High-performance Microwave Absorption Research Articles

Magnetic isocyanate-based polyimide composite foam for efficient microwave absorption

Developing and fabricating high-performance microwave absorption materials with excellent comprehensive properties becomes an urgent necessity. In this work, a facile magnetic isocyanate-based polyimide foam with strong interfacial interaction is fabricated by vacuum-impregnating carbon nanotube (CNT)/anisotropic iron flake polyamide acid (PAA)-suspension on the surface of the skeleton. The successful loading of conductive CNT and anisotropic iron flake can facilitate the optimization of impedance matching and the generation of multiple loss mechanisms in foam, endowing it with an efficient microwave absorption performance. More importantly, self-enhancement effect of PAA as the precursor of polyimide significantly reinforces the interfacial interaction between foam and CNT/anisotropic iron flake, due to the similar molecular structure with the isocyanate-based polyimide. The strong interfacial interaction combined with their intrinsic properties further contributes to the improvement of stability and durability, such as high/low-temperature, corrosion, and flame resistance. Therefore, such excellent comprehensive performance makes it possible to become a promising defense material to be applied in harsh marine environments.

One-step solvothermal synthesis of hollow Fe3O4/single walled carbon nanohorns composites with excellent microwave absorption properties

With the increasingly serious electromagnetic radiation and pollution, high-performance microwave absorption materials are urgently needed. In this work, the hollow Fe3O4/single-walled carbon nanohorns (SWCNHs) composites have been synthesized through one-step solvothermal method. The compositions, morphologies, microstructures, and microwave absorption performance of the hollow Fe3O4/SWCNHs composite have been comprehensively investigated. Benefitting from the unique hollow spherical structure and synergistic effects of dielectric loss and magnetic loss, the as-obtained hollow Fe3O4/SWCNHs composite exhibits an optimum reflection loss of −46.9 dB at 16.8 GHz with a matching thickness of 1.5 mm, and a broad effective absorption bandwidth of 7.21 GHz ranging from 10.79 to 18 GHz with a thickness of 2.0 mm, suggesting that the hollow Fe3O4/SWCNHs composite can be used for high-efficiency microwave absorption.

A nitrogen-enriched strategy to accelerate the remediation of Cr(VI)-contaminated soil by iron-based materials in microwave fields

The existing remediation technologies for Cr(VI) contamination soil suffer from long processing times. Microwave catalysis is an efficient environmental remediation technology, and the reasonable design of microwave catalysts can enable a microwave catalytic system to rapidly complete the remediation of Cr(VI). In this study, a microwave catalyst, NRFC-3, with high microwave absorption performance and electron density was designed via a nitrogen enrichment strategy. Density functional theory (DFT) calculations verified that the electron density of the material was increased by nitrogen-enriched strategy. Under the experimental conditions, the electrons (e−) of NRFC-3 originate from “hot spots” and the current density is not lower than 3.78 × 109 e·g−1·s−1. In addition, the reduction of Cr(VI) in the MW/NRFC-3 system is feasible through DFT predictions, and this conclusion was experimentally verified. The MW/NRFC-3 system has a remediation efficiency of 100 % for Cr(VI)-contaminated soil within 25 min, significantly reduced the toxicity of Cr(VI) to the environment and humans, and had long-term stability. The potential application of the MW/NRFC-3 system was verified by remediation experiments on Cr(VI)-contaminated soils of different degrees. This study provides a new technology for the rapid and harmless treatment of Cr(VI)-contaminated soil.

The microwave absorption performance of CF coated with MnO2 nanowires grown by simple hydrothermal method

Microwave absorber can effectively reduce the influence of electromagnetic interference. MnO2 nanowires were deposited on the CF surface by adopting a simple one-step hydrothermal method to fabricate MnO2/CF composites in order to obtain a high-performance microwave absorber. Its microwave absorption (MA) performance and microstructure could be manipulated by adjusting the coating amount. The introduction of MnO2 makes composites possess good MA performance by improving impedance matching. The minimum reflection loss (RLmin) of the MnO2/CF composite is −42.9 dB (1.2 mm, 17.6 GHz), and its effective absorption bandwidth (EAB) reaches 3.84 GHz (1.6 mm). Moreover, its effective absorption band Δƒ (0.5–4 mm thickness) reaches 11.6 GHz. It shows that the MnO2/CF composite could be regarded as an ideal microwave absorber for high frequency.

Fabrication of hollow Fe3O4 microspheres encapsulated by single-walled carbon nanohorns for high-performance microwave absorption

Due to the increasingly serious electromagnetic radiation and pollution problems, it is urgent to develop high-performance electromagnetic wave absorbing materials. Herein, the hollow Fe3O4 microspheres encapsulated by single-walled carbon nanohorns (H-Fe3O4@SWCNHs) have been synthesized via facile solvothermal approach. The obtained H-Fe3O4@SWCNHs composite exhibits a unique hollow core-shell structure and superior microwave absorption performance. When the matching thickness is 2.0 mm, the composite shows a minimum reflection loss value of −42.2 dB at 13.6 GHz and a maximum effective absorption broadband value of 6.2 GHz covering from 11.8 to 18 GHz. The excellent microwave absorption performance of the H-Fe3O4@SWCNHs composite is mainly attributed to the unique hollow core-shell structure, optimal impedance matching, and synergistic effects of dielectric loss and magnetic loss. Therefore, the present work provides a new kind of ideal microwave absorbing material with light weight, thin thickness, wide bandwidth and strong absorption capability for high-performance microwave absorption.

High-performance honeycomb porous microwave absorbers: Gelatin-based carbon nanotube/nickel nanowire aerogels

Biomass-derived carbon absorbent materials have received significant attention due to their renewability, diverse sources, and ease of preparation. In this work, a honeycomb porous electromagnetic wave absorber with excellent performance was successfully prepared by blending gelatin and multi-walled carbon nanotubes (MWCNTs), followed by freeze-drying. Metallic nickel nanowires (NiNWs) were then introduced as a second phase using an in-situ growth method. The minimum reflection loss (RL) of the aerogel containing 8.06 wt% MWCNTs and 3.36 wt% NiNWs was −36.1 dB at a thickness of 3.1 mm, with the effective absorption bandwidth (EAB) covering the entire X-band. Additionally, the aerogel exhibited a very low density (36 mg/cm3) and remarkable strength, capable of supporting over 1658 times its weight for more than 24 h without deformation. These properties make it highly valuable for commercial use and provide new inspiration for the future development of biomass carbon-based electromagnetic absorbing materials.

Ultralight Cellulose-Derived Carbon Nanofibers from Freeze-Drying Emulsion Towards Superior Microwave Absorption

Carbon nanofibers (CNFs) are usually prepared by the carbonization of cellulose aerogels obtained from freeze-drying. However, cellulose with low concentration (below 1 wt%) is required to maintain the good porosity of the aerogels due to the strong hydrogen bonding between the cellulose molecules. In order to address this problem, here, ultralight cellulose-derived CNFs have been fabricated by freeze-drying cyclohexane (CHE)/cellulose nanofiber emulsions and carbonization. Field emission scanning electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy are used to characterize the resulting CNFs. It is found that the CNFs consist of three-dimensional carbon networks, whose microstructure is easily adjusted by changing the CHE ratio (from 0 to 25 vol%) in the emulsions. The CNFs with high porosity are attributed to the fact that CHE as the oil phase can effectively weaken the hydrogen bonding and reduce the aggregation of the cellulose nanofibers. Carbon lattice defects and residual oxygen-containing functional groups are regarded as polarization centers, leading to the enhancement of dielectric loss. The conductive carbon networks also improve the conductive loss. All these factors improve the microwave absorption performance of the CNFs. So, the produced CNFs exhibit a superior electromagnetic wave performance with a minimum reflection loss of −42.18 dB and effective absorption bandwidth up to 4.9 GHz at 2 mm with a filling ratio of 2 wt%. This work provides a simple, low-cost, and sustainable synthesis route for CNFs used for ultralight high-performance microwave absorption materials.

Thickness-controlled HsGDY/N-doped double-shell hollow carbon tubes for broadband high-performance microwave absorption

With the increasing deterioration of the electromagnetic environment, it is important to develop new and efficient electromagnetic wave-absorbing materials. In this work, bilayer hollow HsGDY/NC nanotubes with controllable thickness are constructed by introducing high conductivity polydopamine (PDA) and hydrogen-substituted graphdiyne (HsGDY) followed by the etching and carbonization. Subsequently, the effects of the composition, coating order, and structural characteristics of nanotubes on the electromagnetic parameters are thoroughly investigated, thereby analyzing the microwave absorption mechanism. The impedance matching of HsGDY/NC is optimized by changing the thickness of NC layer, while utilizing unique multi-heterogeneous interfaces and hierarchical conductive structures that enhance the interface polarization and conductive loss. As a result, HsGDY@NC-3 displays the optimal absorbing performance with an effective absorption bandwidth (EAB) of 7.8 GHz (10.1–17.9 GHz) and a minimum reflection loss (RLmin) of −47.18 dB at the filler content of only 11 %. This work broadens the application scopes of HsGDY and provides a novel insight into the design of lightweight, high-efficiency, and wide-frequency microwave absorbers, which is expected to be a potentially effective microwave-absorbing material.

CO2 plasma inducing steel-slag with active sites for efficient growth of carbon nanotubes for the high-performance microwave absorption

As a solid waste generated in the metallurgical process, the highly efficient catalysis of steel-slag for carbon nanotube (CNT) growth remains a huge challenge. Herein, a CO2 plasma-inducing approach for modifying the steel-slag catalyst with rich active sites was developed for CNT growth in the chemical vapor deposition (CVD) process. Furthermore, the high-energy CO2 plasma refines the particles on the steel-slag surface, reducing the particle size on the surface of steel-slag effectively increasing the active sites of the catalyst. In addition, the thermal effect generated by the gas molecule ionization process under CO2 increases the background temperature of the steel-slag, and the interaction between the oxygen-active substances produced and the iron oxide on the surface of steel-slag undergoes an oxidation reaction upon full contact with high-energy particles, which greatly improves the catalytic efficiency of the steel-slag as a catalyst for CNT, and increases the catalytic efficiency by 50 % compared with the non-plasma modified steel-slag as a catalyst for catalyzing CNTs. In addition, catalytically grown CNTs encapsulate magnetic steel-slag catalysts to form a three-dimensional CNT network structure, with high-performance electromagnetic wave absorption. The composite absorbing material with a thickness of only 3.55 mm has a minimum absorption rate of −64.08 dB for electromagnetic waves at a frequency of 7.9 GHz. The dielectric and the magnetic loss of steel-slag lead to enhanced electromagnetic wave absorption. Therefore, this study provides an inexpensive and environmentally friendly idea for the design of high-efficiency CNT growth and solid waste catalyst modification synthesized with high-performance absorbers.

Construction of a 3D spider web structure with spherical Ho2O3 wrapped by carbon nanofibers for high-efficiency microwave absorption and corrosion protection

Reasonable composition control and microstructure design are the effective ways to realize multi-functional high-performance absorbing materials. In this work, a three-dimensional (3D) spider web structure was designed by the electrospinning and high temperature carbonization technology, where Ho2O3 spheres were wrapped by carbon nanofibers. Herein, the spherical Ho2O3 were surrounded by layers of carbon nanofibers (spider silk), which were like the preys inside the spider's web. This unique bionic structure working in conjunction with the tuned components enables the as-prepared composites with improved impedance matching and enhanced loss capacity. The superior electromagnetic wave absorption performance was obtained as the minimum reflection loss of −61.37 dB at 2.90 mm and the maximum effective absorption bandwidth of 6.88 GHz (11.12–18 GHz) at 2.64 mm. At a thickness of 3.44 mm, the effective absorption bandwidth is 4.80 GHz (8–12.80 GHz), covering the entire X-band. At the same time, the composite soaked in the corrosive medium for 7 days owns a low corrosion current density (10−4 ∼10−6 A cm−2) and a high polarization resistance (105∼107 Ω), which exhibits the obvious anticorrosion ability. This work designs a specific spider web structure with high-performance microwave absorption and corrosion protection.

Oxidative Catalytic Depolymerization of Lignin into Value-Added Monophenols by Carbon Nanotube-Supported Cu-Based Catalysts

Lignin valorisation into chemicals and fuels is of great importance in addressing energy challenges and advancing biorefining in a sustainable manner. In this study, on the basis of the high microwave absorption performance of carbon nanotubes (CNTs), a series of copper-oxide-loaded CNT catalysts (CuO/CNT) were developed to facilitate the oxidative depolymerization of lignin under microwave heating. This catalyst can promote the activation of hydrogen peroxide and air, effectively generating a range of reactive oxygen species (ROS). Through the application of electron paramagnetic resonance techniques, these ROS generated under different oxidation conditions were detected to elucidate the oxidation mechanism. The results demonstrate that the •OH and O2•− play a crucial role in the formation of aldehyde and ketone products through the cleavage of lignin Cβ-O and Cα-Cβ bonds. We further evaluated the catalytic performance of the CuO/CNT catalysts with three typical lignin feedstocks to determine their applicability for lignin biorefinery. The bio-enzymatic lignin produced a 13.9% monophenol yield at 200 °C for 20 min under microwave heating, which was higher than the 7% yield via hydrothermal heating conversion. The selectivity of G-/H-/S-type products was slightly affected, while lignin substrate had a noticeable effect on the selective production. Overall, this study explored the structural characteristics of CuO/CNT catalysts and their implications for lignin conversion and offered an efficient oxidation approach that holds promise for sustainable biorefining practices.

Self-Templating Engineering of Hollow N-Doped Carbon Microspheres Anchored with Ternary FeCoNi Alloys for Low-Frequency Microwave Absorption.

Rational design and precision fabrication of magnetic-dielectric composites have significant application potential for microwave absorption in the low-frequency range of 2-8GHz. However, the composition and structure engineering of these composites in regulating their magnetic-dielectric balance to achieve high-performance low-frequency microwave absorption remains challenging. Herein, a self-templating engineering strategy is proposed to fabricate hollow N-doped carbon microspheres anchored with ternary FeCoNi alloys. The high-temperature pyrolysis of FeCoNi alloy precursors creates core-shell FeCoNi alloy-graphitic carbon nano-units that are confined in carbon shells. Moreover, the anchored FeCoNi alloys play a critical role in maintaining hollow structural stability. In conjunction with the additional contribution of multiple heterogeneous interfaces, graphitization, and N doping to the regulation of electromagnetic parameters, hollow FeCoNi@NCMs exhibit a minimum reflection loss (RLmin) of -53.5dB and an effective absorption bandwidth (EAB) of 2.48GHz in the low-frequency range of 2-8GHz. Furthermore, a filler loading of 20wt% can also be used to achieve a broader EAB of 5.34GHz with a matching thickness of 1.7mm. In brief, this work opens up new avenues for the self-templating engineering of magnetic-dielectric composites for low-frequency microwave absorption.

Multi-dimensional, multi-interface Fe3C/carbon sheets/carbon tubes nanoarchitecture towards high-performance microwave absorption

The serious problem of electromagnetic (EM) interference brings growing demand for developing high-performance electromagnetic shielding materials. In this study, three-dimensional (3D) Fe3C/carbon/carbon tubes (Fe3C/C/CT) absorber with multi-heterointerface was prepared by a facile self-propagating followed by chemical vapor deposition (CVD) strategy. Initially, Fe3O4 nanoparticles were anchored onto carbon nanosheets through the self-propagating process. After different etching times with diluted acid, CTs with diverse dimensions and quantities were catalyzed by the modified Fe3O4 catalysts during the CVD approach and grown from the carbon sheets. Such a special nanoarchitecture, which consists of carbon sheets and carbon tubes, acts as the source of dielectric loss. Meanwhile, Fe3C nanoparticles provide magnetic loss, and the abundant interfaces facilitate synergistic electromagnetic loss. Moreover, large numbers of heterointerfaces from the unique multidimensional nanoarchitecture significantly enhance the impedance matching and produce abundant dipole polarization. Ultimately, with etching time of 30 min, the Fe3C/C/CT-30 achieves excellent electromagnetic wave (EMW) absorption property with a minimum reflection loss of −46.4 dB at 10.56 GHz with a thickness of 3.0 mm. When the thickness is 3.57 mm, the effective absorption bandwidth (EAB) can extend up to 4.48 GHz. Moreover, the practical application of the absorbers was evaluated using radar cross-section (RCS) simulation, indicating that Fe3C/C/CT-30 achieves a maximum RCS reduction value of 58 dBm2. The multi-dimensional and multi-heterointerface absorber presented in this work might offer valuable insights for optimizing electromagnetic absorbers.

Magnetic carbon composites derived from biomass with excellent microwave absorption capacity

It is well known that magnetic iron oxide (Fe3O4) and carbon-based materials are good microwave absorbing materials. However, the frequency bands in which Fe3O4 absorbs electromagnetic waves are usually concentrated in the low-frequency region, whereas carbon materials are in the high-frequency region. Therefore, this study aims to deal with the limitation of the absorption bands of these two substances. In this work, this Fe3O4/C composite with high performance microwave absorption was successfully adoption of hydrothermal-calcination process using mangosteen shells as a biomass carbon material, and with a thickness of 1.97 mm, the optimal reflection loss of the sample can reach −67.49 dB, and the frequency band that can be absorbed is 4.32 GHz. The interface polarization, dipolar polarization and eddy current loss in Fe3O4 and carbon materials produce synergistic effects, and the porous conductive network increases the electromagnetic wave transmission path and generates conductive losses, which results in composites with excellent electromagnetic wave absorption properties. The findings indicated that a composite compound of Fe3O4 and carbon-based material was successfully synthesized by hydrothermal method and obtained a materials with outstanding electromagnetic wave absorption properties and high absorption bandwidth.

Integration of carbon microsheets and helical carbon nanocoils for efficient microwave absorption

The integration of multi-dimensional materials is a powerful approach for the construction of high-performance microwave absorbers. In this work, 2D-like carbon microsheets (CMSs) have been directly synthesized on the surfaces of 3D helical carbon nanocoils (CNCs) through a Cu catalyzed chemical vapor deposition process. The junctions formed between CMSs and CNCs create numerous polarization sites, which enhances interfacial polarization. The planar morphology of CMSs is beneficial to enhance the multiple scattering of microwave, while the 3D helical CNCs prevent the aggregation of 2D-like CMSs and simultaneously enhance the conductive loss and cross-polarization loss. By controlling the growth time, the morphologies of CMS are precisely tailored and their impedance matching is adjusted. Consequently, CMS/CNC demonstrates exceptional microwave absorption (MA) performance with a broad effective bandwidth of 6.5 GHz and a minimum reflection loss of −39.3 dB at a remarkably low filling ratio of 4 wt%. This study provides a novel multi-dimensional integrated structure for efficient MA.

Facile constructing core-shell F–CIP@O/N-SWCNHs composites for high-performance microwave absorption and anti-corrosion

The development of electromagnetic wave-absorbing materials (EWAMs) with good environmental adaptability has emerged as a focal point of research in the realm of electromagnetic protection. Herein, a core-shell structure composite EWAMs, in which flake carbonyl iron powders and O, N co-doped single-walled carbon nanohorns are respectively a core and a shell (F–CIP@O/N-SWCNHs), has been prepared by a simple electrostatic adsorption method. The high-shape anisotropy of the F–CIP core exhibits strong specific saturation magnetization (160.47 emu/g) and excellent magnetic loss capacity. The tunable O/N-SWCNHs shell effectively enhances the dielectric properties and improves impedance matching, while the oxygen and nitrogen doping strengthens the dipole polarization. The surface protection provided by O/N-SWCNHs imparts favorable corrosion resistance and anti-oxidation properties to the F-CIP@O/N-SWCNHs. Moreover, F–CIP@O/N-SWCNHs exhibit excellent wave absorption performance. When the sample thickness is 1.53 mm, the minimum reflection loss reaches −74.8 dB. This study provides a feasible approach for the preparation of efficient EWAMs with strong environmental adaptability for the practical application of composite-absorbing materials.

Bidirectional, Multilayer MXene/Polyimide Aerogels for Ultra-Broadband Microwave Absorption.

To obtain high-performance electromagnetic microwave (EM) absorption materials with broad effective absorption bandwidth (EAB) and reduced thickness, designing structures has proved to be a promising way. Herein, ultra-broadband multilayer bidirectional MXene/polyimide EM absorption aerogels containing multi-structures on scales ranging from the micro- to the macroscale are produced with the aid of electric and temperature fields. On the microscale, under the action of electric force and temperature gradient, the ordered structures made of aligned Ti3C2Tx MXene nanosheets and the microscale layered aerogel walls enable the bidirectional aerogel to achieve a wide EAB of 8.58GHz at a thickness of 2.1mm. This is ascribed to the numerous aligned nanosheets and layered aerogel walls perpendicular to the incident EMs, facilitating the conversion of electromagnetic energy into electrical energy. Furthermore, on the macroscale, the multilayer bidirectional aerogel with non-gradient structures effectively resolves the conflict between impedance matching and energy loss, resulting in an ultrawide EAB of 9.41GHz at a thickness of 3mm. This innovative design of electric-field-assisted multilayer bidirectional aerogels with multiscale structural coupling may provide feasible and effective pathways for the development of advanced EM absorption materials.

Fixed-Point Atomic Regulation Engineered Low-Thickness Wideband Microwave Absorption.

Atomic doping is widely employed to fine-tune crystal structures, energy band structures, and the corresponding electrical properties. However, due to the difficulty in precisely regulating doping sites and concentrations, establishing a relationship between electricity properties and doping becomes a huge challenge. In this work, a modulation strategy on A-site cation dopant into spinel-phase metal sulfide Co9S8 lattice via Fe and Ni elements is developed to improve the microwave absorption (MA) properties. At the atomic scale, accurately controlling doped sites can introduce local lattice distortions and strain concentration. Tunned electron energy redistribution of the doped Co9S8 strengthens electron interactions, ultimately enhancing the high-frequency dielectric polarization (ɛ' from 10.5 to 12.5 at 12GHz). For the Fe-doped Co9S8, the effective absorption bandwidth (EAB) at 1.7mm increases by 5%, and the minimum reflection loss (RLmin) improves by 26% (EAB = 5.8GHz, RLmin = -46dB). The methodology of atomic-scale fixed-point doping presents a promising avenue for customizing the dielectric properties of nanomaterials, imparting invaluable insights for the design of cutting-edge high-performance microwave absorption materials.

Hierarchical triplet-metallic oxide/carbon nanocomposites constructed from 2D layered double hydroxides and metal-organic frameworks for high-performance microwave absorption

In the face of increasingly severe electromagnetic wave radiation and interference, it is of great significance to design and prepare excellent absorbing materials. Particularly, hierarchical structure has emerged with enhanced physicochemical properties, offering enormous potential for designing absorbing materials. Here, a hierarchical structure composite constructed by ZIF-8 and fungus-like nickel-cobalt layered double hydroxide (Ni, Co-LDH) nanosheets were synthesized by in-situ self-assembly growth process. A series of Zn@NiCo-Lc composites were obtained by calcination under air. Calcined derivatives of dielectric and magnetic metallic oxides and carbon give rise to multiple polarizations and magnetic losses. The matching of the dielectric and magnetic losses of the hybrid material is further tuned by varying the feed ratio of the bimetallic LDH nanosheets, resulting in a sample with tunable EMA performance. All samples exhibit comparable EMA performance, especially large EABmax of above 5.5 GHz, and Zn@NiCo-Lc-2 has the strongest EMA intensity performance (RLmin is −67.61 dB at an ultra-thin thickness of 1.71 mm). This study provides a tractable method for the fabrication of hierarchical structural composites of high-performance MOF/LDH-derived absorbers, further broadening the application and development of novel electromagnetic wave absorption materials.

Synergistic microwave absorption effect of graphene-BN-Fe3O4 composite at thin thickness

With the quick evolution of information technology, it is necessary to develop high-performance microwave absorbers to attenuate electromagnetic waves. Herein, we prepared graphene-BN-Fe3O4 composites by a facile solvothermal method using graphene as the dielectric loss component, Fe3O4 as the magnetic loss component and BN as the dielectric modulating component. BN and graphene form a 2D/2D structure adhered with Fe3O4. When the ratio of BN to graphene is 1:1 with Fe3O4 content of 60 %, the absorber exhibits excellent electromagnetic wave absorption performance. A RLmin of −42.31 dB is obtained with an effective band of 4.5 GHz at 1.04 mm, while the maximum EAB of samples can reach 4.59 GHz (13.41–18 GHz) with a RLmin value of –33.16 dB at 1.05 mm. The prepared composite exhibits a wide absorption band at a thin thickness. Enhanced microwave absorption performance is achieved mainly due to the synergistic effect of increased interface polarization loss, appropriate conductive loss, and improved impedance matching.