Multicomponent Nanoparticles Synergistic One-Dimensional Nanofibers as Heterostructure Absorbers for Tunable and Efficient Microwave Absorption

Frontiers in Bioinspired Polymer-Based Helical Nanofibers from Electrospinning

Helices are among the most significant structures in nature, representing an emerging group of materials distinguished by their unique helical geometry. Recently, helical nanofibers have attracted considerable attention due to their exceptional structural characteristics and versatile applications in various fields, including tissue engineering, biomedicine, nanotechnology, and chiral materials. Therefore, developing methods to fabricate biomimetic helical fibers on demand, which can exhibit a diverse range of physical properties and forms, is of great interest across multiple disciplines. Despite the significant interest in helical fibrous materials, the fabrication of such complex structures at the micro- or nanoscale level remains a major challenge. Electrospinning offers a simple and versatile technique for producing micro- and nanofibers in various helical shapes. This review systematically summarizes and classifies the state-of-the-art advancements in electrospun helical nanofibers into four categories based on their forming mechanisms: viscoelastic asymmetric contraction, bending instability motion, jet-induced buckling response, and rotary winding molding. Additionally, the recent applications of these helical nanofibrous materials in areas such as environmental remediation, interactive textiles, and biomedical engineering are also summarized. Furthermore, the current challenges and future perspectives in the field are put forward. We anticipate that the insights provided will contribute to the rational design of advanced artificial helical materials, thereby enhancing their practical applications in the future.

CoOx/CeO2@C nanopetals derived Cobalt-Cerium Prussian blue with enhanced Dual-Enzyme mimetic activity for detection of ascorbic acid in rat brain during calm/ischemic processes

In this study, we demonstrate that a highly efficient colorimetric sensor prepared from carbon-shielded Co-Ce Prussian blue analog (PBA) nanopetals (CoOx/CeO2@C) by green chemical deposition method and thermal annealing processes for detection of ascorbic acid (AA) in cerebral microdialysis fluids. The synthesized CoOx/CeO2@C showed high dual-mimetic activity, i.e., peroxidase- and catalase-like activity, and great catalytic stability. The combination of carbon film and Co-Ce PBA nanopetals (1) greatly enhances the interfacial electron transfer rate of the nanopetals due to excellent electrical conductivity of carbon, and (2) protects nanopetals from acidic chemical environments during the catalytic process, which greatly reduces loss of the catalytic activity of the cobalt-cerium (hydroxide) oxides. Based on the peroxidase-like property of CoOx/CeO2@C nanopetals, this sensor has a good linear range from 0.1 to 150 μM with a low detection limit of 0.04 μM, i.e., improved sensitivity for AA colorimetric measurement. The developed colorimetric strategy with a green synthetic pathway, catalytic stability and wide linear range confirms the monitoring of AA in brain systems during calm/ischemic processes.

Research Progress on the Synthesis of Nanostructured Photocatalysts and Their Environmental Applications

Due to their unique photocatalytic properties, nanostructured photocatalysts have shown broad prospects for application in environmental treatment. In recent years, researchers have significantly enhanced the photocatalytic charge separation efficiency and photocatalytic stability of photocatalysts by regulating semiconductor energy band structures, optimizing interface and surface properties, constructing heterogeneous structures, and introducing noble metal doping. This review systematically summarizes the basic principles, synthesis methods, and modification strategies of nanostructured photocatalysts and focuses on recent research advances in their environmental applications, such as water pollution control, air purification, and carbon dioxide reduction. Meanwhile, this review analyzes current challenges in the field, such as low quantum efficiency, insufficient stability, and limited industrialization, and outlines future development directions, including smart catalytic technology, fabrication of multifunctional composites, and large-scale synthesis, thereby providing a reference for research and application.

Anion Doping Synergistic Strategy Achieving Multi-Interfaces and Modulated Dielectric Coupling for Efficient Electromagnetic Response

Efficient microwave absorbers are needed to address the electromagnetic pollution caused by the proliferation of new radio technologies and equipment. Excellent microwave absorption performance can be achieved by controlling the dielectric constant. Heteroatom-doped bimetallic materials are promising electromagnetic wave absorption (EMA) materials due to their tunable structures and low cost. In particular, the presence of anionic sites significantly affects their dielectric constant and electrical conductivity. Herein, a 1D carbon nanofiber material is prepared by encapsulating FeCo nanoparticles in a fiber cavity by electrostatic spinning. Subsequently, tellurization, vulcanization, and selenization processes are carried out. FeTe2/ CoTe2@C exhibits stronger conductivity and dielectric loss due to the lower electronegativity of Te. The clever configuration of FeTe2, CoTe2, and C heterostructures obtained by Te doping generates multi-heterogeneous interfaces that facilitate charge migration and enhance interfacial polarization, obtaining excellent EMA performance. FeTe2/CoTe2@C exhibits an optimum minimum reflection loss (RLmin) of -51.1 dB with a matching thickness of 2.0 mm, and the effective absorption bandwidth (EAB) reaches 4.2 GHz. Radar cross-section (RCS) calculations show the great potential of FeTe2/CoTe2@C for practical military stealth technology. This study offers novel guidance for improving the EMA properties of transition metal matrix composites via anionic coordination modulation.

Multifunctional bacterial cellulose‑derived carbon hybrid aerogel for ultrabroad microwave absorption and thermal insulation

Carbon aerogel has gained intense attention as one of the most promising microwave absorption materials. It can overcome severe electromagnetic pollution, thanks to its 3D macroscopic structure and superb conductive loss capacity. However, there is still a big challenge to endow multifunctionality to carbon aerogel while maintaining its good electromagnetic wave absorption (EWA) so as to adapt wide practical application. Herein, a novel carbon-based aerogel consisting of Cu and TiO2 nanoparticles dispersed on carbon nanofiber framework was derived from carbonized bacterial cellulose (CBC) decorated with its mother bacteria via freeze-drying, in situ growth and carbonization strategies. The synthesized carbon-based CBC/Cu/TiO2 aerogel achieved an excellent EWA performance with a broad effective absorption bandwidth (EAB) of 8.32 GHz. It is attributed to the synergistic loss mechanism from multiple scattering, conductive network loss, interfacial polarization loss and dipolar polarization relaxation. Meanwhile, the obtained aerogel also shows an excellent thermal insulation with a 3-mm-thick sample generating a temperature gradient of over 42 °C at 85 °C and a maximum radar cross-section (RCS) reduction of 23.88 dB m2 owing to the cellular structure and synergistic effects of multi-components. Therefore, this study proposes a feasible design approach for creating lightweight, effective, and multifunctional CBC-based EWA materials, which offer a new platform to develop ultrabroad electromagnetic wave absorber under the guidance of RCS simulation.

Multiple Tin Compounds Modified Carbon Fibers to Construct Heterogeneous Interfaces for Corrosion Prevention and Electromagnetic Wave Absorption

Currently, the demand for electromagnetic wave (EMW) absorbing materials with specific functions and capable of withstanding harsh environments is becoming increasingly urgent. Multi-component interface engineering is considered an effective means to achieve high-efficiency EMW absorption. However, interface modulation engineering has not been fully discussed and has great potential in the field of EMW absorption. In this study, multi-component tin compound fiber composites based on carbon fiber (CF) substrate were prepared by electrospinning, hydrothermal synthesis, and high-temperature thermal reduction. By utilizing the different properties of different substances, rich heterogeneous interfaces are constructed. This effectively promotes charge transfer and enhances interfacial polarization and conduction loss. The prepared SnS/SnS2/SnO2/CF composites with abundant heterogeneous interfaces have and exhibit excellent EMW absorption properties at a loading of 50 wt% in epoxy resin. The minimum reflection loss (RL) is - 46.74 dB and the maximum effective absorption bandwidth is 5.28 GHz. Moreover, SnS/SnS2/SnO2/CF epoxy composite coatings exhibited long-term corrosion resistance on Q235 steel surfaces. Therefore, this study provides an effective strategy for the design of high-efficiency EMW absorbing materials in complex and harsh environments.

MOFs-Derived Strategy and Ternary Alloys Regulation in Flower-Like Magnetic-Carbon Microspheres with Broadband Electromagnetic Wave Absorption

Broadband electromagnetic (EM) wave absorption materials play an important role in military stealth and health protection. Herein, metal-organic frameworks (MOFs)-derived magnetic-carbon CoNiM@C (M = Cu, Zn, Fe, Mn) microspheres are fabricated, which exhibit flower-like nano-microstructure with tunable EM response capacity. Based on the MOFs-derived CoNi@C microsphere, the adjacent third element is introduced into magnetic CoNi alloy to enhance EM wave absorption performance. In term of broadband absorption, the order of efficient absorption bandwidth (EAB) value is Mn > Fe = Zn > Cu in the CoNiM@C microspheres. Therefore, MOFs-derived flower-like CoNiMn@C microspheres hold outstanding broadband absorption and the EAB can reach up to 5.8 GHz (covering 12.2-18 GHz at 2.0 mm thickness). Besides, off-axis electron holography and computational simulations are applied to elucidate the inherent dielectric dissipation and magnetic loss. Rich heterointerfaces in CoNiMn@C promote the aggregation of the negative/positive charges at the contacting region, forming interfacial polarization. The graphitized carbon layer catalyzed by the magnetic CoNiMn core offered the electron mobility path, boosting the conductive loss. Equally importantly, magnetic coupling is observed in the CoNiMn@C to strengthen the magnetic responding behaviors. This study provides a new guide to build broadband EM absorption by regulating the ternary magnetic alloy.

In situ fabrication of Fe3C nanoparticles and porous-carbon composites as high-performance electromagnetic wave absorber

This study successfully utilized a straightforward approach, choosing liquid-liquid phase separation to build a porous structure and synthesize composite absorbers based on polyimide-based porous carbon/Fe3C (PIC/Fe3C-1, PIC/Fe3C-2) nanoparticles and porous carbon/FeCo alloy nanoparticles (PIC/FeCo). The specially designed network structure pore structures contributed multiple reflection, conduction loss and strong interfacial polarization. After characterization, PIC/Fe3C-2 obtained minimum RL of -35.37 dB at 17.04 GHz with 1.55 mm thickness and effective absorption bandwidth of 4.95 GHz with 1.66 mm thickness. Furthermore, PIC/FeCo, with a thickness of 1.63 mm, exhibits the most robust electromagnetic wave loss ability at 15.6 GHz, with a minimum RL of -56.32 dB and an effective absorption bandwidth of 4.88 GHz. Thus, the design strategy presented in this study could serve as a model for synthesizing other high-performance absorbers, effectively mitigating electromagnetic wave-induced pollution.

Achieving Ultra-Broad Microwave Absorption Bandwidth Around Millimeter-Wave Atmospheric Window Through an Intentional Manipulation on Multi-Magnetic Resonance Behavior

The utilization of electromagnetic waves is rapidly advancing into the millimeter-wave frequency range, posing increasingly severe challenges in terms of electromagnetic pollution prevention and radar stealth. However, existing millimeter-wave absorbers are still inadequate in addressing these issues due to their monotonous magnetic resonance pattern. In this work, rare-earth La3+ and non-magnetic Zr4+ ions are simultaneously incorporated into M-type barium ferrite (BaM) to intentionally manipulate the multi-magnetic resonance behavior. By leveraging the contrary impact of La3+ and Zr4+ ions on magnetocrystalline anisotropy field, the restrictive relationship between intensity and frequency of the multi-magnetic resonance is successfully eliminated. The magnetic resonance peak-differentiating and imitating results confirm that significant multi-magnetic resonance phenomenon emerges around 35 GHz due to the reinforced exchange coupling effect between Fe3+ and Fe2+ ions. Additionally, Mössbauer spectra analysis, first-principle calculations, and least square fitting collectively identify that additional La3+ doping leads to a profound rearrangement of Zr4+ occupation and thus makes the portion of polarization/conduction loss increase gradually. As a consequence, the La3+-Zr4+ co-doped BaM achieves an ultra-broad bandwidth of 12.5 + GHz covering from 27.5 to 40 + GHz, which holds remarkable potential for millimeter-wave absorbers around the atmospheric window of 35 GHz.

In Situ Atomic Reconstruction Engineering Modulating Graphene-Like MXene-Based Multifunctional Electromagnetic Devices Covering Multi-Spectrum

With the diversified development of big data, detection and precision guidance technologies, electromagnetic (EM) functional materials and devices serving multiple spectrums have become a hot topic. Exploring the multispectral response of materials is a challenging and meaningful scientific question. In this study, MXene/TiO2 hybrids with tunable conduction loss and polarization relaxation are fabricated by in situ atomic reconstruction engineering. More importantly, MXene/TiO2 hybrids exhibit adjustable spectral responses in the GHz, infrared and visible spectrums, and several EM devices are constructed based on this. An antenna array provides excellent EM energy harvesting in multiple microwave bands, with |S11| up to - 63.2 dB, and can be tuned by the degree of bending. An ultra-wideband bandpass filter realizes a passband of about 5.4 GHz and effectively suppresses the transmission of EM signals in the stopband. An infrared stealth device has an emissivity of less than 0.2 in the infrared spectrum at wavelengths of 6-14 µm. This work can provide new inspiration for the design and development of multifunctional, multi-spectrum EM devices.

Structural Engineering of Hierarchical Magnetic/Carbon Nanocomposites via In Situ Growth for High-Efficient Electromagnetic Wave Absorption

Materials exhibiting high-performance electromagnetic wave absorption have garnered considerable scientific and technological attention, yet encounter significant challenges. Developing new materials and innovative structural design concepts is crucial for expanding the application field of electromagnetic wave absorption. Particularly, hierarchical structure engineering has emerged as a promising approach to enhance the physical and chemical properties of materials, providing immense potential for creating versatile electromagnetic wave absorption materials. Herein, an exceptional multi-dimensional hierarchical structure was meticulously devised, unleashing the full microwave attenuation capabilities through in situ growth, self-reduction, and multi-heterogeneous interface integration. The hierarchical structure features a three-dimensional carbon framework, where magnetic nanoparticles grow in situ on the carbon skeleton, creating a necklace-like structure. Furthermore, magnetic nanosheets assemble within this framework. Enhanced impedance matching was achieved by precisely adjusting component proportions, and intelligent integration of diverse interfaces bolstered dielectric polarization. The obtain Fe3O4-Fe nanoparticles/carbon nanofibers/Al-Fe3O4-Fe nanosheets composites demonstrated outstanding performance with a minimum reflection loss (RLmin) value of - 59.3 dB and an effective absorption bandwidth (RL ≤  - 10 dB) extending up to 5.6 GHz at 2.2 mm. These notable accomplishments offer fresh insights into the precision design of high-efficient electromagnetic wave absorption materials.

Compositional and Hollow Engineering of Silicon Carbide/Carbon Microspheres as High-Performance Microwave Absorbing Materials with Good Environmental Tolerance

Microwave absorbing materials (MAMs) characterized by high absorption efficiency and good environmental tolerance are highly desirable in practical applications. Both silicon carbide and carbon are considered as stable MAMs under some rigorous conditions, while their composites still fail to produce satisfactory microwave absorption performance regardless of the improvements as compared with the individuals. Herein, we have successfully implemented compositional and structural engineering to fabricate hollow SiC/C microspheres with controllable composition. The simultaneous modulation on dielectric properties and impedance matching can be easily achieved as the change in the composition of these composites. The formation of hollow structure not only favors lightweight feature, but also generates considerable contribution to microwave attenuation capacity. With the synergistic effect of composition and structure, the optimized SiC/C composite exhibits excellent performance, whose the strongest reflection loss intensity and broadest effective absorption reach - 60.8 dB and 5.1 GHz, respectively, and its microwave absorption properties are actually superior to those of most SiC/C composites in previous studies. In addition, the stability tests of microwave absorption capacity after exposure to harsh conditions and Radar Cross Section simulation data demonstrate that hollow SiC/C microspheres from compositional and structural optimization have a bright prospect in practical applications.

Preparation of MoS2@PDA-Modified Polyimide Films with High Mechanical Performance and Improved Electrical Insulation

Polyimide (PI) has been widely used in cable insulation, thermal insulation, wind power protection, and other fields due to its high chemical stability and excellent electrical insulation and mechanical properties. In this research, a modified PI composite film (MoS2@PDA/PI) was obtained by using polydopamine (PDA)-coated molybdenum disulfide (MoS2) as a filler. The low interlayer friction characteristics and high elastic modulus of MoS2 provide a theoretical basis for enhancing the flexible mechanical properties of the PI matrix. The formation of a cross-linking structure between a large number of active sites on the surface of the PDA and the PI molecular chain can effectively enhance the breakdown field strength of the film. Consequently, the tensile strength of the final sample MoS2@PDA/PI film increased by 44.7% in comparison with pure PI film, and the breakdown voltage strength reached 1.23 times that of the original film. It can be seen that the strategy of utilizing two-dimensional (2D) MoS2@PDA nanosheets filled with PI provides a new modification idea to enhance the mechanical and electrical insulation properties of PI films.

Modulation Engineering of Electromagnetic Wave Absorption Performance of Layered Double Hydroxides Derived Hollow Metal Carbides Integrating Corrosion Protection

Layered double hydroxides (LDHs) with unique layered structure and atomic composition are limited in the field of electromagnetic wave absorption (EMA) due to their poor electrical conductivity and lack of dielectric properties. In this study, the EMA performance and anticorrosion of hollow derived LDH composites are improved by temperature control and composition design using ZIF-8 as a sacrifice template. Diverse regulation modes result in different mechanisms for EMA. In the temperature control process, chemical reactions tune the composition of the products and construct a refined structure to optimize the LDHs conductivity loss. Additionally, the different phase interfaces generated by the control components optimize the impedance matching and enhance the interfacial polarization. The results show that the prepared NCZ (Ni3ZnC0.7/Co3ZnC@C) has a minimum reflection loss (RLmin ) of -58.92 dB with a thickness of 2.4 mm and a maximum effective absorption bandwidth (EABmax ) of 7.36 GHz with a thickness of 2.4 mm. Finally, due to its special structure and composition, the sample exhibits excellent anticorrosion properties. This work offers essential knowledge for designing engineering materials derived from metal organic framework (MOF) with cutting-edge components and nanostructures.

Joule-Heating-Driven Synthesis of a Honeycomb-Like Porous Carbon Nanofiber/High Entropy Alloy Composite as an Ultralightweight Electromagnetic Wave Absorber

High entropy alloys (HEA) have garnered significant attention in electromagnetic wave (EMW) absorption due to their efficient synergism among multiple components and tunable electronic structures. However, their high density and limited chemical stability hinder their progress as lightweight absorbers. Incorporating HEA with carbon offers a promising solution, but synthesizing stable HEA/carbon composite faces challenges due to the propensity for phase separation during conventional heat treatments. Moreover, EMW absorption mechanisms in HEAs may be different from established empirical models due to their high-entropy effect. This underscores the urgent need to synthesize stable and lightweight HEA/carbon absorbers and uncover their intrinsic absorption mechanisms. Herein, we successfully integrated a quinary FeCoNiCuMn HEA into a honeycomb-like porous carbon nanofiber (HCNF) using electrostatic spinning and the Joule-heating method. Leveraging the inherent lattice distortion effects and honeycomb structure, the HCNF/HEA composite demonstrates outstanding EMW absorption properties at an ultralow filler loading of 2 wt %. It achieves a minimum reflection loss of -65.8 dB and boasts a maximum absorption bandwidth of up to 7.68 GHz. This study not only showcases the effectiveness of combining HCNF with HEA, but also underscores the potential of Joule-heating synthesis for developing lightweight HEA-based absorbers.

Ultra-flexible silver/iron nanowire decorated melamine composite foams for high-efficiency electromagnetic wave absorption and thermal management

Nowadays, functional electronic devices with excellent flexibility and thermal management capability for effective electromagnetic wave absorption are urgently in demand. Herein, a novel and highly flexible silver nanowire (AgNW)/iron nanowire (FeNW) decorated melamine composite foam (AgFe-MF) was prepared via simple dip-coating process. Owing to optimal impedance matching, synergistic dielectric and magnetic losses as well as three-dimensional porous structure, the AgFe-MF with an ultra-low filler content (0.22 vol%) exhibited an outstanding minimum reflection loss of -69.61 dB, and the best effective absorption bandwidth (EAB) could reach up to 6.37 GHz. Importantly, the EAB of long-time working AgFe-MF was enhanced to 7.01 GHz after 1000 compress-release cycles under 40 % strain. Besides, it also featured considerate Joule heating capacity and achieved a saturation temperature of over 85.7 ℃ under 2.6 V voltage. The impressive thermal isolation and long-term stability ensured the safety used as portable heater. Therefore, this work will provide a vital slight for fabricating smart wearable electronic devices with integrated anti-electromagnetic radiation and personalized thermal management performances towards potential thermal and health threats.

Tracking Regulatory Mechanism of Trace Fe on Graphene Electromagnetic Wave Absorption

Polarization and conductance losses are the fundamental dielectric attenuation mechanisms for graphene-based absorbers, but it is not fully understood in revealing the loss mechanism of affect graphene itself. For the first time, the reduced graphene oxide (RGO) based absorbers are developed with regulatory absorption properties and the absorption mechanism of RGO is mainly originated from the carrier injection behavior of trace metal Fe nanosheets on graphene. Accordingly, the minimum reflection loss (RLmin) of Fe/RGO-2 composite reaches - 53.38 dB (2.45 mm), and the effective absorption bandwidth achieves 7.52 GHz (2.62 mm) with lower filling loading of 2 wt%. Using off-axis electron hologram testing combined with simulation calculation and carrier transport property experiments, we demonstrate here the carrier injection behavior from Fe to graphene at the interface and the induced charge accumulation and rearrangement, resulting in the increased interfacial and dipole polarization and the conductance loss. This work has confirmed that regulating the dielectric property of graphene itself by adding trace metals can not only ensure good impedance matching, but also fully exploit the dielectric loss ability of graphene at low filler content, which opens up an efficient way for designing lightweight absorbers and may be extended to other types materials.

Rapid and effective treatment of chronic osteomyelitis by conductive network-like MoS2/CNTs through multiple reflection and scattering enhanced synergistic therapy

Staphylococcus aureus (S. aureus)-infected chronic osteomyelitis (COM) is one of the most devastating infectious diseases with a high recurrence rate, often leading to amputation and even death. It is incurable by all the current strategies involving the clinical use of radical debridement and systemic intravenous antibiotics. Here, we reported on a microwave (MW)-assisted therapy for COM by constructing a heterojunction formed by flake nanoflower-shaped molybdenum disulfide (MoS2) and tubular carbon nanotubes (CNTs). This composite could achieve a combination of MW thermal therapy (MTT) and MW dynamic therapy (MDT) to accurately and rapidly treat COM with deep tissue infection. In vitro and in vivo experiments showed that MoS2/CNTs were effective in non-invasively treating S. aureus-induced COM due to the heat and reactive oxygen species (ROS) produced under MW irradiation. The mechanism of heat and ROS generation was explained by MW network vector analysis, density of states (DOS), oxygen adsorption energy, differential charge and finite element (FEM) under MW irradiation. Since the Fermi layer was mainly contributed by the Mo-4d and C-2P orbitals, MoS2/CNTs could store a large amount of charge and easily release more electrons. In addition, charge accumulation and dissipation motion were strong on the surface of and inside MoS2/CNTs because of electromagnetic hot spots, resulting in the spilling out of a great deal of high-energy electrons. Due to the low oxygen adsorption energy of MoS2/CNTs-O2, these high-energy electrons combined further with the adsorbed oxygen to produce ROS.

Two-Dimensional Cr5Te8@Graphite Heterostructure for Efficient Electromagnetic Microwave Absorption

Two-dimensional (2D) transition metal chalcogenides (TMCs) hold great promise as novel microwave absorption materials owing to their interlayer interactions and unique magnetoelectric properties. However, overcoming the impedance mismatch at the low loading is still a challenge for TMCs due to the restricted loss pathways caused by their high-density characteristic. Here, an interface engineering based on the heterostructure of 2D Cr5Te8 and graphite is in situ constructed via a one-step chemical vapor deposit to modulate impedance matching and introduce multiple attenuation mechanisms. Intriguingly, the Cr5Te8@EG (ECT) heterostructure exhibits a minimum reflection loss of up to - 57.6 dB at 15.4 GHz with a thin thickness of only 1.4 mm under a low filling rate of 10%. The density functional theory calculations confirm that the splendid performance of ECT heterostructure primarily derives from charge redistribution at the abundant intimate interfaces, thereby reinforcing interfacial polarization loss. Furthermore, the ECT coating displays a remarkable radar cross section reduction of 31.9 dB m2, demonstrating a great radar microwave scattering ability. This work sheds light on the interfacial coupled stimulus response mechanism of TMC-based heterogeneous structures and provides a feasible strategy to manipulate high-quality TMCs for excellent microwave absorbers.

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.

Graphene-like structure of bio-carbon with CoFe Prussian blue derivative composites for enhanced microwave absorption

Traditional carbon materials such as graphene are often applied in the field of electromagnetic wave (EMW) absorption but they have unbalanced impedance matching and high conductivity. Bio-carbon with graphene-like structure derived from apples has many advantages over graphene: it can be prepared in large quantities and the abundant heteroatoms present in the lattice can provide many polarization phenomena. Herein, Prussian blue analogue (PBA) as a source of magnetic component was combined with bio-carbon or reduced graphene oxide (rGO) to study the EMW absorption properties. The fabricated BC/CFC-12-7 displayed performance with a minimum reflection loss (RLmin) of -72.57 dB and a wide effective absorption bandwidth (EAB) of 5.25 GHz with an ultra-thin and nearly equal matching thickness at 1.61 mm. The results show that the good EMW absorption property of bio-carbon composites comes from good conduction loss, large relaxation polarization loss especially from pyridinic-N, and better impedance matching. The optimized radar cross section is found to be -33.55 dB m2 in the far-field condition using CST. This work explored the advantages of bio-carbon as a novel EMW absorbing material compared with graphene and provided ideas for realizing high-performance EMW absorbing materials in the future.

Broadband electromagnetic wave absorption using pure carbon aerogel by synergistically modulating propagation path and carbonization degree

Carbon materials were widely used as electromagnetic (EM) wave absorption due to their advantages of light weight, environmental resistance and high electrical conductivity. However, conventional means were typically available by combining carbon and other materials to achieve effective absorption. Herein, a novel strategy using pure carbon aerogel with oriented structure was reported to enhance the EM wave absorption by synergistically modulating the wave propagation path and carbonization degree. The aerogel contained proposed modified carbon nanofibers (MCNF) derived from bacterial cellulose (BC), and core-shell carbon nanofibers @ reduced oxide graphene (CNF@RGO). The oriented structure was induced by the temperature field, which manifests anisotropic EM constitutive parameters (εx ≠ εz) at different directions of incident wave. The carbonization degree was adjusted by varying the carbonization temperature. At the carbonization temperature of 700 °C, the maximum reflection loss and effective absorption bandwidth reached -53.94 dB and 7.14 GHz, respectively, enabling the aerogel to outperform its previous counterparts. To clarify the EM wave mode-of-action in conjunction, physical models of the aerogel were established in addition to finite element simulation and theoretical analysis. Notably, the aerogel with a density of 3.6 mg/cm3 featured ultra-light weight, superhydrophobicity, superior compressibility, and thermal insulation. Our work offers an efficient strategy for designing broadband and multifunctional EM wave absorption materials (EWAMs), promising great potentials in complex stealth equipment.

Microwave-Responsive Flexible Room-Temperature Phosphorescence Materials Based on Poly(vinylidene fluoride) Polymer

The development of flexible, room-temperature phosphorescence (RTP) materials remains challenging owing to the quenching of their unstable triplet excitons via molecular motion. Therefore, a polymer matrix with Tg higher than room temperature is required to prevent polymer segment movement. In this study, a RTP material was developed by incorporating a 4-biphenylboronic acid (BPBA) phosphor into a poly(vinylidene fluoride) (PVDF) matrix (Tg =-27.1 °C), which exhibits a remarkable UV-light-dependent oxygen consumption phosphorescence with a lifetime of 1275.7 ms. The adjustable RTP performance is influenced by the crystallinity and polymorph (α, β, and γ phases) fraction of PVDF, therefore, the low Tg of the PVDF matrix enables the polymeric segmental motion upon microwave irradiation. Consequently, a reduction in the crystallinity and an increase in the α phase fraction in PVDF film induces RTP after 2.45 GHz microwave irradiation. These findings open up new avenues for constructing crystalline and phase-dependent RTP materials while demonstrating a promising approach toward microwave detection.

Impact mechanisms of aggregation state regulation strategies on the microwave absorption properties of flexible polyaniline

In the field of electromagnetic (EM) wave absorption, intrinsic conductive polymers with conjugated long-chain structures, such as polyaniline (PANI) and polypyrrole (PPy), have gained widespread use due to their remarkable electrical conductivity and loss ability. However, current research in this area is limited to macroscopic descriptions of the absorption properties of these materials and the contribution of various components to the absorption effect. There has been insufficient exploration of the impact mechanisms of polymer aggregation states on the material's absorption performance and mechanism. To address this, a series of flexible PANI sponge absorbers with different molecular weights and aggregation states were prepared. By carefully controlling the crystallinity and other aggregation characteristics of PANI through the adjustment of its preparation conditions, we were able to influence its electrical conductivity and electromagnetic parameters, thereby achieving control over the material's absorption properties. The resulting PANI sponge absorbers exhibited an effective absorption bandwidth (EAB) that covered the entire X-band at a thickness of 3.2 mm. This study comprehensively explores the absorption mechanisms of conductive polymer absorbers, starting from the microstructure of PANI, and providing a more complete theoretical support for the research and promotion of polymer absorbers.

Multiphase Interfacial Regulation Based on Hierarchical Porous Molybdenum Selenide to Build Anticorrosive and Multiband Tailorable Absorbers

Electromagnetic wave (EMW) absorbing materials have an irreplaceable position in the field of military stealth as well as in the field of electromagnetic pollution control. And in order to cope with the complex electromagnetic environment, the design of multifunctional and multiband high efficiency EMW absorbers remains a tremendous challenge. In this work, we designed a three-dimensional porous structure via the salt melt synthesis strategy to optimize the impedance matching of the absorber. Also, through interfacial engineering, a molybdenum carbide transition layer was introduced between the molybdenum selenide nanoparticles and the three-dimensional porous carbon matrix to improve the absorption behavior of the absorber. The analysis indicates that the number and components of the heterogeneous interfaces have a significant impact on the EMW absorption performance of the absorber due to mechanisms such as interfacial polarization and conduction loss introduced by interfacial engineering. Wherein, the prepared MoSe2/MoC/PNC composites showed excellent EMW absorption performance in C, X, and Ku bands, especially exhibiting a reflection loss of - 59.09 dB and an effective absorption bandwidth of 6.96 GHz at 1.9 mm. The coordination between structure and components endows the absorber with strong absorption, broad bandwidth, thin thickness, and multi-frequency absorption characteristics. Remarkably, it can effectively reinforce the marine anticorrosion property of the epoxy resin coating on Q235 steel substrate. This study contributes to a deeper understanding of the relationship between interfacial engineering and the performance of EMW absorbers, and provides a reference for the design of multifunctional, multiband EMW absorption materials.

Anion Exchange of Metal Particles on Carbon-Based Skeletons for Promoting Dielectric Equilibrium and High-Efficiency Electromagnetic Wave Absorption

The combination of carbon materials and magnetic elements is considered as an effective strategy to obtain high-performance electromagnetic wave (EMW) absorption materials. However, using nanoscale regulation to the optimization of composite material dielectric properties and enhanced magnetic loss properties is facing significant challenges. Here, the dielectric constant and magnetic loss capability of the carbon skeleton loaded with Cr compound particles are further tuned to enhance the EMW absorption performance. After 700 °C thermal resuscitation of the Cr3-polyvinyl pyrrolidone composite material, the chromium compound is represented as a needle-shaped structure of nanoparticles, which is fixed on the carbon skeleton derived from the polymer. The size-optimized CrN@PC composites are obtained after the substitution of more electronegative nitrogen elements using an anion-exchange strategy. The minimum reflection loss value of the composite is -105.9 dB at a CrN particle size of 5 nm, and the effective absorption bandwidth is 7.68 GHz (complete Ku-band coverage) at 3.0 mm. This work overcomes the limitations of impedance matching imbalance and magnetic loss deficiency in carbon-based materials through size tuning, and opens a new way to obtain carbon-based composites with ultra-high attenuation capability.

Interfacial and Defect Polarization Enhanced Microwave Noninvasive Therapy for Staphylococcus aureus-Infected Chronic Osteomyelitis

Chronic osteomyelitis (COM), is a long-term, constant, and intractable disease mostly induced by infection from the invasion of Staphylococcus aureus (S. aureus) into bone cells. Here, we describe a highly effective microwave (MW) therapeutic strategy for S. aureus-induced COM based on the in situ growth of interfacial oxygen vacancy-rich molybdenum disulfide (MoS2)/titanium carbide (Ti3C2Tx) MXene with oxygen-deficient titanium dioxide (TiO2-x) on Ti3C2Tx (labeled as HU-MoS2/Ti3C2Tx) by producing reactive oxygen species (ROS) and heat. HU-MoS2/Ti3C2Tx produced heat and ROS, which could effectively treat S. aureus-induced COM under MW irradiation. The underlying mechanism determined by density functional theory (DFT) and MW vector network analysis was that HU-MoS2/Ti3C2Tx formed a high-energy local electric field under MW irradiation, consequently generating more high-energy free electrons to pass and move across the interface at a high speed and accelerate by the heterointerface, which enhanced the charge accumulation on both sides of the interface. Moreover, these charges were captured by the oxygen species adsorbed at the HU-MoS2/Ti3C2Tx interface to produce ROS. MoS2 facilitated multiple reflections and scattering of electromagnetic waves as well as enhanced impedance matching. Ti3C2Tx enhanced the conduction loss of electromagnetic waves, while functional groups induced dipole polarization to enhance attenuation of MW.

Integration of Multiple Heterointerfaces in a Hierarchical 0D@2D@1D Structure for Lightweight, Flexible, and Hydrophobic Multifunctional Electromagnetic Protective Fabrics

The development of wearable multifunctional electromagnetic protective fabrics with multifunctional, low cost, and high efficiency remains a challenge. Here, inspired by the unique flower branch shape of "Thunberg's meadowsweet" in nature, a nanofibrous composite membrane with hierarchical structure was constructed. Integrating sophisticated 0D@2D@1D hierarchical structures with multiple heterointerfaces can fully unleash the multifunctional application potential of composite membrane. The targeted induction method was used to precisely regulate the formation site and morphology of the metal-organic framework precursor, and intelligently integrate multiple heterostructures to enhance dielectric polarization, which improves the impedance matching and loss mechanisms of the electromagnetic wave absorbing materials. Due to the synergistic enhancement of electrospinning-derived carbon nanofiber "stems", MOF-derived carbon nanosheet "petals" and transition metal selenide nano-particle "stamens", the CoxSey/NiSe@CNSs@CNFs (CNCC) composite membrane obtains a minimum reflection loss value (RLmin) of -68.40 dB at 2.6 mm and a maximum effective absorption bandwidth (EAB) of 8.88 GHz at a thin thickness of 2.0 mm with a filling amount of only 5 wt%. In addition, the multi-component and hierarchical heterostructure endow the fibrous membrane with excellent flexibility, water resistance, thermal management, and other multifunctional properties. This work provides unique perspectives for the precise design and rational application of multifunctional fabrics.

Construction of Hollow Carbon Nanofibers with Graphene Nanorods as Nano-Antennas for Lower-Frequency Microwave Absorption

Electromagnetic (EM) wave absorbers at a lower-frequency region (2-8 GHz) require higher attenuation ability to achieve efficient absorption. However, the impedance match condition and attenuation ability are usually inversely related. Herein, one-dimensional hollow carbon nanofibers with graphene nanorods are prepared based on coaxial electrospinning technology. The morphology of graphene nanorods can be controlled by the annealing process. As the annealing time increased from 2 to 8 h, graphene nanospheres grew into graphene nanorods, which were catalyzed by Co catalysts derived from ZIF-67 nanoparticles. These nanorods can play the role of nano-antennas, which can guide EM waves into materials to enhance impedance match conditions. As a result, the carbon nanofibers with graphene nanorods possess a larger impedance match area with higher attenuation ability. The minimum reflection loss reaches -57.1 dB at a thickness of 4.6 mm, and the effective absorption bandwidth can cover almost both the S and C bands (2.4-8 GHz). This work contributes a meaningful perspective into the modulation of microwave absorption performance in the lower-frequency range.

Controlled formation of multiple core-shell structures in metal-organic frame materials for efficient microwave absorption

The design of metal-organic frameworks (MOF) derived composites with multiple loss mechanisms and multi-scale micro/nano structures is an important research direction of microwave absorbing materials. Herein, multi-scale bayberry-like Ni-MOF@N-doped carbon composites (Ni-MOF@NC) are obtained by a MOF assisted strategy. By utilizing the special structure of MOF and regulating its composition, the effective improvement of Ni-MOF@NC's microwave absorption performance has been achieved. The nanostructure on the surface of core-shell Ni-MOF@NC can be regulated and N doping on carbon skeleton by adjusting the annealing temperature. The optimal reflection loss of Ni-MOF@NC is -69.6 dB at 3 mm, and the widest effective absorption bandwidth is 6.8 GHz. This excellent performance can be attributed to the strong interface polarization caused by multiple core-shell structures, the defect and dipole polarization caused by N doping, and the magnetic loss caused by Ni. Meanwhile, the coupling of magnetic and dielectric properties enhances the impedance matching of Ni-MOF@NC. The work proposes a particular idea of designing and synthesizing an applicable microwave absorption material that possesses excellent microwave absorption performance and promising application potential.

Construction of Self-Assembly Based Tunable Absorber: Lightweight, Hydrophobic and Self-Cleaning Properties

Although multifunctional aerogels are expected to be used in applications such as portable electronic devices, it is still a great challenge to confer multifunctionality to aerogels while maintaining their inherent microstructure. Herein, a simple method is proposed to prepare multifunctional NiCo/C aerogels with excellent electromagnetic wave absorption properties, superhydrophobicity, and self-cleaning by water-induced NiCo-MOF self-assembly. Specifically, the impedance matching of the three-dimensional (3D) structure and the interfacial polarization provided by CoNi/C as well as the defect-induced dipole polarization are the primary contributors to the broadband absorption. As a result, the prepared NiCo/C aerogels have a broadband width of 6.22 GHz at 1.9 mm. Due to the presence of hydrophobic functional groups, CoNi/C aerogels improve the stability in humid environments and obtain hydrophobicity with large contact angles > 140°. This multifunctional aerogel has promising applications in electromagnetic wave absorption, resistance to water or humid environments.

Advances and mechanisms in polymer composites toward thermal conduction and electromagnetic wave absorption

Polymer composites have essential applications in electronics due to their versatility, stable performance, and processability. However, with the increasing miniaturization and high power of electronics in the 5G era, there are significant challenges related to heat accumulation and electromagnetic wave (EMW) radiation in narrow spaces. Traditional solutions involve using either thermally conductive or EMW absorbing polymer composites, but these fail to meet the demand for multi-functional integrated materials in electronics. Therefore, designing thermal conduction and EMW absorption integrated polymer composites has become essential to solve the problems of heat accumulation and electromagnetic pollution in electronics and adapt to its development trend. Researchers have developed different approaches to fabricate thermal conduction and EMW absorption integrated polymer composites, including integrating functional fillers with both thermal conduction and EMW absorption functions and innovating processing methods. This review summarizes the latest research progress, factors that affect performance, and the mechanisms of thermal conduction and EMW absorption integrated polymer composites. The review also discusses problems that limit the development of these composites and potential solutions and development directions. The aim of this review is to provide references for the development of thermal conduction and EMW absorption integrated polymer composites.

High Performance Epoxy Composites Containing Nanofiller Modified by Plasma Bubbles

The thermal conductivity of polymer materials is a fundamental parameter in the field of high-voltage electrical insulation. When the operating frequency and power for electrical equipment or electronic devices increase significantly, the internal heat will increase dramatically, and the accumulation of heat will further lead to insulation failure and serious damage of the whole system. The addition of filler with high thermal conductivity into polymer is a common solution. However, the interfacial thermal resistance between filler and bulk materials is the major obstacle to improve thermal conductivity. Herein, in order to reduce the interfacial thermal resistance, nanofillers are modified by plasma technology. The surface modification of nano-Al₂O₃ is carried out using plasma bubbles with three atmospheres (Ar, Ar+O₂, air) as well as coupling agent. The situation of surface grafting before and after the modification is characterized using FTIR, XPS, and SEM. The effect of the mechanism of modification on the thermal conductivity and reaction pathway is investigated. The results showed that the thermal conductivity after plasma modification is increased significantly. Especially, the thermal conductivity is increased by 35% for the sample modified by Ar+O₂ atmosphere. This results because more hydroxyl is introduced on the filler surface by the plasma bubbles, which enhance the interface compatibility between filler and epoxy. In addition, surface insulation performance for the modified samples also is enhanced by 14%. This is associated with the change of surface resistance and trap distribution. These results provide potential support for the development of fabrication for high performance epoxy composites.

Regulation of Impedance Matching and Dielectric Loss Properties of N-Doped Carbon Hollow Nanospheres Modified With Atomically Dispersed Cobalt Sites for Microwave Energy Attenuation

The rational design of lightweight, broad-band, and high-performance microwave absorbers is urgently required for addressing electromagnetic pollution issue. Metal single atoms (M-SAs) absorbers receive considerable interest in the field of microwave absorption due to the unique electronic structures of M-SAs. However, the simultaneous engineering of the morphology and electronic structure of M-SAs based absorbers remains challenging. Herein, a template-assisted method is utilized to fabricate isolated Co-SAs on N-doped hollow carbon spheres (NHCS@Co-SAs) for high-performance microwave absorption. The combination of atomically dispersed Co sites and hollow supports endows NHCS@Co-SAs with excellent microwave absorption properties. Typically, at an ultralow filler content of 8 wt%, the minimum reflection loss and effective absorption bandwidth of the NHCS@Co-SAs are up to -44.96 dB and 5.25 GHz, respectively, while the absorbing thickness is only 2 mm. Theoretical calculations and experimental results indicate that the impedance matching characteristic and dielectric loss of the NHCSs can be tuned via the introduction of M-SAs, which are responsible for the excellent microwave absorption properties of NHCS@Co-SAs. This work provides an atomic-level insight into the relationship between the electronic states of absorbers and their microwave absorption properties for developing advanced microwave absorbers.

Electrospinning Mo-Doped Carbon Nanofibers as an Anode to Simultaneously Boost Bioelectrocatalysis and Extracellular Electron Transfer in Microbial Fuel Cells

The sluggish electron transfer at the interface of microorganisms and an electrode is a bottleneck of increasing the output power density of microbial fuel cells (MFCs). Mo-doped carbon nanofibers (Mo-CNFs) prepared with electrostatic spinning and high-temperature carbonization are used as an anode in MFCs here. Results clearly indicate that Mo₂C nanoparticles uniformly anchored on carbon nanowire, and Mo-doped anodes could accelerate the electron transfer rate. The Mo-CNF ΙΙ anode delivered a maximal power density of 1287.38 mW m^-2, which was twice that of the unmodified CNFs anode. This fantastic improvement mechanism is attributed to the fact that Mo doped on a unique nanofiber surface could enhance microbial colonization, electrocatalytic activity, and large reaction surface areas, which not only enable direct electron transfer, but also promote flavin-like mediated indirect electron transfer. This work provides new insights into the application of electrospinning technology in MFCs and the preparation of anode materials on a large scale.

Polyimide aerogel-derived amorphous porous carbon/crystalline carbon composites for high-performance microwave absorption

High-performance polyimide-based porous carbon/crystalline composite absorbers (PIC/rGO and PIC/CNT) were prepared by vacuum freeze-drying and high-temperature pyrolysis. The excellent heat resistance of polyimides (PIs) ensured the integrity of their pore structure during high-temperature pyrolysis. The complete porous structure improves the interfacial polarization and impedance-matching conditions. Furthermore, adding appropriate rGO or CNT can improve the dielectric losses and obtain good impedance-matching conditions. The stable porous structure and strong dielectric loss enable fast attenuation of electromagnetic waves (EMWs) inside PIC/rGO and PIC/CNT. The minimum reflection loss (RLmin) for PIC/rGO is -57.22 dB at 4.36 mm thickness. The effective absorption bandwidth (EABW, RL below -10 dB) for PIC/rGO is 3.12 GHz at 2.0 mm thickness. The RLmin for PIC/CNT is -51.20 dB at 2.02 mm thickness. The EABW for PIC/CNT is 4.08 GHz at 2.4 mm thickness. The PIC/rGO and PIC/CNT absorbers designed in this work have simple preparations and excellent EMW absorption performances. Therefore, they can be used as candidate materials in EMW absorbing materials.