High Microwave Absorption Research Articles

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.

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.

Impact of chromium substitution on structural, spectroscopic, and dielectric properties of Ba4Ni2Fe36O60 ceramics

Cr-substituted Ni2U hexaferrite series (Ba4Ni2Fe36-xCrxO60for x = 0.0 to x = 2.0 with a step size of 0.5) was prepared via sol-gel auto-combustion route and annealed at 1200 °C for 6 h. The samples were investigated using XRD, FTIR, SEM, XPS, and high frequency (1 MHz–6 GHz) dielectric and microwave absorption measurements (VNA). XRD studies revealed that Cr3+ ions successfully substituted in BaNi2U-type hexaferrite and have a single-phase structure. The average crystallite size decreased while the percentage of porosity increased with the substitution. FTIR spectra confirmed the formation of the hexaferrite phase in all compositions. SEM micrographs revealed that the prepared samples are hexagonal. XPS spectra show the presence of all constituent elements in the samples. The dielectric constant, dielectric loss, and A.C. conductivity of samples was analyzed. Cole-Cole plots with single semicircles of different radii show the grain and grain boundaries affecting the conduction process. Moreover, Cr-substitution enhanced the microwave absorption capability. The hexaferrite sample Ba4Ni2Fe35 Cr1.0O60, with a pellet thickness of 1.81 mm, showed the highest M.W. absorption at 1.09 GHz frequency with a reflection loss (R.L.) value of −55 dB. The hexagonal-shaped morphology, high porosity, and enhanced reflection loss value suggest their use in high-frequency microwave applications.

Graphene-Based Dual-Band Metasurface Absorber with High Frequency Ratio.

In this paper, we propose a novel dual-band metasurface absorber with a high frequency ratio based on graphene. By carefully designing a centrally symmetrical graphene pattern and positioning it on a glass medium, while utilizing ITO as a ground, the metasurface absorber achieves remarkable high frequency ratio microwave absorption. Specifically, this metasurface absorber exhibits two distinct resonance points at 3.7 GHz and 14 GHz, with an impressive frequency ratio over 3.5. It achieves over 90% absorption efficiency in the frequency ranges of 3.5-4.5 GHz and 13.5-14.5 GHz, highlighting its capability to effectively absorb microwaves across widely spaced frequency bands. Furthermore, the metasurface absorber demonstrates optical transparency and polarization insensitivity, adding to its versatility and potential applications. The measured results of the fabricated prototype validate its design and potential for practical use.

Facile process for cost-effective layer-by-layer rGO/SiO2 structure for high microwave absorption

This study introduces a cost-effective and eco-efficient method for fabricating an advanced microwave absorber using a layer-by-layer rGO and SiO2 structure. The rGO/SiO2 composite, synthesized via modified Hummer's and Stöber methods, demonstrates remarkable microwave absorption properties. The resultant porous structure, characterized by an SBET of 294.89 m2/g, enables multiple reflections and scatterings of electromagnetic waves. At a sample thickness of 3.8 mm, the material achieves a reflection loss (RL) of −47.43 dB at 12.56 GHz and an effective absorption bandwidth (EAB) of 11.04 GHz. For a 6 mm thick sample, an exceptionally high EAB of 12.72 GHz is observed, maintaining a high RL of −42.32 dB. These results demonstrate that the rGO/SiO2 material is a promising candidate for applications in electromagnetic wave absorption, offering a simple, scalable solution for mitigating electromagnetic pollution and enhancing military stealth technologies.

MOF-derived ZnCo2O4 @ Ti3C2TX nanosheet with high microwave absorption

Abstract Electromagnetic wave absorbing (EWA) materials have a wide application in military technology, so it is necessary to develop EWA materials with lightweight, and wide absorption bandwidth and strong absorption. Novel two-dimensional material (MXene) with high dielectric constant property and unique structure has attracted extensive focus in microwave absorption. However, the high conductivity of MXene limits its application in microwave absorption. In this work, ZnCO2O4 nanoparticles were obtained via a hydrothermal method and subsequent heat treatment. Then it was anchored on MXene nanosheets. The effective absorption bandwidth (EAB) of the ZnCO2O4@Ti3C2Tx is 4.77GHz at 1.5mm thickness. Composites show great potential in the field of designing a new generation of efficient and lightweight microwave absorbers, which are expected to be used in various EWA applications.

How Domain Segregation in Ionic Liquids Stabilizes Nanoparticles and Establishes Long-Range Ordering─A Computational Study.

Due to their physical properties including high thermal stability, very low vapor pressure, and high microwave absorption, ionic liquids have attracted great attention as solvents for the synthesis of nanomaterials, being considered as greener alternatives to traditional solvents. While usual solvents often need additives like surfactants, polymers, or other ligands to avoid nanoparticle coalescence, some ionic liquids can stabilize nanoparticles in dispersion without any additive. In order to quantify how the ionic liquids can affect both the aggregation thermodynamics and kinetics, molecular dynamics simulations were performed to simulate the evolution of concentrated dispersions and to compute the potential of mean force between nanoparticles of both hydrophilic and hydrophobic natures in two imidazolium-based ionic liquids, which differ from each other by the length of the cation alkyl group. Depending on the nature of the nanoparticle, structured layers of the polar and apolar regions of the ionic liquid can be formed close to its surface, and those layers lead to activation barriers for dispersed particles to get in contact. If the alkyl group of the ionic liquid is long enough to lead to domain segregation between the ionic and apolar portions of the solvent, the layered structure around the particle becomes more structured and propagates several nanometers away from its surface. This leads to stronger barriers close to the contact and also multiple barriers at larger distances that result from the unfavorable superposition of solvent layers of opposing nature when the nanoparticles approach each other. Those long-range solvent-mediated forces not only provide kinetic stability to dispersions but also affect their dynamics and lead to a long-range ordering between dispersed particles that can be explored as a template for the synthesis of complex materials.

BST@Copper Nanowire/Epoxy composites with excellent microwave absorption in the X-band

In this work, hybrid epoxy nanocomposites containing varying loading of copper nanowires (CuNW), Ba0.7Sr0.3TiO3 (BST), and BST@CuNW hybrid nanoparticles were prepared and analyzed for their microwave absorption characteristics. The nanoparticles used in this study were prepared using a facile co-precipitation and hydrothermal methodology. The synthesized nanoparticles were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) for their morphology and phase determination. While the XRD results confirmed the presence of BST and CuNW, the SEM micrographs obtained on the hybrid BST@CuNW nanoparticles show BST anchored on the CuNW surfaces. A series of epoxy composites containing varying loading of synthesized nanoparticles were prepared and characterized for their microwave properties, such as complex permittivity, shielding effectiveness, and power coefficients. The results indicate that nanocomposites containing BST@CuNW hybrids exhibited enhanced dielectric loss and more significant microwave power absorption compared to samples with equivalent CuNW and/or BST loading. The best composite sample, i.e., a one-millimeter-thick epoxy containing 10:15 (wt/wt) CuNW: BST hybrid nanoparticles with an estimated density of 1.49 g/cc attenuated 99.1 % of incident microwave power and exhibited a shielding effectiveness value of 21.2 dB in the X-band (8–12 GHz) of the microwave frequency spectrum. These lightweight polymer composites with high microwave absorption in the X-band are useful for military and civilian applications.

Integration of Heterogeneous Interfaces and Multi‐Dimensional Encapsulation Structure in Fe2N@CNTs Enabling Highly Efficient Thermal Management and Microwave Absorption

AbstractThe opposing effects of interface effect on phonon heat conduction and microwave absorption hinder the integration of thermal conduction with microwave absorption. Reconciling this contradiction by rationally optimizing the material structure remains a challenge. Herein, Fe2N@CNTs with heterogeneous interfaces and multi‐dimensional encapsulated structures are fabricated through in situ chemical vapor deposition (CVD) to realize excellent thermal conductivity and microwave absorption. When the mass fraction of active material is 40 wt.%, the thermal conductivity (λ//) of Fe2N@CNTs composite films is 6.69 W m−1 K−1. The minimum reflection loss (RLmin) is up to −54.55 dB at a thickness of 3.43 mm, and the effective absorption bandwidth (EAB) is 5.52 GHz at 1.82 mm. The well‐designed Fe2N@CNTs is an ideal model for gaining insight into electron transportation and phonon multi‐dimensional heat transport. Heterogeneous interface improves the dielectric loss and facilitates microwave and phonon absorption and conversion. The multi‐dimensional encapsulation structure increases the electron transport path and phonon heat transport paths making axial and radial co‐transfer possible. The multi‐dimensional encapsulation structure demonstrates extremely high microwave absorption and thermal management capabilities, which open up new possibilities for multifunctional applications in host materials with internal hollows.

Preparation and electromagnetic wave absorption properties of CAU-Al MOF and graphene oxide aerogel composites

The application of microwave technology has penetrated all aspects of life, but also lead to the electromagnetic pollution, therefore the research of high efficiency microwave absorption materials has been widely concerned. In this work, a new type of Al based CAU-10-H MOF was prepared by hydrothermal method. The particles were polyhedral in size of 2 [Formula: see text]m. After high temperature annealing, the interplanar spacing increased with the annealing temperature, and the lattice structure was destroyed at 400°C. CAU-Al/rGO aerogels were prepared by freeze-drying of hydrogels. With the increase of CAU-Al content and the annealing temperature, the carbon crystallinity decreases, and the pores of the aerogels became larger and fluffier. The real parts of permittivity of CAU-Al/rGO aerogels were between 5 and 30, which can be tuned by the annealing temperature and CAU-Al content. For the microwave absorption performance, the CAU-Al/rGO aerogel with a ratio of 3:1 achieved the minimum reflection loss of −37.8 dB at 3 mm. Moreover, the CAU-Al/rGO aerogels showed a wide effective bandwidth, which reached 5.1 GHz under the thickness of 2.5 mm. Therefore, the CAU-Al/rGO aerogels could be used as a kind of broadband microwave absorber with excellent microwave absorption performance.

Multifunction integration within magnetic CNT-bridged MXene/CoNi based phase change materials

Developing advanced nanocomposite phase change materials (PCMs) integrating zero-energy thermal management, microwave absorption, photothermal therapy and electrical signal detection can promote the leapfrog development of flexible wearable electronic devices. For this goal, we propose a multidimensional collaborative strategy combining two-dimensional (2D) MXene nanosheets with metal-organic framework-derived one-dimensional (1D) carbon nanotubes (CNTs) and zero-dimensional (0D) metal nanoparticles. After encapsulating paraffin wax (PW) in three-dimensional (3D) networked multidimensional MXene/CoNi–C, the resulting composite PCMs exhibit excellent thermal energy storage capacity and long-term thermally reliable stability. Benefiting from the synergistically enhanced photothermal effects of CNTs, Co/Ni nanoparticles and MXene, PW@MXene/CoNi–C can capture photons efficiently and transfer phonons quickly, yielding an ultrahigh photothermal conversion and storage efficiency of 97.5%. Additionally, PW@MXene/CoNi–C composite PCMs exhibit high microwave absorption with a minimum reflection loss of −49.3 ​dB at 8.03 ​GHz in heat-related electronic application scenarios. More attractively, the corresponding flexible phase change film can simultaneously achieve thermal management and electromagnetic shielding of electronic devices, as well as photothermal therapy and electrical signal detection for individuals. This functional integration design provides an important reference for developing advanced flexible multifunctional wearable materials and devices.

Exploring the Potential of Sustainable Biopolymers as a Shield against Electromagnetic Radiations.

The increasing demand for biodegradable and environmentally friendly materials is shifting the focus from traditional polymer composites to biocomposites in various applications, especially in electromagnetic shielding. Effective utilization of biopolymers demands improved properties and can be achieved to a certain extent by functionalization. Biopolymers such as cellulose, polylactic acid, and starch are some of the potential candidates for mitigating electromagnetic pollution in next-generation electronic devices because of their high aspect ratio, flexibility, light weight, high mechanical strength, thermal stability, and tunable microwave absorption to the electromagnetic interference (EMI) shielding composites. This Review provides an overview of the current advancements in EMI shielding materials and outlines recent research on EMI shielding composites that utilize various biodegradable polymer structures.

Ultrawide Spectra Camouflage Coatings from Metallic Flake Powder.

Ultrawide-spectra-compatible camouflage materials are imperative for military science and national security due to the continuous advancement of various sophisticated multispectral detectors. However, ultrawide spectra camouflage still has challenges, as the spectral requirements for different bands are disparate and even conflicting. This work demonstrates an ultrawide spectra camouflage material compatible with visible (VIS, 400-800 nm), infrared (IR, 3-5 and 8-14 μm), and microwave (S-Ku bands, 2-12 GHz). The carbon nanotubes adsorbed on porous anodic alumina/aluminum flake powder (CNTs@PAA/AFP) material for ultrawide spectra camouflage is composed of bioinspired porous alumina surface layers for low visible reflection and aluminum flake powder substrate for low infrared emissivity, while the surface of the porous alumina layers is loaded with carbon nanotubes for microwave absorption. Compared with previous low-emissivity materials, CNTs@PAA/AFP has omnidirectional low reflectance (Ravg = 0.29) and high gray scale (72%) in the visible band. Further, it exhibits low emissivity (ε3-5μm = 0.15 and ε8-14μm = 0.18) in the dual infrared atmospheric window, which reduces the infrared lock-on range by 59.6%/49.8% in the mid/far-infrared band at high temperatures (573 K). The infrared camouflage performance calculated from the radiation temperature of CNTs@PAA/AFP coatings is enhanced to over 65%, which is at least 4 times greater than that of its substrate. In addition, the CNTs@PAA/AFP coating achieves high microwave absorption (RLmin = -42.46 dB) and an effective absorption bandwidth (EAB = 7.43 GHz) in the microwave band (S-Ku bands) due to the enhancement of interfacial polarization and conductive losses. This study may introduce new insight and feasible methods for multispectral manipulation, electromagnetic signal processing, and thermal management via bioinspired structural design and fabrication.

Lightweight titanium dioxide/carbon nanotube composites prepared by atomic layer deposition for broad-band microwave absorption

The microwave absorbing material with appropriate impedance matching and excellent attenuation ability can be applied to resist electromagnetic radiation. In this work, carbon nanotubes were modified by titanium dioxide via the atomic layer deposition method, to prepare lightweight composites with high microwave absorption performance. The impedance matching and attenuation ability of titanium dioxide/carbon nanotube (TiO2/CNT) composites could be precisely controlled by adjusting the number of titanium dioxide deposition cycles. The relationship between the microstructure and microwave absorption performance of the composite was analyzed in detail. When the number of TiO2 deposition cycles was 100, the composite displayed outstanding microwave absorption performance, due to appropriate impedance matching and strong attenuation ability. The maximum effective absorption bandwidth of the composite reached 5.19 GHz (1.6 mm), which almost covered the Ku band. The microwave attenuation mechanism of the composite has also been investigated. This work provided a new idea for fabricating lightweight microwave absorption materials.

Excellent microwave absorption property of 3D printed SiCN matrix metamaterial

The combination of 3D printing, polymer derived ceramics, and electromagnetic wave (EMW) absorption metamaterials is particularly useful for spacecraft stealth in extreme environments and is gradually gaining significant interest. While the 3D printing of SiOC has been extensively researched, the high temperature stability and mechanical performance of SiOC are not as favorable as SiCN. However, it remains challenging to prepare SiCN metamaterials with both high mechanical and microwave absorption properties by 3D printing. Herein, we demonstrate a SiCN EMW absorption metamaterial with high mechanical properties using digital light processing 3D printing, which achieves a minimum reflection loss of −31.01 dB (99.9 % absorption), and the widest effective absorption bandwidth covers the entire X-band from 8.2 to 12.4 GHz. And the EMW absorption performance can be adjusted based on the size of the unit structure.

EVA copolymer loaded with PAni/CNT/GNP hybrids: A flexible and lightweight material with high microwave absorption

AbstractMicrowave‐absorbing materials are widely used for electromagnetic interference shielding and stealth technology. However, most existing materials are heavy, rigid, and expensive, limiting their practical applications. Therefore, there is a need to develop new materials that are flexible, lightweight, and cost effective. This study aimed to synthesize and characterize a novel ternary composite material based on polyaniline (PAni), carbon nanotubes (CNTs), and graphene nanoplatelets (GNPs) in an ethylene‐vinyl acetate (EVA) copolymer matrix. PAni‐based ternary composites were prepared by in situ polymerization of aniline in toluene dispersion of CNT/GNP hybrids and EVA. The microwave absorption properties were evaluated using a vector network analyzer in the frequency range of 8.2–18 GHz. The presence of as little as 0.8 wt% of CNT/GNP hybrid with appropriate mass ratio increased the conductivity by more than four orders of magnitude compared to the EVA@PAni blend. The minimum reflection loss corresponded to −40.55 dB at 16.31 GHz for the system containing CNT/GNP = 0.3:0.7, whereas those with CNT/GNP = 0.0:1.0 and 0.7:0.3 presented the widest effective absorption bandwidths (RL < −10 dB), covering almost the entire Ku‐band. Due to the excellent flexibility, low weight, and high microwave absorption performance, these composites are potential candidates for microwave absorption applications.

One-step preparation of sea urchin-like conducting polypyrrole-modified porous carbonyl iron powders with excellent microwave absorption properties

Carbonyl iron powder (CIP) is a common microwave absorber frequently utilized to prepare microwave-absorbing materials. However, it exhibits only magnetic loss and no dielectric loss, which inevitably affects its wave-absorbing performance. Here, porous carbonyl iron powder (p-CIP) modified with conductive polypyrrole (PPy) was successfully prepared by one-step chemical etching and in-situ polymerization and then utilized to fabricate epoxy composites with high microwave absorption intensity. The scanning electron microscopy images revealed that conductive PPy was encapsulated on the surface of p-CIP. The reflection loss of the P-200 sample is −41.2 dB at 2.2 mm thickness. Reduction of the sample thickness to 1.8 mm resulted in a still acceptable reflection loss of −35.5 dB. Moreover, the effective absorption bandwidth widened to approximately 6.75 GHz (10.55–17.3 GHz). This provides a valuable approach for the development of microwave-absorbing materials with high absorption capacity.

High temperature stable amorphous SiBCN microwave absorption ceramics derived from one-pot synthesis of single-source precursors

Silicoboron carbonitride (SiBCN) ceramics are developed as microwave absorption material for high-temperature environments under multicomponent doping and in-situ crystallization. In this study, amorphous SiBCN microwave absorption ceramics was derived from single-source hyperbranched polyborosilazanes containing benzene rings synthesized by the one-pot method. The carbon element and ordered carbon ratio of the pyrolyzed SiBCN ceramics enhanced with an increase in the proportion of dichlorodiphenylsilane. By adjusting the monomer ratio and pyrolysis temperature of ceramic precursor, the polymer derived ceramics (PDCs) could achieve good microwave absorption properties while remaining amorphous, with minimum reflection coefficient (RCmin) up to -30.79 dB and maximum effective absorption bandwidth (EABmax) up to 4.07 GHz. Meanwhile, the PDC-SiBCN ceramics exbibited outstanding high temperature stability with essentially no mass loss in argon (Ar) and air atmospheres until 1400 °C. This novel, convenient PDC-SiBCN preparation with potential for scaled-up production provides new ideas for microwave absorption materials for applications in extreme environments.

Porous metal microsphere M@C-rGO (metal = Mn, Fe, Co, Ni, Cu) aerogels with high low-frequency microwave absorption, strong thermal insulation and superior anticorrosion performance

Porous metal microsphere M@C-rGO (metal = Mn, Fe, Co, Ni, Cu) aerogels with high low-frequency microwave absorption, strong thermal insulation and superior anticorrosion performance are successfully constructed.

Preparation and microwave absorption properties of CoFe2O4/NiCo2O4 composite powders

The magnetic spinel cobalt ferrite (CoFe2O4) powders had the high microwave absorption performance at the large thicknesses on account of the low permittivity. Combining the CoFe2O4 powders with other dielectric loss materials had been suggested to improve their impedance matching and microwave absorption performance. In this work, the microwave absorption performance of the CoFe2O4 powders was enhanced by adding the various amounts of the NiCo2O4 nanoparticles as dielectric loss material. The CoFe2O4-x NiCo2O4 composite powders (x = 0, 12.5, 25, and 50 wt %) were prepared by a facile two-pot solution combustion synthesis method. Although the X-ray diffraction peaks of NiCo2O4 phase were absent, but the decrease of saturation magnetization from 61 to 30 emu/g was related to the amount of NiCo2O4 material. Furthermore, the NiCo2O4 nanoparticles were nucleated and grown on the surface of spongy CoFe2O4 powders because the synthesized CoFe2O4 powders were added to the precursor solution of NiCo2O4 material containing the nickel and cobalt nitrates as oxidants and glycine as organic fuel. The microwave absorption performance was analyzed by measuring the permittivity and permeability spectra which were applied for evaluating the reflection loss versus frequency and thickness. The CoFe2O4-25 wt % NiCo2O4 composite powders had the higher microwave absorption performance including the high reflection loss of −40 dB and broad effective bandwidth of 5.6 GHz of Ku band (12–18 GHz) at a small matching thickness of 1.9 mm. The high microwave absorption performance of the x = 25 wt % sample was attributed to its better impedance matching via a proper combination of the permittivity and permeability values.