High-efficiency Microwave Absorption Research Articles

Fe/Fe3O4/biomass carbon derived from agaric to achieve high-performance microwave absorption

Recently, biomass carbon materials as electromagnetic wave-absorbing materials have received widespread attention due to their easy availability, low cost, and environmental friendliness. However, for the vast majority of microwave absorbing materials that possess only dielectric losses, it is difficult for them to achieve satisfactory microwave absorbing performance. This paper proposes a new strategy to prepare a magnetic biomass composite material with tunable high-performance microwave absorption using agaric as the biomass carbon precursor and ferric nitrate as the magnetic precursor. When the carbonization temperature is 800 °C, the Fe/Fe3O4/biomass carbon (Fe/Fe3O4/BC) composite exhibits excellent microwave absorption performance in the X-band. At a thickness of 2.06 mm and a frequency of 9.63 GHz, its minimum reflection loss reaches −30.41 dB, and the effective absorption bandwidth is 2.45 GHz. In the carbonization process, ferric nitrate is transformed into magnetic Fe3O4 and Fe nanoparticles. The magnetic losses generated by Fe/Fe3O4 and the dielectric losses of biomass carbon, interfacial polarization, dipole polarization and multiple reflection synergies improve the impedance matching characteristics of the composite and improve the microwave absorption performance. Therefore, the prepared Fe/Fe3O4/BC composite material has exhibits great potential as a high-efficiency microwave absorber.

Design and Synthesis of 3D-Graphene@C/Co@N-C Composites with Broadband Microwave Absorption Performance

Improving the microwave absorption performance of Co-MOF-derived Co@N-C composite by constructing the morphology and spatial structure is a known challenge. In this work, under the action of the binder polyvinylpyrrolidone, 3D-graphene particles can be well decorated on the surface of the Co@N-C composite after high-temperature pyrolysis. In addition, due to the structural characteristics of MOFs, Co particles can be well covered by a carbon layer, which effectively solves the problem that magnetic metal particles are prone to corrosion and oxidation. The microwave absorption performances of the composite can be well adjusted by changing the average dotted density of the 3D-graphene on the Co@N-C composite. It is worth noting that the maximum reflection loss can reach −58.72 dB at the thickness of 1.64 mm, and the maximum effective absorption bandwidth can achieve 5.74 GHz at the 1.79 mm thickness, which almost covers the whole Ku band. Importantly, these results demonstrate that 3D-graphene@C/Co@N-C composites have great potential as high-efficiency microwave absorption materials.

Flower-like MoS2 self-assembled on multiferroic Z-type Sr3Co2Fe24O41 hexaferrite for ultra-wideband microwave absorption

In this work, a rare system of Sr3Co2Fe24O41/MoS2 composites has been successfully prepared via the sol-gel method and following a facile hydrothermal process, from which the flower-like MoS2 was evenly anchored on the surface of Z-type Sr3Co2Fe24O41 microplatelets. It is confirmed that the effective combination of transition metal sulfide MoS2 and multiferroic Sr3Co2Fe24O41 hexaferrite greatly optimizes the dielectric behaviors of the composites. Meanwhile, the unique hierarchical structure further enhances the microwave absorption properties. When the mass ratio of Sr3Co2Fe24O41 to MoS2 is 1:3 in composites, the smallest reflection loss value is − 39.2 dB at the thickness of 2.0 mm, and note that the adequate absorption bandwidth can reach up to 7.6 GHz (10–17.6 GHz) with 2.2 mm. When the mass ratio is adjusted as 1:5, the optimal reflection loss of the composite reaches − 44.5 dB at 9.28 GHz with a thickness of 3.0 mm. The high-efficiency microwave absorption performance of the composites is attributed to the synergistic effect of dielectric materials and multiferroic materials. The calculation results on delta and attenuation constant display that impedance matching degree and attenuation ability of composites are balanced, which not only reduces the reflection of electromagnetic waves on the absorber surface, but also enhances its consumption. At the same time, the flower-shaped MoS2 is stacked on the surface of Sr3Co2Fe24O41 microplatelets which is conductive to the multiple reflections and scattering of electromagnetic waves between layers, greatly promoting the attenuation of electromagnetic waves. This work opens up an updated pathway for the design of magnetic/dielectric microwave absorbers with vigorous absorption and ultra-wideband.

In-situ construction of nitrogen-doped reduced graphene oxide@carbon nanofibers towards the synergetic enhancement of their microwave absorption properties via integrating point defects and structure engineering

The aim of this work is to develop materials that can absorb microwave to meet the requirements of stealth technology and solve the problem of electromagnetic pollution. However, the challenge is having materials with high-efficient absorption properties at an ultralow filling rate and visualizing the microwave response. The strategy used in this work was to integrate point defect and microstructure in preparing materials, nitrogen-doped reduced graphene oxide@ carbon nanofibers with high-efficient microwave absorption and double-layered structure. Ethylenediamine (nitrogen source), was doped into the materials, resulting in the generation of the defects. The microwave absorption performance of the materials was affected by the degree of defects due to the dipole polarization loss and conductive loss. The optimal samples gained the maximum reflection loss of −54.7 dB and effective absorption bandwidth of 4.74 GHz at a filling rate of only 8 wt%. More significantly, the microwave absorbing mechanism was analyzed visually in the response field. Furthermore, the actual stealth effects were evaluated by the radar cross section reduction, and the value was 29.2 dBm2. The experimental results illustrated that nitrogen-doped reduced graphene oxide@ carbon nanofibers may be alternative materials with high microwave absorption performance at a low filling rate.

Preparation of carbon fibers@NiS/Ni3S4@MoS2 with core-sheath structure for high efficiency and wide-bandwidth microwave absorption

Numerous studies have focused on the preparation of carbon fibers (CFs)-based high-efficiency microwave absorbers with reasonable structural design and surface morphology control, which simultaneously meet the required impedance matching and loss ability. Here, CFs@NiS/Ni3S4@MoS2 (CNNM) with core-sheath structure was prepared through several simple hydrothermal reactions. The morphology of the as-prepared CNNM nanocomposite is controlled by the amount of added sodium molybdate dihydrate, which causes the difference in minimum reflection loss (RL) and effective attenuation bandwidth among the samples. For the microwave absorbing performance, the minimum RL is −18 dB and the effective attenuation bandwidth is 8.7 GHz, which appear at the thickness of 2.8 mm and cover most of the X- and Ku-bands. The excellent absorbing performance is attributed to optimized impedance matching and enhanced polarization loss. These results originate from the transition metal sulfides, which not only effectively prevent the skin effect by decreasing the conductivity of CFs but also increase interfaces and flaws, leading to interface polarization and dipole polarization losses.

Achieving broadband microwave absorption and excellent mechanical properties via constructing 3D reduced graphene oxide networks in glass fiber/epoxy resin composites

The rapid development of electronic information technology makes it more urgent that explore high-efficiency microwave absorption materials to cope with the challenges of electromagnetic pollution for guarding information security and human health. Herein, we prepared functional composites with both broadband microwave absorption and excellent mechanical properties via constructing three-dimensional (3D) reduced graphene oxide (RGO) networks. In these composites, glass fibers (GFs) were uniformly coated by RGO through a straightforwardly feasible repeated dip-coating process and subsequent reduction, which were named (RGO)n@GF (n was dip-coating times). The GFs supported RGO to form 3D networks, which increased the transmission paths and multiple scattering of electromagnetic waves. Meanwhile, the networks improved the electrical conductivity and conduction loss. The results show that the (RGO)10@GF reinforced epoxy resin (EP) composites ((RGO)10@GF/EP) have particularly significant improvement in microwave absorption properties, achieving a broad effective absorption bandwidth of 7.54 GHz and a low reflection loss of −46.02 dB. Compared with GF/EP, the bending strength and modulus of (RGO)10@GF/EP increased by 39% and 45%, respectively. The present work provides an effective solution for developing advanced composites with both broadband absorption and excellent mechanical properties.

Structural engineering and compositional manipulation for high-efficiency electromagnetic microwave absorption

Structural engineering and component modulation are effective strategies for designing superior electromagnetic wave (EMW) absorbing materials. The challenge of understanding the structure-component-property relationship and developing efficient microwave absorbers, however, remains a huge challenge. In this work, we demonstrate a microemulsion phase transition approach to the design of different structures of dielectric microwave absorbing materials. Three different structures of MoO2/C (MC) microspheres, solid, yolk-shell, and hollow can be prepared by regulating the ratio of the two phases of water and oil. The MoO2/MoS2/C (MSC) trilayer dielectric microspheres with Schottky barriers were prepared by a subsequent vulcanization process in which component modulation allowed the construction of multi-interfaces and vacancy engineering. The analysis reveals that the sensitivity of the different structures to component modulation varies considerably, mainly in the number of vacancies generated by the sulfidation process. This difference is determined by both the free space of the microspheres and the number of effective media. Such a phenomenon provides insight into the interplay between structure and components in attenuating EMW. Of these, with the 50% sulfated MoO2/MoS2/C yolk-shell microspheres (YSMSC) exhibiting a reflection loss (RL) of −80.73 dB at a thin thickness of 1.7 mm; the fully sulfated MoS2/C hollow microspheres (HMSC) achieve an effective absorption bandwidth (EAB) of 7.04 GHz at 2.2 mm. Our study contributes to an in-depth understanding of the structure-component-property relationship of EMW absorbers and provides a reference for tuning the product structure using microemulsion phase conversion methods.

Super broadband absorbing hierarchical CoFe alloy/porous carbon@carbon nanotubes nanocomposites derived from metal-organic frameworks

The exploitation of electromagnetic wave absorption (EMA) materials has attracted ever-increasing attention, not only because electromagnetic wave (EMW) originated from overuse of electronic products has threatened human’ health seriously, but also because EMA materials can effectively protect radar stealth from being detected. However, it is still a challenge to obtain broadband and efficient EMA materials to satisfy practical applications. In this work, we developed a series of hierarchical CoFe alloy/porous [email protected] nanotubes (CoFe/[email protected]) nanocomposites through revising the proportion of Fe2+ in the metal-organic frameworks (MOFs) (CoFe-ZIF) precursor and one-step simple pyrolysis process. The cross deposition between CoFe alloy, carbon nanotubes (CNTs), and porous carbon (PC) formed a double conductive network, favoring for achieving excellent EMA property. Surprisingly, when the filler mass ratio is only 10 wt%, the optimized CoFe/[email protected] nanocomposites display the best EMA capability, whose minimum reflection loss (RLmin) value is –68.94 dB at 13.69 GHz and the effective absorption band (EAB, < –10 dB) reaches up 9.14 GHz with a matching thickness of 2.63 mm. In addition, the largest EAB can achieve up to 11 GHz (3.35–14.35 GHz) during all matching thicknesses. The splendid EMA performance benefits the favorable dielectric loss provided by the double conductive network, the good magnetic loss benefited from the evenly distributed CoFe alloy, the excellent impedance matching, rich transmission paths, and multiple polarization. Therefore, such EMA materials with super broadband absorbing provide desirable candidates for lightweight and high-efficient microwave absorbers.

Grow defect-rich bamboo-like carbon nanotubes on carbon black for enhanced microwave absorption properties in X band

• By in-situ growing bamboo-like CNTs on CB, a developed conductive network was constructed and plentiful CB/CNT interfaces were introduced to improve the electromagnetic wave loss ability. • Defect-rich CNTs with open atomic edges can endow nanocarbons with a better balance between good impedance matching and strong loss capacity, causing an effective microwave absorption. • The minimum reflection loss and effective absorption bandwidth of CB-CNT with the CNTs growth time of 40 min reach to −53.6 dB and 4.1 GHz with the matching thickness of 2.7 mm, respectively. Due to the limited electromagnetic wave (EMW) loss capacity and agglomeration, carbon black (CB) gradually fails to meet the increasingly harsh demanding conditions. Herein, defect-rich bamboo-like carbon nanotubes (CNTs) were grown on CB by the process of chemical vapor deposition. CNTs prepared in situ on CB can assist it to build a developed multilevel conductive network and introduce plentiful CB/CNTs nano-interfaces. What's more, the defects that accompany the growth of CNTs endow CNTs with a moderate conductivity and good impedance matching, thereby causing an effective microwave absorption (MA). Meanwhile, the high-density defects on CNTs can induce dipole polarization to further strengthen the EMW loss ability. The influence of CNTs with different growth time on MA performance has been explored. Profiting from the structural merits, the synthesized CB-CNT with CNTs growth time of 40 min exhibits the optimal absorbing property, which has the minimum reflection loss of -53.6 dB and maximum effective absorption bandwidth of 4.1 GHz with the thickness of 2.7 mm, covering almost the entire X band. The introduction of defect-rich CNTs significantly enhances the EMW loss ability of CB, which provides a rational strategy for the design of high-efficient microwave absorption materials.

Metal-organic framework-derived Co/CoO nanoparticles with tunable particle size for strong low-frequency microwave absorption in the S and C bands

Nowadays, constructing strong absorption materials addressing the low-frequency electromagnetic radiation (S and C bands) from electronic devices remains a significant challenge. In this work, size-tunable Co/CoO nanoparticles (NPs) are fabricated by decomposing zeolitic imidazolate framework (ZIF-67) precursors and subsequent hydrogen reduction. All samples show obvious low-frequency attenuation in the S and C bands. At a thin thickness of 2.3 mm, the minimum reflection loss (RL) value for the Co/CoO NPs of 30 nm reaches up to −90.3 dB at 4.4 GHz, and the corresponding effective absorption bandwidth (EAB) of RL ≤ −10 dB ranges from 3.8 to 5.4 GHz. Notably, 90 % of the electromagnetic waves can be absorbed in the frequency range of 2.3–13.2 GHz, covering almost the entire S, C, and X bands at a thickness of 1.0–4.0 mm. The strong low-frequency absorption performance is attributed to the nano-porous structure, high conduction loss, tunable dielectric/magnetic loss, as well as optimized impedance matching. These Co/CoO NPs are promising candidates for high-efficient microwave absorbers in the low-frequency application.

Heterointerface engineering in quaternary magnetic structures for high-efficiency and thermal stable microwave absorption

High-efficiency and thermal stability are two important factors of ideal microwave absorption materials (MAMs), which are becoming desired because of the more complex modern service environment. Herein, a novel quaternary magnetic core-shell-shell structure FeCo-Co@Fe3O4 @SiO2 (FCSF) has been fabricated by a facile and generic route. In this structure, the incipient oxidation temperature of magnetic core can be greatly increased from 523 K to 773 K by the Fe3O4/SiO2 double shells, and the multiple magnetic heterointerfaces can generate electron transfer and spin-orbit interaction based on DFT calculations. The minimum reflection loss (RLmin) and efficient absorption band (RL<−10 dB, feff) of FCSF composites can reach up to −42.8 dB and 7.3 GHz with the thickness of 2 mm, due to the emerged electromagnetic loss mechanisms of interface polarization and exchange resonance. Moreover, owing to the optimized impedance matching and enhanced electromagnetic loss at elevated temperature, the RLmin values of FCSF at 673 K and 773 K increase by 15.4% and 41.2% compared with that at 298 K, respectively. The results demonstrate that the FCSF composite can act as a promising candidate for high-efficiency MAMs in thermal environment, and the synthetic strategy of heterostructures in this work can also be applied to design other MAM systems.

Mixed-dimensional conductive network heterostructures: An effective interfacial strategy to aggrandize dielectric loss for designing microwave absorbers

To effectively boost the dielectric loss, herein, mixed-dimensional Ni foam (NF)/ZnCo2O4 @NiO conductive network heterostructures consisting of three-dimensional (3D) NF, one-dimensional (1D) ZnCo2O4 nanowires and two-dimensional (2D) NiO nanosheets were designed and produced by a simple two-step method. The growth of 1D ZnCo2O4 nanowires on the surface of 3D NF was done by a hydrothermal process, followed by the chemical bath deposition (CBD) of 2D NiO nanosheets. The obtained results indicated that the NiO content in the as-prepared NF/ZnCo2O4 @NiO network heterostructures could be promoted by increasing the CBD time, which improved their specific surface areas. Owing to utilizing the multiple interfaces for enhancing the interfacial polarization, the as-prepared NF/ZnCo2O4 @NiO network heterostructures presented the remarkably enhanced electromagnetic wave absorption performances (EMWAPs) compared to NF/ZnCo2O4 nanowire arrays. Moreover, the EMWAPs of mixed-dimensional NF/ZnCo2O4 @NiO network heterostructures could be further optimized by increasing the NiO content, which was demonstrated to promote the interfacial polarization. Generally, the findings demonstrated that taking full advantage of interface engineering in constructing the mixed-dimensional conductive network heterostructures is a very effective strategy to aggrandize dielectric loss, which provided an efficient and promising strategy to develop the novel and high-efficient microwave absorbers.

Cellular-like sericin-derived carbon decorated reduced graphene oxide for tunable microwave absorption

Sodium hydroxide (NaOH) activation on biomass-derived carbon materials has been a developed strategy to construct the porous and lightweight microwave absorber. However, the resulting random porous structures still remain a formidable challenge to optimize the impedance matching and microwave absorption performance. Here, a sericin-guided NaOH activation and subsequent carbonization process were proposed to synthesize uniform cellular-like sericin-derived carbon decorated reduced graphene oxide (SC/rGO) nanohybrids. The NaOH was used as a bi-functional activator to regulate the self-assembly of sericin protein between graphene oxide lamellas, while the sericin-guided NaOH further in situ activates the nanohybrids to produce uniform cellular nanostructures by carbonization. The abundant natural doped nitrogen and oxygen atoms derived from the industry wastes sericin are in-situ maintained after carbonization, which act as polarization centers to promote the attenuation of microwave energy. Benefiting from these merits, the synthesized cellular-like SC/rGO nanohybrids exhibit excellent impedance matching performance, promoted multiple electromagnetic transmission, excellent relaxation polarization phenomenon and microwave absorption properties. The optimized microwave absorption of SC/rGO40-500 reached −53.68 dB at 15.30 GHz, and the effective absorption bandwidth achieved 4.4 GHz (13.35–17.75 GHz) at the thickness of 1.51 mm with a low surface density of 0.035 g/cm2. Our work demonstrates a novel porous structure design strategy on biomass-derived carbon materials as high-efficiency microwave absorbers.

Facile construction of core–shell Carbon@CoNiO2 derived from yeast for broadband and high-efficiency microwave absorption

Manufacturing dielectric/magnetic composites with hierarchical structure is regard as a promising strategy for the progress of high-performance microwave absorption (MA) materials. In this paper, the nano-grass structured CoNiO2 magnetic shell was uniformly anchored on the yeast-derived carbon microspheres by in-situ one-pot synthesis method. Profiting from the unique nano-grass and core–shell structure, capable dielectric/magnetic loss, along with improved impedance matching, the prepared absorber realizes desirable MA performance. The minimum reflection loss (RLmin) reaches up to −44.06 dB at 6.56 GHz. Moreover, the effective absorption bandwidth (EAB, reflection loss (RL) < -10 dB) accomplishes 7.04 GHz under a low filler loading of 20 wt%. This work endeavors a valuable insight for designing innovative core–shell structured materials with high-efficiency MA and broad bandwidth.

Light-weight, low-loading and large-sheet reduced graphene oxide for high-efficiency microwave absorber

Carbon materials are extensively used in lightweight and efficient microwave absorption (MA) due to their low density. However, the single carbon material has poor impedance matching and absorbing performance. Graphene oxide (GO) and reduced graphene oxide (rGO) are widely used as carbon materials with customizable dielectric properties, but there are still problems of poor MA and high loading. In this work, a series of large-sheet GO with different reduction degrees were prepared by a simple and controlled thermal reduction method, and their MA properties were investigated. The analysis of the composition, structure and MA performance of graphene showed that the MA performance of rGO was closely related to the reduction degree and the size of the sheet. Large sheet graphene was more likely to overlap each other to form a conductive network, reducing the filler loading. Meanwhile, after mixing rGO with different reduction degrees, the optimal reflection loss was −59.12 dB, which was 2.13 times and 1.59 times of the original single component. The effective absorption bandwidth was 3.54 GHz and the loading was only 1.5 wt%. This work provided a promising approach for constructing graphene-based composites with strong MA ability at low filler loadings.

Layered-structure N-doped expanded-graphite/boron nitride composites towards high performance of microwave absorption

High-efficiency microwave absorbers with broadband absorption are strongly desired for electromagnetic protection. Herein, we successfully synthesized a hybrid microwave absorbing material with two-dimensional layered structure, which consisted of expanded graphite (EG) and boron nitride (BN). The introduction of BN is to regulate the conductivity of EG and also to improve the thermal stability of the composite material. The ultrathin BN nano-sheets were uniformly wrapped on the EG sheets via chemical vapor deposition. Attributed to the dielectric loss and conductive loss, the as-prepared hybrid material exhibited high performance for microwave absorption. The effective absorbing bandwidth (reflection loss value < -10 dB) was achieved up to 9.37 GHz with the thickness of 2.4 mm in the frequency range of 5.75–6.98 GHz and 9.86–18 GHz. And the minimum reflection loss was -51.58 dB at the thickness of 3 mm. The excellent performance of microwave absorption was attributed to the dielectric loss, interfacial polarization loss and optimized impedance matching. Moreover, compared to pure EG, the thermal decomposition temperature of EG/BN composite materials had increased by about 100 °C which was up to 714 °C. Taking the advantages of high thermal stability of BN as well as the fine microwave absorbability of EG, the EG/BN composites would be applied in high-temperature microwave absorbing fields.

Development of high-efficient tri-layer microwave absorbers based on fabricated SrFe12O19 with polygonal, rod, and porous ball-like morphologies

Recently, widespread microwave applications have generated plenty of unwanted electromagnetic radiation, which has become a global environmental pollution problem. Therefore, finding an efficient microwave absorbing material (MAM) is a trendy topic, and strontium hexaferrite (SrFe12O19, SrM) is a promising candidate. However, its high ferromagnetic resonance frequency (fFMR) prevents SrM from becoming an excellent MAM for wide-frequency range applications. Herein, as-prepared SrM samples with the morphologies of polygonal shape (Sr-P), rod (Sr-R), and porous ball-like (Sr-PH) were successfully prepared. Differences in morphology were effective to the static magnetic and optical properties. Furthermore, the fFMR of SrM was modified to the X-band frequency range. In particular, Sr-PH samples could reach reflection loss (RL) values of –10 dB for 2.5 and 3 mm thicknesses. The microwave absorption of SrM as-prepared samples could be enhanced by making the tri-layer microwave absorbers from as-prepared samples. The simulated RL curves of the 2mm tri-layer-absorber with Sr-PH as the top layer, Sr-R as the middle layer, and Sr-P as the bottom layer (Sr-PH/Sr-R/Sr-P) could achieve a minimum RL of –12 dB and an effective absorption bandwidth (EAB) value of 2.95 GHz. The microwave absorption performance was significantly increased with an increase of 0.5 mm in the total thickness of the tri-layer absorbers. In detail, the Sr-PH-0.5/Sr-R-1.5/Sr-P-0.5 absorber achieved the best values of RL and EAB at –20 dB (illustrating 99% of the microwave incident wave being absorbed) and 4 GHz (covering 95% of the width of the X band frequency), respectively. The results indicated that the microwave absorption performance of SrM could improve by mixing up its different morphologies types.

Constructing ohmic contact on hollow carbon nanocages to enhance conduction loss enabling high-efficient microwave absorption

Metal organic frameworks (MOFs) derived carbon materials have attracted much attention as hopeful electromagnetic microwave absorbents. However, the poor impedance matching and high filler content severely limited its electromagnetic absorption application. The introduction of hollow structural engineering is beneficial to improving microwave absorption performance. Herein, we designed and constructed Ni-incorporated hollow N-doped carbon nanocages (Ni/NCNs) to reveal interfacial charge transfer in electromagnetic wave attenuation. The hollow carbon structure facilitates impedance matching, highly dispersive Ni nanoparticles not only build a dense magnetic coupling network but also generate a series of Ohmic contact heterogeneous interfaces with hollow NCNs, extremely accelerating the charge transfer and enhancing conduction loss. Thanks to hollow structure, optimized impedance matching, and abundant Ohmic contact heterogeneous interfaces, the Ni50/NCNs exhibit a minimum reflection loss of −57.3 dB. The results demonstrate that Ni50/NCNs composites have great potential to be considered efficient electromagnetic wave materials, and the designed Ohmic contact heterogeneous interfaces pave the way in the study of electromagnetic wave absorption mechanisms.

Composition manipulation of heat-resistant iron-based cores@graphitic carbon@amorphous carbon derived from urea-modulated MOFs for high-efficient microwave absorption

Designing multifunctional microwave absorption materials is crucial in practical application. Herein, the iron-based cores@graphitic carbon@amorphous carbon composites with diverse phase compositions were annealed from urea-modulated metal organic frameworks (MOFs), MIL-88A, as precursors. By simply varying the mass ratio of urea and MIL-88A, the chemical compositions of as-prepared samples were well adjusted, which brought the variation of interfacial polarization, dipole polarization, and magnetic response. Meanwhile, the structure with outer-layered amorphous carbon and inner-layered graphitic carbon enhanced impedance matching. Therefore, with stronger microwave attenuation brought by polarization loss and better impedance matching, the high-efficient microwave absorption performance with a minimum reflection loss (RL) of −67.81 dB at 12.5 GHz and an effective absorption bandwidth of 5.76 GHz was obtained with S-05 (Fe/Fe3C/Fe15.1C@graphitic carbon@amorphous carbon), which was prepared with the weight ratio of MIL-88A and urea at 2:1. Meanwhile, the iron-based cores@graphitic carbon@amorphous carbon composites possess good heat-resistant properties due to the existence of protecting carbon layers. Thus, urea-assisted treatment paves a way for acquiring multifunctional absorbers derived from MOFs with enhanced microwave absorption performance.

Facile construction of low-cost and high-efficiency microwave absorbent of Co/C/CG composite with dual-enhancement performance

Carbon-based composite microwave absorption (MA) materials have been regarded as promising light and high-efficient microwave absorbers, but the cumbersome synthesis procedures of carbon matrix have hindered its large-scale application. Thus, it is necessary to find another environmentally friendly, reproducible and low-cost carrier for replacing these carbon materials, further tackling these issues. Herein, with coal gangue (CG) as the relatively low-quality carbon-contained matrix, starch as the cheap supplementary carbon source, CoCG composite was constructed by a solution impregnation and then a carbothermal reduction process at different temperatures. It was found that the state of carbon and Co species in these composites were strongly determined by carbothermal temperature further determining the electromagnetic properties, especially the dielectric properties. The optimal sample CoCG-600 obtained the best MA properties, which possesses the minimum reflection loss of −39.8 dB at 11.8 GHz, the effect absorption bandwidth of 4.7 GHz with the thickness of 2.5 mm. And the widest effective absorption bandwidth of 5.5 GHz can be achieved as decreasing the thickness to 2 mm. Compared with the Fe/C/CG composite in our previous work, Co/C/CG composite exhibited the dual-enhancement MA performance, due to the magnetic and conductive Co phase can be wholly preserved at the relatively high temperature. The dominant MA mechanism, dielectric loss, was mainly included the conductive loss caused by nono-crystalline graphite and Co particles. Finally, the superior selection principle of magnetic component for constructing another MA composite based other impure low- and high-quality carbon-contained matrix was reasonably conjectured.