Core-shell CoFe2O4@C nanoparticles coupled with rGO for strong wideband microwave absorption

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 Nanocomposites Based on Nanosized Substituted Ferrites (NiZn)1-xMnxFe2O4 on the Surface of Carbon Nanotubes for Effective Interaction with High-Frequency EM Radiation

To create materials that interact effectively with electromagnetic (EM) radiation, new nanosized substituted ferrites (NiZn)1-xMnxFe2O4 (x = 0, 0.5, and 1) anchored on the surface of multi-walled carbon nanotubes (CNTs) have been synthesized. The concentration of CNTs in the (NiZn)1-xMnxFe2O4/CNT system was from 0.05 to 0.07 vol. fractions. The dielectric and magnetic characteristics of both pristine (NiZn)1-xMnxFe2O4 ferrites and (NiZn)1-xMnxFe2O4/CNT composite systems were studied. The introduction of (NiZn)1-xMnxFe2O4/CNT composites into the amorphous epoxy matrix allows to tailor absorbing properties at the high-frequency by effectively shifting the maximum peak values of the absorption and reflection coefficient to a region of lower frequencies (20-30 GHz). The microwave adsorption properties of (NiZn)1-xMnxFe2O4/0.07CNT-ER (x = 0.5) systems showed that the maximum absorption bandwidth with reflection loss below -10 dB is about 11 GHz.

Facile fabrication of ultra-light N-doped-rGO/g-C3N4 for broadband microwave absorption

"Thin thickness", "lightweight", "wide absorption bandwidth" and "strong absorption" are the new standards of contemporary science and technology for microwave absorption(MA) material. In this study, N-doped-rGO/g-C3N4 MA material was prepared for the first time by simple heat treatment, which the N atoms were doped into rGO and g-C3N4 was dispersed on the surface of N-doped-rGO, and its density is only 0.035 g/cm3. The impedance matching of the N-doped-rGO/g-C3N4 composite was well adjusted by decreasing the dielectric constant and attenuation constant due to the g-C3N4 semiconductor property and the graphite-like structure. Moreover, the distribution of g-C3N4 among N-doped-rGO sheets can produce more polarization effect and relaxation effect by increasing the lamellar spacing. Furthermore, the polarization loss of N-doped-rGO/g-C3N4 could be increased successfully by doping N atoms and g-C3N4. Ultimately, the MA property of N-doped-rGO/g-C3N4 composite was optimized significantly, with a loading of 5 wt%, the N-doped-rGO/g-C3N4 composite exhibited the RLmin of -49.59 dB and the effective absorption bandwidth could reach 4.56 GHz when the thickness was only 1.6 mm. The "thin thickness", "lightweight", "wide absorption bandwidth" and "strong absorption" of MA material are actually achieved by the N-doped-rGO/g-C3N4.

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.

3D porous carbon-embedded nZVI@Fe2O3 nanoarchitectures enable prominent performance and recyclability in antibiotic removal

Overcoming the instability and poor recyclability during the practical applications of contaminant scavengers is a challenging topic. Herein, a three-dimensional (3D) interconnected carbon aerogel (nZVI@Fe₂O₃/PC) embedding a core-shell nanostructure of nZVI@Fe₂O₃ was elaborately designed and fabricated via an in-situ self-assembly process. The porous carbon with 3D network architecture exhibits strong adsorption towards various antibiotic contaminants in water, where the stably embedded nZVI@Fe₂O₃ nanoparticles not only serve as magnetic seeds for recycling, but also avoid the shedding and oxidation of nZVI in the adsorption process. As a result, nZVI@Fe₂O₃/PC efficiently captures sulfamethoxazole (SMX), sulfamethazine (SMZ), ciprofloxacin (CIP), tetracycline (TC) and other antibiotics in water. In particular, an excellent adsorptive removal capacity of 329 mg g^-1 and a rapid capture kinetics (99% of removal efficiency in 10 min) under a wide pH adaptability (2-8) are achieved using nZVI@Fe₂O₃/PC as an SMX scavenger. nZVI@Fe₂O₃/PC displays exceptional long-term stability given that it shows excellent magnetic property after it is stored in water solution for 60 d, making it an ideal stable scavenger for contaminants in an etching-resistant and efficient manner. This work would also provide a general strategy to develop other stable iron-based functional architectures for efficient catalytic degradation, energy conversion and biomedicine.

3D lamellar skeletal network of porous carbon derived from hull of water chestnut with excellent microwave absorption properties

Biomass derived carbon has attracted extensive attention in the field of microwave absorption because of its sustainability and porous structure beneficial to microwave attenuation. In this study, 3D lamellar skeletal network porous carbon was successfully obtained from hull of water chestnut using biomass waste as raw material by controlling the ratio of KOH and precursors in a one-step carbonization process. The optimization of biomass carbon morphology was achieved and its microwave absorption properties were investigated. At the temperature of 600 °C, when the ratio of hull of water chestnut to KOH is 1:1, the porous carbon material with filling ratio of 35% can reach the effective absorption bandwidth (RL < -10 dB) of 6.0 GHz (12-18 GHz) at the matching thickness of 1.90 mm, covering the whole Ku band. When the thickness is 2.97 mm, the optimal reflection loss reaches -60.76 dB. The surface defects, interface polarization and dipole polarization of 3D porous skeleton network structure derived from hull of water chestnut contribute to the excellent reflection loss and bandwidth of porous carbon materials. The porous carbon with low density, low cost and simple preparation method has broad application prospects in the preparation of biomass-derived microwave absorbers.

Rational construction of yolk-shell structured Co3Fe7/FeO@carbon composite and optimization of its microwave absorption

The construction of yolk-shell composites with dielectric/magnetic multiple loss mechanisms has become a promising strategy to obtain high-efficiency microwave absorbing materials. An ideal microwave absorber should possess dielectric and magnetic loss abilities, thereby leading to the attenuation and absorption of incident electromagnetic radiation. Herein, the yolk-shell structured CoFe₂O₄@carbon (YS-CoFe₂O₄@C) and Co₃Fe₇/FeO@carbon (YS-Co₃Fe₇/FeO@C) composites were designed and synthesized through a series of processes, which include in-situ coating, heat-treating, etching and subsequent carbonization reduction reaction. The composite materials with specific structure, composition, and electromagnetic parameters could be effectively obtained by controlling the reaction conditions. The combination of alloy with high magnetic loss and carbon with advanced dielectric loss as well as the unique yolk-shell structure endow YS-Co₃Fe₇/FeO@C improved impendence matching and large attenuation constant. The YS-Co₃Fe₇/FeO@C composites show optimized microwave absorption behaviors, the minimum reflection loss is up to -57.6 dB at 12.30 GHz with the of 2.5 mm and the corresponding effective absorption bandwidth is 5.27 GHz (10.10-15.37 GHz). Moreover, the widest effective bandwidth could reach 7.0 GHz (11-18 GHz) with the thickness of 2.3 m. This design provides a novel concept for tuning microwave absorption efficiency of magnetic/dielectric composites to prepare high-performance microwave absorbers.

Synthesis of hollow core-shell ZnFe2O4@C nanospheres with excellent microwave absorption properties

The special hollow core–shell structure and excellent dielectric-magnetic loss synergy of composite materials are two crucial factors that have an important influence on the microwave absorption properties. In this study, hollow ZnFe₂O₄ nanospheres were successfully synthesized by a solvothermal precipitation method firstly; based on this, a C shell precursor phenolic resin was coated on the ZnFe₂O₄ hollow nanospheres' surface by an in situ oxidative polymerization method, and then ZnFe₂O₄@C was obtained by high-temperature calcination. Samples were characterized by SEM, TEM, XRD, XPS, BET, VSM, VNA. The results show that the maximum reflection loss (RL_max) reaches −50.97 dB at 8.0 GHz, and the effective bandwidth (EAB) of hollow core–shell structure ZnFe₂O₄@C is 3.2 GHz (6.16–9.36 GHz) with a coating thickness of 3.5 mm. This work provides a useful method for the design of lightweight and high-efficiency microwave absorbers.

The hollow core–shell structure ZnFe₂O₄@C in this work has excellent EM absorption performance.