Lotus Leaf-Derived Gradient Hierarchical Porous C/MoS2 Morphology Genetic Composites with Wideband and Tunable Electromagnetic Absorption Performance

Multifunctional Film Assembled from N-Doped Carbon Nanofiber with Co-N4-O Single Atoms for Highly Efficient Electromagnetic Energy Attenuation

Single-atom materials have demonstrated attractive physicochemical characteristics. However, understanding the relationships between the coordination environment of single atoms and their properties at the atomic level remains a considerable challenge. Herein, a facile water-assisted carbonization approach is developed to fabricate well-defined asymmetrically coordinated Co-N4-O sites on biomass-derived carbon nanofiber (Co-N4-O/NCF) for electromagnetic wave (EMW) absorption. In such nanofiber, one atomically dispersed Co site is coordinated with four N atoms in the graphene basal plane and one oxygen atom in the axial direction. In-depth experimental and theoretical studies reveal that the axial Co-O coordination breaks the charge distribution symmetry in the planar porphyrin-like Co-N4 structure, leading to significantly enhanced dielectric polarization loss relevant to the planar Co-N4 sites. Importantly, the film based on Co-N4-O/NCF exhibits light weight, flexibility, excellent mechanical properties, great thermal insulating feature, and excellent EMW absorption with a reflection loss of - 45.82 dB along with an effective absorption bandwidth of 4.8 GHz. The findings of this work offer insight into the relationships between the single-atom coordination environment and the dielectric performance, and the proposed strategy can be extended toward the engineering of asymmetrically coordinated single atoms for various applications.

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.

Multifunctional Carbon Fiber Reinforced C/SiOC Aerogel Composites for Efficient Electromagnetic Wave Absorption, Thermal Insulation, and Flame Retardancy

Carbon fiber composites have great application prospects as a potential electromagnetic (EM) wave-absorbing material, yet it remains extremely challenging to integrate multiple functions of EM wave absorption, mechanical strength, thermal insulation, and flame retardancy. Herein, a novel carbon fiber reinforced C/SiOC aerogel (CF/CS) composite is successfully prepared by sol-gel impregnation combined with an ambient drying process for the first time. The density of the obtained CF/CS composites can be controlled just by changing sol-gel impregnation cycles (original carbon fiber felt (S0), and samples with one (S1) and two (S2) impregnation cycles are 0.249, 0.324, and 0.402 g cm-3, respectively), allowing for efficient tuning of their properties. Remarkably, S2 displays excellent microwave absorption properties, with an optimal reflection loss of -65.45 dB, which is significantly improved than S0 (-10.90 dB). Simultaneously, compared with S0 (0.75 and 0.30 MPa in the x/y and z directions), the mechanical performance of S2 is dramatically improved with a maximum compressive strength of 10.37 and 4.93 MPa in the x/y and z directions, respectively. Moreover, CF/CS composites show superior thermal insulation capability than S0 and obtain good flame-retardant properties. This work provides valuable guidance and inspiration for the development of multifunctional EM wave absorbers.

Leakage Proof, Flame-Retardant, and Electromagnetic Shield Wood Morphology Genetic Composite Phase Change Materials for Solar Thermal Energy Harvesting

Phase change materials (PCMs) offer a promising solution to address the challenges posed by intermittency and fluctuations in solar thermal utilization. However, for organic solid-liquid PCMs, issues such as leakage, low thermal conductivity, lack of efficient solar-thermal media, and flammability have constrained their broad applications. Herein, we present an innovative class of versatile composite phase change materials (CPCMs) developed through a facile and environmentally friendly synthesis approach, leveraging the inherent anisotropy and unidirectional porosity of wood aerogel (nanowood) to support polyethylene glycol (PEG). The wood modification process involves the incorporation of phytic acid (PA) and MXene hybrid structure through an evaporation-induced assembly method, which could impart non-leaking PEG filling while concurrently facilitating thermal conduction, light absorption, and flame-retardant. Consequently, the as-prepared wood-based CPCMs showcase enhanced thermal conductivity (0.82 W m-1 K-1, about 4.6 times than PEG) as well as high latent heat of 135.5 kJ kg-1 (91.5% encapsulation) with thermal durability and stability throughout at least 200 heating and cooling cycles, featuring dramatic solar-thermal conversion efficiency up to 98.58%. In addition, with the synergistic effect of phytic acid and MXene, the flame-retardant performance of the CPCMs has been significantly enhanced, showing a self-extinguishing behavior. Moreover, the excellent electromagnetic shielding of 44.45 dB was endowed to the CPCMs, relieving contemporary health hazards associated with electromagnetic waves. Overall, we capitalize on the exquisite wood cell structure with unidirectional transport inherent in the development of multifunctional CPCMs, showcasing the operational principle through a proof-of-concept prototype system.

Constructing gradient reflection and scattering porous framework in composite aerogels for enhanced microwave absorption

Developing high-performance microwave absorption (MA) materials becomes an urgent concern in the field of electromagnetic protection. Constructing porous framework is an efficient approach to MA owing to the abilities of adjusting impedance matching and providing more reflection and scattering paths for electromagnetic waves. Herein, a cellulose nanofibril (CNF)/honeycomb-like carbon-shell encapsulated FeCoNi@C/carbon nanotube (CNT) composite aerogel was fabricated via a facile freeze-drying method. The super-lightweight composites showed a distinctive gradient structure for reflection and scattering inside aerogel pores, micrometer small pores, and nano-fillers on the pore walls. The composite aerogel showed an ideal minimum reflection loss (RLmin) of -43.6 dB and remarkable adjustable effective absorption bandwidth (EAB) of 12.18 GHz due to good impedance matching, unique gradient porous structure, and synergies of multiple loss mechanisms. Therefore, this work will provide a viable strategy to improve the MA capability of absorbers by taking full advantage of constructing gradient reflection and scattering porous structure.

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.

Linkage Effect Induced by Hierarchical Architecture in Magnetic MXene-based Microwave Absorber

Hierarchical architecture engineering is desirable in integrating the physical-chemical behaviors and macroscopic properties of materials, which present great potential for developing multifunctional microwave absorption materials. However, the intrinsic mechanisms and correlation conditions among cellular units have not been revealed, which are insufficient to maximize the fusion of superior microwave absorption (MA) and derived multifunctionality. Herein, based on three models (disordered structure, porous structure, lamellar structure) of structural units, a range of MXene-aerogels with variable constructions are fabricated by a top-down ice template method. The aerogel with lamellar structure with a density of only 0.015 g cm-3 exhibits the best MA performance (minimum reflection loss: -53.87 dB, effective absorption bandwidth:6.84 GHz) at a 6 wt.% filling ratio, which is preferred over alternative aerogels with variable configurations. This work elucidates the relationship between the hierarchical architecture and the superior MA performance. Further, the MXene/CoNi Composite aerogel with lamellar structure exhibits >90% compression stretch after 1000 cycles, excellent compressive properties, and elasticity, as well as high hydrophobicity and thermal insulation properties, broadening the versatility of MXene-based aerogel applications. In short, through precise microstructure design, this work provides a conceptually novel strategy to realize the integration of electromagnetic stealth, thermal insulation, and load-bearing capability simultaneously.

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.

Bilayer fiber membrane electrospun from polylactic acid/alginate/bromelain and polylactic acid for enhancing the functionality of tea bags

Tea bags have been extensively used in the food industry and daily life as an efficient way to pack tea. However, the large pores of the commercial tea bags not only lead to the inner contents of tea bag susceptible to bacteria and moisture but also result in the faster water infusion which is undesired during tea brewing. In this study, the polylactic acid (PLA)-PLA/sodium alginate (SA)/bromelain (BL) bilayer fiber membrane imitating the asymmetric wetting structure of lotus leaf blades was fabricated to avoid the above disadvantages of commercial tea bag. The PLA/SA/BL skin-core nanofiber membrane which imitating the skin-core structure of lotus leaf stems was first prepared as the hydrophilic and support layer, then a hydrophobic PLA layer was deposited on top via electrospinning. The PLA-PLA/SA/BL bilayer fiber membrane had a breaking strength of 5.5 MPa and started to decompose at 260 °C. Using this bilayer membrane, tea bags were designed with a novel structure where the hydrophobic PLA layer was placed in the same direction. The novel structure endow the those tea bags a slow and directional water transfer property. Therefore, the PLA-PLA/SA/BL bilayer fiber membrane has great potential for applications as tea bags.

Hierarchical Co2 P/CoS2 @C@MoS2 Composites with Hollow Cavity and Multiple Phases Toward Wideband Electromagnetic Wave Absorption

The synergistic effect of hollow cavities and multiple hetero-interfaces displays huge advantages in achieving lightweight and high-efficient electromagnetic wave absorption, but still confronts huge challenges. Herein, hierarchical Co2 P/CoS2 @C@MoS2 composites via the self-sacrificed strategy and a subsequent hydrothermal method have been successfully synthesized. Specifically, ZIF-67 cores first act as the structural template to form core-shell ZIF-67@poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) (ZIF-67@PZS) composites, which are converted into hollow Co2 P@C shells with micro-mesoporous characteristics because of the gradient structural stabilities and preferred coordination ability. The deposition of hierarchical MoS2 results in phase transition (Co2 P→Co2 P/CoS2 ), yielding the formation of hierarchical Co2 P/CoS2 @C@MoS2 composites with hollow cavities and multiple hetero-interfaces. Benefiting from the cooperative advantages of hollow structure, extra N,P,S-doped sources, lattice defects/vacancies, diverse incoherent interfaces, and hierarchical configurations, the composites deliver superior electromagnetic wave capability (-56.6 dB) and wideband absorption bandwidth (8.96 GHz) with 20 wt.% filler loading. This study provides a reliable and facile strategy for the precise construction of superior electromagnetic wave absorbents with efficient absorption attenuation.

A Bioinspired Gradient Design Strategy for Cellulose-Based Electromagnetic Wave Absorbing Structural Materials

Cellulose nanofiber (CNF) possesses excellent intrinsic properties, and many CNF-based high-performance structural and functional materials have been developed recently. However, the coordination of the mechanical properties and functionality is still a considerable challenge. Here, a CNF-based structural material is developed by a bioinspired gradient structure design using hollow magnetite nanoparticles and the phosphorylation-modified CNF as building blocks, which simultaneously achieves a superior mechanical performance and electromagnetic wave absorption (EMA) ability. Benefiting from the gradient design, the flexural strength of the structural material reached ∼205 MPa. Meanwhile, gradient design improves impedance matching, contributing to the high EMA ability (-59.5 dB) and wide effective absorption width (5.20 GHz). Besides, a low coefficient of thermal expansion and stable storage modulus was demonstrated as the temperature changes. The excellent mechanical, thermal, and EMA performance exhibited great potential for application in stealth equipment and electromagnetic interference protecting electronic packaging materials.

From VIB- to VB-Group Transition Metal Disulfides: Structure Engineering Modulation for Superior Electromagnetic Wave Absorption

The laminated transition metal disulfides (TMDs), which are well known as typical two-dimensional (2D) semiconductive materials, possess a unique layered structure, leading to their wide-spread applications in various fields, such as catalysis, energy storage, sensing, etc. In recent years, a lot of research work on TMDs based functional materials in the fields of electromagnetic wave absorption (EMA) has been carried out. Therefore, it is of great significance to elaborate the influence of TMDs on EMA in time to speed up the application. In this review, recent advances in the development of electromagnetic wave (EMW) absorbers based on TMDs, ranging from the VIB group to the VB group are summarized. Their compositions, microstructures, electronic properties, and synthesis methods are presented in detail. Particularly, the modulation of structure engineering from the aspects of heterostructures, defects, morphologies and phases are systematically summarized, focusing on optimizing impedance matching and increasing dielectric and magnetic losses in the EMA materials with tunable EMW absorption performance. Milestones as well as the challenges are also identified to guide the design of new TMDs based dielectric EMA materials with high performance.

High-Density Nanopore Confined Vortical Dipoles and Magnetic Domains on Hierarchical Macro/Meso/Micro/Nano Porous Ultra-Light Graphited Carbon for Adsorbing Electromagnetic Wave

Atomic-level structural editing is a promising way for facile synthesis and accurately constructing dielectric/magnetic synergistic attenuated hetero-units in electromagnetic wave absorbers (EWAs), but it is hard to realize. Herein, utilizing the rapid explosive volume expansion of the CoFe-bimetallic energetic metallic triazole framework (CoFe@E-MTF) during the heat treatment, the effective absorption bandwidth and the maximum absorption intensity of a series of atomic CoFe-inserted hierarchical porous carbon (CoFe@HPC) EWAs can be modified under the diverse synthetic temperature. Under the filler loading of 15 wt%, the fully covered X and Ku bands at 3 and 2.5 mm for CoFe@HPC800 and the superb minimum reflection loss (RLmin ) of -53.15 dB and specific reflection loss (SRL) of -101.24 dB mg-1 mm-1 for CoFe@HPC1000 are achieved. More importantly, the single-atomic chemical bonding among Co─Fe on the nanopores is captured by extended X-ray absorption fine structure, which reveals the formation mechanism of nanopore-confined vortical dipoles and magnetic domains. This work heralds the infinite possibilities of atomic editing EWA in the future.

A review on composite strategy of MOF derivatives for improving electromagnetic wave absorption

To address the electromagnetic wave (EMW) pollution issues caused by the development of electronics and wireless communication technology, it is urgent to develop efficient EMW-absorbing materials. With controllable composition, diverse structure, high porosity, and large specific surface area, metal-organic framework (MOF) derivatives have sparked the infinite passion and creativity of researchers in the electromagnetic field. Against the challenges of poor inherent impedance matching and insufficient attenuation capability of pure MOF derivative, designing and developing MOF derivative-based composites by compounding MOF with other materials, such as graphene, CNTs, MXene, and so on, has been an effective strategy for constructing high-efficiency EMW absorbing materials. This review systematically expounds the research progress of MOF derivative-based composite strategies, and discusses the challenges and opportunities faced by MOF derivatives in the field of EMW absorption. This work can provide some good ideas for researchers to design and prepare high-efficiency MOF-based EMW absorbing materials in applications of next-generation electronics and aerospace.

Symbiotic strategy of Cu on CuFe2O4 realizing high-efficiency electromagnetic wave absorption

Low complex permittivity and easy magnetic agglomeration prevent ferrites from achieving high-efficiency electromagnetic wave (EMW) absorption owing to the resultant narrow absorption bandwidth. Existing composition- and morphology-controlled strategies have made limited progress in fundamentally improving the intrinsic complex permittivity and absorption performance of pure ferrite. In this study, Cu/CuFe₂O₄ composites were synthesized using a facile and low-energy sol-gel self-propagating combustion, and the metallic Cu content was adjusted by changing the ratio of the reductant (citric acid) to the oxidant (ferric nitrate). The symbiosis and coexistence of metallic Cu with ferritic CuFe₂O₄ increases the intrinsic complex permittivity of CuFe₂O₄, which can be regulated by changing the metallic Cu content_. Moreover, the unique ant-nest-like microstructure overcomes the issue of magnetic agglomeration. Because of the favorable impedance matching and strong dielectric loss (interfacial polarization and conduction loss) provided by the moderate metallic Cu content, S0.5 concurrently displays broadband absorption with an effective absorption bandwidth (EAB) of 6.32 GHz at an ultrathin thickness of 1.7 mm and strong absorption relying on minimum reflection loss (RL_min) of -48.81 dB at 4.08 GHz and 4.0 mm. This study provides a new perspective for improving the EMW absorption performance of ferrites.

Facile synthesis of Fe3O4 nanoparticles/reduced graphene oxide sandwich composites for highly efficient microwave absorption

Component regulation and microstructure design are two effective strategies to adjust electromagnetic parameters and improve the microwave absorption performance of materials. In this study, a facile synthesis strategy consisting of ultrasonic dispersion, blast drying, and roasting is proposed to build a sandwich-like graphene-based absorbent, in which Fe₃O₄ nanoparticles with adjustable content are sandwiched uniformly between reduced graphene oxide nanosheets. The sandwich structure can form multiple interfaces, prevent the aggregation of nanoparticles, facilitate interface polarization, and endow the material with multiple electromagnetic loss mechanisms, which is very beneficial for impedance matching and microwave attenuation. Notably, the effective absorption bandwidth achieves 5.7 GHz, and the minimum reflection loss value is -49.9 dB. In addition, the synthesis process is simple and suitable for large-scale production and possible industrial applications. Thus, this facile route to fabricate sandwich-like graphene-based absorbents provides new ideas and approaches for designing new graphene-based nanocomposites.

Flexible cobalt nanoparticles/carbon nanofibers with macroporous structures toward superior electromagnetic wave absorption

The increasing electromagnetic (EM) pollution that has seriously threatened human health and electronic devices urgently required high-performance absorbents toward attenuating EM wave (EMW). The combination of microstructure modulation and appropriate components regulation has proven to be a feasible strategy for improving the EMW absorption performance of absorbents. In this work, well-designed one-dimensional carbon nanofibers with macroporous structures and uniformly magnetic metal nanoparticles modification were prepared by the hard-template assisted electrospinning method followed by carbonization and template-elimination processes. The strong interfacial polarization loss and multireflection strengthened by the hollow structures and the magnetic loss induced by the introduced cobalt nanoparticles evidently enhanced the impedance matching level of the macroporous carbon nanofibers/cobalt nanoparticles (MCF/Co). As a result, MCF/Co composite offers broad absorption bandwidth (6.24 GHz) and strong electromagnetic wave absorption performance (-40.1 dB) at a thickness of 3.0 mm. This work inspires the rational one-dimensional macroporous carbon nanofibers design for new-generation EMW materials and provides an important research basis for the porous flexible EMW absorption materials.

Engineering of the Core-Shell Boron Nitride@Nitrogen-Doped Carbon Heterogeneous Interface for Efficient Heat Dissipation and Electromagnetic Wave Absorption

The effective integration of multiple functions into electromagnetic wave-absorbing (EWA) materials is the future development direction but remains a huge challenge. A rational selection of components and the design of structures can make the material have excellent EWA performance and heat dissipation. Herein, the core-shell structured boron nitride@nitrogen-doped carbon (BN@NC) is prepared by using waterborne polyurethane (WPU) as the carbon source via a facile pyrolysis treatment process, where NC is used as the conductive loss shell, and BN serves as an impedance matching core and dominant heat transfer media. As a result, the BN@NC-900 filled with paraffin wax yields a minimum reflection loss of -42.2 dB at 2.2 mm and an effective absorbing bandwidth of 4.48 GHz at 1.8 mm, and its thermal conductivity reaches up to 0.92 W/m·K in epoxy resin. Most importantly, flexible BN@NC/WPU films are prepared and simultaneously achieve the dual-functional capability of efficiently dissipating heat and electromagnetic waves (-50.0 dB). Besides, an attractive multiband absorption feature (>99%) from C to Ku bands is realized and a strong absorbing over -27.0 dB at the S band (2.88 GHz) is even achieved. This study may pave a new route for the rational design of multifunctional EWA materials.

Polystyrene-Modulated Polypyrrole to Achieve Controllable Electromagnetic-Wave Absorption with Enhanced Environmental Stability

The moderation of the dielectric properties of polymer composites and their environmental stability need to be considered comprehensively in the design of microwave-absorbing materials. In this work, polypyrrole/polystyrene (PPy/PS) composited particles were synthesized through a facile in situ bulk polymerization procedure. The PS component can be modulated conveniently by controlling the polymerization time. FTIR and Raman analyses disclosed that the PS component was immobilized in PPy via covalent bonds. The electromagnetic characterization results indicated that the dielectric properties and, thus, the microwave absorption could be controlled when the styrene polymerization was prolonged from 6 h (PPy-6) to 19 h (PPy-19). The composite PPy-19 displayed an optimal reflection loss of -51.7 dB with a matching thickness of 3.16 mm, and the effective absorption bandwidth (EAB) even reached 5.8 GHz at 2.4 mm. The PS component endowed PPy/PS composites with more robust environmental stability than homogeneous PPy. After being exposed to air for 365 days and hydrothermally treated at 100 °C for 12 h, PPy-19 still exhibited a reflection loss superior to -20 dB. The present work provides a new insight into the adjustment of the electromagnetic properties of PPy composites to fabricate high-performance microwave absorbers with superior environmental stability.

Regression Analysis of the Dielectric and Morphological Properties for Porous Nanohydroxyapatite/Starch Composites: A Correlative Study

This paper aims to investigate the dielectric properties, i.e., dielectric constant (ε′), dielectric loss factor (ε″), dielectric tangent loss (tan δ), electrical conductivity (σ), and penetration depth (Dp), of the porous nanohydroxyapatite/starch composites in the function of starch proportion, pore size, and porosity over a broad band frequency range of 5 MHz−12 GHz. The porous nanohydroxyapatite/starch composites were fabricated using different starch proportions ranging from 30 to 90 wt%. The results reveal that the dielectric properties and the microstructural features of the porous nanohydroxyapatite/starch composites can be enhanced by the increment in the starch proportion. Nevertheless, the composite with 80 wt% of starch proportion exhibit low dielectric properties (ε′, ε″, tan δ, and σ) and a high penetration depth because of its highly interconnected porous microstructures. The dielectric properties of the porous nanohydroxyapatite/starch composites are highly dependent on starch proportion, average pore size, and porosity. The regression models are developed to express the dielectric properties of the porous nanohydroxyapatite/starch composites (R2 > 0.96) in the function of starch proportion, pore size, and porosity from 1 to 11 GHz. This dielectric study can facilitate the assessment of bone scaffold design in bone tissue engineering applications.

MoS2 /MXene Aerogel with Conformal Heterogeneous Interfaces Tailored by Atomic Layer Deposition for Tunable Microwave Absorption

In the design of electromagnetic (EM) wave absorbing materials, it is still a great challenge to optimize the relationship between the attenuation capability and impedance matching synergistically. Herein, a 3D porous MoS₂ /MXene hybrid aerogel architecture with conformal heterogeneous interface has been built by atomic layer deposition (ALD) based on specific porous templates to optimize the microwave absorption (MA) performance comprehensively. The original porous structure of pristine Ti₃ C₂ T_x aerogel used as templates can be preserved well during ALD fabrication, which prolongs the reflection and scattering path and ameliorates the dielectric loss. Meanwhile, plenty of heterointerfaces between MoS₂ and Ti₃ C₂ T_x have been fabricated based on conformally ALD-deposited MoS₂ with controlled thickness on the porous surfaces of the templates, which can effectively optimize the impedance matching and transform its response to EM waves from shielding into absorbing. Moreover, the interaction between the attenuation capability and impedance matching can also be modulated by the number of ALD cycle in MoS₂ fabrication. After optimization, MoS₂ /MXene hybrid aerogel obtained under 300 ALD cycles shows a minimum reflection loss of -61.65 dB at the thickness of 4.53 mm. In addition, its preferable lightweight, high surface area, mechanical, and hydrophobicity properties will also be conducive to further practical applications.

Architecture Design and Interface Engineering of Self-assembly VS4/rGO Heterostructures for Ultrathin Absorbent

The employment of microwave absorbents is highly desirable to address the increasing threats of electromagnetic pollution. Importantly, developing ultrathin absorbent is acknowledged as a linchpin in the design of lightweight and flexible electronic devices, but there are remaining unprecedented challenges. Herein, the self-assembly VS4/rGO heterostructure is constructed to be engineered as ultrathin microwave absorbent through the strategies of architecture design and interface engineering. The microarchitecture and heterointerface of VS4/rGO heterostructure can be regulated by the generation of VS4 nanorods anchored on rGO, which can effectively modulate the impedance matching and attenuation constant. The maximum reflection loss of 2VS4/rGO40 heterostructure can reach - 43.5 dB at 14 GHz with the impedance matching and attenuation constant approaching 0.98 and 187, respectively. The effective absorption bandwidth of 4.8 GHz can be achieved with an ultrathin thickness of 1.4 mm. The far-reaching comprehension of the heterointerface on microwave absorption performance is explicitly unveiled by experimental results and theoretical calculations. Microarchitecture and heterointerface synergistically inspire multi-dimensional advantages to enhance dipole polarization, interfacial polarization, and multiple reflections and scatterings of microwaves. Overall, the strategies of architecture design and interface engineering pave the way for achieving ultrathin and enhanced microwave absorption materials.

Hierarchical engineering of Large-caliber carbon Nanotube/Mesoporous Carbon/Fe3C nanoparticle hybrid nanocomposite towards Ultra-lightweight electromagnetic microwave absorber

The rational regulation of the magnetic-dielectric composition and microstructures of the absorber is considered an important approach to optimize both the impedance matching and the electromagnetic microwave attenuation ability. Along these lines, a novel architecture-controlled large-caliber carbon nanotube/mesoporous carbon/Fe₃C nanoparticle-based hybrid nanocomposites (CNT/C/Fe₃C), which were derived from the CNT/polyimide (PI) assemblies anchoring ferric oxide hydrate nanoprecipitates, are presented in this work. The proposed configurations were prepared by applying a cooperative co-assembly strategy and high-temperature pyrolysis procedure for the development of an ultra-lightweight electromagnetic microwave absorber. The employed hierarchically tubular heterogeneous architecture is composed of a highly graphited CNT supporting skeleton, polyimide assemblies-converted carbon interlayer with mesopores, and uniformly distributed magnetic Fe₃C nanoparticles. This unique hierarchical structure can not only induce multiple reflection and scattering effects of the incident electromagnetic microwave but also trigger dipole/interfacial polarization, ferromagnetic resonance and eddy current loss that are beneficial for the synergistic dielectric and magnetic loss. Moreover, the large-caliber CNT and mesoporous carbon interlayer can endow the as-prepared absorber with lightweight characteristics. Hence, the proposed CNT/C-EDA/Fe₃C-900 hybrid nanocomposite exhibits a minimum reflection loss (RL) of -48.4 dB at a matching thickness of 3.2 mm, and the effective absorption bandwidth (RL ≤ -10 dB) almost covers the whole X-band only with a 5 wt% filler loading. Undoubtedly, these encouraging outcomes will promote the development of hierarchical engineering techniques of novel magnetic-dielectric nanocomposite absorbers.

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.

Layered Foam/Film Polymer Nanocomposites with Highly Efficient EMI Shielding Properties and Ultralow Reflection

Lightweight, high-efficiency and low reflection electromagnetic interference (EMI) shielding polymer composites are greatly desired for addressing the challenge of ever-increasing electromagnetic pollution. Lightweight layered foam/film PVDF nanocomposites with efficient EMI shielding effectiveness and ultralow reflection power were fabricated by physical foaming. The unique layered foam/film structure was composed of PVDF/SiCnw/MXene (Ti₃C₂T_x) composite foam as absorption layer and highly conductive PVDF/MWCNT/GnPs composite film as a reflection layer. The foam layer with numerous heterogeneous interfaces developed between the SiC nanowires (SiCnw) and 2D MXene nanosheets imparted superior EM wave attenuation capability. Furthermore, the microcellular structure effectively tuned the impedance matching and prolonged the wave propagating path by internal scattering and multiple reflections. Meanwhile, the highly conductive PVDF/MWCNT/GnPs composite (~ 220 S m^-1) exhibited superior reflectivity (R) of 0.95. The tailored structure in the layered foam/film PVDF nanocomposite exhibited an EMI SE of 32.6 dB and a low reflection bandwidth of 4 GHz (R < 0.1) over the Ku-band (12.4 - 18.0 GHz) at a thickness of 1.95 mm. A peak SE_R of 3.1 × 10^-4 dB was obtained which corresponds to only 0.0022% reflection efficiency. In consequence, this study introduces a feasible approach to develop lightweight, high-efficiency EMI shielding materials with ultralow reflection for emerging applications.

Structural Design Strategies of Polymer Matrix Composites for Electromagnetic Interference Shielding: A Review

With the widespread application of electronic communication technology, the resulting electromagnetic radiation pollution has been significantly increased. Metal matrix electromagnetic interference (EMI) shielding materials have disadvantages such as high density, easy corrosion, difficult processing and high price, etc. Polymer matrix EMI shielding composites possess light weight, corrosion resistance and easy processing. However, the current polymer matrix composites present relatively low electrical conductivity and poor EMI shielding performance. This review firstly discusses the key concept, loss mechanism and test method of EMI shielding. Then the current development status of EMI shielding materials is summarized, and the research progress of polymer matrix EMI shielding composites with different structures is illustrated, especially for their preparation methods and evaluation. Finally, the corresponding key scientific and technical problems are proposed, and their development trend is also prospected.

Construction of 1D Heterostructure NiCo@C/ZnO Nanorod with Enhanced Microwave Absorption

Layered double hydroxides (LDHs) have a special structure and atom composition, which are expected to be an excellent electromagnetic wave (EMW) absorber. However, it is still a problem that obtaining excellent EMW-absorbing materials from LDHs. Herein, we designed heterostructure NiCo-LDHs@ZnO nanorod and then subsequent heat treating to derive NiCo@C/ZnO composites. Finally, with the synergy of excellent dielectric loss and magnetic loss, an outstanding absorption performance could be achieved with the reflection loss of - 60.97 dB at the matching thickness of 2.3 mm, and the widest absorption bandwidth of 6.08 GHz was realized at 2.0 mm. Moreover, this research work provides a reference for the development and utilization of LDHs materials in the field of microwave absorption materials and can also provide ideas for the design of layered structural absorbers.

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

Ordered porous carbon materials (PCMs) have potential applications in various fields due to their low mass densities and porous features. However, it yet remains extremely challenging to construct PCMs with multifunctionalization for electromagnetic wave absorption. Herein, the honeycombed-like carbon aerogels with embedded Co@C nanoparticles are fabricated by a directionally freeze-casting and carbonization method. The optimized aerogel possesses low density (0.017 g cm^-3 ), fire-retardant, robust mechanical performance (compression moduli reach 1411 and 420 kPa in the longitudinal and transverse directions at 80% strain, respectively), and high thermal management (high thermal insulation capability and high-efficiency electrothermal conversion ability). Notably, the optimized aerogel exhibits the excellent electromagnetic wave absorption properties with broad effective absorption bandwidth (13.12-17.14 GHz) and strong absorption (-45.02 dB) at a thickness of only 1.5 mm. Density functional theory calculations and the experimental results demonstrate that the excellent electromagnetic wave absorption properties stem from the synergetic effects among high electrical conductivity, numerous interfaces and dipoles and unique ordered porous structure. Meanwhile, the computer simulation technology (CST) simulation confirms that the multifunctional aerogel can attenuate more electromagnetic energy in a practical environment. This work paves the way for rational design and fabrication of the next-generation electromagnetic wave absorbing materials.

Atomic-Scale Layer-by-Layer Deposition of FeSiAl@ZnO@Al2O3 Hybrid with Threshold Anti-Corrosion and Ultra-High Microwave Absorption Properties in Low-Frequency Bands

Developing highly efficient magnetic microwave absorbers (MAs) is crucial, and yet challenging for anti-corrosion properties in extremely humid and salt-induced foggy environments. Herein, a dual-oxide shell of ZnO/Al₂O₃ as a robust barrier to FeSiAl core is introduced to mitigate corrosion resistance. The FeSiAl@ZnO@Al₂O₃ layer by layer hybrid structure is realized with atomic-scale precision through the atomic layer deposition technique. Owing to the unique hybrid structure, the FeSiAl@ZnO@Al₂O₃ exhibits record-high microwave absorbing performance in low-frequency bands covering L and S bands with a minimum reflection loss (RL_min) of -50.6 dB at 3.4 GHz. Compared with pure FeSiAl (RL_min of -13.5 dB, a bandwidth of 0.5 GHz), the RL_min value and effective bandwidth of this designed novel absorber increased up to ~ 3.7 and ~ 3 times, respectively. Furthermore, the inert ceramic dual-shells have improved 9.0 times the anti-corrosion property of FeSiAl core by multistage barriers towards corrosive medium and obstruction of the electric circuit. This is attributed to the large charge transfer resistance, increased impedance modulus |Z|_0.01 Hz, and frequency time constant of FeSiAl@ZnO@Al₂O₃. The research demonstrates a promising platform toward the design of next-generation MAs with improved anti-corrosion properties.

3D core-shell Fe3O4@SiO2@MoS2 composites with enhanced microwave absorption performance

In this work, a 3D ternary core-shell Fe₃O₄@SiO₂@MoS₂ composite is synthesized by a hydrothermal technique and a modified Stöber method, where magnetic Fe₃O₄@SiO₂ microsphere with the core of raspberry-like Fe₃O₄ nanoparticles is completely coated by the flower-like MoS₂. Herein, the electromagnetic parameters of the composites are effectively tuned by the combination of magnetic Fe₃O₄ with dielectric SiO₂ and MoS₂. The obtained ternary composites exhibit remarkable enhancement of microwave absorption. The measurement results indicate that the minimum reflection loss (RL) of Fe₃O₄@SiO₂@MoS₂ composites reaches -62.98 dB at 1.83 mm with the effective absorption bandwidth (RL < -10 dB) of 5.76 GHz (from 11.28 to 17.04 GHz) at 1.92 mm, much higher than those of pure Fe₃O₄ particles and Fe₃O₄@SiO₂ microsphere. It is believed that the improved performances come from the specific structural design and the plentiful interfacial construction. Further, the synergistic effect of the dielectric and magnetic loss as well as the promoted impedance matching also help to enhance the microwave absorption of the composites. The microwave absorption behavior of the composites conforms to the quarter-wavelength cancellation theory. Our study offers an effective and promising strategy in the structural design and interfacial construction of the novel magnetic/dielectric composites with high-efficiency microwave absorption.

Flexible and Waterproof 2D/1D/0D Construction of MXene-Based Nanocomposites for Electromagnetic Wave Absorption, EMI Shielding, and Photothermal Conversion

ABSTRACT

High-performance electromagnetic wave absorption and electromagnetic interference (EMI) shielding materials with multifunctional characters have attracted extensive scientific and technological interest, but they remain a huge challenge. Here, we reported an electrostatic assembly approach for fabricating 2D/1D/0D construction of Ti₃C₂T_x/carbon nanotubes/Co nanoparticles (Ti₃C₂T_x/CNTs/Co) nanocomposites with an excellent electromagnetic wave absorption, EMI shielding efficiency, flexibility, hydrophobicity, and photothermal conversion performance. As expected, a strong reflection loss of -85.8 dB and an ultrathin thickness of 1.4 mm were achieved. Meanwhile, the high EMI shielding efficiency reached 110.1 dB. The excellent electromagnetic wave absorption and shielding performances were originated from the charge carriers, electric/magnetic dipole polarization, interfacial polarization, natural resonance, and multiple internal reflections. Moreover, a thin layer of polydimethylsiloxane rendered the hydrophilic hierarchical Ti₃C₂T_x/CNTs/Co hydrophobic, which can prevent the degradation/oxidation of the MXene in high humidity condition. Interestingly, the Ti₃C₂T_x/CNTs/Co film exhibited a remarkable photothermal conversion performance with high thermal cycle stability and tenability. Thus, the multifunctional Ti₃C₂T_x/CNTs/Co nanocomposites possessing a unique blend of outstanding electromagnetic wave absorption and EMI shielding, light-driven heating performance, and flexible water-resistant features were highly promising for the next-generation intelligent electromagnetic attenuation system. [Image: see text]

HIGHLIGHTS

The 2D/1D/0D Ti₃C₂T_x/carbon nanotubes/Co nanocomposite is successfully synthesized via an electrostatic assembly. Nanocomposites exhibit an excellent electromagnetic wave absorption and a remarkable electromagnetic interference shielding efficiency. The flexible, waterproof, and photothermal conversion performances are achieved.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40820-021-00673-9.

Carbon-Based MOF Derivatives: Emerging Efficient Electromagnetic Wave Absorption Agents

To tackle the aggravating electromagnetic wave (EMW) pollution issues, high-efficiency EMW absorption materials are urgently explored. Metal-organic framework (MOF) derivatives have been intensively investigated for EMW absorption due to the distinctive components and structures, which is expected to satisfy diverse application requirements. The extensive developments on MOF derivatives demonstrate its significantly important role in this research area. Particularly, MOF derivatives deliver huge performance superiorities in light weight, broad bandwidth, and robust loss capacity, which are attributed to the outstanding impedance matching, multiple attenuation mechanisms, and destructive interference effect. Herein, we summarized the relevant theories and evaluation methods, and categorized the state-of-the-art research progresses on MOF derivatives in EMW absorption field. In spite of lots of challenges to face, MOF derivatives have illuminated infinite potentials for further development as EMW absorption materials.