Self-Assembled 3D Flower-like Composites of Heterobimetallic Phosphides and Carbon for Temperature-Tailored Electromagnetic Wave Absorption

Self-Standing MOF-Derived Co@SiCnw Nanocomposite Aerogel with a Hierarchical Microstructure for Highly Effective and Wideband Electromagnetic Attenuation

To meet the requirements of lightweight and wideband attenuation for advanced electromagnetic (EM) absorption materials, the combination of both MOF composition and hierarchical structural design was applied as the strategy to prepare the MOF-derived Co@SiC nanowire (Co@SiCnw) nanocomposite aerogel. The hierarchical and laminated structures with multiple Co@SiCnw layers were constructed via a mixed growth-assisted freeze-drying and calcination process. The ultralightweight Co@SiCnw presents a low density of 0.11 g/cm3. With abundant second-phase polarization interfaces and enlarged EM wave attenuation channels to enhance dielectric and conductive loss, the optimized Co@SiCnw offers a minimal reflection loss (RLmin) of -61.4 dB at 10.0 GHz (2.64 mm) and an effective absorption bandwidth (EAB) as wide as 7.44 GHz with a sample thickness of only 2.16 mm. Furthermore, multifunctionalities, including low density, thermal insulation, and self-standing, were demonstrated for Co@SiCnw, making it a high-performance and practical microwave absorption material.

A Self-foaming Strategy to Construct Small Mo2C Nanoparticles Decorated 3D Carbon Foams as Superior Electromagnetic Wave Absorbing Materials with Strong Corrosion Resistance

3D macroporous carbon-based foams are always considered as promising candidates for high-performance electromagnetic (EM) wave absorbing materials due to the collaborative EM contribution and salutary structure effect. However, the uneven distribution of heterogeneous EM components and the cumbersome preparation process have become key issues to hinder their performance improvement and practical popularity. Herein, the fabrication of 3D carbon foam decorated with small and highly dispersed Mo2C nanoparticles is realized by an innovative self-foaming strategy. The foaming mechanism can be attributed to the decomposition of nitrate during the softening process of organic polymers. The good dispersion of Mo2C nanoparticles boosts interfacial polarization significantly. After regulating the content of Mo2C nanoparticles, the optimal Mo2C/CF-x exhibits good EM absorption performance, whose minimum reflection loss intensity value can reach up to -72.2 dB, and effective absorption bandwidth covers 6.7 GHz with a thickness of 2.30 mm. Very importantly, the resultant Mo2C/CF-x exhibits hydrophobicity and strong acidic anticorrosion, and a long-time treatment in HCl solution (6.0 mol L-1) produces negligible impacts on their EM functions. It is believed that this extraordinary feature may render Mo2C/C foams as qualified and durable EM wave absorbing materials (EWAMs) under rigorous conditions.

Hierarchical Magnetic Carbon Nanoflowers for Ultra-Efficient Electromagnetic Wave Absorption

Porous carbon nanomaterials are widely applied in the electromagnetic wave absorption (EMWA) field. Among them, an emerging flower-like carbon nanomaterial, termed carbon nanoflowers (CNFs), has attracted tremendous research attention due to their unique hierarchical flower-like structure. However, the design of flower-like carbon nanomaterials with different magnetic cores for EMWA has rarely been reported. Herein, a general template method is proposed to achieve a set of high-quality magnetic CNFs, namely Co@Void@CNFs, CoNi@CNFs, and Ni@CNFs. The prepared magnetic CNFs have highly accessible surface area and internal space, rich heteroatom content, multi-scale pore system, and uniform and highly dispersed magnetic nanoparticles, as a result, deliver superior EMWA performance. Specifically, when the thickness is 2.6 mm, the Co@Void@CNFs exhibit a maximum refection loss (RLmax) of -56.6 dB and an effective absorption bandwidth (EAB) from 8.0 to 12.1 GHz covering the whole X band. The CoNi@CNFs have an RLmax of up to -57.6 dB and a wide EAB of 5.6 GHz at just 1.9 mm. For the Ni@CNFs, possess an ultra-broad EAB of 6.1 GHz, covering the entire Ku band at 2.0 mm. Overall, the hierarchical magnetic carbon nanoflowers proposed here offer new insights toward realizing multifunctional integrated carbon nanomaterials for EMWA.

Progress in microwave absorbing materials: A critical review

Microwave-absorbing materials play a significant role in various applications that involve the attenuation of electromagnetic radiation. This critical review article provides an overview of the progress made in the development and understanding of microwave-absorbing materials. The interaction between electromagnetic radiation and absorbing materials is explained, with a focus on phenomena such as multiple reflections, scattering, and polarizations. Additionally, types of losses that affect the performance of microwave absorbers are also discussed, including dielectric loss, conduction loss, relaxation loss, magnetic loss, and morphological loss. Each of these losses has different implications for the effectiveness of microwave absorbers. Further, a detailed review is presented on various types of microwave absorbing materials, including carbonaceous materials, conducting polymers, magnetic materials, metals and their composites, 2D materials (such as MXenes and 2D-transition metal dichalcogenides), biomass-derived materials, carbides, sulphides, phosphides, high entropy (HE) materials and metamaterials. The characteristics, advantages, and limitations of each material are examined. Overall, this review article highlights the progress achieved in the field of microwave-absorbing materials. It underlines the importance of optimizing different types of losses to enhance the performance of microwave absorbers. The review also recognizes the potential of emerging materials, such as 2D materials and high entropy materials, in further advancing microwave-absorbing properties.

Polymer self-assembly guided heterogeneous structure engineering towards high-performance low-frequency electromagnetic wave absorption

Magnetic-dielectric synergy is currently regarded as among the most effective approaches to achieve low-frequency electromagnetic wave absorption (EMA). However, designing and fabricating EMA materials with tunable magnetic-dielectric balance towards high-performance low-frequency EMA remains challenging. Herein, a polymer self-assembly guided heterogeneous structure engineering strategy is proposed to fabricate hierarchical magnetic-dielectric nanocomposite. Polymer assemblies not only can be employed as intermediates to encapsulate metal-organic frameworks and load metal hydroxide, but also that they play a crucial role for the in-situ formation of polycrystalline FeCo/Co composite nanoparticles. As a result, the minimum reflection loss (RLmin) can reach -59.61 dB at 5.4 GHz (4.8 mm) with a 20 wt% filler loading, while the effective absorption bandwidth (EAB, RLmin ≤ -10 dB) is 2.16 GHz, exhibiting excellent low-frequency EMA performance. Systematic investigations demonstrate that hierarchical mesoporous carbon matrix that supports FeCo/Co composite nanoparticles is beneficial for optimizing impedance matching and increasing attenuation capacity. In general, this study opens up new prospects for developing magnetic-dielectric EMA materials using a polymer self-assembly guided heterogeneous structure engineering strategy, which may receive significant attention in future research.

Microstructure optimization strategy of ZnIn2S4/rGO composites toward enhanced and tunable electromagnetic wave absorption properties

Although microstructure optimization is an effective strategy to improve and regulate electromagnetic wave (EMW) absorption properties, preparing microwave absorbents with enhanced EMW absorbing performance and tuned absorption band by a simple method remains challenging. Herein, ZnIn2S4/reduced graphene oxide (rGO) composites with flower-like and cloud-like morphologies were fabricated by a convenient hydrothermal method. The ZnIn2S4/rGO composites with different morphologies realize efficient EMW absorption and tunable absorption bands, covering a wide frequency range. The flower-like structure has an optimal reflection loss (RL) of up to -49.2 dB with a maximum effective absorption bandwidth (EAB) of 5.7 GHz, and its main absorption peaks are concentrated in the C and Ku bands. The minimal RL of the cloud-like structure can reach -36.3 dB, and the absorption peak shifts to the junction of X and Ku bands. The distinguished EMW absorption capacity originates from the uniquely optimized microstructure, complementary effect of ZnIn2S4 and rGO in dielectric constant, and synergy of various loss mechanisms, such as interfacial polarization, dipole polarization, conductive loss, and multiple reflections. This study proposes a guide for the structural optimization of an ideal EMW absorber to achieve efficient and tunable EMW absorption performance.

Controllable preparation of 2D carbon paper modified with flower-like WS2 for efficient microwave absorption

In the practical application of microwave absorbing materials, traditional powder materials need to be mixed with the matrix to fabricate composite coatings. However, the complex preparation process of composite coatings and the uneven dispersion of powders in the matrix limit their application. To solve these problems, two-dimensional (2D) F-WS₂/CP composite films were prepared by using carbon paper (CP) as a dispersion matrix and loading flower-like WS₂ on its surface through a simple hydrothermal method. The morphology and microwave absorption (MA) performance of the composite films are easily regulated by adjusting the amount of reaction precursors. The combination of WS₂ and CP facilitates impedance matching and improves the electromagnetic wave attenuation performance based on the synergistic effect of different loss mechanisms including multiple reflections and scattering, interfacial polarization, dipolar polarization, and conduction loss. At a low filler content (5 wt%), the maximum reflection loss (RL) of the composite film is up to -50 dB (99.999% energy absorption) at 12.5 GHz with 2.8 mm thickness. Moreover, at a relatively thin 1.8 mm thickness, its maximum RL remains -35 dB (>99.9% energy absorption). The as-prepared composite film shows excellent MA properties at a thinner thickness and lower filling content, providing inspiration for the preparation of light weight and efficient 2D thin-film microwave absorbers in the future.

Ultralight Hierarchically Structured RGO Composite Aerogels Embedded with MnO2/Ti3C2Tx for Efficient Microwave Absorption

Although intensive efforts have been devoted to fabricating Ti₃C₂T_x MXene composites for microwave absorption, it remains a great challenge to achieve excellent MA performance at low loading and thin thickness. Herein, a three-dimensional (3D) lightweight hierarchically structured MnO₂/Ti₃C₂T_x/RGO composite aerogel with abundant heterointerfaces was fabricated via a hydrothermal and chemical reduction self-assembly method. The RGO aerogel embedded with laminated MnO₂/Ti₃C₂T_x provides a lot of heterogeneous interfaces, 3D porous interconnected conductive networks, and reasonable combination of various loss materials for rich interfacial polarization, conductivity loss, multiple reflections and scattering, and good impedance matching. Benefiting from the synergy of different loss mechanisms, the maximum reflection loss (RL) is up to -66.5 dB (>99.9999% energy absorption) at only 10 wt % loading and 2.0 mm thickness, and even at only 1.5 mm thickness, the maximum RL value remains at -36 dB (>99.9% energy absorption). The work provides a promising route to construct 3D hierarchically heterogeneous composite aerogels for efficient MA at thin thickness and low loading.

Texture Regulation of Metal-Organic Frameworks, Microwave Absorption Mechanism-Oriented Structural Optimization and Design Perspectives

Texture regulation of metal-organic frameworks (MOFs) is essential for controlling their electromagnetic wave (EMW) absorption properties. This review systematically summarizes the recent advancements in texture regulation strategies for MOFs, including etching and exchange of central ions, etching and exchange of ligands, chemically induced self-assembly, and MOF-on-MOF heterostructure design. Additionally, the EMW absorption mechanisms in approaches based on structure-function dependencies, including nano-micro topological engineering, defect engineering, interface engineering, and hybrid engineering, are comprehensively explored. Finally, current challenges and future research orientation are proposed. This review aims to provide new perspectives for designing MOF-derived EMW-absorption materials to achieve essential breakthroughs in mechanistic investigations in this promising field.

Autogenous and Tunable CNTs for Enhanced Polarization and Conduction Loss Enabling Sea Urchin-Like Co3ZnC/Co/C Composites with Excellent Microwave Absorption Performance

ZIF-67-derived magnetic metal/carbon composites are considered prospective candidates for use as microwave absorption (MA) materials owing to their magnetoelectric synergy. However, the structure of ZIF-67-derived MA materials mainly depends on the morphology and composition of pristine metal-organic frameworks (MOFs), and their microstructures lack a rational design. Herein, a multidimensional sea urchin-like carbon nanotubes (CNTs)-grafted carbon polyhedra-encapsulated Co₃ZnC/Co nanoparticle composite was prepared by one-step catalytic pyrolysis of ZIF-67/ZnO using a rational structural design. The autogenous and tunable CNTs obtained with the assistance of zinc evaporation not only overcome the limitation of homogeneous dispersion but also endow the Co₃ZnC/Co/C composite with outstanding MA properties owing to the conduction loss provided by CNTs, polarization loss caused by multiple components, and electromagnetic wave trap composed of a special sea urchin-like structure. Consequently, the minimum reflection loss of ZZ_0.1-600 reaches -60.3 dB at 1.6 mm, the maximum absorption bandwidth of ZZ_0.05-600 is 6.24 GHz (covering nearly the entire Ku band) at 1.9 mm, and the structure has a low weight ratio (30 wt %). Compared with Z-600 and pure ZnO, the MA performance of the sea urchin-like Co₃ZnC/Co/C composite obtained by rational structural design has been greatly improved; this strategy offers a new approach for optimizing the MA performance of materials according to their structural design.

High-performance electromagnetic wave absorption in cobalt sulfide flower-like nanospheres

A heterophase cobalt sulfide absorbing material with petal-like surface structure was prepared by a simple hydrothermal method. The cobalt sulfide sample with the optimal microwave absorption capacity was achieved through regulating the reaction temperature. By regulating the reaction temperature to 200 °C, the optimal reflection loss was -48.4 dB at 16.8 GHz with filler loading of 50%, and the effective absorption bandwidth was 4.3 GHz at Ku band corresponding to a thickness of only 1.5 mm. The petal-like surface structure of cobalt sulfide gradually disappears as the reaction temperature rises, and the reduction of specific surface area has a negative effect on the microwave absorption capacity of the sample. Meanwhile, by adjusting the sample thickness from 1.5 to 5.0 mm, the effective absorption bandwidth could cover almost the whole test frequency range. The results show that the cobalt sulfide absorbing material with regulated reaction temperature has a strong electromagnetic wave absorption ability, light weight, thin thickness and simple synthesis, which is a promising microwave absorbing material for actual application.

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.

Magnetic CoNi alloy particles embedded N-doped carbon fibers with polypyrrole for excellent electromagnetic wave absorption

Increasing electromagnetic (EM) radiation has driven the rapid development of carbon-based EM wave absorption materials, but the design of light-weight and efficient carbon-based materials remains a huge challenge. Herein, N-doped carbon fibers embedded with CoNi alloy particles (CoNi/C fibers) were synthesized via electrospinning technology and carbonization. Then, conductive polypyrrole-coated CoNi/C fibers (CoNi/C@PPy composites) were synthesized by chemical polymerization. As-synthesized CoNi/C@PPy composites showed outstanding EM wave absorption property due to the synergistic effect between CoNi, N-doped carbon fibers and PPy. The optimal reflection loss (RL) is -68.78 dB (12.90 GHz) with the thickness of 2.43 mm and the low filler loading of 15 wt%. The widest effective absorption bandwidth (EAB) is 5.62 GHz with the thickness of 2.10 mm and the low filler loading of 20 wt%. The outstanding EM wave absorption property is mainly attributed to 3D network structure, great impedance matching and strong dielectric loss. The results showed that embedding magnetic alloy particles in carbon fibers coated with conductive polymers is an effective strategy for constructing efficient lightweight EM wave absorption materials.

Lightweight TiO2@C/Carbon Fiber Aerogels Prepared from Ti3C2Tx/Cotton for High-Efficiency Microwave Absorption

Carbon fiber aerogel (CFA) derived from cotton wool as a potential microwave absorbing material has received intensive attention owing to the low density, high conductivity, large surface area, and low cost, but its applications are limited by the relatively high complex permittivity. To solve this problem, TiO₂@C (derived from Ti₃C₂T_x) is introduced into CFA to prepare lightweight TiO₂@C/CFA composites based on electromagnetic (EM) parameter optimization and enhanced EM wave attenuation performance. The microwave absorption capacity of TiO₂@C/CFA-2 composite is obviously better than that of CFA. It is confirmed that good impedance matching derived from the combination of TiO₂@C and CFA is the main factor to achieve excellent microwave absorption. Moreover, the improved microwave absorption capabilities are closely related to multiple EM wave absorbing mechanisms including multiple reflections and scattering, dipolar and interfacial polarization, and conductivity loss. TiO₂@C/CFA-2 possesses a maximum reflection loss (RL) of -43.18 dB at a low response frequency of 6.0 GHz. As the matching thickness is less than 2.0 mm, the maximum RL values can still exceed -20 dB, and at the same time, the wide effective absorption bandwidth (EAB) below -10 dB achieves 4.36 GHz at only 1.9 mm thickness. Our work confirms that the lightweight and high-performance TiO₂@C/CFA composites are promising choices and offer a new approach to design and construct carbon-based microwave absorbents derived from biomass.

Synergetic Dielectric and Magnetic Losses of a Core-Shell Co/MnO/C Nanocomplex toward Highly Efficient Microwave Absorption

High-performance microwave-absorbing materials (MAMs) derived from metal-organic frameworks (MOFs) have attracted considerable attention due to their tunable chemical composition and microstructure. In this contribution, a core-shell-structured Co/MnO/C nanocomplex was prepared using a CoMn-MIL MOF by a facile hydrothermal synthesis and subsequent pyrolysis process. The optimal microwave absorption (MA) property of the as-prepared Co/MnO/C nanocomplex was achieved by the regulation of the Co²⁺/Mn²⁺ molar ratio. The minimum reflection loss (RL_min) of the Co/MnO/C-31 nanocomplex was low to -55.0 dB at 16.2 GHz with a thickness of 1.49 mm, and the effective absorption bandwidth (EAB) was high to 5.95 GHz (12.05-18 GHz) at a thickness of 1.8 mm. The mixed-metal nanocomplex with the core-shell structure exhibited outstanding MA performance, corresponding to the synergetic effect of the magnetic and dielectric loss. It provides a high efficiency strategy for rendering low reflection loss and broad EAB to high-performance MAMs.

Adjusting the match-degree between electron library and surface-active sites and forming surface polarization in MOF-based photo-cocatalysts for accelerating electron transfer

The Ni-CoP supported by a carbon matrix as the cocatalyst is synthesized by precisely controlling the pyrolysis temperature for the metal–organic framework, then loaded onto the CdS host catalyst by means of self-assembly for photocatalytic hydrogen production.

Molybdenum Blue Preassembly Strategy to Design Bimetallic Fe0.54Mo0.73/Mo2C@C for Tunable and Low-Frequency Electromagnetic Wave Absorption

Advanced electromagnetic wave absorption nanomaterials can play an important role in addressing the issue of increasing electromagnetic pollution in wireless communication field. Herein, a series of coralloid bimetallic Fe0.54Mo0.73/Mo2C@C (FMC)...

Improvement of multiple attenuation characteristics of two-dimensional lamellar ferrocobalt@carbon nanocomposites as excellent electromagnetic wave absorber

The lightweight carbon skeleton compounded with magnetic nanoparticles as excellent electromagnetic wave absorbers have attracted much attention considering their strong dielectric loss and magnetic loss, as well as the optimized...

Anchoring 1D nanochain-like Co3O4 on a 2D layered Ti3C2Tx MXene with outstanding electromagnetic absorption

3D superstructure Ti3C2Tx/Co3O4 nanochain composites were synthesized through electrostatic self-assembly, in which 1D Co3O4 nanochains were anchored on a 2D layered Ti3C2Tx surface.

Room-Temperature One-Step Synthesis of Silver/Reduced Graphene Oxide Nanocomposites as an Excellent Microwave Absorber

The present study is focused on room-temperature synthesis carried out by reduction of an aqueous silver nitrate (AgNO₃) and AgNO₃/graphene oxide (GO) dispersion using a low-cost commercial Fehling B solution in one step to form silver quantum dots (Ag QDs) and their Ag/reduced graphene oxide (Ag/RGO) nanocomposites and their characterization. The crystallinity, surface chemistry, structural, and morphological studies indicated the formation of crystalline small-sized quasispherical-functionalized Ag particles distributed uniformly on the surface of RGO. The conductivity measurements further showed an improvement in the conductivity of Ag/RGO nanocomposites as compared to neat Ag QDs. Our findings showed that Ag/RGO nanocomposites prepared by using 0.055 wt % of GO exhibited a total enhanced electromagnetic interference (EMI)-shielding efficiency (SE_T) of ∼39.2-42.3 dB (2-8 GHz) with a maximum value of ∼43.8 dB at 7. 5 GHz due to conduction loss, an interconnected conducting network, and a synergistic effect, and it followed an absorption mechanism. Furthermore, this superior absorption-dominated shielding conferred reflection loss (R_L) in the range of -79 to -82.5 dB with a R_L minima of -88 dB at 7.5 GHz, considering an effective absorption bandwidth of ∼6 GHz with 99.9% absorptivity. It is anticipated that Ag/RGO nanocomposites prepared in one step at room temperature could find potential EMI-shielding applications.

Preparation of core-shell C@TiO2 composite microspheres with wrinkled morphology and its microwave absorption

In this work, we successfully synthesize the core-shell structure carbon@titanium dioxide (C@TiO₂) composite microspheres with wrinkled surface through a three-step method and build up the relationship between the TiO₂ layer thickness and the microwave absorption property. The absorbing mechanism of the novel microsphere is revealed. Interface polymerization is applied for preparation of wrinkled poly glycidyl methacrylate/divinylbenzene polymer microspheres (PGMA/PDVB); Then, TiO₂ layer is controllably coated on the surface of PGMA/PDVB microspheres by hydrolysis of tetrabutyl titanate (TBT); C@TiO₂ composite microspheres are obtained by vacuum carbonization with PGMA/PDVB@TiO₂ microspheres as the precursor. TiO₂ layer thickness on the surface of C@TiO₂ composite microspheres can be effectively adjusted by controlling the amount of TBT. When the amount of TBT is 0.75 mL, C@TiO₂ composite microspheres exhibit the outstanding electromagnetic loss performance. The maximum reflection loss value (RLmax) reaches -49.21 dB at the thickness of 2 mm, corresponding effective absorption bandwidth is 5.27 GHz. The maximum effective absorption bandwidth is 5.5 GHz at 2.2 mm. The results show that the introduction of TiO₂ can regulate electromagnetic parameters and enhance interface polarization ability. Meanwhile, the surface wrinkle structure offers more opportunities for multiple reflections of electromagnetic and introduces a large number of defective skeleton structure. The synergy of multiple advantages makes the absorbing performance of C@TiO₂ composite microspheres significantly improved. This work plays a guiding role for the composition and the structure optimization of existing microwave absorbers.

Multi-Path Electron Transfer in 1D Double-Shelled Sn@Mo2 C/C Tubes with Enhanced Dielectric Loss for Boosting Microwave Absorption Performance

1D tubular micro-nano structural materials have been attracting extensive attention in the microwave absorption (MA) field for their anisotropy feature, outstanding impedance matching, and electromagnetic energy loss capability. Herein, unique double-shelled Sn@Mo₂ C/C tubes with porous Sn inner layer and 2D Mo₂ C/C outer layer are successfully designed and synthesized via a dual-template method. The composites possess favorable MA performance with an effective absorption bandwidth of 6.76 GHz and a maximum reflection loss value of -52.1 dB. Specifically, the rational and appropriate construction of Sn@Mo₂ C/C tubes promotes the multi-path electron transfer in the composites to optimize the dielectric constant and consequently to enhance the capacity of electromagnetic wave energy dissipation. Three mechanisms dominate the MA process: i) the conductive loss resulted from the rapid electron transmission due to the novel 1D hollow coaxial multi-shelled structure, especially the metallic Sn inner layer; ii) the polarization loss caused by abundant heterogeneous interfaces of Sn-Mo₂ C/C and Mo₂ CC from the precise double-shelled structure; iii) the capacitor-like loss by the potential difference between Mo₂ C/C nanosheets. This work hereby sheds light on the design of the 1D hierarchical structure and lays out a profound insight into the MA mechanism.

Wrinkled Fe3O4@C magnetic composite microspheres: Regulation of magnetic content and their microwave absorbing performance

In this work, we develop a novel synthetic strategy for wrinkled magnetic composite microspheres (Fe₃O₄@C). Firstly, hydrophobic oleic acid modified Fe₃O₄ (OA-Fe₃O₄) nanoparticles acted as the magnetic component are prepared by synchronous modification coprecipitation method. The macromolecular emulsifier with initiating activity is obtained by means of soap-free emulsion polymerization under the presence of 1,1-diphenylethylene (DPE). Then, interfacial polymerization is employed to synthesis Fe₃O₄@polymethylglycidyl ester/divinylbenzene composite microspheres (Fe₃O₄@PGMA/DVB). Fe₃O₄@C composite microspheres are obtained by vacuum carbonization of the microspheres. The effect of magnetic content on the microwave absorbing properties of Fe₃O₄@C composite microspheres is explored. The results show that Fe₃O₄@C composite microspheres exhibit the excellent application performance at the Fe₃O₄ content of 0.15 g. The reflection loss can reach -53.7 dB at only thickness of 1.7 mm. The Maximum effective absorption bandwidth is up to 5.26 GHz with a thickness of 1.9 mm. The microwave attenuation mechanism of Fe₃O₄@C composite microspheres is revealed. The excellent absorbing performance is attributed to the enhanced interfacial polarization ability, the surface wrinkled structure and the good synergy between dielectric and magnetic losses. This work provides an effective strategy for the design and preparation of new magnetic composite materials.

Constructing a nitrogen-doped carbon and nickel composite derived from a mixed ligand nickel-based a metal-organic framework toward adjustable microwave absorption

The rational design of nanostructures for absorbers has great potential in the microwave absorption field. In this work, a mixed ligand nickel metal-organic framework (ML-Ni MOF) was first prepared by the self-assembly of pyrazine and 1,3,5-benzenetricarboxylic acid with nickel ions. Then, the as-prepared ML-Ni MOF was used as a precursor to fabricate a nitrogen-doped carbon and nickel composite (ML-Ni/C). With the molar ratio of pyrazine and 1,3,5-benzenetricarboxylic acid of 1 : 1, the flower-like ML-Ni MOF was obtained. After pyrolysis, the ML-Ni MOF-derived ML-Ni/C composite showed an optimal reflection loss value of -65.33 dB with a thickness of 2.4 mm and a corresponding effective absorbing bandwidth (EAB, RL ≤ -10 dB) of 5.1 GHz. Besides, the broadest EAB of 7.6 GHz was achieved when the thickness was about 2.8 mm. This strategy paves a new way to design novel MOFs as precursors for fabricating absorbers.

Multiple interface-induced evolution of electromagnetic patterns for efficient microwave absorption at low thickness

Mo-Ni₂P/rGO composites with heterojunction structures were successfully prepared by phosphating NiMoO₄/rGO precursors at a specific temperature, which exhibit excellent microwave absorption performances at low thickness.

Design of a novel carbon nanotube and metal-organic framework interpenetrated structure with enhanced microwave absorption properties

The exploitation of carbon nanotube (CNT) and metal-organic framework (MOF) composite materials has been highly desirable in a number of applications. However, the construction of high dispersibility and stability CNT/MOF complex structures is still an enormous challenge. Herein, a novel assembly method is established for the construction of a CNT/Ni-MOF (0.1 CNT/MOF, 0.2 CNT/MOF, 0.3 CNT/MOF) interpenetrated structure by a solvothermal process. The MOFs can be robustly anchored on the surface of CNTs. Through a series of characterizations, the MOF can be comfortably integrated into the CNT fibers, which exhibits the enhancement of carrier mobility and fluorescence properties. The microwave absorption properties of  the CNT/MOF are explored by a vector network analyzer. The 0.1 CNT/MOF has a maximum absorption of -9.2 dB at 18 GHz with a thickness of 5 mm, while the 0.2 CNT/MOF has a maximum absorption of -24.32 dB at 4.5 GHz with a thickness of 5 mm, a performance maximum. Therefore, the 0.2 CNT/MOF structures are potential candidates to ameliorate the microwave absorption properties.

Tailored design of p-phenylenediamine functionalized graphene decorated with cobalt ferrite for microwave absorption

Structural design and componential optimization are two primary directions in the study of microwave absorbers. In this study, a novel cobalt ferrite (CoFe2O4) decorated with p-phenylenediamine (PPD) functionalized graphene (PG/CoFe2O4) binary hybrid with unique hierarchical porous structure was synthesized by a two-step route. The chemical composition, morphology and electromagnetic parameters of the as-prepared sample were investigated successively. The porous CoFe2O4 microspheres with an average diameter of about 160 nm were uniformly anchored on rGO nanosheets. Owing to the uniquely hierarchical porous structure, synergistic effects of dielectric loss (conductive loss, interface and dipole polarization) and magnetic loss (eddy current loss, natural and exchange resonance), the as-prepared sample exhibited excellent microwave absorption (MA) performance. The maximum reflection loss (RLmax) could attain up to -53.3 dB, and the effective absorption bandwidth (EAB) reached 6.6 GHz (11.4-18.0 GHz) at 2.40 mm, which completely covered the K u band. These results showed that this functional material can be applied in the MA field.

Deformable BCN/Fe3O4/PCL composites through electromagnetic wave remote control

Electromagnetic wave (EMW) induction of shape memory polymer (SMP) composites with multifunctional inorganic fillers is a high efficiency, uniform, and non-contact method. Herein, the shape memory effect of ternary BCN/Fe₃O₄/PCL composites induced by EMWs are explored. The components of Fe₃O₄ and the BCN nanotubes serve as wave-absorbing materials. The electromagnetic properties and EMW absorption performance of BCN/Fe₃O₄/PCL are discussed in detail. The EMWs absorbed by BCN/Fe₃O₄/PCL are dissipated by dielectric loss and magnetic loss. The shape memory mechanism of BCN/Fe₃O₄/PCL is based on the Fe₃O₄ and BCN nanotubes dissipating absorbed EMW energy into heat to boost the temperature of the composites, thereby responding to EMW remote control. This work introduces a new direction for SMPs induced by EMWs as potential candidates in the application of shape recovery in a restricted space.

3D Nest-Like Architecture of Core-Shell CoFe2O4@1T/2H-MoS2 Composites with Tunable Microwave Absorption Performance

As a promising microwave absorber filler, molybdenum disulfide (MoS₂), because of the unique structure, high electrical conductivity, and polarization effect, is receiving more and more interest. Developing MoS₂-based composites with specific structure and morphology is a hot top in the field of microwave absorbers, because of its strong multiple scattering and reflecting for microwaves as well as its unique interfacial characteristics. Now, with a facile solvothermal method, a novel core-shell CoFe₂O₄@1T/2H-MoS₂ composite is synthesized, where the CoFe₂O₄ nanospheres are entirely embedded in a special three-dimensional (3D) nest-like 1T/2H phase MoS₂. Notably, in comparison with superparamagnetic CoFe₂O₄ nanospheres, the coercivities of as-synthesized CoFe₂O₄@1T/2H-MoS₂ composites greatly increase. Here, 1T/2H-MoS₂ exhibits ferromagnetism superimposed onto large diamagnetism. It is noted that, by adjusting the content of 1T/2H-phase MoS₂, the microwave absorption performance of as-synthesized composites can be effectively tuned. The combination of 1T/2H-MoS₂ with CoFe₂O₄ helps to adjust the permittivity and optimize the impedance matching of the composites. Impressively, a minimum reflection loss (RL_min) of -68.5 dB for the as-synthesized composites with a thickness of 1.81 mm is gained at 13.2 GHz; meanwhile, a broad effective bandwidth of 4.56 GHz ranged from 13.2 to 17.76 GHz is achieved at 1.6 mm. Further, the overall effective bandwidth (RL < -10 dB) is obtained up to 14.5 GHz from 3.5 to 18.0 GHz, covering more than 90% of the measured frequency range. The high microwave absorption performance is ascribed to the special structure design with the core of magnetic CoFe₂O₄ nanospheres and the shell of dielectric nest-like 1T/2H-MoS₂ as well as their appropriate impedance matching. From the perspective of basic research and practical microwave application, this study provides another feasible and effective pathway to design novel MoS₂-based magnetic/dielectric microwave absorbers.

Enhanced Microwave Absorption and Electromagnetic Properties of Si-Modified rGO@Fe3O4/PVDF-co-HFP Composites

Graphene has been regarded as one of the most promising two-dimensional nanomaterials. Even so, graphene was still faced with several key issues such as impedance mismatching and narrow bandwidth, which have hindered the practical applications of graphene-based nanocomposites in the field of microwave absorption materials. Herein, a series of Si-modified rGO@Fe3O4 composites were investigated and fabricated by a simple method. On one hand, the degree of defects in graphene carbon could be tuned by different silane coupling reagents, which were beneficial to enhancing the dielectric loss. On the other hand, the spherical Fe3O4 nanoparticles provided the magnetic loss resonance, which contributed to controlling the impedance matching. Subsequently, the electromagnetic absorption (EMA) properties of Si-modified rGO@Fe3O4 composites with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) were investigated in this work. As a result, the Si(2)-rGO@Fe3O4/PVDF-co-HFP composite exhibited the excellent EMA performance in the range of 2-18 GHz. The maximum reflection loss (RLmax) reached -32.1 dB at 3.68 GHz at the thickness of 7 mm and the effective absorption frequency bandwidth for reflection loss (RL) below -10 dB was 4.8 GHz at the thickness of 2 mm. Furthermore, the enhanced absorption mechanism revealed that the high-efficiency absorption performance of Si(2)-rGO@Fe3O4/PVDF-co-HFP composite was attributed to the interference absorption (quarter-wave matching model) and the synergistic effects between Si(2)-rGO@Fe3O4 and PVDF-co-HFP. This work provides a potential strategy for the fabrication of the high-performance EMA materials.