Facile synthesis and excellent microwave absorption properties of FeCo-C core-shell nanoparticles

Exploring the Microstructural Effect of FeCo Alloy on Carbon Microsphere Deposition and Enhanced Electromagnetic Wave Absorption

The rational design of magnetic carbon composites, encompassing both their composition and microstructure, holds significant potential for achieving exceptional electromagnetic wave-absorbing materials (EAMs). In this study, FeCo@CM composites were efficiently fabricated through an advanced microwave plasma-assisted reduction chemical vapor deposition (MPARCVD) technique, offering high efficiency, low cost, and energy-saving benefits. By depositing graphitized carbon microspheres, the dielectric properties were significantly enhanced, resulting in improved electromagnetic wave absorption performances through optimized impedance matching and a synergistic effect with magnetic loss. A systematic investigation revealed that the laminar-stacked structure of FeCo exhibited superior properties compared to its spherical counterpart, supplying a higher number of exposed edges and enhanced catalytic activity, which facilitated the deposition of uniform and low-defect graphitized carbon microspheres. Consequently, the dielectric loss performance of the FeCo@CM composites was dramatically improved due to increased electrical conductivity and the formation of abundant heterogeneous interfaces. At a 40 wt% filling amount and a frequency of 7.84 GHz, the FeCo@CM composites achieved a minimum reflection loss value of -58.2 dB with an effective absorption bandwidth (fE) of 5.13 GHz. This study presents an effective strategy for developing high-performance EAMs.

Core-shell FeCo@carbon nanocages encapsulated in biomass-derived carbon aerogel: Architecture design and interface engineering of lightweight, anti-corrosion and superior microwave absorption

The development of multifunctional microwave absorbing materials for practical applications in complex environments is a challenging research hotspot. Herein, the core-shell structure FeCo@C nanocages were successfully anchored on the surface of biomass-derived carbon (BDC) from pleurotus eryngii (PE) via freeze-drying and electrostatic self-assembly process, achieving lightweight, anti-corrosive, and excellent absorption properties. The superior versatility benefits from the large specific surface area, high conductivity, three-dimensional cross-linked networks, and appropriate impedance matching characteristics. The as-prepared aerogel realizes a minimum reflection loss (RL_min) of -69.5 dB with a corresponding effective absorption bandwidth (EAB) of 8.6 GHz at 2.9 mm. Simultaneously, the computer simulation technique (CST) further proves that the multifunctional material can dissipate microwave energy in actual applications. More importantly, the special heterostructure of aerogel endows excellent resistance to acid, alkali, salt medium, allowing potential applications of the microwave absorbing materials under complex environmental conditions.

Hierarchical HCF@NC/Co Derived from Hollow Loofah Fiber Anchored with Metal-Organic Frameworks for Highly Efficient Microwave Absorption

Hierarchical electromagnetic wave (EMW) absorption materials with a dielectric-magnetic dual-loss mechanism are promising candidates for highly efficient EMW attenuation. Herein, hierarchical dielectric-magnetic composite hollow carbon fiber@nitrogen-doped carbon/Co (HCF@NC/Co) was successfully synthesized via in situ growth of two-dimensional (2D) Co metal-organic framework (MOF) (ZIF-67) nanosheets on the surface of hollow loofah fiber (HLF), followed by a calcination process, where the aggregation of carbonized MOFs was effectively avoided to construct a homogeneous hierarchical one-dimensional structure. Based on the advantages of the carbon/Co dielectric-magnetic dual-loss mechanism that results in good impedance matching and multiple polarization loss arising from the extensive heterointerfaces (e.g., HCF-NC/Co, air-carbon, nitrogen-carbon, and Co-carbon interfaces), dipole active sites (e.g., doped N, Co particle, and crystalline defects in graphitic carbon), and hierarchical porous structures, optimal EMW absorption performance of HCF@NC/Co is achieved through regulating the calcination temperature and filler content, where the HCF@NC/Co calcinated at 700 °C exhibits a minimum reflection loss (RL_min) value of -50.14 dB with only 14% filler loading and 2.25 mm thickness, and the maximum effective absorption bandwidth (EAB_max) also reaches 7.36 GHz. Meanwhile, adjustable EAB can also be achieved by optimizing the sample thickness, making it applicable in a wider frequency region. It is expected that our prepared HCF@NC/Co might shed light on designing lightweight and highly efficient EMW MOF-derived EMW absorbing materials.

A comparative study on the dielectric response and microwave absorption performance of FeNi-capped carbon nanotubes and FeNi-cored carbon nanoparticles

The mechanisms responsible for the dielectric response of C-based microwave absorbers remain a long-standing theoretical question. Uncovering these mechanisms is critical to enhance their microwave absorption performance. To determine how different C forms alter the dielectric response of C-based absorbers, FeNi-capped carbon nanotubes (FeNi-CNTs) and FeNi-cored carbon nanoparticles (FeNi-CNPs) are synthesized, and a comparative study of their dielectric responses is then carried out in this study. The as-synthesized FeNi-CNTs and FeNi-CNPs have similar magnetic properties and complex permeabilities, but differ in complex permittivities. It is shown that FeNi-CNTs have a much stronger dielectric loss than FeNi-CNPs. At a thickness of 2.8 mm, a low optimal reflection loss of -32.2 dB and a broad effective absorption bandwidth of 8.0 GHz are achieved for FeNi-CNTs. Meanwhile, equivalent circuit models reveal that the CNT network of the FeNi-CNTs could introduce an electrical inductance that can effectively improve its dielectric loss capability. This study demonstrates that designing a composite with a tailored C form and composition is a successful strategy for tuning its microwave absorption performance. Furthermore, the equivalent circuit modeling is an effective tool for analyzing the dielectric response of the microwave absorbers, as is expected to be applicable for other metal-C composites.

Synthesis and microwave absorption properties of Fe@carbon fibers

Composites of carbon and magnetic metal can overcome the eddy current effects and high density of traditional magnetic metals based on their synergistic loss mechanism and tunable electromagnetic properties. Herein, Fe@carbon fiber particles were synthesized by growing iron nanoflakes on the surface of carbon fibers via in situ reduction. The surface morphology, lattice structure and element composition of the synthesized Fe@carbon fibers were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy disperse spectroscopy (EDS) respectively. Based on these qualitative analyses, a possible growth mechanism was proposed for guide production. In order to investigate their electromagnetic absorbing properties, electromagnetic parameters of Fe@carbon fibers-paraffin composites have been evaluated by coaxial reflection/transmission technique. The Fe@carbon fibers-paraffin composites containing different particle contents were prepared to clarify the optimum material ratio. The results showed that the composite loaded with 30 wt% carbon fibers@Fe particles exhibited the most prominent microwave absorption, with strong absorption (maximum reflection loss of −39.8 dB), effective absorption bandwidth (2.9 GHz) and small thickness (1.5 mm).

The structure of iron nanosheets on the surface of carbon fiber improves the absorption characteristics of carbon fiber.

Trimetallic FeCoNi@C Nanocomposite Hollow Spheres Derived from Metal-Organic Frameworks with Superior Electromagnetic Wave Absorption Ability

Organic ligands and metal ions in the metal-organic frameworks (MOFs, a type of porous magnetic metal/carbon nanocomposites obtained through high-temperature carbonization) have caused widespread concerns in the field of microwave absorption because of the existence of various microwave loss mechanisms in these materials. However, MOF-driven microwave absorbing materials with high absorption intensity and wide absorption band still require further research and development. In this work, hollow sphere trimetallic FeCoNi@C microwave absorbing materials via high-temperature carbonization were obtained using FeCoNi-based MOF-74 (FeCoNi-MOF) as the precursor. The effects of different carbonization conditions on the microwave absorption properties of the materials were studied. FeCoNi-MOF-74 annealed at 700 °C showed superior microwave absorption capacity, where the RL value reached -64.75 dB at 15.44 GHz corresponding to the actual application thickness of the absorber (only 2.1 mm), and the minimum RL values reached -69.03 dB at 5.52 GHz. Furthermore, the as-prepared sample can fully cover the Ku band and X band at only 2.1 and 3.1 mm, respectively. The maximum EAB reached 8.08 GHz (9.92-18 GHz) when the thickness of the absorber was 2.47 mm. Such remarkable absorption performance is attributed to the synergetic effects between the multiple loss mechanisms of the FeCoNi@C, and the improved impedance matching characteristic came from the hollow sphere morphology.

Enhanced microwave-absorption with carbon-encapsulated Fe-Co particles on reduced graphene oxide nanosheets with nanoscale-holes in the basal plane

In this study, an Fe-Co alloy is coated with carbon and decorated on a holey reduced graphene oxide nanosheet (FeCo@C/HRGO) composite. The structure is synthesized using liquid-phase reduction and hydrothermal processes followed by high-temperature calcination. The FeCo@C/HRGO composite is identified and characterized using XRD, XPS, Raman spectroscopy, TEM, and SEM. This novel composite exhibits excellent electromagnetic-wave absorption properties. The maximum reflection loss for FeCo@C/HRGO reaches -76.6 dB at 16.64 GHz with a thickness of 1.7 mm. The R_L below -10 dB reaches 14.32 GHz for a thickness of 1.7-5.0 mm. This confirms that microwave absorption of FeCo@C can be substantially improved upon decoration with HRGO nanosheets.

Bimetallic MOF-derived porous CoNi/C nanocomposites with ultra-wide band microwave absorption properties

The CoNi bimetallic MOF-derived composites were synthesized in this work. The target product is composed of fine particles with uniformly distributed elements of Ni, Co, C. The CoNi/C-650 sample displays good microwave absorbing properties.

Optimizing the Electromagnetic Wave Absorption Performances of Designed Co3Fe7@C Yolk-Shell Structures

Due to the increasing demand for military and commercial applications, magnetic metal-based core@shell nanostructures have attracted extensive attention in the field of electromagnetic wave (EMW) absorption materials. To further improve the overall performance, herein, an effective strategy is designed to fabricate Co₃Fe₇@C yolk-shell structures by using (Co_0.9Fe_0.1)Fe₂O₄@phenolic resin core@shell structures as precursors. The structure parameters, including the size of the CoFe alloy cores, the thickness of the carbon shell, and the void between the core and the shell, can be tailored by controlling the reaction conditions. It is demonstrated that the EMW absorption properties of the as-prepared Co₃Fe₇@C yolk-shell structures are closely related to their structure parameters. The optimized Co₃Fe₇@C yolk-shell structure shows excellent EMW absorption performance, the strongest reflection loss (RL) is up to -35.3 dB at 9.1 GHz with the matching thickness of 2.0 mm, and the effective bandwidth (RL < -10 dB) can reach 8.4 GHz (9.6-18 GHz) with a thickness of only 1.5 mm. It is revealed that the excellent performances stem from the unique yolk-shell structure as well as the complementarities and synergies between the dielectric loss and the magnetic loss. By rational designing, the magnetic metal alloy@carbon yolk-shell structures will be convinced to have the potential as novel high-efficiency EMW absorption materials with lightweight, low thickness, wide absorption frequency, high stability, and strong absorption characteristics.

Facile synthesis of porous Fe3O4@C core/shell nanorod/graphene for improving microwave absorption properties

Porous Fe₃O₄@C core/shell nanorods decorated with reduced graphene oxide were synthesized by a facile one-pot method, and exhibit high microwave absorption performance: maximum reflection loss reaches −48.6 dB.