Magnetic CoNi alloy particles embedded N-doped carbon fibers with polypyrrole for excellent electromagnetic wave absorption

Atomic spin engineering of Fe-N-C by axial chlorine-ligand modulation for lightweight and efficient electromagnetic wave absorption

Introducing atomic magnetic factors to regulate the electromagnetic parameters of graphene is essential to achieving new-generation electromagnetic wave (EMW) absorbing materials. Herein, a new strategy of endowing graphene with atomic magnetic moments was developed by implanting high-spin FeN4 moieties with axial Cl ligands into 3D N-doped graphene (Cl-Fe-NG). The design facilitates the multi-reflection loss, dielectric loss and magnetic loss of EMW at ultra-low filling. Its minimum reflective loss (RL) is up to -65.9 dB with the biggest effective absorption bandwidth (EAB) of up to 5.5 GHz in the thin thickness of 1.9 mm and a low filler loading of 5 wt%. Meanwhile, a waterborne polyurethane wave-absorbing coating filled with 5 wt% Cl-Fe-NG demonstrates its high absorption performance with a dominant absorption loss of 90 %. Additionally, theory calculations reveal that introducing axial Cl-ligand FeN4 moiety with high-spin Fe into graphene not only generates additional electric dipoles but also induces an atomic magnetic moment, effectively enhancing the dielectric and magnetic loss of graphene for EMW absorption. This work provides a new approach to designing graphene with atomic magnetic moments for developing EMW absorbing materials with "thin, wide, light, and strong" characteristics instead of the conventional route of graphene with magnetic nanoparticles.

Carbon nanofiber coated ionic crystal architecture withconfinement effect for high-performance microwave absorption along with high-efficiency water harvesting from air

Water is considered an effective microwave absorber due to its high transmittance and frequency-dispersive dielectric constant, yet it is challenging to form it into a stable state as an absorber. Herein, we developed a water-containing microwave absorber using chemical vapor deposition (CVD), namely, the bifunctional carbon/NaCl multi-interfaces hybrid with excellent water harvesting and microwave absorption performance. Carbon/NaCl exhibits remarkable water harvesting abilities from air, exceeding 210 % of its weight in 12 h. The development of the hydrophilic/hydrophobic heterojunction interface is responsible for this outstanding performance. Additionally, the interfacial polarization provided by carbon/NaCl, along with the dipole polarization induced by the internally captured water and defects, enhances its microwave absorption. The carbon/NaCl hybrid achieved a minimum reflection loss (RLmin) of -69.62 dB at 17.1 GHz with a thickness of 2.13 mm, and a maximum effective absorption bandwidth (EABmax) of 6.74 GHz at a thickness of 2.5 mm. Compared with raw NaCl (RLmin of -24.5 dB, EABmax of 3.88 GHz), the RLmin and EABmax values of the absorber increased by approximately 2.85 and 1.74 times. These results highlight the potential for bifunctional carbon/NaCl hybrid in applications within extreme environments, presenting a promising avenue for further research and development.

CsPbBr3 perovskite quantum dots-based Janus membrane with multifunction of luminescence, magnetism and aeolotropic electroconductivity

Lead halide perovskite quantum dots (QDs) are promising semiconductors for next-generation photoelectric devices. However, the development of perovskite QDs-based multifunctional materials still needs to be addressed in order to further advance the application of perovskite QDs. Herein, a successful synthesis of Janus microfibers array Janus membrane (JMAJM) with up-down structure and multifunction of luminescence, magnetism and electroconductivity is firstly achieved based on CsPbBr3 QDs through a parallel electrospinning. JMAJM comprises up-down two layers tightly bonded together. The up-layer of JMAJM is luminescence/magnetism Janus microfibers array (L/M-JMAJM) constructed by [CsPbBr3/polymethyl methacrylate (PMMA)]//[CoFe2O4/PMMA] Janus microfibers as building elements. The down-layer of JMAJM is luminescence/electroconductivity Janus microfibers array (L/E-JMAJM) fabricated by [CsPbBr3/PMMA]//[polyaniline (PANI)/PMMA] Janus microfibers as building elements. Two independent microcosmic regions are designed and realized in a Janus microfiber, confining luminescence with magnetic or conductive substances into their respective regions, thus minimizing adverse effects of other dark-colored functional substances on the fluorescence of CsPbBr3 QDs. This peculiar Janus microfiber enables the effective separation and high integration of CsPbBr3 QDs with other functional substances. The up-down structure of JMAJM ensures a high integration of luminescence, magnetism and conductivity. Meanwhile, JMAJM addresses the environmental instability of CsPbBr3 QDs while simultaneously endows perovskite QDs-based materials with additional functions to realize multifunction. Under ultraviolet excitation, fluorescence characteristics of the CsPbBr3 QDs in JMAJM are maintained, exhibiting a vibrant green emission at 517 nm. Meanwhile, JMAJM achieves a maximum saturation magnetization of 20.32 emu·g-1, high conductance of 10-2 S and aeolotropic electroconductivity degree of 107. The combination of micro-partition with macro-partition in JMAJM receives superior concurrent luminescence-magnetic-conductive multifunction. This work provides a novel idea and strategy for advancing perovskite QDs-based multifunctional materials.

Recent advances on outstanding microwave absorption and electromagnetic interference shielding nanocomposites of ZnO semiconductor

The electromagnetic interference shielding and microwave attenuation capabilities of ZnO semiconductor nanocomposites have recently been improved using a variety of approaches by correctly modifying their permittivity. To improve microwave attenuation, ZnO semiconductor nanostructures have been combined with graphene, multi-wall carbon nanotubes, metal nanoparticles and their alloys, two-dimensional MXene, spinel ferrite magnetic nanoparticles, polymer systems, and textiles. This paper covers the opportunities and constraints that these cutting-edge nanocomposites in the field of electromagnetic wave absorption encounter as well as the research progress of ZnO semiconductor-based nanocomposite. The structure-function relationship of electromagnetic wave absorption nanocomposites, design strategies, synthesis techniques, and various types of advanced nanocomposites based on ZnO semiconductor are also covered. In order to design and prepare high efficiency ZnO semiconductor based electromagnetic wave absorbing materials for use in applications of next-generation electronics and aerospace, this article can offer some useful ideas.

Enhanced microwave absorption performance of Fe3Al flakes by optimizing the carbon nanotube coatings

Fe3Al is a good magnetic loss absorber for microwave absorption. However, due to the relatively high density and poor impedance matching ratio, the potential of Fe3Al cannot be fully released. Herein, a dielectric loss absorber of carbon nanotubes (CNTs) is coupled with Fe3Al to form Fe3Al/CNTs composite absorbers. CNTs are randomly tangled and coated on the surface of the Fe3Al flakes, forming a connecting conductive network. By carefully tuning the content of CNTs, the optimized Fe3Al/CNTs composite absorber with 1.5% of CNTs can combine both magnetic loss and dielectric loss mechanisms, thus achieving an impedance matching ratio close to 1 while keeping strong attenuation for enhanced microwave absorption. As a result, an effective absorption bandwidth (RL ≤ -10 dB) of 4.73 GHz at a thickness of 2 mm is achieved.

Fabrication of cobalt-zinc bimetallic oxides@polypyrrole composites for high-performance electromagnetic wave absorption

Composite materials that combine magnetic and dielectric losses offer a potential solution to enhance impedance match and significantly improve microwave absorption. In this study, Co3O4/ZnCo2O4 and ZnCo2O4/ZnO with varying metal oxide compositions are successfully synthesized, which are achieved by modifying the ratios of Co2+ and Zn2+ ions in the CoZn bimetallic metal-organic framework (MOF) precursor, followed by a high-temperature oxidative calcination process. Subsequently, a layer of polypyrrole (PPy) is coated onto the composite surfaces, resulting in the formation of core-shell structures known as Co3O4/ZnCo2O4@PPy (CZCP) and ZnCo2O4/ZnO@PPy (ZCZP) composites. The proposed method allows for rapid adjustments to the metal oxide composition within the inner shell, enabling the creation of composites with varying degrees of magnetic losses. The inclusion of PPy in the outer shell serves to enhance the bonding strength of the entire composite structure while contributing to conductive and dielectric losses. In specific experimental conditions, when the loading is set at 50 wt%, the CZCP composite exhibits an effective absorption bandwidth (EAB) of 5.58 GHz (12.42 GHz-18 GHz) at a thickness of 1.53 mm. Meanwhile, the ZCZP composite demonstrates an impressive minimum reflection loss (RLmin) of -71.2 dB at 13.04 GHz, with a thickness of 1.84 mm. This study offers a synthesis strategy for designing absorbent composites that possess light weight and excellent absorptive properties, thereby contributing to the advancement of electromagnetic wave absorbing materials.

Design and synthesis of one-dimensional magnetic composites with Co nanoparticles encapsulated in carbon nanofibers for enhanced microwave absorption

With the increased usage of electromagnetic microwaves (EM) in wireless communication technology, the problem of electromagnetic radiation pollution has grown dramatically. This study successfully prepared novel Co/C magnetic nanocomposite fibers for EM absorption using the electrospinning and carbonization methods. The morphology, composition, magnetic properties, and EM absorption performance were extensively characterized. This material shows exceptional EM absorption performance, achieving -72.01 dB (at 2.08 mm) for minimum reflection loss (RLmin) and 5.4 GHz (at 1.68 mm) for effective absorption bandwidth (EAB). The performance surpasses not only any single precursor but also stands as the best in similar investigations. It can be attributed to the microstructure of magnetic Co nanoparticles encapsulated in carbon nanofibers and the macrostructure of cross-linked three-dimensional (3D) conductive networks. The combination of these structures resulted in excellent dielectric loss, magnetic loss, and impedance matching. This research offers new insights into the production of one-dimensional (1D) carbon-based absorbers, while also establishing a theoretical foundation for exploring the application potential of this material. These findings may contribute to the development of more efficient and practical EM absorption materials in the future.

Simple fabrication of cobalt-nickel alloy/carbon nanocomposite fibers for tunable microwave absorption

A series of CoNi/C nanocomposite fibers with different Co and Ni ratios were successfully prepared by electrospinning and carbonization techniques for the study of electromagnetic microwave (EMW) absorbing materials. We systematically studied the influence of Co and Ni content on the microstructure, chemical composition, magnetic properties, and EMW absorption characteristics of the samples. The results showed that CoNi/C nanocomposite fibers obtained excellent EMW absorption ability through the reasonable design of the composition, and the Co/Ni ratio significantly affected the microstructure and EMW absorption performance. When the Co/Ni ratio was 1/3, the minimum reflection loss (RLmin) is -71.2 dB (2.4 mm, 13.4 GHz), and the maximum effective absorption bandwidth (EAB, RL＜-10 dB) is up to 5.9 GHz (2.2 mm, 12.1-18 GHz), covering almost the entire Ku band. This study demonstrated the enormous potential of one-dimensional structure in the field of EMW absorption. In addition, the CoNi/C nanocomposite fiber synthesized using a straightforward and low-cost method not only has excellent EMW absorption performance but also has the potential for practical application. The results of this study provide a simple and effective approach for designing high-performance EMW absorbing materials.

Nitrogen-doped porous carbon nanomaterials synthesized using a magadiite template as efficient peroxidase mimics for colorimetric detection of ascorbic acid as an antioxidant

Nanomaterials with intrinsic enzyme-like activity have gained substantial scientific attention as viable substitutes to natural biological enzymes owing to their cheap price and great stability. Numerous artificial enzyme mimics have been employed effectively in sectors such as sensing, environmental processing, and cancer treatment. In this study, novel nitrogen-doped porous carbon nanomaterials (CPs) were produced by modifying polypyrrole with magadiite using chemical oxidative polymerization and calcination methods. The obtained nitrogen-doped porous carbon nanomaterials exhibited improved peroxidase-like activity, which catalyzed the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2) to produce colorful compounds. Kinetic investigation revealed that the affinity for TMB of nitrogen-doped porous carbon peroxidase mimics was higher than that of genuine horseradish peroxidase (HRP). In addition, a sensitive assay with encouraging performance for the colorimetric detection of ascorbic acid (AA) was successfully fabricated employing nitrogen-doped porous carbon nanomaterials as peroxidase mimics. The results were satisfactory and demonstrated its potential application in antioxidant detection.

Nanocomposites Based on Pyrolyzed Polyacrylonitrile Doped with FeCoCr/C Transition Metal Alloy Nanoparticles: Synthesis, Structure, and Electromagnetic Properties

In the last decade, the development of new materials that absorb electromagnetic radiation (EMR) has received research interest as they can significantly enhance the performance of electronic devices and prevent adverse effects caused by electromagnetic pollution. Electromagnetic radiation absorbers with a low weight and small thickness of the absorber layer, good absorption capacity, and a wide frequency response bandwidth are highly demanded. Here, for the first time, the properties of polymer nanocomposites FeCoCr/C synthesized by doping FeCoCr alloy nanoparticles into a polymer matrix of pyrolyzed polyacrylonitrile are investigated. An analysis of the magnetic properties of FeCoCr/C nanocomposites showed that increasing the synthesis temperature increased the specific magnetization and coercive force values of the FeCoCr/C nanocomposites. The dependence between the ratio of metals in the precursor of pyrolyzed polyacrylonitrile and the electromagnetic and wave-absorbing properties of FeCoCr/C nanocomposites is considered, and the results of complex dielectric and magnetic permeability measurements are analyzed. It is found that the most promising of all the studied materials are those obtained at T = 700 °C with the ratio of metals Fe:Co:Cr = 35:35:30.

Urchin-like Fe3O4@C hollow spheres with core-shell structure: Controllable synthesis and microwave absorption

The steadily increasing use of microwave stealth materials in aerospace flying vehicles needs the development of lightweight absorbers with low density and high thermal stability for printing or spraying. In that regard, the structural designability of typical microwave absorbers made of Fe₃O₄ seems to be a significant roadmap. In this work, a hollow spherical structure with a uniform carbon shell around the urchin-like Fe₃O₄ core (Fe₃O₄@C) was produced via a two-step hydrothermal method and annealing. The Fe₃O₄@C absorber exhibited a strong minimum reflection loss (RL_min) of -73.5 dB at the matching thickness of 3.23 mm. The maximum effective absorption bandwidth (EAB_max) was 4.78 GHz at 4.55 mm. The proposed urchin-like core-shell structure was shown to provide good impedance matching and electromagnetic loss ability due to the synergistic effect of Fe₃O₄ and C. In particular, the urchin-like structure increases the heterogeneous interfaces and effectively improves their polarization and relaxation. On the other hand, it reduces the density of the absorber and enhances multiple scattering attenuations of electromagnetic waves (EMWs). Therefore, the findings of the present study open up prospects for the design of high-efficiency lightweight microwave absorbers with specialized structures.

Electromagnetic Response of Multistage-Helical Nano-Micro Conducting Polymer Structures and their Enhanced Attenuation Mechanism of Multiscale-Chiral Synergistic Effect

Nowadays, the rapidly development of advanced antidetection technology raises stringent requirements for microwave absorption materials (MAMs) to focus more attention on wider bandwidth, thinner thickness, and lower density. Adding magnetic medium to realize broadband absorption may usually result in the decline of service performance and accelerating corrosion of MAMs. Chiral MAMs can produce extra magnetic loss without adding magnetic medium due to the unique electromagnetic cross polarization effect. However, more efforts should be taken to furtherly promote efficient bandwidth of chiral MAMs and reveal attenuation mode and modulation method of chiral structure. Herein, a novel superhelical nano-microstructure based on chiral polyaniline and helical polypyrrole is successfully achieved via in situ polymerization strategy. The enhanced multiscale-chiral synergistic effect contributes to broaden effective absorption bandwidth, covering 8.6 GHz at the thickness of 3.6 mm, and the minimum reflection loss can reach -51.3 dB simultaneously. Besides, to further explain response modes and loss mechanism of superhelical nano-microstructures, the electromagnetic simulation and test analysis are applied together to reveal their synergistic enhancement attenuation mechanism. Taken together, this strategy gives a new thought of how to design, prepare, and optimize the hierarchical structure materials to achieving broadband and high-performance microwave absorption.

Flexible cobalt nanoparticles/carbon nanofibers with macroporous structures toward superior electromagnetic wave absorption

The increasing electromagnetic (EM) pollution that has seriously threatened human health and electronic devices urgently required high-performance absorbents toward attenuating EM wave (EMW). The combination of microstructure modulation and appropriate components regulation has proven to be a feasible strategy for improving the EMW absorption performance of absorbents. In this work, well-designed one-dimensional carbon nanofibers with macroporous structures and uniformly magnetic metal nanoparticles modification were prepared by the hard-template assisted electrospinning method followed by carbonization and template-elimination processes. The strong interfacial polarization loss and multireflection strengthened by the hollow structures and the magnetic loss induced by the introduced cobalt nanoparticles evidently enhanced the impedance matching level of the macroporous carbon nanofibers/cobalt nanoparticles (MCF/Co). As a result, MCF/Co composite offers broad absorption bandwidth (6.24 GHz) and strong electromagnetic wave absorption performance (-40.1 dB) at a thickness of 3.0 mm. This work inspires the rational one-dimensional macroporous carbon nanofibers design for new-generation EMW materials and provides an important research basis for the porous flexible EMW absorption materials.

Transferring A4 Paper to FeNi3/NiCx Coated Carbon Skeleton for Efficient Absorption of Multiband Microwave

Herein, A4 typing paper was used as a novel source to manufacture FeNi3 and NiCx coated carbon skeleton via facile routes. The product was examined for its ability to absorb electromagnetic emission which can be a health hazard. The impact of precursor concentration on the final electromagnetic wave absorption of samples was evaluated; the composite prepared under suitable concentration possesses outstanding multiband absorption ability of −34.64 dB and −26.7 dB at 2.32 GHz and 17.2 GHz, respectively, together with an ultra-wide effective absorption bandwidth of 9.58 GHz at only 3.9 mm. The strong dipole polarization and broad frequency range of preferable impedance matching, along with the coupling of other auxiliary mechanisms, are responsible for this excellent property. The as-prepared absorber has great potency for multiband absorption of electromagnetic waves.

Hydrophobic, flexible electromagnetic interference shielding films derived from hydrolysate of waste leather scraps

With the rapid development of wireless telecommunication technologies, it is of fundamental and technological significance to design and engineer high-performance shielding materials against electromagnetic interference (EMI). Herein, a three-step procedure is developed to produce hydrophobic, flexible nanofiber films for EMI shielding and pressure sensing based on hydrolysate of waste leather scraps (HWLS): (i) electrospinning preparation of HWLS/polyacrylonitrile (PAN) nanofiber films, (ii) adsorption of silver nanowires (AgNWs) onto HWLS/PAN nanofiber films, and (iii) coating of HWLS/PAN/AgNWs nanofiber films with polydimethylsiloxane (PDMS). Scanning electron microscopy studies show that AgNWs are interweaved with HWLS/PAN nanofibers to form a conductive network, exhibiting an electrical conductivity of 10⁵ S m^-1 and shielding efficiency of 65 dB for a 150 μm-thick HWLS/PAN/AgNWs film. The HWLS/PAN/AgNWs/PDMS film displays an even better electromagnetic shielding efficiency of 80 dB and a water contact angle of 132.5°. Results from this study highlight the unique potential of leather solid wastes for the production of high-performance, environmentally friendly, and low-cost EMI shielding materials.

Highly active CoNi nanoparticles confined in N-doped carbon microtubes for efficient catalytic performance

CoNi@NCMT magnetic composites with a tubular structure and high coverage of tiny CoNi bimetallic nanoparticles are fabricated as efficient catalysts for the reduction of 4-nitrophenol (4-NP).