Preparation of Honeycomb SnO₂ Foams and Configuration-Dependent Microwave Absorption Features

Frontal polymerization-triggered simultaneous ring-opening metathesis polymerization and cross metathesis affords anisotropic macroporous dicyclopentadiene cellulose nanocrystal foam

Multifunctionality and effectiveness of macroporous solid foams in extreme environments have captivated the attention of both academia and industries. The most recent rapid, energy-efficient strategy to manufacture solid foams with directionality is the frontal polymerization (FP) of dicyclopentadiene (DCPD). However, there still remains the need for a time efficient one-pot approach to induce anisotropic macroporosity in DCPD foams. Here we show a rapid production of cellular solids by frontally polymerizing a mixture of DCPD monomer and allyl-functionalized cellulose nanocrystals (ACs). Our results demonstrate a clear correlation between increasing % allylation and AC wt%, and the formed pore architectures. Especially, we show enhanced front velocity (v_f) and reduced reaction initiation time (t_init) by introducing an optimal amount of 2 wt% AC. Conclusively, the small- and wide-angle X-ray scattering (SAXS, WAXS) analyses reveal that the incorporation of 2 wt% AC affects the crystal structure of FP-mediated DCPD/AC foams and enhances their oxidation resistance.

Fabrication of three-dimensional nitrogen-doped reduced graphene oxide/tin oxide composite aerogels as high-performance electromagnetic wave absorbers

Developing light-weight and high-efficiency electromagnetic wave (EMW) absorbers has been considered as an effective strategy to resolve the electromagnetic radiation pollution problem. Herein, nitrogen-doped reduced graphene oxide/tin oxide (NRGO/SnO₂) composite aerogels were facilely prepared through the hydrothermal process and subsequent lyophilization treatment. Morphological characterization results manifested that the attained NRGO/SnO₂ composite aerogels possessed unique three-dimensional (3D) porous network structure constituted by the tiny SnO₂ nanoparticles decorated wrinkled surfaces of flake-like NRGO. Moreover, excellent EMW absorption performance could be achieved through facilely regulating the additive volumes of ethylenediamine and filler contents. Impressively, the composite aerogel with a doped nitrogen concentration of 6.5 wt% displayed the optimal minimum reflection loss of -62.3 dB at a matching thickness of 3.5 mm and the broadest effective absorption bandwidth of 5.1 GHz under an ultrathin thickness of merely 1.6 mm. Furthermore, the as-synthesized composite aerogels showed a light-weight characteristic with the low bulk density of 19.9-25.7 mg·cm^-3. Additionally, the potential EMW absorption mechanisms of obtained composite aerogels were revealed, which were mainly ascribed to the unique 3D porous network structure, synergistic effects between conduction loss and polarization loss, as well as the balanced attenuation loss and impedance matching. This work could be valuable for the structural design and fabrication of 3D graphene-based dielectric composites as light-weight and high-efficiency EMW absorbers.

A novel microwave stimulus remote-controlled anticancer drug release system based on Janus TiO2-x&mSiO2 nanocarriers

In this work, we used a simple method to construct Janus-shaped TiO_2-x&mSiO₂ nanoparticles composed of gray-black titanium dioxide (TiO_2-x) and mesoporous silica (mSiO₂) serving as carriers to improve the microwave-controlled release performance. In the composite materials, on one hand, the rod-shaped mSiO₂ could realize high-efficiency drug loading, on the other hand, spherical TiO_2-x featuring oxygen vacancy acted as the main microwave absorber. The overall spatial separation between titanium dioxide and silicon dioxide was crucial to enhance microwave conversion efficiency. The Janus-liked nanomaterial was made up of TiO_2-x nanosphere with a diameter of approximately 180 nm on one end and rod-shaped mesoporous silica with about 220 nm in length and 100 nm in diameter on the other end, and the specific surface area of the entire material was 203.25 m²/g. Meanwhile, the cumulative doxorubicin hydrochloride (DOX) loading rate of the carrier reached up to 38 wt% after 24 h. The loading process of the DOX was exothermic, and the noncovalent interaction between the DOX and Janus TiO_2-x&mSiO₂ carrier was mainly van der Waals force. Furthermore, the rates of drug release at 24 h were up to 61 wt%, 69 wt% and 89 wt% at pH 7.0, 5.0 and 3.0, respectively. After microwave stimulation at pH 7.0, the rate of drug release increased observably from 61% to 88% compared to that of non-microwave irradiation. The order of the microwave thermal conversion capability of the samples was Janus TiO_2-x&mSiO₂ > Janus TiO₂&mSiO₂ > core-shell TiO_2-x@mSiO₂. Besides, cytotoxicity tests indicated that Janus TiO_2-x&mSiO₂ nanoparticles had good biocompatibility. Therefore, the multifunctional carrier of the Janus-shaped configuration could not only release drugs under pH control, but also be further triggered by microwave stimulation. The Janus-shaped TiO_2-x&mSiO₂ nanoparticles will look forward to laying foundation to the application in drug delivery systems.

Recent progress of microwave absorption microspheres by magnetic-dielectric synergy

Designing and developing high-performance microwave absorption (MA) materials for electromagnetic protection and radar detection have received widespread attention. Recently, magnetic-dielectric MA materials have become a research hotspot due to their unique complementary functions and synergy loss mechanism. Herein, we review important research progress of excellent MA systems combining strong magnetic components and dielectric substrates. The functional materials involve magnetic materials, carbon components, semiconductors, polymer and so on. For a comprehensive analysis, current development and challenges are firstly introduced in the background. Modern requirements for microwave energy conversion are elaborated in the following part. To highlight the key points, more attention has been paid to the magnetic-dielectric synergy microsphere: (i) core/yolk-shell structure, (ii) multi-component assembly and (iii) MOF-derived synergy composites. Meanwhile, classical and typical high-performance MA composites with a multi-loss mechanism are also mentioned in this review paper. Finally, the design principles, electromagnetic synergy, future mechanism exploration and device application are presented, which provides guidance for understanding MA materials.

Highly Compressible Polymer Composite Foams with Thermal Heating-Boosted Electromagnetic Wave Absorption Abilities

Polymer composite foams are desirable materials for electromagnetic (EM) energy attenuation. However, a number of challenges limit improvement in the EM energy attenuation properties of foams. In this study, a simple microcellular injection molding method was used to fabricate highly compressible thermoplastic urethane (TPU)/carbon nanotube (CNTs) composite foams, which also had increased conductivity with an increase in CNT content. Compared to unfoamed composites, foamed composites exhibited higher conductivity and EM attenuation properties because of the presence of a microcellular structure. Moreover, the TPU/CNT foam with 4 wt % CNTs (F(4)) demonstrated strong EM dissipation and an optimal reflection loss (RL) value of -30.4 dB. Furthermore, stimulated by thermal heating and cyclic compression, EM attenuation was observed to increase because of the higher conductivity. Note that F(4) foam having a small thickness of 1.3 mm when treated at 333 K had the highest EM dissipation and the lowest RL value of -51.8 dB. Enhanced polarization and ohmic losses and multiscattering were responsible for the increased EM absorption. This behavior is attributed to the movement of CNTs within the TPU elastomer walls via thermal or compression stimulation. For designing stimulation-dependent multifunctional materials, composite foams with response to thermal heating were proved to be an alternative approach.

Preparation of CTCNFs/Co9S8 hybrid nanofibers with enhanced microwave absorption performance

A three-step synthesis strategy has been applied to the preparation of Co₉S₈-loaded tubular carbon nanofibers (CTCNFs/Co₉S₈ hybrid nanofibers) with excellent microwave absorbing ability. Firstly, tubular polymer nanofibers (TPNFs) are synthesized using the confined self-condensation method that we developed. Afterwards, TPNFs are converted into surface carboxylated tubular carbon nanofibers (CTCNFs) by carbonization and subsequent acidification processes. Finally, a hydrothermal method is used for the controllable growth of Co₉S₈ nanoparticles on CTCNFs, and a series of CTCNFs/Co₉S₈ hybrid nanofibers with different Co₉S₈ loading are obtained. The prepared CTCNFs/Co₉S₈ hybrid nanofibers possess abundant effective interface and defect dipoles, which will lead to stronger polarization. Using the strategy of enhancing dielectric loss, the microwave dissipation ability of CTCNFs/Co₉S₈ hybrid nanofibers has been significantly improved, showing an excellent low-frequency absorbing performance with a minimum reflection loss of -46.81 dB@5.3 GHz. In addition, the composition, structure and properties of nanofibers have been systematically characterized. The Co₉S₈ loading on CTCNFs and the filler content of CTCNFs/Co₉S₈ hybrid nanofibers in matrix are studied and optimized. The microwave attenuation mechanism is also explained.

Polymer Nanocomposites Containing Semiconductors as Advanced Materials for EMI Shielding

Miniaturization of electronic devices and systems enhances the complexity of inbuilt circuitry, thereby giving rise to electromagnetic interference (EMI). EMI is a serious cause of concern as it affects the performance of a device, transmission channel, or system. In a quest to find an effective solution to this problem, several materials, apart from the conventional metals, such as carbon derivatives, have been extensively explored recently. In addition to carbon derivatives, hybrid structures such as core-shell, conjugated systems, etc. have also been researched. However, semiconducting fillers have received less attention, especially in this application. Hence, this review article will primarily focus on the systematic understanding of the use of semiconductor-based polymer nanocomposites and how the band gap plays a crucial role in deciding the dielectric properties and subsequently the electromagnetic absorption behavior for shielding applications. Our primary aim is to highlight the mechanism of shielding involved in such nanocomposites in addition to discussing the synthesis and properties that lead to effective shielding. Such nanocomposites containing semiconductors can pave the way for alternate materials for EMI shielding applications that are lightweight, flexible, and easy to integrate.

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

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

Cu2ZnSnS4 nanocrystals for microwave thermal and microwave dynamic combination tumor therapy

Cu2ZnSnS4 nanocrystals (CZTS NCs) have been demonstrated to be effective in tumor therapy as a novel susceptible agent for microwave thermal and microwave dynamic therapy. CZTS NCs intensify the heating effect of microwaves with a significant temperature increase of about 15 °C compared to the control group and showed remarkable anti-tumor performance after 5 min of microwave irradiation. For the first time, we report the microwave absorption performance and singlet oxygen production of CZTS NCs used in microwave therapy, which reveals new opportunities for novel combined mechanisms of microwave thermal and microwave dynamic tumor therapies.

Fabrication of Three-Dimensional Flower-like Heterogeneous Fe3O4/Fe Particles with Tunable Chemical Composition and Microwave Absorption Performance

Heterogeneous Fe₃O₄ and Fe composites are highly desirable for microwave absorption application because of their complementary electromagnetic (EM) properties. With three-dimensional (3D) Fe₂O₃ as a sacrificing template, we realize the construction of Fe₃O₄/Fe composites with tunable chemical composition, and more importantly, these composites inherit the unique 3D microstructure from their precursor. The change in chemical composition produces significant impacts on the EM functions of these composites. On the one hand, dielectric loss can be improved greatly through positive interfacial polarization and reach the peak when the mass contents of Fe₃O₄ and Fe are 72.1 and 27.9 wt %, respectively. On the other hand, high Fe content slightly pulls down magnetic loss in the low-frequency range but favors strong magnetic loss in the high-frequency range because of the breakthrough of Snoek's limitation. The attenuation constant reveals that dielectric loss dominates overall consumption of incident EM waves. As a result, the optimized composite, F-350 (the reduction of Fe₂O₃ is conducted at 350 °C), shows the best microwave absorption performance, whose strongest reflection loss is -56.0 dB at 17.5 GHz and the effective bandwidth can cover the frequency range of 12.0-15.5 GHz with the thickness of 1.5 mm. Furthermore, an ultrawide effective bandwidth of 15.3 GHz can be achieved with the integrated thickness of 1.0-5.0 mm. Such a performance is superior to those of many reported Fe₃O₄/Fe composites, and a comparative analysis manifests that good microwave absorption of F-350 is also benefited from its unique 3D architecture.

A new flexible and ultralight carbon foam/Ti3C2TX MXene hybrid for high-performance electromagnetic wave absorption

A new ultralight carbon foam/Ti₃C₂T_X (CF/MXene) electromagnetic (EM) absorbing hybrid with three-dimensional network structure was fabricated by vacuum impregnation and freeze-drying process. These hybrids display excellent flexibility and steady compression-resilience properties and also the special three-dimensional structure with ultralow density of only 5–7 mg cm⁻³ shows higher EM absorption than most foam-based EM absorbers. Studies have shown that the minimum reflection loss of CF/MXene-N2 reaches −45 dB at 8.8 GHz with the Ti₃C₂T_X nanosheets content of 9.8%. In the meanwhile, the effective absorption bandwidth of CF/MXene-N2 can also reach up to 5 GHz (from 6.9 GHz to 11.9 GHz) with the thickness of 4.5 mm. Moreover, the fundamental EM absorption mechanism of CF/MXene hybrids involved to impedance matching, conductive loss and polarization loss is carefully analyzed. Thus, it is expected that the new ultralight carbon foam/Ti₃C₂T_X hybrids with three-dimensional network structure will have great application prospects in the fields of EM absorption.

Schematic illustrating the fabrication of carbon foam/Ti₃C₂T_X hybrids.

The effect of ZnCl2 activation on microwave absorbing performance in walnut shell-derived nano-porous carbon

Porous carbon has been expected to be a potential candidate as a lightweight and efficient microwave absorber.

Synthesis of nitrogen-doped graphene wrapped SnO2 hollow spheres as high-performance microwave absorbers

Nitrogen-doped graphene (NG)/SnO₂ hollow sphere hybrids were synthesized in this work. The chemical composition, crystal structure and morphology have been characterized by FT-IR spectra, XRD, Raman spectra, XPS, SEM and TEM in detail. Reflection loss (RL) values of NG/SnO₂ hollow sphere hybrids less than −10 dB and −20 dB are found in the wide frequency range of 4.5–18 GHz and 5–16.2 GHz within 1.3–3.5 mm, and a minimum RL of −50.3 dB is achieved at 8.6 GHz with the matching thickness of only 2.3 mm. The results indicate that the NG/SnO₂ hollow sphere hybrids with high-performance microwave absorption properties have a promising future in decreasing electromagnetic wave irradiation and interference.

Nitrogen-doped graphene/SnO₂ hollow sphere hybrids were synthesized and show high-performance microwave absorption properties.

Ultralight MXene-Coated, Interconnected SiCnws Three-Dimensional Lamellar Foams for Efficient Microwave Absorption in the X-Band

Two-dimensional (2D) few-layered Ti₃C₂T _X MXene (f-Ti₃C₂T _X) has been proved to be one of the most promising electromagnetic interference (EMI) materials, but its electromagnetic (EM) absorption properties and loss mechanism have not been studied so far. Herein, for the first time, ordered lamellar f-Ti₃C₂T _X/SiCnws hybrid foams with ultralow density are synthesized by a combination of self-assembly and bidirectional freezing processes. The freestanding foams exhibit excellent EM absorption properties superior to most of the current foam-based counterparts. The effective absorption bandwidth is always able to cover the whole X-band, when the sample thicknesses of f-Ti₃C₂T _X/SiCnws hybrid foams distribute in any value between 3.5 and 3.8 mm, and the minimum reflection coefficient reaches -55.7 dB at an ultralow density of only about 0.029 g·cm^-3. The fundamental mechanism associated with optimized impedance matching, enhanced polarization loss, and conductive loss is discussed in detail. Our results evidence that 2D flexible f-Ti₃C₂T _X MXene has great potential in EM absorption field like graphene.

The flaky porous Fe3O4 with tunable dimensions for enhanced microwave absorption performance in X and C bands

Special electric and magnetic characteristics make Fe₃O₄ widely applied in the electromagnetic (EM) wave absorption region. However, for pure Fe₃O₄, it is still a challenge to simultaneously obtain high absorption intensity and broadband absorption at a low thickness, owing to its low dielectric property. As we realized, flake configuration and the porous structure have obviously promote the EM wave absorption property. Because the former can lead to multi-reflection between flakes and the latter is conductive to interface polarization, flaky Fe₃O₄ with a porous and coarse surface was designed to overcome the deficiency of traditional Fe₃O₄ particles. The experimental results demonstrate that the flaky configuration is conductive to enhancing the dielectric coefficient and optimizing impedance matching. Moreover, the complex permittivity rises with the aspect ratio of the sheet. Under a suitable dimension, the flaky Fe₃O₄ could acquire targeted EM wave absorption capacity in the X band (8-12 GHz). In detail, the maximum reflection loss (RL) could reach a strong intensity of -49 dB at 2.05 mm. The effective absorption bandwidth (EAB) with RL below -10 dB is 4.32 (7.52-11.84) GHz, which is almost equivalent to the whole X band (8-12 GHz). Even more exciting, when regulating the thickness between 2.05 and 3.05 mm, the EAB could cover the entire C and X bands (4-12 GHz). This study provides a good reference for the future development of other ferromagnetic materials toward specific microwave bands.

Facile synthesis and excellent microwave absorption properties of FeCo-C core-shell nanoparticles

FeCo-C core-shell nanoparticles (NPs) with diameters of 10-50 nm have been fabricated on a large scale by one-step metal-organic chemical vapor deposition using the mixture of cobalt acetylacetonate and iron acetylacetonate as the precursor. The Fe/Co molar ratio of the alloy nanocores and graphitization degree of C shells, and thus the magnetic and electric properties of the core-shell NPs, can be tuned by the deposition temperature ranging from 700 °C to 900 °C. Comparative tests reveal that a relatively high Fe/Co molar ratio and low graphitization degree benefit the microwave absorption (MA) performance of the core-shell NPs. The composite with 20 wt% core-shell NP obtained at 800 °C and 80 wt% paraffin exhibits an optimal reflection loss [Formula: see text] of -60.4 dB at 7.5 GHz with a thickness of 3.3 mm, and an effective absorption bandwidth (frequency range for RL ≤10 dB) of 9.2 GHz (8.8-18.0 GHz) under an absorber thickness of 2.5 mm. Our study provides a facile route for the fabrication of alloy-C core-shell nanostructures with high MA performance.

A novel sponge-like 2D Ni/derivative heterostructure to strengthen microwave absorption performance

One of the major hurdles of Ni-based microwave absorbing materials is the preparation of two-dimensional (2D) Ni flakes that can improve magnetic anisotropy to tune complex permeability.

Fe3O4 nanoparticles decorated on a CuS platelet-based sphere: a popcorn chicken-like heterostructure as an ideal material against electromagnetic pollution

A popcorn chicken-like CuS/Fe₃O₄ heterostructure was fabricated via the solvothermal deposition method to investigate its potential as a high electromagnetic wave absorber.

Facile synthesis of porous Fe3O4@C core/shell nanorod/graphene for improving microwave absorption properties

Porous Fe₃O₄@C core/shell nanorods decorated with reduced graphene oxide were synthesized by a facile one-pot method, and exhibit high microwave absorption performance: maximum reflection loss reaches −48.6 dB.

Cross-Linking-Derived Synthesis of Porous CoxNiy/C Nanocomposites for Excellent Electromagnetic Behaviors

The magnet/dielectric composites with tunable structure and composition have drawn much attention because of their particular merits in magnetoelectric properties compared with the sole dielectric or magnetic composites. In addition, porous materials at the nanoscale can satisfy the growing requirements in many industries. Therefore, constructing porous metal alloy/carbon nanocomposites is to be an admirable option. Unfortunately, traditional synthesis methods involve multistep routes and complicated insert-and-remove templates approaches. Here we report a facile process to synthesize Co_xNi_y/C composites via a spontaneous cross-linking reaction and subsequent calcination process, during which multiple processes, including reducing polyvalent metal ions, forming alloy, and encapsulating alloy nanoparticles into porous carbon matrix, are achieved almost simultaneously. By adjusting the feed ratio of Co²⁺ to Ni²⁺ ions, controllable composition of Co_xNi_y/C composites can be gained. It should be noted that the Co_xNi_y/C composites are demonstrated to be excellent microwave absorbers from every aspect of assessment criteria including reflection loss, effective bandwidth, thickness, and weight of absorber. Our study opens up a promising technique for the synthesis of alloy/carbon composites with porous nanostructures with target functionalities.

Ultra-broad polypyrrole (PPy) nano-ribbons seeded by racemic surfactants aggregates and their high-performance electromagnetic radiation elimination

Ribbon-like nano-structures possess high aspect ratios, and thus have great potential in the development of high-performance microwave absorption (MA) materials that can effectively eliminate adverse electromagnetic radiation. However, these nano-structures have been scarcely constructed in the field of MA, because of the lack of efficient synthetic routes. Herein, we developed an efficient method to successfully construct polypyrrole (PPy) nano-ribbons using the self-assembly aggregates of a racemic surfactant as the seeds. The frequency range with a reflection loss value of lower than -10 dB reached 7.68 GHz in the frequency range of 10.32-18.00 GHz, and surpassed all the currently reported PPy nano-structures, as well as most other MA nano-materials. Through changing the amount of surfactant, both the nano-structures and MA performance can be effectively regulated. Furthermore, the reason behind the high-performance MA of PPy nano-ribbons has been deeply explored. It opens up the opportunity for the application of conducting polymer nano-ribbons as a lightweight and tunable high-performance MA material, especially in applications of special aircraft and flexible electronics.

Flexible, Ultrathin, and High-Efficiency Electromagnetic Shielding Properties of Poly(Vinylidene Fluoride)/Carbon Composite Films

In this study, we fabricated conductive poly(vinylidene fluoride) (PVDF)/carbon composites simply by dispersing multiwalled carbon nanotubes (MWCNTs) and graphene nanoplatelets into a PVDF solution. The electrical conductivity and the electromagnetic interference (EMI) shielding of the PVDF/carbon composites were increased by increasing the conductive carbon filler amounts. Moreover, we also found that the EMI shielding properties of the PVDF/CNT/graphene composites were higher than those of PVDF/CNT and PVDF/graphene composites. The mean EMI shielding values of PVDF/5 wt %-CNT, PVDF/10 wt %-graphene, and PVDF/CNT/graphene composite films with a thickness of 0.1 mm were 22.41, 18.70, and 27.58 dB, respectively. An analysis of the shielding mechanism showed that the main contribution to the EMI shielding came from the absorption mechanism, and that the EMI shielding could be tuned by controlling the films' thickness. The total shielding of the PVDF/CNT/graphene films increased from 21.90 to 36.46 dB as the thickness was increased from 0.06 mm to 0.25 mm. In particular, the PVDF/carbon composite films, with a thickness of 0.1 mm, achieved the highest specific shielding values of 1 310 dB cm²/g for the PVDF/5 wt %-CNT composite and 1 557 dB cm²/g for the PVDF/CNT/graphene composite, respectively. This was due to the ultrathin thickness. Our study provides the groundwork for an effective way to design flexible, ultrathin conductive polymer composite film for application in miniaturized electronic devices.

Carbon Hollow Microspheres with a Designable Mesoporous Shell for High-Performance Electromagnetic Wave Absorption

In this work, mesoporous carbon hollow microspheres (PCHMs) with designable mesoporous shell and interior void are constructed by a facile in situ stöber templating approach and a pyrolysis-etching process. The PCHMs are characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectra, Raman spectroscopy, and nitrogen adsorption and desorption system. A uniform mesoporous shell (pore size 4.7 nm) with a thickness of 55 nm and a cavity size of 345 nm is realized. The composite of paraffin mixed with 20 wt % PCHMs exhibits a minimum reflection coefficient (RC_min) of -84 dB at 8.2 GHz with a sample thickness of 3.9 mm and an effective absorption bandwidth (EAB) of 4.8 GHz below -10 dB (>90% electromagnetic wave is attenuated). Moreover, the composite of phenolic resin mixed with 20 wt % PCHMs exhibits an ultrawide EAB of 8 GHz below -10 dB with a thinner thickness of 2.15 mm. Such excellent electromagnetic wave absorption properties are ascribed to the large carbon-air interface in the mesoporous shell and interior void, which is favorable for the matching of characteristic impedance as compared with carbon hollow microspheres and carbon solid microspheres. Considering the excellent performance of PCHMs, we believe the as-fabricated PCHMs can be promising candidates as highly effective microwave absorbers, and the design philosophy can be extended to other spherical absorbers.

Hierarchical porous Ni@boehmite/nickel aluminum oxide flakes with enhanced microwave absorption ability

Hierarchical core–shell composites with porous cores and flaky shells show superior absorption which possess many features, such as lightweight, wide band, small thickness and high efficiency absorption.

1D Cu@Ni nanorods anchored on 2D reduced graphene oxide with interfacial engineering to enhance microwave absorption properties

In this work, one-dimensional core–shell Cu@Ni nanorods which were anchored on two dimensional reduced graphene oxide (rGO) heterostructures were successfully prepared by a simple co-reduction method.

Facile synthesis of NiS2@MoS2 core–shell nanospheres for effective enhancement in microwave absorption

Core–shell structural NiS₂@MoS₂ nanospheres have been successfully fabricated and they possess enhanced microwave absorption properties as compared to single NiS₂ nanospheres or MoS₂ nanoplates due to this core–shell structure.

Lightweight porous Co3O4 and Co/CoO nanofibers with tunable impedance match and configuration-dependent microwave absorption properties

In this study, we fabricated one-dimensional porous Co₃O₄ and Co/CoO nanofibers by calcination of cobalt(ii) oxalate dehydrate precursors in an environment filled with air and N₂, respectively.

Tailoring the input impedance of FeCo/C composites with efficient broadband absorption

Cross-linking coin-like porous FeCo/C nanocomposites were successfully prepared by a simple carbon thermal reduction method. The excellent absorbent with a frequency broadband of 6 GHz was obtained though tailoring the input impedance of FeCo/C.

Lightweight NiFe2O4 with controllable 3D network structure and enhanced microwave absorbing properties

3D network structure NiFe₂O₄ was successfully synthesized by a templated salt precipitation method using PMMA colloid crystal as templates. The morphology, phase composition and microwave absorbing properties of as-prepared samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), vector network analyzer (VNA), and so on. The results revealed that the 3D network structure was configurated with smooth spherical walls composed of NiFe₂O₄ nanocrystals and their pore diameters being in the range of 80–250 nm. The microwave absorption properties of the 3D network structure NiFe₂O₄ were crucially determined by the special structure. The synergy of intrinsic magnetic loss of magnetic NiFe₂O₄ and the interfacial polarization enhanced by 3D network structure and the interaction of multiple mechanisms endowed the sample with the feature of strong absorption, broad bandwidth and lightweight. There is more than one valley in the reflection loss curves and the maximum reflection loss is 27.5 dB with a bandwidth of 4 GHz. Moreover, the 3D network structure NiFe₂O₄ show a greater reflection loss with the same thickness comparing to the ordinary NiFe₂O₄ nanoparticles, which could achieve the feature of lightweight of the microwave absorbing materials.

Excellent microwave absorption properties of Fe ion-doped SnO2/multi-walled carbon nanotube composites

Fe ions doped SnO₂/MWCNTs composites with 48.8% Fe ions doping content showed the maximum reflection loss was −44.54 dB at 15.44 GHz, and the maximum absorption bandwidth of reflection loss below −10 dB was 4.5 GHz in the Ku band.

A facile post-process method to enhance crystallinity and electrochemical properties of SnO2/rGO composites with three-dimensional hierarchically porous structure

In this work, three SnO₂/reduced graphene oxide (SnO₂/rGO) composites with a three-dimensional hierarchically porous structure were synthesized via freeze drying and different annealing temperatures in an air atmosphere.

One-pot synthesis of FeCo alloy and iron borate composite nanorods with excellent electromagnetic wave absorption properties

FeCo alloy and iron borate composites with homogeneous morphologies of the nanorods were successfully synthesized by heat treatments on iron oxide and Co–B composites.

Facile synthesis of net-like Fe3O4/MWCNTs decorated by SnO2 nanoparticles as a highly efficient microwave absorber

SnO₂ nanocrystals were introduced into Fe₃O₄/MWCNTs to tune the complex permittivity. The synergistic interaction of different components and special net-like structure contribute to a highly efficient MA.

Solvothermal synthesis of flower-like CoS hollow microspheres with excellent microwave absorption properties

In this study, flower-like CoS hollow spheres (CHSs), synthesized via a facile solvothermal method in the presence of CTAB, were initially investigated as microwave absorbers.

Synthesis of Cu and Ni chalcogenides and evaluation of their properties for electromagnetic wave absorption

Cu and Ni chalcogenides were synthesized by hydrothermal methods and characterized by XRD and SEM.