Pea-like Fe/Fe3C Nanoparticles Embedded in Nitrogen-Doped Carbon Nanotubes with Tunable Dielectric/Magnetic Loss and Efficient Electromagnetic Absorption

Multiple heteroatom doped carbon nanocages with an open structure enabling superior electromagnetic wave absorption

In comparison with pure carbon materials, the introduction of heteroatoms and the construction of hollow nanostructures can significantly enhance electromagnetic wave absorption properties. Herein, a multiple heteroatom-doped open nanocages with an amorphous structure was successfully designed and prepared. The introduction of heteroatoms, including Zn, Co, and N, results in charge redistribution and the formation of localized polarization centers within the carbon matrix, consequently enhancing dielectric loss. Meanwhile, the synergistic interplay between heteroatoms and defects in the carbon layer further intensifies space charge accumulation and local electric field formation, leading to enhanced dielectric loss. Furthermore, the open-structured nanocage dramatically improves electromagnetic wave penetration depth and energy dissipation efficiency by lowering material density, promoting impedance matching, and providing multiple scattering pathways. Experimental findings indicate that optimized sample achieves a minimum reflection loss of -48.59 dB at a thickness of only 1.82 mm, and an effective absorption bandwidth of 5.92 GHz. This approach thus represents a promising structural design strategy for advancing the performance of lightweight carbon-based microwave absorbing materials.

One Heterogeneous Catalyst Drives Two Selective Fenton-like Reaction Modes for Sustainable Water Decontamination

Heterogeneous Fenton-like reactions based on nonradical reactive oxygen species (ROS) are desirable for selective water decontamination, and different pollutants coexisting in real scenarios necessitate a rational combination of multiple ROS for efficient and sustainable decontamination. However, the general one-catalyst-for-one-ROS strategy toward selective ROS generation inevitably renders the combinational process lengthy and cost ineffective. Herein, we developed a new approach to enable the separate but selective generation of two distinct ROS in one catalyst via peroxymonosulfate activation. The unique catalyst is comprised of a graphitic layer bottom-wrapped Fe@Fe3C encapsulated inside nitrogen-doped carbon nanotubes. The Fe3C shell facilitates selective formation of surface-bound FeIV═O with up to 96.0% selectivity, and the applied electric field could switch ROS generation toward free 1O2 with 90.5% selectivity, as enabled by C atoms adjacent to graphite N. One dual-site catalyst enables both high cumulative concentration for FeIV═O and 1O2 up to 16605 and 7674 μM at 30 min, respectively. Based on such a simple electricity on/off switch mode, a tandem process operated in one unit was proposed to efficiently degrade mixed pollutants of distinct adsorption properties. This study presents a simple but very effective strategy to modulate selective ROS generation that simplifies tandem Fenton-like systems for sustainable water decontamination.

Progress, Challenges and Prospects of Biomass-Derived Lightweight Carbon-Based Microwave-Absorbing Materials

The widespread use of electronic devices in daily life, industry and military has led to a large amount of electromagnetic pollution, which has become an increasingly serious security issue. To eliminate or mitigate such risks and hazards, various advanced microwave absorption technologies and materials have been reported. As a new type of microwave absorber, biomass-derived carbon-based materials have received extensive attention. They have the characteristics of low cost, easy preparation, high porosity and environmental friendliness while retaining the advantageous adjustable dielectric properties, high conductivity and good stability of traditional carbon materials. The development of biomass microwave-absorbing materials not only provides a new idea for solving electromagnetic radiation but also helps to create an environmentally friendly and harmonious environment. Herein, various biomass-derived carbon-based microwave-absorbing materials (MAMs) including plant shells, plant fibers and other potential biomass materials are generalized and discussed including their preparation technology, microstructure design and so on. The two critical factors affecting microwave absorption properties, impedance matching and attenuation characteristics, are analyzed in detail. Finally, the confronting challenges and future development prospects of biomass-based microwave-absorbing materials are pointed out.

Synthesis of a Leaf-Like Co/C Nanosheet for Efficient Microwave Absorption

Elaborate engineering of the microstructure of electromagnetic (EM) absorption materials affords infinite potential for achieving superior EM wave absorption performance. In this work, a leaf-like Co/C nanosheet was rationally fabricated by a facile pyrolysis of a CoZn-based zeolitic imidazolate framework-L (Co/Zn-ZIF-L) precursor. Herein, Co nanoparticles (NPs) are uniformly confined in the leaf-like porous carbon matrix, forming attractive heterostructures. A suitable 2D morphology and Co/C binary components endow the composite with superior impedance matching and synergetic EM losses for excellent microwave absorption and radar stealth performance. When the filler content is as low as 25 wt %, the strong absorption intensity of -47.6 dB is reached at a thickness of 2.1 mm, and a broad effective bandwidth of 4.9 GHz is achieved at a thickness of only 1.6 mm. At the detection theta of 0°, the maximum radar cross-sectional (RCS) reduction value reaches 17.9 dB·m2. Hence, it is expected that the leaf-like Co/C nanosheet exhibits significant advantages in the field of EM wave absorption and radar stealth, which paves the way for future exploration of high-performance EM wave absorption materials.

Synthesis, magnetic properties, biotoxicity and potential mechanism of modified nano zero-valent iron for decolorization of dye wastewater

SiO2-coated nano zero-valent iron (nZVI) has emerged as a fine material for the treatment of dye wastewater due to its large specific surface area, high surface activity, and strong reducibility. However, the magnetic properties based on which SiO2-coated nZVI (SiO2-nZVI) could effectively separate and recover from treated wastewater, and the biotoxicity analysis of degradation products of the dye wastewater treated by SiO2-nZVI remain unclear. In this study, SiO2-nZVI was synthesized using a modified one-step synthesis method. The SiO2-nZVI nanoparticles were characterized using Transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, Fully automatic specific surface and porosity analyzer, Vibrating sample magnetometer, and Zeta potential analyzer. The removal rate of methyl orange (MO) by SiO2-nZVI composite reached 98.35% when the degradation performance of SiO2-nZVI treating MO was optimized. Since SiO2-nZVI analysed by magnetic hysteresis loops had large saturation magnetization and strong magnetic properties, SiO2-nZVI exhibited excellent ferromagnetic behaviour. The analysis of the degradation products showed that the MO treated by SiO2-nZVI was converted into a series of intermediates, resulting in reducing the toxicity of MO. The potential mechanism of MO degradated by SiO2-nZVI was speculated through degradation process and degradation kinetics analysis. Overall, the SiO2-nZVI composite may be regarded as a promising catalyst for decolorization of dye wastewater.

Current progress and frontiers in three-dimensional macroporous carbon-based aerogels for electromagnetic wave absorption: a review

In the present era of rapid development in electronic information technology, electromagnetic (EM) pollution is increasingly receiving widespread concerns due to its potential threats to electronic devices and human health. EM wave absorbing materials (EWAMs) play an increasingly important role in preventing exposure to EM waves because they can attenuate incident EM waves through sustainable energy dissipation. Among the numerous EWAMs developed in recent years, three-dimensional (3D) macroporous carbon-based aerogels have been considered one of the most promising candidates as high-performance EWAMs not only due to their flexible component options and the beneficial synergies between their different components but also for their open skeletons, which provide a unique structural contribution to accelerating the consumption of EM waves. In this review, we focus on the current progress of 3D macroporous carbon-based aerogels toward EM absorption and highlight different strategies for their preparation, including biomass transformation, template method, hydrothermal/solvothermal self-assembly, polymer foaming, and metal-organic frameworks (MOFs) topological transformation. Moreover, we discuss and analyze the effects of composition, optimization and structural engineering on their EM absorption performances. After a comprehensive evaluation of the performance of 3D macroporous carbon-based aerogels, we further propose some challenges and perspectives for the development of 3D macroporous carbon-based aerogels, and envision their broad application prospects in the future.

Two-phase magnetic nanospheres with magnetic coupling effect encapsulated in porous carbon to achieve lightweight and efficient microwave absorbers

Component selection is crucial for microwave absorbents. Multi-component absorbers are increasingly useful and can be prepared through the rational design and control of various electrical, magnetic, and other auxiliary components. In this paper, Ni3Fe/NiFe2O4 nanospheres with two-phase magnetism were designed for use as a multi-component absorber. Specifically, a Ni3Fe/ NiFe2O4@SPC composite with 3D networks was successfully fabricated by hydrothermal method, high-temperature carbonization for activation, and electrostatic self-assembly. The contact interface and coupling effect between the two magnetic components can promote the attenuation of electromagnetic waves. Moreover, the introduction of porous carbon successfully inhibits the easy aggregation of the magnetic particles. Impressively, with a filling load of 10 wt%, the optimal RL of the prepared Ni3Fe/NiFe2O4@SPC composite reaches -60.6 dB, and the effective absorption bandwidth is 5.2 GHz at 2 mm. The combination of two magnetic components and porous carbon in this multiphase microwave-absorbing composite demonstrates a feasible strategy for designing efficient microwave absorbers in the future.

Ultrafine Ir nanoparticles anchored on carbon nanotubes as efficient bifunctional oxygen catalysts for Zn-air batteries

Ultrafine iridium particles anchored on nitrogen-doped CNTs were obtained from Ir(ppy)3 and CNTs using a simple annealing method and acted as highly efficient bifunctional oxygen catalysts for Zn-air batteries. A synergistic effect, efficient *OH adsorption and rapid *OOH deprotonation were demonstrated from in situ FTIR spectroscopy, EIS and activation energy measurements.

Data-Driven oriented diatomic doping strategy to customize frequency dispersion for considerable microwave absorption

The electromagnetic (EM) parameters are the key factors to decode the complex microwave absorption properties, including matching thickness, absorption bandwidth and intensity. Numerous works hence have been focused on optimizing EM parameters to reinforce the comprehensive absorption performance, while most of the adopted experimental means still remain in sporadic and random attempts. In this work, the data-driven approach is first employed to forecast that a fierce frequency-dispersion of permittivity is necessary for the broad absorption, and the appropriate magnetic component can mitigate this elusive trend of required permittivity. Oriented by the simulated results, the B/N diatomic doped C/Fe3C magnetoelectric composites are successfully constructed, aiming at the precise regulation of electronic properties to achieve these specially customized EM parameters by forming multi-polarization resonances. The results demonstrate that the introduction of N defects and B defects could enrich the types of dipole pairs (CN, C-B, CNB, vacancy, etc.) and thus activate multi-polarization behavior. The charge density differences calculated by the first-principle further demonstrate that the occupation of B for C bonded with Pyridinic-N and Pyrrolic-N contributes to intense polarization behaviors over the lower frequency range. As a result, excellent microwave absorption properties can be finally achieved with an effective absorbing bandwidth reaching 7.2 GHz at 2.1 mm, implying that the joint use of data-driven and doping engineering strategies to customize frequency dispersion characteristics provides precious guidelines for boosting microwave absorption performance.

Hierarchical Fe-Co@TiO2 with Incoherent Heterointerfaces and Gradient Magnetic Domains for Electromagnetic Wave Absorption

Induced polarization response and integrated magnetic resonance show prosperous advantages in boosting electromagnetic wave absorption but still face huge challenges in revealing the intrinsic mechanism. In this work, we propose a self-confined strategy to construct hierarchical Fe-Co@TiO2 microrods with numerous incoherent heterointerfaces and gradient magnetic domains. The results demonstrate that the use of polyvinylpyrrolidone (PVP) coating is crucial for the subsequent deposition of Co-zeolitic imidazolate frameworks (ZIF-67), the distance of ordered arranged metal ions manipulates the size of magnetic domains, and the pyrolysis of PVP layers restricts the eutectic process of Fe-Co alloys to some extent. As a result, these introduced lattice defects, oxygen vacancies, and incoherent heterointerfaces inevitably generate a strong polarization response, and the regulated gradient magnetic domains realize integrated magnetic resonance, including macroscopic magnetic coupling, long-range magnetic diffraction, and nanoscale magnetic bridge connection, and both of the intrinsic mechanisms in dissipating electromagnetic energy are quantitatively clarified by Lorentz off-axis electron holography. Owing to the cooperative merits, the Fe-Co@TiO2 absorbents exhibit enhanced absorption intensity and strong absorption bandwidth. This study inspires us to develop a generalized strategy for manipulating the size of magnetic domains, and the integrated magnetic resonance theory provides a versatile methodology in clarifying magnetic loss mechanism.

State-of-the-art in carbides/carbon composites for electromagnetic wave absorption

Electromagnetic wave absorbing materials (EWAMs) have made great progress in the past decades, and are playing an increasingly important role in radiation prevention and antiradar detection due to their essential attenuation toward incident EM wave. With the flourish of nanotechnology, the design of high-performance EWAMs is not just dependent on the intrinsic characteristics of single-component medium, but pays more attention to the synergistic effects from different components to generate rich loss mechanisms. Among various candidates, carbides and carbon materials are usually labeled with the features of chemical stability, low density, tunable dielectric property, and diversified morphology/microstructure, and thus the combination of carbides and carbon materials will be a promising way to acquire new EWAMs with good practical application prospects. In this review, we introduce EM loss mechanisms related to dielectric composites, and then highlight the state-of-the-art progress in carbides/carbon composites as high-performance EWAMs, including silicon carbide/carbon, MXene/carbon, molybdenum carbide/carbon, as well as some uncommon carbides/carbon composites and multicomponent composites. The critical information regarding composition optimization, structural engineering, performance reinforcement, and structure-function relationship are discussed in detail. In addition, some challenges and perspectives for the development of carbides/carbon composites are also proposed after comparing the performance of some representative composites.

Construct of CoZnO/CSP biomass-derived carbon composites with broad effective absorption bandwidth of 7.2 GHz and excellent microwave absorption performance

Biomass-carbon materials have excellent electromagnetic wave attenuation properties, which is one of the essential factors for developing ultra-thin matched-thickness, and high-performance microwave absorption materials. This study reports a two-step procedure consisting of carbonization and subsequent in-situ growth for preparing a wrinkle-like multilayer biomass-derived composites with magnetic Co particles and ZnO particles (CoZnO/C-X). The synergistic effect of a wrinkle-like multilayer structure and Co and ZnO particles, as well as the existence of many heterogeneous interfaces in the composites structure, and efficiently creates multiple scattering and reflections, which gives the composites the strong microwave absorption properties. The minimum reflection loss value (RL_min) of CoZnO/C-X reaches - 54.90 dB with a thickness of 1.8 mm, and the effective absorption bandwidth (lower than - 10 dB) is 7.2 GHz covering from 10.8 GHz to18.0 GHz with matching thickness of 2.0 mm. Furthermore, the reasonable dielectric/magnetic losses, optimized impedance matching and enhanced polarization loss play an indispensable role among improving microwave absorption performance. Thus, this result provides a good potential method for preparation of magnetic particle/metal oxide/biomass-derived carbon microwave absorbing structural materials.

Synthesis of a one-dimensional carbon nanotube-decorated three-dimensional crucifix carbon architecture embedded with Co7Fe3/Co5.47N nanoparticles for high-performance microwave absorption

Low-dimensional cell-decorated three-dimensional (3D) hierarchical structures are considered excellent candidates for achieving remarkable microwave absorption. In the present work, a one-dimensional (1D) carbon nanotube (CNT)-decorated 3D crucifix carbon framework embedded with Co₇Fe₃/Co_5.47N nanoparticles (NPs) was fabricated by the in-situ pyrolysis of a trimetallic metal-organic framework (MOF) precursor (ZIF-ZnFeCo). Co₇Fe₃/Co_5.47N NPs were uniformly dispersed on the carbon matrix. The 1D CNT nanostructure was well regulated on the 3D crucifix surface by changing the pyrolysis temperature. The synergistic effect of 1D CNT and the 3D crucifix carbon framework increased the conductive loss, and Co₇Fe₃/Co_5.47N NPs induced interfacial polarization and magnetic loss; thus, the composite manifested superior microwave absorption performance. The optimum absorption intensity was -54.0 dB, and the effective absorption frequency bandwidth reached 5.4 GHz at a thickness of 1.65 mm. The findings of this work could provide significant guidance for the fabrication of MOF-derived hybrids for high-performance microwave absorption applications.

Bird-Nest-Like Multi-Interfacial MXene@SiCNWs@Co/C Hybrids with Enhanced Electromagnetic Wave Absorption

Newly emerged two-dimensional transition metal carbides and/or nitrides (MXenes) have attracted considerable interest in the field of electromagnetic wave absorption, but their excessive conductivity and single loss mechanism limit their applicability. Herein, an MXene decorated with SiC_NWs@Co/C was prepared by in situ growth and carbonization processes, followed by electrostatic self-assembly. The electromagnetic wave absorption performance of MXene@SiC_NWs@Co/C with a bird-nest-like structure could be effectively regulated and optimized by changing the proportion of MXene and SiC_NWs@Co/C. The prepared MXene@SiC_NWs@Co/C hybrid absorbers reveal superior impedance matching, complementary dissipation mechanism, and plentiful heterointerfaces. Profiting from the synergy of abovementioned factors, the resultant MXene@SiC_NWs@Co/C absorber exhibits an optimum reflection loss (RL) value of -76.5 dB at 6.36 GHz under a thickness of 3.9 mm and broad effective absorption bandwidth (EAB, RL ≤ -10 dB) of 6.2 GHz (11.8-18.0 GHz) with a thickness of only 2.0 mm, covering the entire Ku band. This work offers new insights into designing and fabricating highly efficient MXene-based electromagnetic absorbers.

Autogenous and Tunable CNTs for Enhanced Polarization and Conduction Loss Enabling Sea Urchin-Like Co3ZnC/Co/C Composites with Excellent Microwave Absorption Performance

ZIF-67-derived magnetic metal/carbon composites are considered prospective candidates for use as microwave absorption (MA) materials owing to their magnetoelectric synergy. However, the structure of ZIF-67-derived MA materials mainly depends on the morphology and composition of pristine metal-organic frameworks (MOFs), and their microstructures lack a rational design. Herein, a multidimensional sea urchin-like carbon nanotubes (CNTs)-grafted carbon polyhedra-encapsulated Co₃ZnC/Co nanoparticle composite was prepared by one-step catalytic pyrolysis of ZIF-67/ZnO using a rational structural design. The autogenous and tunable CNTs obtained with the assistance of zinc evaporation not only overcome the limitation of homogeneous dispersion but also endow the Co₃ZnC/Co/C composite with outstanding MA properties owing to the conduction loss provided by CNTs, polarization loss caused by multiple components, and electromagnetic wave trap composed of a special sea urchin-like structure. Consequently, the minimum reflection loss of ZZ_0.1-600 reaches -60.3 dB at 1.6 mm, the maximum absorption bandwidth of ZZ_0.05-600 is 6.24 GHz (covering nearly the entire Ku band) at 1.9 mm, and the structure has a low weight ratio (30 wt %). Compared with Z-600 and pure ZnO, the MA performance of the sea urchin-like Co₃ZnC/Co/C composite obtained by rational structural design has been greatly improved; this strategy offers a new approach for optimizing the MA performance of materials according to their structural design.

In Situ Growth of Nitrogen-Doped Carbon Nanotubes Based on Hierarchical Ni@C Microspheres for High Efficiency Bisphenol A Removal through Peroxymonosulfate Activation

N-doped carbon nanotubes (NCNTs) are promising metal-free heterogeneous catalysts toward peroxymonosulfate (PMS) activation in advanced oxidation processes for wastewater remediation. However, conventional CNTs always suffer from serious agglomeration and low N content, which renders their design synthesis as an important topic in the related field. With hierarchical Ni@C microspheres as a nutritious platform, we have successfully induced in situ growth of NCNTs on their surface by feeding melamine under high-temperature inert atmospheres. These as-grown NCNTs with a small diameter (ca. 20 nm) are firmly rooted in Ni@C microspheres and present loose accumulation on their surface, and their relative content can be tailored easily by manipulating the mass ratio of melamine to Ni@C microspheres. The investigation on bisphenol A (BPA) removal reveals that the loading amount of NCNTs affects the catalytic performance greatly, and the optimum ratio of melamine to Ni@C microspheres is 5.0 because the corresponding MNC-5.0 possesses sufficient surface N sites and moderate electron transfer, resulting in powerful PMS activation and sufficient utilization of reactive oxidative species (ROS). MNC-5.0 also addresses its advantages as compared with other NCNTs from post treatment and spontaneous growth strategies. The primary ROS responsible for BPA degradation are identified as hydroxyl radical, sulfate radical, superoxide radical, and singlet oxygen through quenching experiments and electron paramagnetic resonance, and the corresponding catalytic mechanism is also put forward based on these results.

1D Colloidal chains: recent progress from formation to emergent properties and applications

Integrating nanoscale building blocks of low dimensionality (0D; i.e., spheres) into higher dimensional structures endows them and their corresponding materials with emergent properties non-existent or only weakly existent in the individual building blocks. Constructing 1D chains, 2D arrays and 3D superlattices using nanoparticles and colloids therefore continues to be one of the grand goals in colloid and nanomaterial science. Amongst these higher order structures, 1D colloidal chains are of particular interest, as they possess unique anisotropic properties. In recent years, the most relevant advances in 1D colloidal chain research have been made in novel synthetic methodologies and applications. In this review, we first address a comprehensive description of the research progress concerning various synthetic strategies developed to construct 1D colloidal chains. Following this, we highlight the amplified and emergent properties of the resulting materials, originating from the assembly of the individual building blocks and their collective behavior, and discuss relevant applications in advanced materials. In the discussion of synthetic strategies, properties, and applications, particular attention will be paid to overarching concepts, fresh trends, and potential areas of future research. We believe that this comprehensive review will be a driver to guide the interdisciplinary field of 1D colloidal chains, where nanomaterial synthesis, self-assembly, physical property studies, and material applications meet, to a higher level, and open up new research opportunities at the interface of classical disciplines.

Dimensional Design and Core-Shell Engineering of Nanomaterials for Electromagnetic Wave Absorption

Electromagnetic (EM) wave absorption materials possess exceptionally high EM energy loss efficiency. With vigorous developments in nanotechnology, such materials have exhibited numerous advanced EM functions, including radiation prevention and antiradar stealth. To achieve improved EM performance and multifunctionality, the elaborate control of microstructures has become an attractive research direction. By designing them as core-shell structures with different dimensions, the combined effects, such as interfacial polarization, conduction networks, magnetic coupling, and magnetic-dielectric synergy, can significantly enhance the EM wave absorption performance. Herein, the advances in low-dimensional core-shell EM wave absorption materials are outlined and a selection of the most remarkable examples is discussed. The derived key information regarding dimensional design, structural engineering, performance, and structure-function relationship are comprehensively summarized. Moreover, the investigation of the cutting-edge mechanisms is given particular attention. Additional applications, such as oxidation resistance and self-cleaning functions, are also introduced. Finally, insight into what may be expected from this rapidly expanding field and future challenges are presented.

Hierarchical engineering of Large-caliber carbon Nanotube/Mesoporous Carbon/Fe3C nanoparticle hybrid nanocomposite towards Ultra-lightweight electromagnetic microwave absorber

The rational regulation of the magnetic-dielectric composition and microstructures of the absorber is considered an important approach to optimize both the impedance matching and the electromagnetic microwave attenuation ability. Along these lines, a novel architecture-controlled large-caliber carbon nanotube/mesoporous carbon/Fe₃C nanoparticle-based hybrid nanocomposites (CNT/C/Fe₃C), which were derived from the CNT/polyimide (PI) assemblies anchoring ferric oxide hydrate nanoprecipitates, are presented in this work. The proposed configurations were prepared by applying a cooperative co-assembly strategy and high-temperature pyrolysis procedure for the development of an ultra-lightweight electromagnetic microwave absorber. The employed hierarchically tubular heterogeneous architecture is composed of a highly graphited CNT supporting skeleton, polyimide assemblies-converted carbon interlayer with mesopores, and uniformly distributed magnetic Fe₃C nanoparticles. This unique hierarchical structure can not only induce multiple reflection and scattering effects of the incident electromagnetic microwave but also trigger dipole/interfacial polarization, ferromagnetic resonance and eddy current loss that are beneficial for the synergistic dielectric and magnetic loss. Moreover, the large-caliber CNT and mesoporous carbon interlayer can endow the as-prepared absorber with lightweight characteristics. Hence, the proposed CNT/C-EDA/Fe₃C-900 hybrid nanocomposite exhibits a minimum reflection loss (RL) of -48.4 dB at a matching thickness of 3.2 mm, and the effective absorption bandwidth (RL ≤ -10 dB) almost covers the whole X-band only with a 5 wt% filler loading. Undoubtedly, these encouraging outcomes will promote the development of hierarchical engineering techniques of novel magnetic-dielectric nanocomposite absorbers.

Hollow Beaded Fe3C/N-Doped Carbon Fibers toward Broadband Microwave Absorption

Microwave-absorbing materials have attracted enormous attention for electromagnetic (EM) pollution. Herein, hollow beaded Fe₃C/N-doped carbon fibers (Fe₃C/NCFs) were synthesized through convenient electrospinning and subsequent thermal treatment. The special hollow morphology of the samples is conducive to achieve lightweight and broadband microwave absorption properties. The thermal treatment temperatures exhibit a significant impact on conductivity and EM properties. The broadest effective absorption bandwidth (EAB) is 5.28 GHz at 2.16 mm when the thermal treatment temperature is 700 °C, and the EAB can cover 13.13 GHz with a tunable absorber thickness from 1.0 to 3.5 mm when the thermal treatment temperature is 750 °C. The excellent microwave absorption properties of the samples are due to the synergistic effect of impedance matching and strong EM energy attenuation abilities. Hence, the magnetic hollow beaded Fe₃C/NCFs are expected to be an attractive candidate material as a lightweight and efficient microwave absorber in the future.

Hierarchical Ti3 C2 Tx MXene/Carbon Nanotubes Hollow Microsphere with Confined Magnetic Nanospheres for Broadband Microwave Absorption

Hierarchical hollow structure with unique interfacial properties holds great potential for microwave absorption (MA). Ti₃ C₂ T_x MXene has been a hot topic due to rich interface structure, abundant defects, and functional groups. However, its overhigh permittivity and poor aggregation-resistance limit the further application. Herein, a hierarchical MXene-based hollow microsphere is prepared via a facile spray drying strategy. Within the microsphere, few-layered MXene nanosheets are separated by dispersed carbon nanotubes (CNTs), exposing abundant dielectric polarization interfaces. Besides, numerous magnetic Fe₃ O₄ nanospheres are uniformly dispersed and confined within nano-cavities between 1D network and 2D framework. Such a novel structure simultaneously promotes interfacial polarization by ternary MXene/CNTs/Fe₃ O₄ interfaces, enhances magnetic loss by microscale and nanoscale coupling network, enlarges conduction loss by MXene/CNTs dual-network, and optimizes impedance matching by hierarchical porous structure. Therefore, Fe₃ O₄ @Ti₃ C₂ T_x /CNTs composite achieves excellent MA property with a maximum reflection loss of -40.1 dB and an effective bandwidth of 5.8 GHz at the thickness of only 2 mm. This work demonstrates a feasible hierarchical structure design strategy for multi-dimension MXene composite to realize the high-efficiency MA performance.

Molybdenum Blue Preassembly Strategy to Design Bimetallic Fe0.54Mo0.73/Mo2C@C for Tunable and Low-Frequency Electromagnetic Wave Absorption

Advanced electromagnetic wave absorption nanomaterials can play an important role in addressing the issue of increasing electromagnetic pollution in wireless communication field. Herein, a series of coralloid bimetallic Fe0.54Mo0.73/Mo2C@C (FMC)...

Activating bimetallic ZIF-derived polymers using facile steam-etching for the ORR

An α-Fe2O3/Fe@NPC catalyst for the ORR is synthesized via a thermal shock reaction with precursors 1 and 2.

In situ construction of Fe3Al@Al2O3 core-shell particles with excellent electromagnetic absorption

To obtain Fe₃Al@Al₂O₃ core-shell absorbents, DO₃-type Fe₃Al powder was thermal treated in an argon atmosphere containing a trace amount of oxygen at different temperatures. Since Al atoms have a higher diffusion rate than that of the Fe atoms, Al atoms can migrate to the surface of the Fe₃Al particle and in-situ convert to Al₂O₃ nanoparticles during the thermal treatment process. With the increase of the thermal treatment temperature, the Al₂O₃ nanoparticles grow larger, exhibiting different microwave absorption properties. In particular, the Fe₃Al@Al₂O₃ obtained by controllable oxidation at 800 ℃ exhibits the best microwave absorption properties, with the minimum reflection loss of -34 dB at 11.5 GHz when the thickness is 2 mm, and the bandwidth below -10 dB is as broad as 6.7 GHz. Since a dielectric Al₂O₃ shell with a proper thickness can increase the impedance matching ratio of the Fe₃Al absorbent, more electromagnetic waves can come into the absorbent. In addition, the magnetic Fe₃Al core can efficiently attenuate the absorbed electromagnetic waves by dimensional resonance and natural resonance.

Composition Optimization and Microstructure Design in MOFs-Derived Magnetic Carbon-Based Microwave Absorbers: A Review

Magnetic carbon-based composites are the most attractive candidates for electromagnetic (EM) absorption because they can terminate the propagation of surplus EM waves in space by interacting with both electric and magnetic branches. Metal-organic frameworks (MOFs) have demonstrated their great potential as sacrificing precursors of magnetic metals/carbon composites, because they provide a good platform to achieve high dispersion of magnetic nanoparticles in carbon matrix. Nevertheless, the chemical composition and microstructure of these composites are always highly dependent on their precursors and cannot promise an optimal EM state favorable for EM absorption, which more or less discount the superiority of MOFs-derived strategy. It is hence of great importance to develop some accompanied methods that can regulate EM properties of MOFs-derived magnetic carbon-based composites effectively. This review comprehensively introduces recent advancements on EM absorption enhancement in MOFs-derived magnetic carbon-based composites and some available strategies therein. In addition, some challenges and prospects are also proposed to indicate the pending issues on performance breakthrough and mechanism exploration in the related field.

Dumbbell-Like Fe3O4@N-Doped Carbon@2H/1T-MoS2 with Tailored Magnetic and Dielectric Loss for Efficient Microwave Absorbing

Ferroferric oxide (Fe₃O₄)/C composites have received much attention as a result of converting electromagnetic waves to heat for harvesting efficient electromagnetic wave (EMW) absorbing performance. However, the practical EMW absorbing of these absorbers is still greatly hindered by the unmatched impedance properties and limited EMW absorbing ability. Tuning the morphologies at nanoscale and assembling the nanoarchitecture construction are essential to address this issue. Herein, dumbbell-like Fe₃O₄@N-doped carbon (NC)@2H/1T-MoS₂ yolk-shell nanostructures are rationally designed and fabricated via a facile etching and wet chemical synthesis strategy. By manipulating the etching time toward the magnetic Fe₃O₄ component, the dielectric and magnetic loss of absorbers could be well-tuned, thus achieving the optimized impedance characteristics. As a result, the maximum refection losses (RL_maxs) of Fe₃O₄@NC-9h and Fe₃O₄@NC-15h are -19.8 dB@7.9 GHz and -39.5 dB@8.3 GHz, respectively. Moreover, the MoS₂ nanosheets with a mixed 2H/1T phase anchored on Fe₃O₄@NC-15h (Fe₃O₄@NC-15h@MoS₂) further boost the RL_max to -68.9 dB@5.8 GHz with an effective absorbing bandwidth of ∼5.25 GHz. The tailored synergistic effect between dielectric and magnetic loss and the introduced interfacial polarization (Fe₃O₄@NC/MoS₂) are discussed to explain the drastically enhanced microwave absorbing ability. This work opens up new possibilities for effective manipulation of electromagnetic wave attenuation performance in magnetic-dielectric-type nanostructures.

Enhanced Microwave Absorbing Ability of Carbon Fibers with Embedded FeCo/CoFe2O4 Nanoparticles

In the face of increasingly severe electromagnetic (EM) wave pollution, the research of EM wave absorbing materials is an effective solution. To reduce the density of traditional absorbing materials, in this work, FeCo/CoFe₂O₄/carbon nanofiber composites were successfully prepared by electrospinning for the EM wave attenuation application. Benefiting from the loss ability of interface polarization, dipole polarization, and magnetic loss, the composites obtained a bandwidth of 5.0 GHz at a 1.95 mm thickness and an absorption peak of -52.3 dB. More importantly, the radar cross section (RCS) reduction of composite coatings calculated by ANSYS Electronics Desktop 2018 (HFSS) can reach 34.5 dBm², and the RCS value is almost less than -10 dBm² when the incident angle is greater than 20°, demonstrating great scattering ability of the material coating to EM waves. This work, combined with the exploration of the mechanism and the simulation analysis of the absorbing coating, will be of significance for the development of absorbing materials.

Carbon-Based MOF Derivatives: Emerging Efficient Electromagnetic Wave Absorption Agents

To tackle the aggravating electromagnetic wave (EMW) pollution issues, high-efficiency EMW absorption materials are urgently explored. Metal-organic framework (MOF) derivatives have been intensively investigated for EMW absorption due to the distinctive components and structures, which is expected to satisfy diverse application requirements. The extensive developments on MOF derivatives demonstrate its significantly important role in this research area. Particularly, MOF derivatives deliver huge performance superiorities in light weight, broad bandwidth, and robust loss capacity, which are attributed to the outstanding impedance matching, multiple attenuation mechanisms, and destructive interference effect. Herein, we summarized the relevant theories and evaluation methods, and categorized the state-of-the-art research progresses on MOF derivatives in EMW absorption field. In spite of lots of challenges to face, MOF derivatives have illuminated infinite potentials for further development as EMW absorption materials.

Tuning the Dielectric and Microwaves Absorption Properties of N-Doped Carbon Nanotubes by Boron Insertion

It is of great significance to regulate the dielectric parameters and microstructure of carbon materials by elemental doping in pursuing microwave absorption (MA) materials of high performance. In this work, the surface electronic structure of N-doped CNTs was tuned by boron doping, in which the MA performance of CNTs was improved under the synergistic action of B and N atoms. The B,N-doped carbon nanotubes (B,N-CNTs) exhibited excellent MA performance, where the value of minimum reflection loss was -40.04 dB, and the efficient absorption bandwidth reached 4.9 GHz (10.5-15.4 GHz). Appropriate conductance loss and multi-polarization loss provide the main contribution to the MA of B,N-CNTs. This study provides a novel method for the design of CNTs related MA materials.

Highly stretchable and self-foaming polyurethane composite skeleton with thermally tunable microwave absorption properties

Stretchable and lightweight polymer composite material possessing tunable microwave absorption (MA) properties under thermal radiations remain a significant challenge. Here, we proposed a facile strategy to fabricate stretchable, magnetic composite skeletons by incorporating the tadpole-like CNTs@Fe₃O₄nanoparticles into self-foaming polyurethane (PU) matrix and the electromagnetic responsive of CNTs@Fe₃O₄/PU composite foams with different CNTs contents under heating-cooling cycle in a temperature range of 253 -333 K were carefully investigated. Enhanced complex permittivity and shifting peak frequency were observed at elevated temperatures. For instance, the 70-CNTs@Fe₃O₄/PU sample with 15 wt% loading content at 333 K exhibits excellent MA properties including a minimum reflection loss (RL_m) of -66.9 dB and ultrabroad effective frequency bandwidth (RL ≤ -20 dB) of 9.98 GHz at the thickness of 1.58-3.37 mm. Meanwhile, great recoverability in terms of RL-fprofile was achieved in the process of thermal cooling back to 253 K. Such adjustable MA property was attributed to the well-matched impedance and dramatic attenuation ability, benefiting from the temperature-dependant electrical conductivity, abundant interfacial polarization and interior microcellular structures. Besides, the rising temperature increased the sample elongation and electrical conductivity with a slight sacrifice of maximum tensile strength. This stretchable PU skeleton with a unique assembly of CNTs and Fe₃O₄nanoparticles are expected to be promising candidates as smart absorbers for application in the harsh environments.

Fe/N co-doped mesoporous carbon derived from cellulose-based ionic liquid as an efficient heterogeneous catalyst toward nitro aromatic compound reduction reaction

Iron and nitrogen-doped carbon substances with abundant active sites that related to dispersion of heteroatom species (Fe and N) on the surface of carbonous structure, are promising choice for eco-friendly catalytic reactions. Herein, cellulose-based ionic liquid (IL) derivative not only employed as the both nitrogen and iron heteroatom precursors, but also has been used as the green and biodegradable substrate. The non-noble Fe-NC@550, was successfully fabricated by convenient carbonization of cellulose-based IL. Further, the FeCl₄^- anion was used as the iron precursor and also it has been applied to elevate the SSA (specific surface area) of catalyst (from 40.96 to 160.42 m²/g) due to the presence of chlorine. On the basis of several pertinent physicochemical and experimental outcomes, the structure of the catalyst was successfully proved in different synthetic steps. As expected, the Fe-NC@550 exhibited the substantial efficiency toward hydrogenation of nitroarenes with high TOF value and also remarkable reusability.

A Review on Metal-Organic Framework-Derived Porous Carbon-Based Novel Microwave Absorption Materials

The development of microwave absorption materials (MAMs) is a considerable important topic because our living space is crowed with electromagnetic wave which threatens human's health. And MAMs are also used in radar stealth for protecting the weapons from being detected. Many nanomaterials were studied as MAMs, but not all of them have the satisfactory performance. Recently, metal-organic frameworks (MOFs) have attracted tremendous attention owing to their tunable chemical structures, diverse properties, large specific surface area and uniform pore distribution. MOF can transform to porous carbon (PC) which is decorated with metal species at appropriate pyrolysis temperature. However, the loss mechanism of pure MOF-derived PC is often relatively simple. In order to further improve the MA performance, the MOFs coupled with other loss materials are a widely studied method. In this review, we summarize the theories of MA, the progress of different MOF-derived PC‑based MAMs, tunable chemical structures incorporated with dielectric loss or magnetic loss materials. The different MA performance and mechanisms are discussed in detail. Finally, the shortcomings, challenges and perspectives of MOF-derived PC‑based MAMs are also presented. We hope this review could provide a new insight to design and fabricate MOF-derived PC-based MAMs with better fundamental understanding and practical application.

Excellent, Lightweight and Flexible Electromagnetic Interference Shielding Nanocomposites Based on Polypropylene with MnFe2O4 Spinel Ferrite Nanoparticles and Reduced Graphene Oxide

In this work, various tunable sized spinel ferrite MnFe₂O₄ nanoparticles (namely MF20, MF40, MF60 and MF80) with reduced graphene oxide (RGO) were embedded in a polypropylene (PP) matrix. The particle size and structural feature of magnetic filler MnFe₂O₄ nanoparticles were controlled by sonochemical synthesis time 20 min, 40 min, 60 min and 80 min. As a result, the electromagnetic interference shielding characteristics of developed nanocomposites MF20-RGO-PP, MF40-RGO-PP, MF60-RGO-PP and MF80-RGO-PP were also controlled by tuning of magnetic/dielectric loss. The maximum value of total shielding effectiveness (SE_T) was 71.3 dB for the MF80-RGO-PP nanocomposite sample with a thickness of 0.5 mm in the frequency range (8.2–12.4 GHz). This lightweight, flexible and thin nanocomposite sheet based on the appropriate size of MnFe₂O₄ nanoparticles with reduced graphene oxide demonstrates a high-performance advanced nanocomposite for cutting-edge electromagnetic interference shielding application.

Rutile TiO2 Nanoparticles Encapsulated in a Zeolitic Imidazolate Framework-Derived Hierarchical Carbon Framework with Engineered Dielectricity as an Excellent Microwave Absorber

Aiming to solve the poor response of titanium dioxide (TiO₂) in the microwave frequency, versatile series of N-doped carbon (NC) components are employed to improve the conductivity and polarization strength of TiO₂-based composites. The bimetallic zeolitic imidazolate framework-derived TiO₂@NC complex (TNC-3) exhibits hierarchical microstructures and large-scale hetero-interfaces, whereas the pyrolysis composite of metal-polydopamine-coated TiO₂ (TNC-4) possesses the vesicle-like NC shell and bulk TiO₂ core. Thus, the optimal reflection loss and efficient absorption bandwidth of TNC-3 realize -44.0 dB at 3.0 mm and 5.4 GHz at only 2.0 mm of coating thickness, respectively. Nevertheless, the corresponding attenuation ability of TNC-4 is separately -24.3 dB and 4.8 GHz with a thickness of 5.0 and 2.0 mm, respectively. Importantly, the conduction and polarization loss can be enhanced by the large-scale interfacial contacts between nanoscale rutile nanoparticles and hierarchical graphitized carbon. Meanwhile, the superior performance of TNC-3 stems from the large proportion of pyridinic N and pyrrolic N, which provides asymmetric lone pairs to strengthen the dipole rotation. These results are of great value in constructing semiconductor-based complexes by carbon-coating engineering as functional materials.

Constructing and optimizing hollow ZnxFe3-xO4@polyaniline composites as high-performance microwave absorbers

In this study, a series of hollow Zn_xFe_3-xO₄@polyaniline composites (ZFO@PANI) were synthesized by a facile solvothermal process and followed by in-situ chemical oxidation polymerization method, and then evaluated as microwave absorption (MA) absorbers. The effect of ZFO content on the electrical conductivity, electromagnetic parameters and MA performance of the ZFO@PANI composites was also elaborately investigated. As anticipated, the optimized composites of S2 exhibits the minimum reflection loss (RL_min) of -59.44 dB at 11.04 GHz with a matching thickness of 2.31 mm, and the broadest effective absorption bandwidth (EAB, RL < -10 dB, >90% absorption) of up to 4.65 GHz (13.35-18.0 GHz) at 1.72 mm. Noticeably, by adjusting the thickness from 1.5 to 5.0 mm, it can be observed that its RL_min values are all much lower than -10 dB and the qualified EAB can cover the entire C, X and Ku bands. The enhanced MA performance of S2 is mainly due to the efficient synergistic effect between dielectric loss (PANI) and magnetic loss (ZFO nanosphere), and thus achieving the relative balance of impedance matching (appropriate ZFO content) and attenuation capability. Therefore, it has great prospect to be explored as attractive candidate in practical application.

Confining Tiny MoO2 Clusters into Reduced Graphene Oxide for Highly Efficient Low Frequency Microwave Absorption

Herein, a supermolecular-scale cage-confinement pyrolysis strategy is proposed to build two dielectric electromagnetic wave absorbents, in which MoO₂ nanoparticles are sandwiched uniformly between porous carbon shells and reduced graphene oxide (RGO). Both sandwich structures are derived from hybrid hydrogels doped by two different crosslinkers (with/without oxygen bridge), which can precisely confine Mo source (e.g., PMo₁₂ ). Without adding magnetic components, both absorbents exhibit excellent low frequency absorption performance in combination with electrically tunable ability and enhanced reflection loss value, which is superior over other relative 2D dielectric absorbers and satisfies the requirements of portable electronics. Notably, introducing oxygen bridges in the crosslinker generates a more stable confining configuration, which in turn renders its corresponding derivative exhibiting an extra multifrequency electromagnetic wave absorption trait. The intrinsic electromagnetic wave adjustment mechanism of the ternary hybrid absorbent is also explored. The result reveals that the elevated electromagnetic wave absorbing property is attributed to moderate attenuation constant and glorious impendence matching. The cage-confinement pyrolysis route to fabricate 2D MoO₂ -based dielectric electromagnetic wave absorbents opens a new path for the design of electromagnetic wave absorbents used in multi/low frequency.

An Easy Method of Synthesis CoxOy@C Composite with Enhanced Microwave Absorption Performance

Design of interface-controllable magnetic composite towards the wideband microwave absorber is greatly significance, however, it still remains challenging. Herein, we designed a spherical-like hybrids, using the Co3O4 and amorphous carbon as the core and shell, respectively. Then, the existed Co3O4 core could be totally reduced by the carbon shell, thus in CoxOy core (composed by Co and Co3O4). Of particular note, the ratios of Co and Co3O4 can be linearly tuned, suggesting the controlled interfaces, which greatly influences the interface loss behavior and electromagnetic absorption performance. The results revealed that the minimum reflection loss value (RLmin) of -39.4 dB could be achieved for the optimal CoxOy@C sample under a thin thickness of 1.4 mm. More importantly, the frequency region with RL < -10 dB was estimated to be 4.3 GHz, ranging from 13.7 to 18.0 GHz. The superior wideband microwave absorption performance was primarily attributed to the multiple interfacial polarization and matched impedance matching ability.

Oxygen-sulfur Co-substitutional Fe@C nanocapsules for improving microwave absorption properties

Heteroatom substitution has been investigated to be a feasible way to optimize microwave absorption properties of core-shell structural nanocapsules at gigahertz. Although dielectric capacity has been increased at specific frequency with substituted absorbents, its broadband absorption performance is still relatively poor ascribed to the low dipole oscillation amplitude of single substituted heteroatom. In this study we demonstrate that sulfur and oxygen co-substituted heterostructure leads to high microwave absorption property of core-shell structural Fe@C nanocapsules at broadened frequency range, comparable to the single sulfur substitutional Fe@C nanocapsules. Experimental characterizations coupled with first-principles calculations reveal that the microwave absorption enhancement is triggered by the sulfur-oxygen co-substitution, which results in the serious symmetry breaking and thus leads to the charge separation at the co-substituted area. In particular, the nanocapsules exhibt the minimum reflection loss capcacity R(dB) of -52 dB at 6.8 GHz and the bandwith for R(dB) <-20 dB is in the frequency range of 3.1-12.7 GHz. The present study not only offers a deep insight into the relationship between heteroatom and microwave absorption property, but also puts forward a mentality for further designing microwave absorbents.

Morphology Design of Co-electrospinning MnO-VN/C Nanofibers for Enhancing the Microwave Absorption Performances

To enhance microwave loss abilities, constructing composites with one-dimensional (1D) structure is an excellent scheme. In this work, a high-efficiency microwave absorber of MnO nanograins decorated vanadium nitride/carbon nanofibers (MnO-VN/C NFs) was successfully prepared for the first time via co-electrospinning technology and subsequent nitriding treatment. Studying in detail the specific relationship between nitriding time and the morphology of the as-prepared NFs, the precipitations of MnO nanoparticles with tailored structures were attached on the surface of VN/C NFs to optimize their electromagnetic parameters. When the nitriding time was 2.0 h at 600 °C, the MnO-VN/C NFs displayed good microwave absorption performances: the minimum reflection loss (RL) value was -63.2 dB at 8.8 GHz, and the bandwidth of RL < -10 dB was up to 6.4 GHz from 11.6 to 18 GHz at the thickness of 2.8 mm. Meanwhile, the absorption bandwidth (RL< -10 dB) could cover the whole X and Ku band by adjusting the thickness, respectively. The outstanding performances could be attributed to the good impedance matching and various loss pathways including conductive loss and interfacial and dipole polarizations. In these regards, MnO-VN/C NFs are likely to be utilized as a high-efficiency microwave absorber. And the strategy in this work can provide great help to design other 1D structural microwave absorbers with a broader absorbing band.

Sandwich-Like Fe&TiO2@C Nanocomposites Derived from MXene/Fe-MOFs Hybrids for Electromagnetic Absorption

Electromagnetic pollution has been causing a series of problems in people's life, and electromagnetic absorbers with lightweight and broad absorbing bandwidth properties are widely desired. In this work, novel sandwich-like 2D laminated Fe&TiO2 nanoparticles@C nanocomposites were rationally designed and successfully developed from the MXene-MOFs hybrids. The formation of Fe and rutile-TiO2 nanoparticles sandwiched by the two-dimensional carbon nanosheets provided strong electromagnetic energy attenuation and good impedance matching for electromagnetic wave (EMW) absorption. As expected, the nanocomposites achieved a broad effective absorption bandwidth of 6.5 GHz at a thickness of only 1.6 mm and the minimum reflection loss (RL) value of - 51.8 dB at 6.6 GHz with a thickness of 3 mm. This work not only provides a good design and fabricating concept for the laminated metal and functional nanoparticles@C nanocomposites with good EMW absorption, but also offers an important guideline to fabricate various two-dimensional nanocomposites derived from the MXene precursors.