Fabrication of one-dimensional ZnFe2O4@carbon@MoS2/FeS2 composites as electromagnetic wave absorber

Porous Structure Fibers Based on Multi-Element Heterogeneous Components for Optimized Electromagnetic Wave Absorption and Self-Anticorrosion Performance

The excellent performance of electromagnetic wave absorbers primarily depends on the coordination among components and the rational design of the structure. In this study, a series of porous fibers with carbon nanotubes uniformly distributed in the shape of pine leaves are prepared through electrospinning technique, one-pot hydrothermal synthesis, and high-temperature catalysis method. The impedance matching of the nanofibers with a porous structure is optimized by incorporating melamine into the spinning solution, as it undergoes gas decomposition during high-temperature calcination. Moreover, the electronic structure can be modulated by controlling the NH4F content in the hydrothermal synthesis process. Ultimately, the Ni/Co/CrN/CNTs-CF specimen (P3C NiCrN12) exhibited superior performance, while achieving a minimum reflection loss (RLmin) of -56.18 dB at a thickness of 2.2 mm and a maximum absorption bandwidth (EABmax) of 5.76 GHz at a thickness of 2.1 mm. This study presents an innovative approach to fabricating lightweight, thin materials with exceptional absorption properties and wide bandwidth by optimizing the three key factors influencing electromagnetic wave absorption performance.

Large Microsphere Structure of a Co/C Composite Derived from Co-MOF with Excellent Wideband Electromagnetic Microwave Absorption Performance

In the field of electromagnetic wave (EMW) absorption, carbon matrix materials based on metal-organic frameworks (MOFs) have drawn more interest as a result of their outstanding advantages, such as porous structure, lightweight, controlled morphology, etc. However, how to broaden the effective absorption bandwidth [EAB; reflection loss (RL) ≤ -10 dB] is still a challenge. In this paper, large microsphere structures of a Co/C composite composed of small particle clusters were successfully prepared by the solvothermal method and annealing treatment. At a filling ratio of 40 wt %, the Co/C composite shows attractive microwave absorption (MA) performance after being annealed at 600 °C in an atmosphere of argon. With an EAB of 6.32 GHz (9.92-16.24 GHz) and a thickness of just 2.57 mm, the minimum RL can be attained at -54.55 dB. Most importantly, the EAB can attain 7.12 GHz (10.88-18.0 GHz) when the thickness is 2.38 mm, which is larger than that of the majority of MOF-derived composites. The superior MA performance is strongly related to excellent impedance matching and a higher attenuation constant. This study provides a simple strategy for synthesizing a MOF-derived Co/C composite with a wide EAB.

One-dimensional core-shell CoC@CoFe/C@PPy composites for high-efficiency microwave absorption

In recent years, electromagnetic pollution has become more and more serious, and there is an urgent need for microwave absorbing materials with superior performance. Prussian blue analogue (PBA) is a metal organic framework material with the advantages of diverse morphology and tunable composition. Therefore, PBA has attracted a lot of attention in the field of microwave absorption. In this work, PBA was coated on the surface of carbon composites by hydrothermal method, and then PPy was compounded on its surface after carbonization treatment to construct hierarchical core-shell CoC@CoFe/C@PPy fibers. The fibers have Co-doped C composites as the core and CoFe/C decorated with PPy as the shell. This unique hierarchical structure and various microwave absorption mechanisms are described in detail. The microwave absorption performance is optimized by adjusting the filling of the sample. The best microwave absorption performances are achieved at 25 wt% filling of CoC@CoFe/C@PPy. At a thickness of just 1.69 mm, CoC@CoFe/C@PPy fiebrs have a minimum reflection loss (RLmin) of -64.32 dB. When the thickness is 1.88 mm, CoC@CoFe/C@PPy achieves a maximum effective absorption bandwidth (EABmax) of 5.38 GHz. The results indicate that the CoC@CoFe/C@PPy composite fibers have a great potential in the field of microwave absorption.

Defect- and Interface-Induced Dielectric Loss in ZnFe2O4/ZnO/C Electromagnetic Wave Absorber

Controlling defects and interfaces in composite absorbers can effectively regulate electromagnetic (EM) parameters and enhance the electromagnetic wave (EMW) absorption ability, but the mechanism still needs to be further elucidated. In this study, ZnFe₂O₄/ZnO/C composite was synthesized via the hydrothermal method followed by post-annealing in different atmospheres. Defects and interfaces were characterized by Raman, PL spectroscopy, XPS and TEM, and their relationship with dielectric loss and EMW absorption performance was discussed in detail. Results show that the N₂-annealed ZnFe₂O₄/ZnO/C composite with abundant defects and interfaces as well as an optimized composition exhibits excellent EMW dissipation ability, with a RL_min value of -17.4 dB and an f_e of 3.85 GHz at a thickness of 2.28 mm. The excellent EMW absorption performance originates from suitable impedance matching, significant conduction loss and strong dielectric loss (interfacial polarization, diploe polarization and defect polarization) dominated by lattice defects and interfaces. This study provides a view into the relationship between defects, interfaces, EM parameters and EMW absorption ability, and also suggests an effective way to promote EMW dissipation ability of the absorbers by controlling defects and interfaces.

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

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

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

Increasing electromagnetic (EM) radiation has driven the rapid development of carbon-based EM wave absorption materials, but the design of light-weight and efficient carbon-based materials remains a huge challenge. Herein, N-doped carbon fibers embedded with CoNi alloy particles (CoNi/C fibers) were synthesized via electrospinning technology and carbonization. Then, conductive polypyrrole-coated CoNi/C fibers (CoNi/C@PPy composites) were synthesized by chemical polymerization. As-synthesized CoNi/C@PPy composites showed outstanding EM wave absorption property due to the synergistic effect between CoNi, N-doped carbon fibers and PPy. The optimal reflection loss (RL) is -68.78 dB (12.90 GHz) with the thickness of 2.43 mm and the low filler loading of 15 wt%. The widest effective absorption bandwidth (EAB) is 5.62 GHz with the thickness of 2.10 mm and the low filler loading of 20 wt%. The outstanding EM wave absorption property is mainly attributed to 3D network structure, great impedance matching and strong dielectric loss. The results showed that embedding magnetic alloy particles in carbon fibers coated with conductive polymers is an effective strategy for constructing efficient lightweight EM wave absorption materials.

MoS2 decorated on one-dimensional MgFe2O4/MgO/C composites for high-performance microwave absorption

Advanced microwave absorption (MA) materials have attracted widespread attention to meet the challenges of electromagnetic (EM) pollution. Herein, MgFe₂O₄/MgO/C fibers were successfully prepared via electrospinning technology and carbonization, and their surfaces were coated by MoS₂ via hydrothermal method. The EM wave absorption performance of composites was enhanced due to the introduction of MoS₂. The results showed that the EM wave absorption performance of MgFe₂O₄/MgO/C could not meet the requirements due to low dielectric loss and poor impedance matching. The performance of the composites was improved after coating of MoS₂, which showed the strong wave absorption capability and the broad absorption bandwidth. The optimal reflection loss (RL) is -56.94 dB at 9.5 GHz and the effective absorption bandwidth is 3.9 GHz (8.08-11.98 GHz) with a thickness of 2.7 mm. The excellent MA performance can be mainly attributed to excellent synergistic effect between MgFe₂O₄/MgO/C and MoS₂. Furthermore, MoS₂ also contributes to dielectric loss and ideal impedance matching. MgFe₂O₄/MgO/C@MoS₂ composites may be utilized for lightweight and high-efficient MA materials.

Construction of Ni-Zn bimetal sulfides Heterostructured-hybrids for High-performance electromagnetic wave absorption

Utilizing the synergistic effect of multiple components in heterostructured composites has been regarded as a promising strategy for achieving high-performance electromagnetic wave absorption. Nonetheless, rationally collocate the components of absorbers in order to legitimately achieve synergy remains an intractable problem. By adjusting the NiS and ZnS composition ratios in the ZnS/NiS/C composites, the optimal impedance matching and dissipation capability can be obtained. The formation of a ZnS/NiS heterostructure is found to significantly enhance polarization relaxation, and the relative ratios of ZnS and NiS have a significant effect on the electromagnetic properties. The optimal performance was obtained on Z1N2, with a minimum reflection loss of -51.45 dB at 4.72 GHz and -56.69 dB at 11.12 GHz, respectively, and an effective absorption bandwidth of up to 3.68 GHz at 1.16 mm. The potential of heterogeneous bimetal sulfides as high-performance absorbers is demonstrated in this study.

Core-shell Fe3O4@SnO2 nanochains toward the application of radar-infrared-visible compatible stealth

Multiband-compatible stealth materials play an increasingly crucial role in the field of modern military defence because they can enable the targeted objects to dodge advance detection technologies. In this study, chain-like Fe₃O₄@poly(ethyleneglycol dimethacrylate-co-methacrylic acid) nanocomposites were constructed as precursors through the magnetic field-induced distillation precipitation polymerisation. Then, the liquid-phase seed-mediated growth method, together with subsequent calcination, was applied to introduce SnO₂ shells and remove poly(ethyleneglycol dimethacrylate-co-methacrylic acid) shells, which led to the successful preparation of innovative core-shell Fe₃O₄@SnO₂ nanochains. The unique microstructure and appropriate components endowed nanochains with multiple functional applications. The minimum reflection loss value was approximately -39.4 dB (5.67 GHz), exhibiting excellent microwave absorption performance. The possible microwave absorption mechanisms involve interfacial polarisation, space charge polarisation, natural resonance, and multiple reflections and scatterings. The optimal infrared reflectivity reached 0.64, 0.51, and 0.37 in three atmospheric windows, indicating outstanding infrared stealth performance, which was attributed to the intense infrared reflection of SnO₂ shells. Furthermore, three nanochains showed different colours (dark green, brick red, and bright orange), revealing selection absorption for visible light. This can be attributed to the combined effect of visible responses of SnO₂ shells along with Bragg diffraction from the periodic arrangement of Fe₃O₄ particles in a single nanochain. Thus, core-shell Fe₃O₄@SnO₂ nanochains can be considered as promising radar-infrared-visible compatible stealth materials. This discovery opens a new means to exploit multiband-compatible stealth materials.

Construction of MOF-derived plum-like NiCo@C composite with enhanced multi-polarization for high-efficiency microwave absorption

Nowadays, facing the inevitable electromagnetic (EM) pollution caused by many electronic products, it is urgent to develop high-performance microwave absorbing materials. In particular, the bimetallic carbon-based composites derived from MOFs exhibit excellent microwave absorption potential due to their simple preparation, low cost, adjustable morphology and magnetoelectric synergy mechanism. In this work, we successfully prepared plum-like NiCo@C composite by simple solvothermal method and carbonization treatment, which displays strong absorption (-55.4 dB) and wide effective absorption band (EAB, 7.2 GHz) when the loading is 20 wt%. The plum-like structure greatly enriches the non-uniform interface and the structural anisotropy contributes to the dissipation of electromagnetic waves. At the same time, the band hybridization and magnetic coupling of NiCo@C contribute to the coordination of EM characteristics. Overall, this work proves the feasibility of NiCo@C hierarchical composite in the field of microwave absorbing, and provides insight for the development of high-performance absorbers.

Fabrication of one-dimensional CoFe2/C@MoS2 composites as efficient electromagnetic wave absorption materials

New types of electromagnetic (EM) wave absorption materials with a light weight, strong absorption ability and wide absorption frequency have been widely explored. Nevertheless, it is still an intractable challenge to design the structure of the materials and rationalize multiple components. In this work, one-dimensional (1D) CoFe₂/C@MoS₂ composites were prepared via electrospinning technology, high-temperature carbonization and hydrothermal method. SEM and TEM images reveal that the as-prepared CoFe₂/C fibers with a 1D structure are well coated with MoS₂. The excellent absorption performance of the composites is mainly attributed to the 1D structure and the ideal impedance matching. CoFe₂/C@MoS₂ composites show strong absorption ability with an optimal reflection loss (RL) of -66.8 dB (13.28 GHz) at a matching thickness of 2.12 mm. Meanwhile, the composite possesses an effective absorption frequency range between 10.70 and 16.02 GHz with a bandwidth of 5.32 GHz. These results indicate that CoFe₂/C@MoS₂ composites will become promising lightweight and highly efficient MA materials.

One-dimensional Ag-CoNi nanocomposites modified with amorphous Sn(OH)2/SnO2 shells for broadband microwave absorption

High-performance microwave absorption absorbers play important roles in the fields of radar stealth, electromagnetic protection, and antenna technology. In this work, high aspect-ratio Ag nanowires were decorated with magnetic CoNi nanoparticles via a PVP-induced solvothermal method, and then amorphous Sn(OH)₂/SnO₂ shells were introduced through an in-situ oxidative hydrolysis method, successfully preparing Ag-CoNi@Sn(OH)₂/SnO₂ composites. The morphology and ingredient of composites were ascertained by SEM, TEM, XRD, EDX, and XPS. As Ag-CoNi nanocomposites are coated by Sn(OH)₂/SnO₂ shells, the minimum reflection loss value is decreased from -31.7 dB (10.1 GHz) to -37.8 dB (6.4 GHz), and the maximum effective absorption bandwidth is extended from 3.9 GHz (10.3-14.2 GHz) to 5.8 GHz (10.7-16.5 GHz). Analyses of electromagnetic parameters reveal the possible mechanisms, involving surface plasma resonance, conductive loss, interfacial polarization, dipole polarization, exchange resonance, eddy current effect, multiple reflection and scattering. Thus, Ag nanowires modified with CoNi nanoparticles and amorphous Sn(OH)₂/SnO₂ shells can effectively balance the impedance matching and attenuation capability. It is a new strategy to achieve broadband microwave absorbers.

Multilayer polymeric nanocomposites for electromagnetic interference shielding: fabrication, mechanisms, and prospects

Fabrication of multilayer EMI shield opens a creative avenue for designing and constructing flexible nanocomposite films simultaneously featuring excellent EMI shielding performance, fascinating heat removal ability, and robust mechanical properties.