and exchange resonance, relaxation loss, secondary fields, as well as eddy current loss. Interestingly, the shielding property of the nanocomposite was significantly generated from its absorbing features, reducing the secondary electromagnetic pollutions produced by the shielding materials applying the impedance mismatching mechanism.

Magnetic Energy Morphing, Capacitive Concept for Ni0.3Zn0.4Ca0.3Fe2O4 Nanoparticles Embedded in Graphene Oxide Matrix, and Studies of Wideband Tunable Microwave Absorption

Nanoparticles of Ni_0.3Zn_0.4Ca_0.3Fe₂O₄ (NZCF) were successfully prepared by the facile wet chemical method coupled with the sonochemical method. These nanoparticles were embedded in a graphene oxide (GO) matrix (NZCFG). Rietveld analyses of X-ray diffraction, transmission electron microscope, scanning electron microscope, and X-ray photoelectron spectroscopy were carried out to extract different relevant information regarding the structure, morphology, and ionic state. A major improvement in saturation magnetization is achieved due to substitution of Ca²⁺ in the ferrite lattice. Interestingly, the observed value of electromagnetic absorption for a sample thickness of 1.5 mm is ∼-67.7 dB at 13.3 GHz, and the corresponding bandwidth is 5.73 GHz. The Cole-Cole plot, the Jonscher power-law fitting, and the Nyquist plot confirm the probability of improved hopping conductance and attractive capacitive behavior in NZCFG. The presence of magnetic energy morphing in combination with a higher attenuation constant, lower skin depth, and various forms of resonance and relaxation makes NZCFG the most suitable for microwave absorption.

Ti3C2Txnanohybrids: tunable local conductive network and efficient EMI shielding performance for multifunctional materials and devices

Ti₃C₂T_xis an important member of the MXenes family. Due to its excellent electrical conductivity, adjustable atomic layer, and modifiable active surface, Ti₃C₂T_xhas attracted great attention in the field of electromagnetic interference (EMI) shielding. This paper introduces the important role of regulating conductive network to improve the EMI shielding performance of materials and summarizes the EMI shielding performance of Ti₃C₂T_xnanohybrids reported in recent years. In addition, Ti₃C₂T_xbased EMI shielding materials towards multifunctional devices are also systematically introduced. After that, the development status of Ti₃C₂T_xnanohybrids in the field of EMI shielding is objectively described, and the main problems and challenges are evaluated. Finally, the prospect of Ti₃C₂T_xnanohybrids for advanced and green EMI shielding materials is forecasted.

Preparation of self-healing hydrogel toward improving electromagnetic interference shielding and energy efficiency

In this study, a self-healing hydrogel was prepared that is transparent to visible (Vis) light while absorbing ultraviolet (UV), infrared (IR), and microwave. The optothermal features of the hydrogel were explored by monitoring temperature using an IR thermometer under an IR source. The hydrogel was synthesized using sodium tetraborate decahydrate (borax) and polyvinyl alcohol (PVA) as raw materials based on a facile thermal route. More significantly, graphene oxide (GO) and graphite-like carbon nitride (g-C3N4) nanostructures as well as carbon microsphere (CMS) were applied as guests to more dissect their influence on the microwave and optical characteristics. The morphology of the fillers was evaluated using field emission scanning electron microscopy (FE-SEM). Fourier transform infrared (FTIR) attested that the chemical functional groups of the hydrogel have been formed and the result of diffuse reflection spectroscopy (DRS) confirmed that the hydrogel absorbs UV while is transparent in Vis light. The achieved result implied that the hydrogel acts as an essential IR absorber due to its functional groups desirable for energy efficiency and harvesting. Interestingly, the achieved results have testified that the self-healing hydrogels had the proper self-healing efficiency and self-healing time. Eventually, microwave absorbing properties and shielding efficiency of the hydrogel, hydrogel/GO, g-C3N4, or CMS were investigated, demonstrating the salient microwave characteristics, originated from the established ionic conductive networks and dipole polarizations. The efficient bandwidth of the hydrogel was as wide as 3.5 GHz with a thickness of 0.65 mm meanwhile its maximum reflection loss was 75.10 dB at 14.50 GHz with 4.55 mm in thickness. Particularly, the hydrogel illustrated total shielding efficiency (SET) > 10 dB from 1.19 to 18 and > 20 dB from 4.37 to 18 GHz with 10.00 mm in thickness. The results open new windows toward improving the shielding and energy efficiency using practical ways.

Architecting functionalized carbon microtube/carrollite nanocomposite demonstrating significant microwave characteristics

Biomass-derived materials have recently received considerable attention as lightweight, low-cost, and green microwave absorbers. On the other hand, sulfide nanostructures due to their narrow band gaps have demonstrated significant microwave characteristics. In this research, carbon microtubes were fabricated using a biowaste and then functionalized by a novel complementary solvothermal and sonochemistry method. The functionalized carbon microtubes (FCMT) were ornamented by CuCo2S4 nanoparticles as a novel spinel sulfide microwave absorber. The prepared structures illustrated narrow energy band gap and deposition of the sulfide structures augmented the polarizability, desirable for dielectric loss and microwave attenuation. Eventually, the architected structures were blended by polyacrylonitrile (PAN) to estimate their microwave absorbing and antibacterial characteristics. The antibacterial properties against Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) were scrupulously assessed. Noteworthy, the maximum reflection loss (RL) of the CuCo2S4/PAN with a thickness of 1.75 mm was 61.88 dB at 11.60 GHz, while the architected FCMT/PAN composite gained a broadband efficient bandwidth as wide as 7.91 GHz (RL > 10 dB) and 3.25 GHz (RL > 20 dB) with a thickness of 2.00 mm. More significantly, FCMT/CuCo2S4/PAN demonstrated an efficient bandwidth of 2.04 GHz (RL > 20 dB) with only 1.75 mm in thickness. Interestingly, FCMT/CuCo2S4/PAN and CuCo2S4/PAN composites demonstrated an electromagnetic interference shielding efficiency of more than 90 and 97% at the entire x and ku-band frequencies, respectively.

Functionalized carbonized monarch butterfly wing scales (FCBW) ornamented by β-Co(OH)2 nanoparticles: an investigation on its microwave, magnetic, and optical characteristics

In this research, a bioinspired carbon structure was applied as a novel, unique, green, affordable, light weight, thin, and broadband microwave absorbing material. Briefly, the monarch butterfly wing scales were pyrolyzed and then CBWs were functionalized using oxidative treatments, following that they were ornamented by hexagonal β-Co(OH)₂ nanoparticles to improve their microwave absorbing features based on an innovative complementary method by combining sonochemistry and hydrothermal routes. Noticeably, the polyacrylonitrile (PAN) was used as a practical medium to fabricate the microwave absorbers developing an integrated structure and augmenting the relaxation loss mechanism. Various analyses were applied to identify the prepared samples including x-ray powder diffraction, diffuse reflection spectroscopy, Fourier transform infrared, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), vibrating sample magnetometer, and vector network analyzer. The net-like morphology of FCBWs were fully coated by the hierarchical hexagonal β-Co(OH)₂ nanoparticles. FCBW illustrated a saturation magnetization of 0.06 emu g^-1 originated from its defects, distortions, dislocations, unique morphology, as well as folding, developing localized magnetic moments. Noticeably, inserting FCBWs narrow the energy bandgap of β-Co(OH)₂ nanoparticles, amplifying their light absorption and polarizability, desirable for the microwave attenuation. As revealed, FCBW/β-Co(OH)₂/PAN nanocomposite gained strong reflection loss (RL) of 68.41 at 9.08 GHz, while FCBW/PAN achieved broadband efficient bandwidth as wide as 7.97 GHz (RL > 10 dB) with a thickness of 2.00 mm. More significantly, β-Co(OH)₂/PAN nanocomposites demonstrated salient efficient bandwidth of 3.62 GHz (RL > 20 dB) with only 2.50 mm in thickness. Noteworthy, the eye-catching microwave absorptions were obtained by only filler loading of 10 Wt%. The remarkable microwave absorbing properties of the samples were generated from their microwave absorbing mechanisms which were scrupulously dissected. More significantly, the negative imaginary parts were obtained, originated from the produced secondary fields.

Developing MXenes from Wireless Communication to Electromagnetic Attenuation

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

Three-Dimensional Ordered Mesoporous Carbon Spheres Modified with Ultrafine Zinc Oxide Nanoparticles for Enhanced Microwave Absorption Properties

Currently, electromagnetic radiation and interference have a significant effect on the operation of electronic devices and human health systems. Thus, developing excellent microwave absorbers have a huge significance in the material research field. Herein, a kind of ultrafine zinc oxide (ZnO) nanoparticles (NPs) supported on three-dimensional (3D) ordered mesoporous carbon spheres (ZnO/OMCS) is prepared from silica inverse opal by using phenolic resol precursor as carbon source. The prepared lightweight ZnO/OMCS nanocomposites exhibit 3D ordered carbon sphere array and highly dispersed ultrafine ZnO NPs on the mesoporous cell walls of carbon spheres. ZnO/OMCS-30 shows microwave absorbing ability with a strong absorption (- 39.3 dB at 10.4 GHz with a small thickness of 2 mm) and a broad effective absorption bandwidth (9.1 GHz). The outstanding microwave absorbing ability benefits to the well-dispersed ultrafine ZnO NPs and the 3D ordered mesoporous carbon spheres structure. This work opened up a unique way for developing lightweight and high-efficient carbon-based microwave absorbing materials.

Functionalized carbon microfibers (biomass-derived) ornamented by Bi2S3 nanoparticles: an investigation on their microwave, magnetic, and optical characteristics

The biomass-derived materials emerged as novel, low-cost, green, and light-weight microwave absorbers. On the other hand, the sulfide nanostructures due to narrow band gap demonstrated significant dielectric features. In this research, the pure carbon microfibers were prepared using Erodium cicutarium harvest and they were functionalized by a sonochemistry method. The treated microfibers were coated by Bi₂S₃ nanoparticles, obtained by a novel modified solvothermal route. X-ray powder diffraction, Fourier transform infrared, diffuse reflection spectroscopy, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy, and vector network analyzer analyses were applied to characterize the features of the prepared structures. The obtained results manifest that the anchoring nanoparticles onto the functionalized microfibers narrowed band gap to 1.35 eV and reinforced polarizability of the nanocomposite, desirable for dielectric attenuation. In this study, the interfacial interactions were modulated using polyacrylonitrile (PAN) and polyvinylidene fluoride. Interestingly, FCMF blended in PAN demonstrated an eye-catching efficient bandwidth as wide as 8.13 GHz (RL > 10 dB) with only 2.00 mm in thickness, whereas it illustrated an outstanding reflection loss of 81.96 at 11.48 GHz with a thickness of 2.50 mm. More significantly, FCMF/Bi₂S₃/PAN nanocomposite promoted the efficient bandwidth to 3.07 GHz (RL > 20 dB). Noteworthy, all of the samples illustrated total electromagnetic interference shielding effectiveness (SE_T) more than 15 dB entire the x and ku-band frequency.

Preparation of graphite-like carbon nitride (g-C3N4)/NiCo2S4 nanocomposite toward salient microwave characteristics and evaluation of medium influence on its microwave features

In this paper, NiCo₂S₄ sulphide spinel nanoparticles are prepared using a modified solvothermal route, after which the obtained siegenite nanoparticles are tailored on graphite-like carbon nitride (g-C₃N₄) nanosheets. The morphology of tailored nanostructures is accomplished via an ion exchange process. Interestingly, the g-C₃N₄ stick structures are fabricated based on an innovative approach. Moreover, interfacial polarizations at heterojunction interfaces, and medium effects on microwave characteristics are examined, using polystyrene (PS) and polyvinylidene fluoride (PVDF) as polymeric matrices. The specimens are characterized via Fourier transform infrared (FTIR), X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM) analyses. The optical performance of nanostructures is studied by means of diffuse reflection spectroscopy (DRS) analysis, and is suggestive of a narrow band gap for NiCo₂S₄ and NiCo₂S₄/g-C₃N₄ nanostructures. Finally, the material's microwave absorbing features are clarified using a vector network analyzer (VNA) instrument via a wave guide technique. The resulting significant microwave absorptions reveal that our g-C₃N₄/NiCo₂S₄/PVDF 40% nanocomposite exhibited seven notches of reflection loss (RL), more than 30 dB in its curve, at 1.75 mm in thickness, while its maximum RL was 59.39 dB at 13.07 GHz. Interestingly, this composite, in a mass fraction of 60%, illustrates an efficient bandwidth of 5.1 GHz (RL > 10 dB) at only 1 mm thickness. It is worth noting that the maximum RL of g-C₃N₄ stick structures/PVDF measures 74.53 dB at 14.86 GHz, with a broadband efficient bandwidth of 7.96 GHz (RL > 10 dB). More significantly, both g-C₃N₄/NiCo₂S₄/PVDF and NiCo₂S₄/PVDF demonstrated salient electromagnetic interference shielding effectiveness (SE) > 30 dB across both x- and ku-band frequencies.

Exfoliation and Defect Control of Two-Dimensional Few-Layer MXene Ti3C2Tx for Electromagnetic Interference Shielding Coatings

Defect-controlled exfoliation of few-layer transition-metal carbide (f-Ti₃C₂T_x) MXene was demonstrated by optimizing chemical etching conditions, and electromagnetic interference (EMI) shielding coatings were explored. The structural features such as layer morphology, lateral size, layer thickness, defect density, and mechanical stability of the exfoliated f-Ti₃C₂T_x were strongly dependent on exfoliation conditions. By selecting appropriate exfoliation conditions, moderate etching time leads to the formation of quality f-Ti₃C₂T_x with lesser defects, whereas longer etching time can break the layer structure and increase defect density, structural misalignment, and oxidative products of f-Ti₃C₂T_x. The resultant fabricated free-standing flexible f-Ti₃C₂T_x films exhibited electrical conductivity and electromagnetic interference (EMI) shielding effectiveness (SE) in the X-band of about 3669 ± 33 S/m and 31.97 dB, respectively, at a thickness of 6 μm. The large discrepancy in EMI SE performance between quality (31.97 dB) and defected (3.164 dB) f-Ti₃C₂T_x sheets is attributed to interconnections between f-Ti₃C₂T_x nanolaminates interrupted by defects and oxidative products, influencing EMI attenuation ability. Furthermore, the demonstrated solution-processable high-quality f-Ti₃C₂T_x inks are compatible and, when applied for EM barrier coating on various substrates, including paper, cellulose fabric, and PTFE membranes, exhibited significant EMI shielding performance. Moreover, controlling defects in f-Ti₃C₂T_x and assembly of heterogeneous disordered carbon-loaded TiO₂-Ti₃C₂T_x ternary hybrid nanostructures from f-Ti₃C₂T_x by tuning etching conditions could play an enormous role in energy and environmental applications.

Advances of 3D graphene and its composites in the field of microwave absorption

The intensive progress of information technology increases the demand for urgent development of practical materials for microwave absorption (MA), meeting the general requirement "thin, wide, light and strong". In the past 6 years, graphene is of great interest for MA performance due to its unique properties such as high specific surface area, high electrical conductivity, strong dielectric loss, and low density. Taking in account that the structure of absorber plays a key role in MA performance, the attempts to produce an efficient microwave absorbing materials (MAMs) have led to 3D graphene - aerogels and foams - due to their extremely high porosity, large specific surface area, excellent mechanical properties with ability of compression and further maintaining the original shape, lightweight, reduced agglomeration of graphene sheets. All listed parameters enhance the impedance matching of MAMs, generate the synergistic loss effects, thereby improving the MA properties. The review describes the bases of MA theory and summarizes the recent achievements in the fabrication of pure 3D graphene networks and their composites with magnetic, ceramic nanoparticles and nanowires, polymers, MXenes, and multicomponent systems, directed to improve the impedance matching and generate loss mechanisms for the overall improvement of their performance as MAMs.

Assembling Nano-Microarchitecture for Electromagnetic Absorbers and Smart Devices

Smart devices, nowadays, are inspiring the infinite vitality and possibilities of intelligent life, such as self-power electromagnetic (EM) nanogenerator and microsensor, smart window, thermally-driven EM absorber, interstellar energy deliverer, and so on. Herein, the latest and most impressive works of 3D nano-micro architectures and their smart EM devices are highly focused on. The most key information, including assembly strategy and mechanism, EM response, and approach-structure-function relationship, is extracted and well-organized with profundity and easy-to-understand approach. The merit and demerit are revealed by comparison. What's more, the brightest and most cutting-edge smart EM devices constructed by 3D nano-micro architectures are reported as highlights, and the device principles are deeply dissected. Finally, a profound and top comment on the fast-growing field as well as challenges are proposed, and the future directions are predicted intelligently.

Heterostructure Composites of CoS Nanoparticles Decorated on Ti3C2Tx Nanosheets and Their Enhanced Electromagnetic Wave Absorption Performance

As a typical two-dimensional material, MXene possesses excellent conductivity and tunable interlayer space, which makes it have an impressive development potential in the field of electromagnetic (EM) waves absorbing materials. In this work, we fabricated a sandwich structure CoS@Ti₃C₂T_x composite using a simple solvothermal process. The CoS nanoparticles are anchored on the Ti₃C₂T_x MXene sheets, forming a heterolayered structure. The results demonstrate that the CoS@Ti₃C₂T_x composites with the sandwich-like architecture showed excellent EM absorbing performance due to the synergistic effects of the conductivity loss, interface polarization, and dipole polarization. When the doping ratio was 40 wt %, the maximum reflection loss value of CoS@Ti₃C₂T_x was up to –59.2 dB at 14.6 GHz, and the corresponding effective absorption bandwidth (below –10 dB) reached 5.0 GHz when the thickness was only 2.0 mm. This work endows a new candidate for the design of MXene-based absorption materials with optimal performance.

Smart Ti3C2Tx MXene Fabric with Fast Humidity Response and Joule Heating for Healthcare and Medical Therapy Applications

An increasing utilization of flexible healthcare electronics and biomedicine-related therapeutic materials urges the development of multifunctional wearable/flexible smart fabrics for personal therapy and health management. However, it is currently a challenge to fabricate multifunctional and on-body healthcare electronic devices with reliable mechanical flexibility, excellent breathability, and self-controllable joule heating effects. Here, we fabricate a multifunctional MXene-based smart fabric by depositing 2D Ti₃C₂T_x nanosheets onto cellulose fiber nonwoven fabric via special MXene-cellulose fiber interactions. Such multifunctional fabrics exhibit sensitive and reversible humidity response upon H₂O-induced swelling/contraction of channels between the MXene interlayers, enabling wearable respiration monitoring application. Besides, it can also serve as a low-voltage thermotherapy platform due to its fast and stable electro-thermal response. Interestingly, water molecular extraction induces electrical response upon heating, i.e., functioning as a temperature alarm, which allows for real-time temperature monitoring for thermotherapy platform without low-temperature burn risk. Furthermore, metal-like conductivity of MXene renders the fabric an excellent Joule heating effect, which can moderately kill bacteria surrounding the wound in bacteria-infected wound healing therapy. This work introduces a multifunctional smart flexible fabric suitable for next-generation wearable electronic devices for mobile healthcare and personal medical therapy.

MOF-Derived Ni1-xCox@Carbon with Tunable Nano-Microstructure as Lightweight and Highly Efficient Electromagnetic Wave Absorber

Intrinsic electric-magnetic property and special nano-micro architecture of functional materials have a significant effect on its electromagnetic wave energy conversion, especially in the microwave absorption (MA) field. Herein, porous Ni1-xCox@Carbon composites derived from metal-organic framework (MOF) were successfully synthesized via solvothermal reaction and subsequent annealing treatments. Benefiting from the coordination, carbonized bimetallic Ni-Co-MOF maintained its initial skeleton and transformed into magnetic-carbon composites with tunable nano-micro structure. During the thermal decomposition, generated magnetic particles/clusters acted as a catalyst to promote the carbon sp2 arrangement, forming special core-shell architecture. Therefore, pure Ni@C microspheres displayed strong MA behaviors than other Ni1-xCox@Carbon composites. Surprisingly, magnetic-dielectric Ni@C composites possessed the strongest reflection loss value - 59.5 dB and the effective absorption frequency covered as wide as 4.7 GHz. Meanwhile, the MA capacity also can be boosted by adjusting the absorber content from 25% to 40%. Magnetic-dielectric synergy effect of MOF-derived Ni1-xCox@Carbon microspheres was confirmed by the off-axis electron holography technology making a thorough inquiry in the MA mechanism.

Magnetized MXene Microspheres with Multiscale Magnetic Coupling and Enhanced Polarized Interfaces for Distinct Microwave Absorption via a Spray-Drying Method

As a typical 2D (two dimensional) material, Ti₃C₂T_x, has been used as a promising microwave absorber (MA) because of its massive interface architecture, abundant natural defects, and chemical surface functional groups. However, its single dielectric-type loss and excessive high conductivity seriously restrict the further enhancement of MA performance. Herein, we first describe a simple spray-drying routine to reshape the 2D MXene into a confined and magnetized microsphere with tightly embedded Fe₃O₄ nanospheres (designated as M/F), contributing to the enhanced specific interfaces and strong dielectric polarization. These Fe₃O₄ magnetic units are highly dispersed into the dielectric Mxene framework, leading to the optimized impedance balance and electromagnetic coordination capability. This composite way effectively exceeds the conventionally physical mixing, simple loading, and local phase separation method. Meanwhile, strong magnetic loss capability with significantly improved magnetic flux line density is achieved from microscale MXene and nanoscale Fe₃O₄, confirming our 3D multiscale magnetic coupling network. Accordingly, the M/F composites hold distinct microwave absorption property with the strong reflection loss (-50.6 dB) and effective absorption bandwidth (4.67 GHz) at the thickness as thin as only 2 mm. Our encouraging strategy provides important designable implications for MXene-based functional materials and high-performance absorbers.

Urchin-like Amorphous Nitrogen-Doped Carbon Nanotubes Encapsulated with Transition-Metal-Alloy@Graphene Core@Shell Nanoparticles for Microwave Energy Attenuation

Herein, we report three-dimensional (3D) urchin-like amorphous nitrogen-doped CNT (NCNT) arrays with embedded cobalt-nickel@graphene core@shell nanoparticles (NPs) in the inner parts of NCNTs (CoNi@G@NCNTs) for highly efficient absorption toward microwave (MW). The CoNi NPs are covered with about seven layers of graphene shell, resulting in the formation of CoNi@G core-shell structures. In the meanwhile, the CoNi@G core-shell NPs are further encapsulated within NCNTs. Benefitting from the multiple scattering of the unique 3D structure toward MW, cooperative effect between magnetic loss and dielectric loss, and additional interfacial polarizations, the 3D urchin-like CoNi@G@NCNTs exhibit excellent MW energy attenuation ability with a broad absorption bandwidth of 5.2 GHz with a matching thickness of merely 1.7 mm, outperforming most reported absorbers. Furthermore, the chemical stability of the 3D urchin-like CoNi@G@NCNTs is improved greatly due to the presence of the graphene coating layers and outmost NCNTs, facilitating their practical applications. Our results highlight a novel strategy for fabrication of 3D nanostructures as high-performance MW-absorbing materials.

Sandwich-Like Fe&TiO2@C Nanocomposites Derived from MXene/Fe-MOFs Hybrids for Electromagnetic Absorption

Electromagnetic pollution has been causing a series of problems in people's life, and electromagnetic absorbers with lightweight and broad absorbing bandwidth properties are widely desired. In this work, novel sandwich-like 2D laminated Fe&TiO2 nanoparticles@C nanocomposites were rationally designed and successfully developed from the MXene-MOFs hybrids. The formation of Fe and rutile-TiO2 nanoparticles sandwiched by the two-dimensional carbon nanosheets provided strong electromagnetic energy attenuation and good impedance matching for electromagnetic wave (EMW) absorption. As expected, the nanocomposites achieved a broad effective absorption bandwidth of 6.5 GHz at a thickness of only 1.6 mm and the minimum reflection loss (RL) value of - 51.8 dB at 6.6 GHz with a thickness of 3 mm. This work not only provides a good design and fabricating concept for the laminated metal and functional nanoparticles@C nanocomposites with good EMW absorption, but also offers an important guideline to fabricate various two-dimensional nanocomposites derived from the MXene precursors.

Ultrathin MXene/aramid nanofiber composite paper with excellent mechanical properties for efficient electromagnetic interference shielding

MXenes, new two-dimensional compounds with hydrophilic surfaces and high metallic conductivity, have attracted significant interest in the electromagnetic interference shielding field in recent years. Nevertheless, poor mechanical properties and brittle nature are bottlenecks for their commercial application. Herein, one-dimensional ANFs were designed as the intermolecular cross-linker between d-Ti₃C₂T_x flakes and MXene (d-Ti₃C₂T_x)/aramid nanofiber (ANF) composite paper with a multi-layered structure was fabricated via the vacuum-assisted filtration approach. Further investigation revealed that the ANFs and MXene displayed good combination by hydrogen bonding, and MXene/ANF composite papers exhibited excellent mechanical properties and superior electrical conductivity. The MXene/ANF composite paper possessed a favorable shielding effectiveness (SE) which reached ∼28 dB in 8.2-12.4 GHz (X band) with an ultra-thin thickness ∼17 μm and showed potential application prospects as an advanced composite in sensitive electronic products.