Lightweight, Fire-Retardant, and Anti-Compressed Honeycombed-Like Carbon Aerogels for Thermal Management and High-Efficiency Electromagnetic Absorbing Properties

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.

Two-phase magnetic nanospheres with magnetic coupling effect encapsulated in porous carbon to achieve lightweight and efficient microwave absorbers

Component selection is crucial for microwave absorbents. Multi-component absorbers are increasingly useful and can be prepared through the rational design and control of various electrical, magnetic, and other auxiliary components. In this paper, Ni3Fe/NiFe2O4 nanospheres with two-phase magnetism were designed for use as a multi-component absorber. Specifically, a Ni3Fe/ NiFe2O4@SPC composite with 3D networks was successfully fabricated by hydrothermal method, high-temperature carbonization for activation, and electrostatic self-assembly. The contact interface and coupling effect between the two magnetic components can promote the attenuation of electromagnetic waves. Moreover, the introduction of porous carbon successfully inhibits the easy aggregation of the magnetic particles. Impressively, with a filling load of 10 wt%, the optimal RL of the prepared Ni3Fe/NiFe2O4@SPC composite reaches -60.6 dB, and the effective absorption bandwidth is 5.2 GHz at 2 mm. The combination of two magnetic components and porous carbon in this multiphase microwave-absorbing composite demonstrates a feasible strategy for designing efficient microwave absorbers in the future.

Anisotropic composite aerogel with thermal insulation and flame retardancy from cellulose nanofibers, calcium alginate and boric acid

With the increasing severity of energy shortages and environmental pollution, there is an urgent need for advanced thermal insulation materials with excellent comprehensive performance, including low thermal conductivity, high flame resistance, and strong compressive strength. Herein, an anisotropic composite aerogel based on cellulose nanofibers (CNF), calcium alginate (CA), and boric acid (BA) is fabricated using a directional freeze-drying strategy. The CA and BA, as double cross-linking agents, associated with oriented porous structure provide the resultant aerogel with good mechanical strength. Additionally, self-flame retardant CA and BA act as synergistic flame retardants that endow the aerogel with excellent flame retardance properties such as a limiting oxygen index value of 44.2 %, UL-94 V-0 rating, and low heat release. Furthermore, this composite aerogel exhibits outstanding thermal insulation performance with a low thermal conductivity of approximately 30 mW m-1 K-1. Therefore, the composite aerogel is expected to have a wide potential application in areas such as construction, automotive industry, batteries, petrochemical pipelines, and high-temperature reaction devices.

Anisotropic Rotunda-Shaped Carboxymethylcellulose/Carbon Nanotube Aerogels Supported Phase Change Materials for Efficient Solar-Thermal Energy Conversion

For the drawbacks of phase change materials such as poor shape stability and weak solar-thermal conversion ability, a rotunda-shaped carboxymethylcellulose/carbon nanotube aerogel (CA) with three-dimensional network was constructed by freeze casting with a special mold, and then impregnated with polyethylene glycol (PEG) in this work. The PEG/CA had an enthalpy of 183.21 J/g, and a thermal conductivity of 0.324 W m-1 K-1, which was 57 % higher than the pure PEG. The ability of PEG/CA to convert solar energy to thermal energy was a positive correlation between the inclusion of CNTs and the composite material's thermal conductivity. Under simulated sunlight, its solar-thermal conversion efficiency reaches 94.41 %, and after 10 min of irradiation, the surface temperature can reach 65 °C and the internal temperature can reach 44.67 °C. This rotunda-shaped PEG/CA is promising for the efficient use of renewable solar energy due to its strong solar-thermal conversion and thermal storage capabilities.

One-step sintering construction of electromagnetic synergistic Co7Fe3/Co@CBC nanocomposites for enhanced microwave absorption properties

Based on the synergistic modulation of electromagnetic parameters and microstructure design, multidimensional porous magnetic carbon-based nanocomposites have become ideal materials with efficient absorption properties. What's more, a carbon-magnetic alloy composite is a commonly used and efficient microwave absorber. In this paper, Co7Fe3/Co@CBC (CFCC) nanocomposites with strong magnetism, a three-phase composition, and a three-dimensional porous structure were synthesized by reducing Fe2+ and Co2+ using chestnut-shell biomass carbon (CBC). Biomass carbon with a higher specific surface area provides numerous active sites for Co7Fe3 nanosheets and Co nanospheres to form three-dimensional ping-pong chrysanthemum-like nanocomposites, which generate rich heterogeneous interfaces and conductive network structures. By adjusting the amount of added biomass, the electromagnetic parameters can be effectively regulated to achieve efficient microwave absorption properties. When the amount of biomass added varies within the range of 1.0 to 2.5 g, all samples exhibit a favorable effective absorption bandwidth (EAB) of over 5.88 GHz. In particular, the CFCC-2.0 composite exhibits optimal microwave absorption properties, with a minimum reflection loss (RLmin) value of -59.25 dB and an EAB of 6.34 GHz at a thickness of 2.8 mm. The simulation and modeling analysis results of radar cross section (RCS) further confirm the exceptional attenuation capability of composite materials at multiple incident angles. The exceptional microwave absorption properties and stability of EAB for the Co7Fe3/Co@CBC nanocomposite make it a promising candidate in the field of absorbing materials. This work also provides some feasible ideas for designing stable broadband wave-absorbing materials.

Promoting Electromagnetic Wave Absorption Performance by Integrating MoS2@Gd2O3/MXene Multiple Hetero-Interfaces in Wood-Derived Carbon Aerogels

Multi-component composite materials with a magnetic-dielectric synergistic effect exhibit satisfactory electromagnetic wave absorption performance. However, the effective construction of the structure for these multi-component materials to fully exploit the advantages of each component remains a challenge. Inspired by natural biomass, this study utilizes wood as the raw material and successfully prepares high-performance MoS2@Gd2O3/Mxene loaded porous carbon aerogel (MGMCA) composite material through a one-pot hydrothermal method and carbonization treatment process. With a delicate structural design, the MGMCA is endowed with abundant heterogeneous interface structures, favorable impedance matching characteristics, and a magnetic-dielectric synergistic system, thus demonstrating multiple electromagnetic wave loss mechanisms. Benefiting from these advantages, the obtained MGMCA exhibits outstanding electromagnetic wave absorption performance, with a minimum reflection loss of -57.5 dB at an ultra-thin thickness of only 1.9 mm. This research proposes a reliable strategy for the design of multi-component composite materials, providing valuable insight for the design of biomass-based materials as electromagnetic wave absorbers.

High-Performance, Multifunctional, and Designable Carbon Fiber Felt Skeleton Epoxy Resin Composites EP/CF-(CNT/AgBNs)x for Thermal Conductivity and Electromagnetic Interference Shielding

In this work, high-performance epoxy resin (EP) composites with simultaneous excellent thermal conductivity (TC) and outstanding electromagnetic shielding properties are fabricated through the structural synergy of 1D carbon nanotubes and 2D silver-modified boron nitride nanoplates (CNT/AgBNs) to erect microscopic 3D networks on long-range carbon fiber (CF) felt skeletons. The line-plane combination of CNT/AgBNs improve the interfacical bonding involving EP and CF felts and alleviate the phonon scattering at the interface. Eventually, the TC of the EP composites is enhanced by 333% (up to 0.91 W m-1 K-1 ) with respect to EP due to the efficient and orderly transmission of phonons along the 3D pathway. Meanwhile, the unique anisotropic structure of CF felt and exceptional insulating BNs diminishes the electronic conduction between CNT and CFs, which protects the through-plane insulating properties of EP composites. Furthermore, the EP composites present favorable electromagnetic shielding properties (51.36 dB) attributed to the multiple reflection and adsorption promoted by the multiple interfaces of stacked AgBNs and heterointerface among CNT/AgBNs, CF felt and EP. Given these distinguishing features, the high-performance EP composites open a convenient avenue for electromagnetic wave (EMW) shielding and thermal management applications.

Drawing Inspiration from Nature: Trinitarian Strategies for Designing Polyoxometalates and Metal-Organic Framework-Based Biomimetic Microhoneycomb Electromagnetic Wave-Absorbing Materials

Trinitarian designs in the morphology, components, and microstructure remain challenging for advanced electromagnetic wave absorption (EMWA) materials with light weight, strong absorption, and well-defined structure-function relationships. Herein, a series of X-doped MoS2/Cu9S5 with multilevel honeycomb structures (X-MoS2/Cu9S5 MHs, X = P, Si, Ge) were designed by space-confined growth and in situ sulfidation of a polyoxometalate-based metal-organic framework. X-MoS2/Cu9S5 MHs possess low density, high surface area, and abundant cation-cuprum and anion-sulfur double vacancies (VCu and VS) simultaneously that are unmatched by conventional EMWA materials. Also, the systematic investigation of the doping effect of various polyoxometalate heteroatoms on VCu and VS in the microhoneycomb has been conducted. Experimental results and density functional theory calculations reveal that the excellent EMWA performance (-56.21 dB) results from the synergistic effect of morphology design, component optimization, and vacancy regulation. This study not only provides an important opportunity to understand a morphology-component-microstructure strategy in electromagnetic wave absorption but also builds a noteworthy bridge between bioinspired engineering and microscale absorbers.

MOF Derivatives with Gradient Structure Anchored on Carbon Foam for High-Performance Electromagnetic Wave Absorption

The impedance matching and high loss capabilities of composites with homogeneous distribution are limited owing to high addition and lack of structural design. Developing composites with heterogeneous distribution can achieve strong and wide electromagnetic (EM) wave absorption. However, challenges such as complex design and unclear absorption mechanisms still exist. Herein, a novel composite with a heterogeneous distribution gradient is successfully constructed via MOF derivatives Co@ nitrogen-doped carbon (Co@NC) anchored on carbon foam (CF) matrix (MDCF). Notably, the concentration of MOF can easily control the gradient structure. In particular, the morphologies of MOF derivatives on the surface of CF undergo a transition from the collapse of the inner layer to the integrity of the outer layer, accompanied by a continuous reduction in the size of Co nanoparticles. Correspondingly, enhanced interface polarization from the core-shell of Co@NC and good impedance matching of MDCF can be obtained. The optimized MDCF exhibits the minimum reflection loss of -68.18 dB at 2.01 mm and effective absorption bandwidth covering the entire X-band. Moreover, MDCF exhibits lightweight characteristics, excellent compressive strength, and low radar cross-section reduction. This work highlights the immense potential of composites with heterogeneous distribution for achieving high-performance EM wave absorption.

Bimetallic nanocubes embedded in biomass-derived porous carbon to construct magnetic/carbon dual-mechanism layered structures for efficient microwave absorption

Biomass-derived porous carbon materials have great potential for the development of lightweight and efficient broadband microwave absorbers. In this study, we reported the successful immobilization of Co3O4/CoFe2O4 nanocubes on porous carbon derived from ginkgo biloba shells by activated carbonization and electrostatic self-assembly processes. The optimal reflection loss value of the prepared BPC@Co3O4/CoFe2O4 reaches -68.5 dB when the filling load is 10 wt%, and the effective absorption bandwidth is 6.2 GHz with a matching thickness of 2 mm. The excellent microwave absorption (MA) performance is attributed to the rational three-dimensional structural design, the modulation of magnetic/carbon components, the optimized impedance matching, and the coordinated action of multiple mechanisms. It was further demonstrated by high-frequency structural simulation that the composite can effectively dissipate microwave energy in practical applications. Therefore, the results indicate a favorable potential of the synthesis and application of semiconductor/magnetic component/biomass-derived carbon microwave absorbing materials.

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

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

Impact mechanisms of aggregation state regulation strategies on the microwave absorption properties of flexible polyaniline

In the field of electromagnetic (EM) wave absorption, intrinsic conductive polymers with conjugated long-chain structures, such as polyaniline (PANI) and polypyrrole (PPy), have gained widespread use due to their remarkable electrical conductivity and loss ability. However, current research in this area is limited to macroscopic descriptions of the absorption properties of these materials and the contribution of various components to the absorption effect. There has been insufficient exploration of the impact mechanisms of polymer aggregation states on the material's absorption performance and mechanism. To address this, a series of flexible PANI sponge absorbers with different molecular weights and aggregation states were prepared. By carefully controlling the crystallinity and other aggregation characteristics of PANI through the adjustment of its preparation conditions, we were able to influence its electrical conductivity and electromagnetic parameters, thereby achieving control over the material's absorption properties. The resulting PANI sponge absorbers exhibited an effective absorption bandwidth (EAB) that covered the entire X-band at a thickness of 3.2 mm. This study comprehensively explores the absorption mechanisms of conductive polymer absorbers, starting from the microstructure of PANI, and providing a more complete theoretical support for the research and promotion of polymer absorbers.

Engineering Phase to Reinforce Dielectric Polarization in Nickel Sulfide Heterostructure for Electromagnetic Wave Absorption

Engineering phase transition in micro-nanomaterials to optimize the dielectric properties and further enhance the electromagnetic microwave absorption (EMA) performance is highly desirable. However, the severe synthesis conditions restrict the design of EMA materials featuring controllable phases, which hinders the tunability of effective absorption bandwidth (EAB) and leads to an unclear loss mechanism. Herein, a seed phase decomposition-controlled strategy is proposed to induct nickel sulfide (NiSx ) absorbers with controllable phases and hollow sphere nature. Transmission electron microscopy holography and theoretical calculations evidence that the reconstruction of atoms in phase transition induces numerous heterogeneous interfaces and lattice defects/sulfur vacancies to cause varied work functions and local electronic redistribution, which contributes to reinforced dielectric polarization. As a result, the optimized NiS2 /NiS heterostructure enables enhanced EM attenuation capability with a wide EAB of 5.04 GHz at only 1.6 mm, compared to that of NiS2 and NiS. Moreover, the correlation between EAB and NiS phase content is demonstrated as the "volcano" feature. This study on the concept of phase transition of micro-nanomaterials can offer a novel approach to constructing highly efficient absorbers for EMA and other functionalities.

High-Quality Ultrathin Gd2O2S Nanosheets with Oxygen Vacancy-Decorated rGO for Enhanced Electromagnetic Wave Absorption

The development of extreme performance and multifunctional electromagnetic (EM) wave absorption materials is essential to eliminating undesirable frequency EM pollution. As a promising rare-earth compound, gadolinium oxysulfide (Gd2O2S) has become a significant field of study among nanomaterials with multidisciplinary applications. Herein, the ultrathin Gd2O2S nanosheets with 1 nm thickness were fabricated via a facile hot injection method and then mixed with reduced graphene oxide (rGO) through coassemble and carbonization methods to form Gd2O2S/rGO composites. As a new kind of multifunction EM-wave absorption materials, Gd2O2S/rGO composites exhibited excellent EM-wave absorption performance with an absorption capacity of -65 dB (2.1 mm) and an adequate absorption bandwidth of 5.6 GHz at 1.9 mm. Additionally, their EM-wave absorption mechanisms have been unveiled for the first time. The outstanding EM-wave absorption performance of Gd2O2S/rGO composites could be attributed to the ultrathin Gd2O2S nanosheets with oxygen vacancy and rGO layers with high conductivity and large specific surface area, which will also facilitate the polarization loss, conductivity loss, and multiple reflection and scattering of EM waves between the rGO layer and Gd2O2S nanosheets. Overall, compared to previously reported rGO-based EM-wave absorption materials, this work provides a promising approach for the exploitation and synthesis of Gd2O2S/rGO composites with lightweight and high-performance microwave attenuation.

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

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

In situ generated gas bubble-directed self-assembly of multifunctional MgO-based hybrid foams for highly efficient thermal conduction, microwave absorption, and self-cleaning

Developing multifunctional materials with superior thermal conductivity and microwave absorption is an effective means to address the increasingly serious electromagnetic (EM) compatibility and heat dissipation problems in modern electron devices. Here, multifunctional MgO/Mg(OH)2/C, MgO/M/C (M = Co, Ni, Cu), and MgO/NOx/C (N = Fe, Mn) hybrid foams were synthesized using a facile one-step gas-bubble-assisted combustion method, and their texture, composition, and properties were regulated by tuning salt type and feeding ratio. Our results show that the MgO/Co/C foams have high thermal conductivity (3.40-4.09 W m-1 K-1) with a filler load of 20-50 wt% at the Co2+ molar content of φ = 70 mol% and excellent EM wave absorption (EABW = 11.44 GHz), with a thickness of 2.1 mm and a minimal reflection loss of -59.42 dB at φ = 90 mol%. The enhanced properties are ascribed to the construction of foams with 3D interconnected networks and the synergistic effect of magnetic Co, insulating MgO, and dielectric C, which provide a continuous pathway for electron/phonon relay transmission and magnetic/dielectric dual losses. Moreover, the MgO/Co/C foams possess strong mechanical/hydrophobicity performance, tunable magnetic properties, and electrical conductivity, and can be applied in self-cleaning, electromagnetic interference, and heat management. Overall, this study offers a novel understanding of preparing multifunctional heat conductive-EM wave absorptive foam materials in modern electronic devices.

Scrolling reduced graphene oxides to induce room temperature magnetism via spatial coupling of defects

Due to its intriguing features and numerous applications, graphene has garnered a lot of interest in recent years. However, it is still very difficult to create graphene-based room-temperature magnets without transition metals or rare earth elements since pristine graphene is inherently diamagnetic due to the delocalized π bonding network. Herein, room-temperature ferromagnetism with a saturation magnetization of 0.93 emu g-1 (300 K) is achieved in defect-rich-reduced graphene oxide (DR-rGO) nanoscrolls by creating a spatial coupling of defects. The experiments and DFT calculations verify that spatial coupling of defects could enhance Rudermann-Kittel-Kasuya-Yosida interactions to induce magnetism in graphene. It displays high-efficiency electromagnetic wave absorption performance with a minimal reflection loss of -62.1 dB and an effective absorption bandwidth of 7.8 GHz (3.0 mm) thanks to greatly improved magnetism. This breakthrough serves as a building block for the creation of room-temperature magnetic carbon materials and expands their applications in many pertinent domains.

Anion Exchange of Metal Particles on Carbon-Based Skeletons for Promoting Dielectric Equilibrium and High-Efficiency Electromagnetic Wave Absorption

The combination of carbon materials and magnetic elements is considered as an effective strategy to obtain high-performance electromagnetic wave (EMW) absorption materials. However, using nanoscale regulation to the optimization of composite material dielectric properties and enhanced magnetic loss properties is facing significant challenges. Here, the dielectric constant and magnetic loss capability of the carbon skeleton loaded with Cr compound particles are further tuned to enhance the EMW absorption performance. After 700 °C thermal resuscitation of the Cr3-polyvinyl pyrrolidone composite material, the chromium compound is represented as a needle-shaped structure of nanoparticles, which is fixed on the carbon skeleton derived from the polymer. The size-optimized CrN@PC composites are obtained after the substitution of more electronegative nitrogen elements using an anion-exchange strategy. The minimum reflection loss value of the composite is -105.9 dB at a CrN particle size of 5 nm, and the effective absorption bandwidth is 7.68 GHz (complete Ku-band coverage) at 3.0 mm. This work overcomes the limitations of impedance matching imbalance and magnetic loss deficiency in carbon-based materials through size tuning, and opens a new way to obtain carbon-based composites with ultra-high attenuation capability.

Synthesis of CuCo2S4@Expanded Graphite with crystal/amorphous heterointerface and defects for electromagnetic wave absorption

The remarkable advantages of heterointerface and defect engineering and their unique electromagnetic characteristics inject infinite vitality into the design of advanced carbon-matrix electromagnetic wave absorbers. However, understanding the interface and dipole effects based on microscopic and macroscopic perspectives, rather than semi-empirical rules, can facilitate the design of heterointerfaces and defects to adjust the impedance matching and electromagnetic wave absorption of the material, which is currently lacking. Herein, CuCo2S4@Expanded Graphite heterostructure with multiple heterointerfaces and cation defects are reported, and the morphology, interfaces and defects of component are regulated by varying the concentration of metal ions. The results show that the 3D flower-honeycomb morphology, the crystal-crystal/amorphous heterointerfaces and the abundant cation defects can effectively adjust the conductive and polarization losses, achieve the impedance matching balance of carbon materials, and improve the absorption of electromagnetic wave. For the sample CEG-6, the effective absorption of Ku band with RLmin of -72.28 dB and effective absorption bandwidth of 4.14 GHz is realized at 1.4 mm, while the filler loading is only 7.0 wt. %. This article reports on the establishment of potential relationship between crystal-crystal/amorphous heterointerfaces, cation defects, and the impedance matching of carbon materials.

Preparation of MoS2/MXene/NC Porous Composite Microspheres with Wrinkled Surface and Their Microwave Absorption Performances

In this paper, a MoS2/MXene/N-doped carbon (NC) porous composite microsphere with a wrinkled surface was designed and constructed. Lithium fluoride exfoliation and lithium-ion etching fabricated two types of 2D assembly elements, MXene (Ti3C2Tx) and MoS2 nanosheets. The two nanosheets were self-assembled by an ultrasonic spray technique with high-temperature reduction, and MoS2/MXene microspheres with 3Dwrinkled shapes were obtained. The coating of the surface NC layer was achieved by the carbonization of a polydopamine (PDA) precursor formed by the self-polymerization of dopamine. The amount of PDA coating and raw material ratio significantly affect the microstructure and electromagnetic wave absorption performance. The optimal MXene to MoS2 mass ratio is 5:1, and the optimal coating time and filler amount are 8 h and 40%. MoS2/MXene/NC composite microspheres exhibit excellent absorption performance with low reflection losses (RLmin) of -52.9 dB at 6.4 GHz and high adequate absorption bandwidths of 5.2 GHz. By adjusting the thickness of the absorber, the full coverage of the C-Ku band (4-18 GHz) can be achieved. As a new composite absorber, it has significant potential applications.

Customizable Resilient Multifunctional Graphene Aerogels via Blend-spinning assisted Freeze Casting

Graphene aerogels have gained considerable attention due to their unique physical properties, but their poor mechanical properties and lack of functionality have hindered their advanced applications. In this study, we propose a blend-spinning-assisted freeze-casting (BSFC) strategy to incorporate particle-modified carbon fibers into graphene aerogels for mechanical strengthening and functional enhancement. This method offers a great deal of freedom in the creation of customizable multimaterial, multiscale structural graphene aerogels. For example, we fabricated silicon carbide particle modified carbon fiber reinforced graphene (SiC/CF-GA) aerogels. The resulting aerogels display excellent properties such as being ultralightweight and highly resilient and having fatigue compression resistance (1000 cycles at 50% strain). Meanwhile, enhanced resilience inspired the effective strain-sensing capabilities of SiC/CF-GA aerogels with a sensitivity of 13.8 kPa-1. The adjustable dielectric properties due to SiC particle incorporation endow the SiC/CF-GA aerogel with a broad-band (8.0 GHz) effective electromagnetic wave attenuation performance. Besides, different particles could be incorporated into graphene aerogels via the BSFC strategy, allowing for customizable designs. Moreover, multifunctionalities were demonstrated by the modified aerogels, including noise absorption, thermal insulation, fire resistance, and waterproofing, further diversifying their practicality. Hence, the BSFC strategy provides a customized solution for fabricating modified graphene aerogels for advanced functional applications.

Colorimetric Aerogel Gas Sensor with High Sensitivity and Stability

The detection of formic acid vapor in the usage environment is extremely important for human health and safety. The utilization of metal-organic frameworks (MOFs) for the detection of gaseous molecules is an attractive strategy. However, the rational design and construction of MOF-based gas sensors with high sensitivity and mechanical stability remain a significant challenge. In this study, a simple approach is reported to fabricate colorimetric aerogel sensors assembled from MOF particles via ice template-assisted methods. As the aerogel sensor with staggered lamellae structures significantly provides a high air-volume intake of flowing gas, it generates a sufficient probability of contact reactions for highly mobile target molecules. Additionally, it enhances the mechanical stability by providing stress resistance between the staggered lamellae structures. Compared to conventional film sensors for the detection of formic acid molecules, aerogel sensors exhibit an 8-fold lower limit of detection, 15-fold better sensitivity at low concentrations, 34-fold faster response time, and higher stability. This approach shows great potential for rapid and real-time detection of target molecules as well as superior performance in the structural construction of various gas-sensitive materials.

Flexible 3D Substrate of Ag Nanoparticle-Loaded Carbon Aerogels with Outstanding Surface-Enhanced Raman Scattering Performance

Surface-enhanced Raman scattering (SERS), an ultra-sensitive and non-destructive analytic technique, has attracted wide attention from the scientific community. Despite its rapid development, limited hotspots on the SERS substrates have restricted their potential in practical applications. Herein, we developed a facile method to fabricate a flexible three-dimensional (3D) SERS substrate composed of silver nanoparticles (Ag NPs)-loaded carbon aerogels (CAs). Such a flexible Ag NPs/CAs substrate exhibited numerous hotspots, which can facilely be adjusted not only by tuning the density of Ag NPs but also by controlling the bending degree of the flexible substrate. In addition, the influence of hotspots on the local electric field enhancement was investigated by theoretical calculations. Moreover, the 3D network structure of the CAs with a large specific surface area and strong adsorption ability can improve the capture of target molecules. Consequently, the optimal Ag NPs/CAs substrate has a low detection limit of 10^-12 M for rhodamine 6G molecules as well as good repeatability. Furthermore, based on the good performance of SERS detection of the Ag NPs/CAs substrate, it can also be practically used for the detection of thiram molecules on the surface of cherry tomatoes. Such a flexible 3D Ag NPs/CAs substrate has great potential for practical environmental monitoring applications.

Oxidative Molecular Layer Deposition Tailoring Eco-Mimetic Nanoarchitecture to Manipulate Electromagnetic Attenuation and Self-Powered Energy Conversion

Advanced electromagnetic devices, as the pillars of the intelligent age, are setting off a grand transformation, redefining the structure of society to present pluralism and diversity. However, the bombardment of electromagnetic radiation on society is also increasingly serious along with the growing popularity of "Big Data". Herein, drawing wisdom and inspiration from nature, an eco-mimetic nanoarchitecture is constructed for the first time, highly integrating the advantages of multiple components and structures to exhibit excellent electromagnetic response. Its electromagnetic properties and internal energy conversion can be flexibly regulated by tailoring microstructure with oxidative molecular layer deposition (oMLD), providing a new cognition to frequency-selective microwave absorption. The optimal reflection loss reaches ≈  - 58 dB, and the absorption frequency can be shifted from high frequency to low frequency by increasing the number of oMLD cycles. Meanwhile, a novel electromagnetic absorption surface is designed to enable ultra-wideband absorption, covering almost the entire K and Ka bands. More importantly, an ingenious self-powered device is constructed using the eco-mimetic nanoarchitecture, which can convert electromagnetic radiation into electric energy for recycling. This work offers a new insight into electromagnetic protection and waste energy recycling, presenting a broad application prospect in radar stealth, information communication, aerospace engineering, etc.

Core-shell FeCo@carbon nanocages encapsulated in biomass-derived carbon aerogel: Architecture design and interface engineering of lightweight, anti-corrosion and superior microwave absorption

The development of multifunctional microwave absorbing materials for practical applications in complex environments is a challenging research hotspot. Herein, the core-shell structure FeCo@C nanocages were successfully anchored on the surface of biomass-derived carbon (BDC) from pleurotus eryngii (PE) via freeze-drying and electrostatic self-assembly process, achieving lightweight, anti-corrosive, and excellent absorption properties. The superior versatility benefits from the large specific surface area, high conductivity, three-dimensional cross-linked networks, and appropriate impedance matching characteristics. The as-prepared aerogel realizes a minimum reflection loss (RL_min) of -69.5 dB with a corresponding effective absorption bandwidth (EAB) of 8.6 GHz at 2.9 mm. Simultaneously, the computer simulation technique (CST) further proves that the multifunctional material can dissipate microwave energy in actual applications. More importantly, the special heterostructure of aerogel endows excellent resistance to acid, alkali, salt medium, allowing potential applications of the microwave absorbing materials under complex environmental conditions.

Multifunctional carbon nanotubes-based hybrid aerogels with high-efficiency electromagnetic wave absorption at elevated temperature

In the complex engineering applications of electromagnetic (EM) wave-absorbing materials, it is insufficient for these materials to exhibit only efficient EM wave attenuation ability. EM wave-absorbing materials featuring numerous multifunctional properties are increasingly attractive for next-generation wireless communication and smart devices. Herein, we constructed a lightweight and robust multifunctional hybrid aerogel consisting of carbon nanotubes/aramid nanofibers/polyimide with low shrinkage and high porosity. The hybrid aerogels exhibit excellent EM wave attenuation, with an effective absorption bandwidth covering the entire X-band from 25 °C to 400 °C. The conductive loss capacity of the hybrid aerogel is enhanced under thermal drive, which results in an enhanced ability to attenuate EM waves, as evidenced by the fact that the best-fit thickness drops from 5.3 to 3.6 mm with increasing temperature. In addition, the hybrid aerogels are capable to efficiently absorb sound waves, with an average absorption coefficient as high as 0.86 at 1-6.3 kHz, and they exhibit superior thermal insulation properties, with a thermal conductivity as low as 41 ± 2 mW/mK. They are thus suitable for applications in the anti-icing and infrared stealth fields. The prepared multifunctional aerogels have considerable potential for EM protection, noise reduction, and thermal insulation in harsh thermal environments.

Additive Manufacturing of Carbon Using Commodity Polypropylene

Carbon materials are essential to the development of modern society with indispensable use in various applications, such as energy storage and high-performance composites. Despite great progress, on-demand carbon manufacturing with control over 3D macroscopic configuration is still an intractable challenge, hindering their direct use in many areas requiring structured materials and products. This work introduces a simple and scalable method to generate complex, large-scale carbon structures using easily accessible materials and technologies. 3D-printed, commercial polypropylene (PP) parts can be thermally stabilized through cracking-facilitated diffusion and crosslinking. The newly elucidated mechanism from this work allows thick PP parts to yield carbonaceous products with complex structures through a subsequent pyrolysis step. The approach for enabling PP-to-carbon conversion has consistent product yield and controlled dimensional shrinkage. Under optimized processing conditions, these PP-derived carbons exhibit robust mechanical properties and excellent joule heating performance, demonstrated by their versatile use as heating elements. Furthermore, this process can be extended to recycled PP, enabling the conversion of waste plastic materials to value-added products. This work provides an innovative approach to create structured carbon materials with direct access to complex geometry, which can be transformative to, and broadly benefit, many important technological applications.

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.

Intelligent diffusion regulation induced in-situ growth of cobalt nanoclusters on carbon nanotubes for excellent electromagnetic wave absorption

To achieve strong electromagnetic wave absorption performance at thin thicknesses, a chemical vapor deposition approach was employed to prepare Co nanoclusters modified carbon nanotubes. The main mechanism lies in the formation of dispersed oxides on the basis of low melting point and decomposition temperature of cobalt nitrate hexahydrate, while solid oxides are not easy to agglomerate during reduction due to their poor diffusion properties. Additionally, the abundant nitrogen-doped on carbon nanotubes provides abundant metal deposition sites, which further inhibits metal agglomeration. As expected, the reflection loss was robust at -59.96 dB with a low filler loading of 10 wt%, and the bandwidth was broad at 5.4GHz. Several factors contribute to excellent electromagnetic wave absorption, such as multiple reflections and scattering in the internal space, dipole polarization loss induced by plenty of functional groups, and interfacial polarization loss at the interfaces between Co nanoclusters and carbon nanotubes.

Ultrafast and on-demand oil/water separation with vertically aligned cellulosic smart sponge

Slow oil sorption speed of commercial non-woven polypropylene (PP) sorbent remains a major challenge for efficient clean-up of oil spillage. Adsorption-based polymeric sponge oil removing offers an appealing way to solve this challenge by increasing surface area. However, the tortuous oil sorption path and plastic waste after oil uptake are two long-standing bottlenecks for realizing efficient oil spill removal. Here, we report a vertically aligned-biomass fiber junctioned sorbents (a-BFJS), by confining delignified biomass with carbon nanotube (CNT), polyvinyl alcohol (PVA), and methyltrimethoxysilane (MTMS). The sorbent shows an excellent performance towards xylene sorption capacity with uptake about 50 g g^-1 within 10 s. This is due to the wide and short pathway of their aligned channels, which improves the capillary effect and fast oil transport in the oriented channels. Moreover, the sponge exhibits fast oil sorption-desorption kinetics enabled by simple mechanical squeezing. We further engineered a scalable rapid continuous oil skimming with simple peristaltic pump. The oil recovering using a-BFJS realized high oil selectivity from xylene/water emulsion. Our demonstration of the high-performance aligned channel sorbent and scalable oil removing sponge offers an eco-friendly and promising strategy for efficiently removing oil from oil spills from water.

Morphology engineering of defective graphene for microwave absorption

Graphene with abundant defects has been considered as the most lightweight electromagnetic functional materials. Although important, the dominant electromagnetic response of defective graphene with diverse morphologies is rarely the focus of existing research. Herein, the defective graphene with two-dimensional planar structure (2D-ps) and three-dimensional continuous network (3D-cn) morphologies were dexterously designed with 2D mixing and 3D filled systems of polymeric matrix. A comparison between the topologies of defective graphene-based nanofillers and the microwave attenuation behaviors was examined. Defective graphene with 3D-cn morphology can achieve ultralow filling content and broadband absorption, which is attributed to the presence of numerous pore structures that promote impedance matching, induce continuous conduction loss and provide multiple reflection and scattering sites for electromagnetic wave attenuation. Comparatively, by virtue of the increased filling content of 2D-ps, the dielectric losses primarily originate from the dielectric genes, including aggregation-induced-charge transport, abundant defect and dipole polarization, resulting in good microwave absorption at low thickness and low frequency. Therefore, this work provides a pioneering insight into morphology engineering of defective graphene microwave absorbers, and it will guide future exploration of customizing high-performance microwave absorption materials based on graphene-based low-dimensional building blocks.

Polyimide aerogel-derived amorphous porous carbon/crystalline carbon composites for high-performance microwave absorption

High-performance polyimide-based porous carbon/crystalline composite absorbers (PIC/rGO and PIC/CNT) were prepared by vacuum freeze-drying and high-temperature pyrolysis. The excellent heat resistance of polyimides (PIs) ensured the integrity of their pore structure during high-temperature pyrolysis. The complete porous structure improves the interfacial polarization and impedance-matching conditions. Furthermore, adding appropriate rGO or CNT can improve the dielectric losses and obtain good impedance-matching conditions. The stable porous structure and strong dielectric loss enable fast attenuation of electromagnetic waves (EMWs) inside PIC/rGO and PIC/CNT. The minimum reflection loss (RL_min) for PIC/rGO is -57.22 dB at 4.36 mm thickness. The effective absorption bandwidth (EABW, RL below -10 dB) for PIC/rGO is 3.12 GHz at 2.0 mm thickness. The RL_min for PIC/CNT is -51.20 dB at 2.02 mm thickness. The EABW for PIC/CNT is 4.08 GHz at 2.4 mm thickness. The PIC/rGO and PIC/CNT absorbers designed in this work have simple preparations and excellent EMW absorption performances. Therefore, they can be used as candidate materials in EMW absorbing materials.

NiO/Ni Heterojunction on N-Doped Hollow Carbon Sphere with Balanced Dielectric Loss for Efficient Microwave Absorption

Hollow carbon spheres are potential candidates for lightweight microwave absorbers. However, the skin effect of pure carbon-based materials frequently induces a terrible impedance mismatching issue. Herein, small-sized NiO/Ni particles with heterojunctions on the N-doped hollow carbon spheres (NHCS@NiO/Ni) are constructed using SiO₂ as a sacrificing template. The fabricated NHCS@NiO/Ni displayed excellent microwave absorbability with a minimum reflection loss of -44.04 dB with the matching thickness of 2 mm and a wider efficient absorption bandwidth of 4.38 GHz with the thickness of 1.7 mm, superior to most previously reported hollow absorbers. Experimental results demonstrated that the excellent microwave absorption property of the NHCS@NiO/Ni are attributed to balanced dielectric loss and optimized impedance matching characteristic due to the presence of NiO/Ni heterojunctions. Theoretical calculations suggested that the redistribution of charge at the interfaces and formation of dipoles induced by N dopants and defects are responsible for the enhanced conduction and polarization losses of NHCS@NiO/Ni. The simulations for the surface current and power loss densities reveal that the NHCS@NiO/Ni has- applicable attenuation ability toward microwave under the practical application scenario. This work paves an efficient way for the reasonable design of small-sized particles with well-defined heterojunctions on hollow nanostructures for high-efficiency microwave absorption.

Electrostatic Adsorption Enables Layer Stacking Thickness-Dependent Hollow Ti3 C2 Tx MXene Bowls for Superior Electromagnetic Wave Absorption

Although transition metal carbides/carbonitrides (MXenes) exhibit immense potential for electromagnetic wave (EMW) absorption, their absorbing ability is hindered by facile stacking and high permittivity. Layer stacking and geometric structures are expected to significantly affect the conductivity and permittivity of MXenes. However, it is still a formidable task to simultaneously regulate layer stacking and microstructure of MXenes to realize high-performance EMW absorption. Herein, a simple and viable strategy using electrostatic adsorption is developed to integrate 2D Ti₃ C₂ T_x MXene nanosheets into 3D hollow bowl-like structures with tunable layer stacking thickness. Density functional theory calculations indicate an increase in the density of states of the d orbital from the Ti atom near the Fermi level and the generation of additional electrical dipoles in the MXene nanosheets constituting the bowl walls upon reducing the layer stacking thickness. The hollow MXene bowls exhibit a minimum reflection loss (RL_min ) of -53.8 dB at 1.8 mm. The specific absorbing performance, defined as RL_min (dB)/thickness (mm)/filler loading (wt%), exceeds 598 dB mm^-1 , far surpassing that of the most current MXene and bowl-like materials reported in the literature. This work can guide future exploration on designing high-performance MXenes with "lightweight" and "thinness" characteristics for superior EMW absorption.

Ultrabroad Microwave Absorption Ability and Infrared Stealth Property of Nano-Micro CuS@rGO Lightweight Aerogels

Developing ultrabroad radar-infrared compatible stealth materials has turned into a research hotspot, which is still a problem to be solved. Herein, the copper sulfide wrapped by reduced graphene oxide to obtain three-dimensional (3D) porous network composite aerogels (CuS@rGO) were synthesized via thermal reduction ways (hydrothermal, ascorbic acid reduction) and freeze-drying strategy. It was discovered that the phase components (rGO and CuS phases) and micro/nano structure (microporous and nanosheet) were well-modified by modulating the additive amounts of CuS and changing the reduction ways, which resulted in the variation of the pore structure, defects, complex permittivity, microwave absorption, radar cross section (RCS) reduction value and infrared (IR) emissivity. Notably, the obtained CuS@rGO aerogels with a single dielectric loss type can achieve an ultrabroad bandwidth of 8.44 GHz at 2.8 mm with the low filler content of 6 wt% by a hydrothermal method. Besides, the composite aerogel via the ascorbic acid reduction realizes the minimum reflection loss (RL_min) of - 60.3 dB with the lower filler content of 2 wt%. The RCS reduction value can reach 53.3 dB m², which effectively reduces the probability of the target being detected by the radar detector. Furthermore, the laminated porous architecture and multicomponent endowed composite aerogels with thermal insulation and IR stealth versatility. Thus, this work offers a facile method to design and develop porous rGO-based composite aerogel absorbers with radar-IR compatible stealth.

Preparation of porous CoNi/N-doped carbon microspheres based on magnetoelectric coupling strategy: A new choice against electromagnetic pollution

Magnetoelectric coupling is a key strategy to obtain high-performance microwave absorption materials. Especially for carbon matrix composites, the absorbing capacity can be optimized via the tuning of the graphitization degree and the content ratio of the magnetic and dielectric components. Based on this theory, a simple strategy, consisting of the solvothermal method and annealing in an inert atmosphere, is adopted in this study to combine CoNi magnetic alloys with graphitized carbon into micron-scale composite spherical particles. Additionally, special attention is paid to the correlation among the graphitization degree of carbon matrix, component proportion, and dielectric response ability, so as to achieve a flexible micromorphology design and a tunable microwave absorption performance. When the pyrolysis temperature is offset to the best of 700 ℃, a broadband absorption of 6.61 GHz (reflection loss <  - 10 dB) is achieved at an ultrathin matching thickness of 1.9 mm. Adjusting the carbon content can further optimize the impedance matching and realize a high-intensity absorption with a reflection loss of - 72.7 dB. Our work proposes a useful strategy to realize the effective combination of the magnetic and dielectric loss mechanisms and boost the microwave absorption capacity toward achieving the desired broadband and a high-efficiency absorption performance.

Electroactive Fe-biochar for redox-related remediation of arsenic and chromium: Distinct redox nature with varying iron/carbon speciation

Electroactive Fe-biochar has attracted significant attention for As(III)/Cr(VI) immobilization through redox reactions, and its performance essentially lies in the regulation of various Fe/C moieties for desired redox performance. Here, a series of Fe-biochar with distinct Fe/C speciation were rationally produced via two-step pyrolysis of iron minerals and biomass waste at 400-850 °C (BCX-Fe-Y, X and Y represented the first- and second-step pyrolysis temperature, respectively). The redox transformation of Cr(VI) and As(III) by Fe-biochar was evaluated in simulated wastewater under oxic or anoxic conditions. Results showed that more effective Cr(VI) reduction could be achieved by BCX-Fe-400, while a higher amount of As (III) was oxidized by BCX-Fe-850 under the anoxic environment. Besides, BCX-Fe-400 could generate more reactive oxygen species (e.g.,^•OH) by reducing the O₂, which enhanced the redox-related transformation of pollutants under the oxic situation. The evolving redox performance of Fe-biochar was governed by the transition of the redox state from reductive to oxidative related to the Fe/C speciation. The small-sized amorphous/low-crystalline ferrous minerals contributed to a higher electron-donating capacity (0.43-1.28 mmol g^-1) of BCX-Fe-400. In contrast, the oxidative surface oxygen-functionalities (i.e., carboxyl and quinoid) on BCX-Fe-850 endowed a stronger electron-accepting capacity (0.71-1.39 mmol g^-1). Moreover, the graphitic crystallites with edge-type defects and porous structure facilitated the electron transfer, leading to a higher electron efficiency of BCX-Fe-850. Overall, we unveiled the roles of both Fe and C speciation in maneuvering the redox reactivity of Fe-biochar, which can advance our rational design of electroactive Fe-biochar for redox-related environmental remediation.

Ti3 C2 Tx /MoS2 Self-Rolling Rod-Based Foam Boosts Interfacial Polarization for Electromagnetic Wave Absorption

Heterogeneous interface design to boost interfacial polarization has become a feasible way to realize high electromagnetic wave absorbing (EMA) performance of dielectric materials. However, interfacial polarization in simple structures such as particles, rods, and flakes is weak and usually plays a secondary role. In order to enhance the interfacial polarization and simultaneously reduce the electronic conductivity to avoid reflection of electromagnetic wave, a more rational geometric structure for dielectric materials is desired. Herein, a Ti₃ C₂ T_x /MoS₂ self-rolling rod-based foam is proposed to realize excellent interfacial polarization and achieve high EMA performance at ultralow density. Different surface tensions of Ti₃ C₂ T_x and ammonium tetrathiomolybdate are utilized to induce the self-rolling of Ti₃ C₂ T_x sheets. The rods with a high aspect ratio not only remarkably improve the polarization loss but also are beneficial to the construction of Ti₃ C₂ T_x /MoS₂ foam, leading to enhanced EMA capability. As a result, the effective absorption bandwidth of Ti₃ C₂ T_x /MoS₂ foam covers the whole X band (8.2-12.4 GHz) with a density of only 0.009 g cm^-3 , at a thickness of 3.3 mm. The advantages of rod structures are verified through simulations in the CST microwave studio. This work inspires the rational geometric design of micro/nanostructures for new-generation EMA materials.

Ultralight Magnetic and Dielectric Aerogels Achieved by Metal-Organic Framework Initiated Gelation of Graphene Oxide for Enhanced Microwave Absorption

Metal-organic frameworks (MOFs) are used to directly initiate the gelation of graphene oxide (GO), producing MOF/rGO aerogels. The ultralight magnetic and dielectric aerogels show remarkable microwave absorption performance with ultralow filling contents. The development of a convenient methodology for synthesizing the hierarchically porous aerogels comprising metal-organic frameworks (MOFs) and graphene oxide (GO) building blocks that exhibit an ultralow density and uniformly distributed MOFs on GO sheets is important for various applications. Herein, we report a facile route for synthesizing MOF/reduced GO (rGO) aerogels based on the gelation of GO, which is directly initiated using MOF crystals. Free metal ions exposed on the surface of MIL-88A nanorods act as linkers that bind GO nanosheets to a three-dimensional porous network via metal-oxygen covalent or electrostatic interactions. The MOF/rGO-derived magnetic and dielectric aerogels Fe₃O₄@C/rGO and Ni-doped Fe₃O₄@C/rGO show notable microwave absorption (MA) performance, simultaneously achieving strong absorption and broad bandwidth at low thickness of 2.5 (- 58.1 dB and 6.48 GHz) and 2.8 mm (- 46.2 dB and 7.92 GHz) with ultralow filling contents of 0.7 and 0.6 wt%, respectively. The microwave attenuation ability of the prepared aerogels is further confirmed via a radar cross-sectional simulation, which is attributed to the synergistic effects of their hierarchically porous structures and heterointerface engineering. This work provides an effective pathway for fabricating hierarchically porous MOF/rGO hybrid aerogels and offers magnetic and dielectric aerogels for ultralight MA.

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.

Study on Microwave Absorption Performance Enhancement of Metamaterial/Honeycomb Sandwich Composites in the Low Frequency Band

With the rapid development of electronic technology and modern radar detection system, there is increasingly urgent demand for microwave absorbing composites working efficiently in the low frequency range (e.g., 1−2 GHz). In this work, a type of metamaterial/honeycomb sandwich composite (MHSC) was proposed and fabricated, which exhibited a light weight structure and excellent wave-absorbing performance in the low frequency band. The relationship between the wave-absorbing properties and the design parameters of the composite, such as the thickness of the wave-transmitting skin, the thickness and dielectric properties of the wave-absorbing honeycomb, was systematically investigated. The electromagnetic coupling interference between the honeycomb absorber and metamaterial resonator proved to be a crucial factor that affects synergistic wave-absorbing performance in the low-frequency band. Under the rational design, the incorporation of subwavelength-sized phase-gradient metamaterial units in the composite can significantly improve low-frequency wave-absorbing performance for greater than 5 dB (an increment larger than 100%); and the obtained MHSC exhibits averaged reflectivity (Ra) less than −10 dB in the low frequency band of 1−2 GHz as well as outstanding performance (Ra < −14.6 dB) over an extremely wide frequency range (1−18 GHz). The MHSC reported in this study could be a promising candidate for the key material in high-performance radar stealth and other related applications.

Heterointerface Engineering of β-Chitin/Carbon Nano-Onions/Ni-P Composites with Boosted Maxwell-Wagner-Sillars Effect for Highly Efficient Electromagnetic Wave Response and Thermal Management

The rational construction of microstructure and composition with enhanced Maxwell-Wagner-Sillars effect (MWSE) is still a challenging direction for reinforcing electromagnetic wave (EMW) absorption performance, and the related EMW attenuation mechanism has rarely been elucidated. Herein, MWSE boosted β-chitin/carbon nano-onions/Ni-P composites is prepared according to the heterointerface engineering strategy via facile layer-by-layer electrostatic assembly and electroless plating techniques. The heterogeneous interface is reinforced from the aspect of porous skeleton, nanomaterials and multilayer construction. The composites exhibit competitive EMW response mechanism between the conductive loss and the polarization/magnetic loss, as describing like the story of "The Hare and the Tortoise". As a result, the composites not only achieve a minimum reflection loss (RL_min) of - 50.83 dB and an effective bandwidth of 6.8 GHz, but also present remarkable EMW interference shielding effectiveness of 66.66 dB. In addition, diverse functions such as good thermal insulation, infrared shielding and photothermal performance were also achieved in the hybrid composites as a result of intrinsic morphology and chemicophysics properties. Therefore, we believe that the boosted MWSE open up a novel orientation toward developing multifunctional composites with high-efficient EMW response and thermal management.

Monolithic carbon aerogels within foam framework for high-temperature thermal insulation and organics absorption

Carbon aerogels exhibit high porosity, good electrical conductivity, and low thermal conductivity, but their practical applications are greatly hindered by their tedious preparation and inherent structure brittleness. Herein, monolithic carbon aerogels (MCAs) with low density and large size are prepared via a facile sol-gel polymerization of phenolic resin within melamine foam (MF), followed by ambient pressure drying and co-carbonization. During ambient pressure drying process, the MF matrix can deliver supporting force to counteract against the solvent evaporation surface tension, thus inhibiting volume shrinkage and shape deformation. Upon co-carbonization process, the MF matrix and organic aerogel could pyrolyze and shrink cooperatively, which could effectively prevent the brittle fracture of monolith. Therefore, large-sized MCAs (up to 250 × 250 × 20 mm) with low densities of 0.12-0.22 g·cm^-3 are obtained. The as-obtained MCAs possess high compressive strength (2.50 MPa), ultra-low thermal conductivity (0.051 W·m^-1·K^-1 at 25 °C and 0.111 W·m^-1·K^-1 at 800 °C), and high-volume organic absorption capability (77.3-88.0%, V/V). This facile and low-cost method for the fabrication of large-sized monolithic carbon aerogels with excellent properties could envision enormous potential for high-temperature thermal insulation and organics absorption.

Environmentally Tough and Stretchable MXene Organohydrogel with Exceptionally Enhanced Electromagnetic Interference Shielding Performances

Conductive hydrogels have potential applications in shielding electromagnetic (EM) radiation interference in deformable and wearable electronic devices, but usually suffer from poor environmental stability and stretching-induced shielding performance degradation. Although organohydrogels can improve the environmental stability of materials, their development is at the expense of reducing electrical conductivity and thus weakening EM interference shielding ability. Here, a MXene organohydrogel is prepared which is composed of MXene network for electron conduction, binary solvent channels for ion conduction, and abundant solvent-polymer-MXene interfaces for EM wave scattering. This organohydrogel possesses excellent anti-drying ability, low-temperature tolerance, stretchability, shape adaptability, adhesion and rapid self-healing ability. Two effective strategies have been proposed to solve the problems of current organohydrogel shielding materials. By reasonably controlling the MXene content and the glycerol-water ratio in the gel, MXene organohydrogel can exhibit exceptionally enhanced EM interference shielding performances compared to MXene hydrogel due to the increased physical cross-linking density of the gel. Moreover, MXene organohydrogel shows attractive stretching-enhanced interference effectiveness, caused by the connection and parallel arrangement of MXene nanosheets. This well-designed MXene organohydrogel has potential applications in shielding EM interference in deformable and wearable electronic devices.

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.

Magnetic modulation of core@shell MoS2-based flower-like multicomponent nanocomposites to improve microwave attenuation

Nanocomposites with a three-dimensional (3D) flower-like geometrical morphology were considered as excellent microwave absorbers (MAs) because of the numerous effective sites for the multiple reflections of electromagnetic (EM) wave. Herein, for optimizing the EM matching characteristic and taking full advantage of interface polarization, a strategy of magnetic modulation was proposed to further improve the EM wave absorption performances (EMWAPs) of MoS₂-based nanocomposites. We adopted a simple hydrothermal route and a combined method of hydrothermal treatment/hydrogen reduction to synthesize core@shell CoFe₂O₄@MoS₂ and CoFe@MoO₂/MoS₂ flower-like nanocomposites, respectively. The obtained results indicated that the hydrogen reduction effectively improved their magnetic properties and magnetic loss capabilities, and their 3D flower-like geometrical morphologies were well maintained during the hydrogen reduction process. The obtained core@shell CoFe@MoO₂/MoS₂ flower-like nanocomposites presented the extraordinary comprehensive EMWAPs including the optimal reflection loss value of -54.83 dB with the matching thicknesses (d_m) value of 2.05 mm and effective absorption bandwidth value of 6.40 GHz with the d_m value of 2.59 mm, which were evidently superior to the properties of CoFe₂O₄@MoS₂. Therefore, the findings provided an effective pathway to further improve EMWAPs of MoS₂-based core@shell nanocomposites and the as-prepared core@shell CoFe@MoO₂/MoS₂ flower-like nanocomposites could be utilized as the novel high-efficient MAs.

Heterointerface Engineering in Electromagnetic Absorbers: New Insights and Opportunities

Electromagnetic (EM) absorbers play an increasingly essential role in the electronic information age, even toward the coming "intelligent era". The remarkable merits of heterointerface engineering and its peculiar EM characteristics inject a fresh and infinite vitality for designing high-efficiency and stimuli-responsive EM absorbers. However, there still exist huge challenges in understanding and reinforcing these interface effects from the micro and macro perspectives. Herein, EM response mechanisms of interfacial effects are dissected in depth, and with a focus on advanced characterization as well as theoretical techniques. Then, the representative optimization strategies are systematically discussed with emphasis on component selection and structural design. More importantly, the most cutting-edge smart EM functional devices based on heterointerface engineering are reported. Finally, current challenges and concrete suggestions are proposed, and future perspectives on this promising field are also predicted.

Ultrahigh-strength carbon aerogels for high temperature thermal insulation

Carbon aerogels with nanoporous structure are attractive for thermal insulation under extreme conditions, but their practical applications are usually plagued by the inherent brittleness and easy-oxidation characteristic at high temperature. Herein, silica-modified carbon aerogels (SCAs) with extraordinarily high strength are prepared via a facile sol-gel polymerization of phenolic resin and siloxane, followed by ambient pressure drying and carbonization. The resulting SCAs possess medium-high density of ∼0.5 g·cm^-3 and mesoporous structure with the mean pore size of 33 nm. During carbonization process, the siloxane could be gradually transformed into the amorphous SiO₂ particles and crystalline SiC particles, which are coated on the surface of carbon nanoparticle and consequently improve the oxidation-resistance of carbon aerogels. Due to the density-porosity trade-off, the SCAs have high compressive strength of 10.0 MPa and satisfied thermal conductivities of 0.118 W·m^-1·K^-1 at 25 °C and 0.263 W·m^-1·K^-1 at 1000 °C. Furthermore, needled carbon fiber-reinforced SCAs (CF-SCAs) with ultrahigh compressive strength of 210.5 MPa are prepared, which exhibit good thermal conductivities of 0.207 W·m^-1·K^-1 at 25 °C and 0.407 W·m^-1·K^-1 at 1000 °C. The ultrahigh mechanical strength, good oxidation-resistance, good thermal insulation as well as the facile preparation make the SACs great promising in high-temperature insulations especially under harsh conditions.