Superior Microwave Absorption Properties Research Articles

Well-Dispersed CoNiO2 Nanosheet/CoNi Nanocrystal Arrays Anchored onto Monolayer MXene for Superior Electromagnetic Absorption at Low Frequencies

Developing microwave absorbers with superior low-frequency electromagnetic wave absorption properties is one of the foremost important factors driving the boom in 5G technology development. In this study, via a simple hydrothermal and pyrolysis strategy, randomly interleaved CoNiO2 nanosheets and uniformly ultrafine CoNi nanocrystals are anchored onto both sides of a single-layered MXene. The absorption mechanism demonstrated that the hierarchical heterostructure prevents the aggregation of MXene nanoflakes and magnetic crystallites. In addition, the introduction of the double-magnetic phase of CoNiO2/CoNi arrays can not only enhance the magnetic loss capacity but also generate larger void spaces and abundant heterogeneous interfaces, collectively promoting impedance-matching and furthering microwave attenuation capabilities at a low frequency. Hence, the reflection loss of the optimal absorber (M–MCNO) is −45.33 dB at 3.24 GHz, which corresponds to a matching thickness of 5.0 mm. Moreover, its EAB can entirely cover the S-band and C-band by tailoring the matching thickness from 2 to 7 mm. Satellite radar cross-section (RCS) simulations demonstrated that the M–MCNO can reduce the RCS value to below −10 dB m2 over a multi-angle range. Thus, the proposed hybrid absorber is of great significance for the development of magnetized MXene composites with superior low-frequency microwave absorption properties.

A three-dimensional BaFe11.6(ZrSm)0.2O19/rGO composite aerogel with superior microwave absorption properties

The combination of dielectric and magnetic materials can significantly improve microwave absorption properties. In this work, we introduce a novel Zr-Sm doped barium ferrite BaFe11.6(ZrSm)0.2O19, which is compounded with rGO aerogel and presents superior microwave absorption properties. The results show that the BaFe11.6(ZrSm)0.2O19/rGO composite aerogel exhibits a unique three-dimensional porous network structure which enhances the reflection and scattering of electromagnetic waves. Meanwhile, the addition of BaFe11.6(ZrSm)0.2O19 abounds the folds and defects on the surface of rGO sheet layer, generating a large amount of polarisation and relaxation. In addition, with the increase of BaFe11.6(ZrSm)0.2O19 content, the permeability gradually increases, while the dielectric constant gradually decreases. At a certain content, both of them can be well balanced to obtain high attenuation constants and great impedance matching, which regulates the wave-absorbing properties of the material. The minimum reflection loss (RLmin) of BaFe11.6(ZrSm)0.2O19/rGO composite aerogel can reach -53.17 dB at a matching thickness of 2.9 mm, and the absorption bandwidth reaches 7.04 GHz, which has been improved by 40% than pure BaFe11.6(ZrSm)0.2O19. Therefore, it is expected to be a candidate for lightweight, thin, high loss, large bandwidth microwave absorbing materials.

Superior microwave absorption properties of anisotropic Y2Fe16‒xCoxSi/paraffin composites by orientation tuning

Y2Fe16-xCoxSi/paraffin composites were prepared by three different orientation methods. The effect of these orientation methods and the magnetocrystalline anisotropy of Y2Fe16‒xCoxSi alloys on the electromagnetic parameters and the microwave absorption properties were investigated. The results demonstrated that orientation tuning improved the electromagnetic parameters and microwave absorption properties. Anisotropy in dielectric properties and magnetic properties of Y2Fe16-xCoxSi/paraffin composites were achieved by tuning the orientation of Y2Fe16-xCoxSi powders. The planar and conical anisotropic materials had superior microwave absorption properties than uniaxial anisotropic materials for the same orientation method. The Y2Fe16‒xCoxSi/paraffin composite had an effective absorption bandwidth of 8.4 GHz (9.6–18 GHz) and a reflection loss of ‒59.6 dB which can almost cover the X–Ku bands and exceed the performance of many reported absorbing materials, showing its great prospects for microwave absorption in the X–Ku bands.

Superior microwave absorption properties of carbon-coated FeSiCr micro flakes

Carbon-coated ferromagnetic alloys can protect from microwave radiation due to their tunable electromagnetic parameters and multiple loss mechanisms. We prepared carbon-coated flaky FeSiCr (FFSC@C) powders by the encapsulation and thermal decomposition of epoxy resin. The crystallization degree and thickness of carbon coating were tuned to optimize the microwave absorption of FFSC@C. The phase composition, morphology, magnetic properties, electromagnetic parameters, and microwave absorption properties of FFSC@C were comprehensively investigated. The oriented flaky FeSiCr possessed strong attenuation capacity, the amorphous carbon improved the impedance matching of flaky FeSiCr. The sample carbonized at 500 ℃, with the epoxy addition amount of 45 wt% exhibited a broad effective absorption bandwidth of 5.60 GHz at a thickness of 2.4 mm. Compared with other absorbents, the FFSC@C exhibited stronger absorption capacity at a lower thickness and filler loading in the X-band (8−12 GHz). This work demonstrated the facile fabrication of a high-performance carbon-coated ferromagnetic microwave absorber.

Surface modification by CO2 plasma boosting core shells structural Fe/Fe3C/FeN @ graphite carbon nanoparticles toward high performance microwave absorber

The surface modification of three-dimensional (3D) materials is an efficient method for adjusting their interfacial defect concentration, electronic conductivity and content of functional groups with extensive applications in catalysis, electrode materials and bioengineering. In this work, a multiphase iron nanocrystals consisting of Fe3C, Fe and FeN nanoparticles encapsulated in hierarchical structure of graphite carbon (denoted as Fe/Fe3C/FeN@GC) is synthesized for the first time by a novel high temperature plasma method. Meanwhile, more defects and functional groups are introduced by surface modification of graphite carbon layer of Fe/Fe3C/FeN@GC with controllable CO2 (low temperature) plasma. Benefiting from the advantages of multiple heterogenous interface and the abundant interfacial polarization relaxation that represent strong electromagnetic (EM) wave dissipation as well as an applicable impedance matching, the optimized Fe/Fe3C/FeN@GC demonstrate superior microwave absorption (MA) properties. The minimum reflection loss (RL) achieves −54.4 dB (more than 99.9% MA) at 17.6 GHz with a thin thickness of 1.8 mm, and the maximum effective absorption bandwidth (EAB, RL < −10 dB) is up to 6.2 GHz (11.8–18.0 GHz) at 2.0 mm. The above results reveal that the optimized Fe/Fe3C/FeN@GC composites with strong absorption, broad EAB, light mass (only filling content of 30 wt%) and ultrathin thickness are prospective candidate for high performance EM wave absorbers.

Hierarchical-Bioinspired MOFs Enhanced Electromagnetic Wave Absorption.

Proteins exhibit complex and diverse multi-dimensional structures, along with a wide range of functional groups capable of binding metal ions. By harnessing the unique characteristics of proteins, it is possible to enhance the synthesis of metal-organic frameworks (MOFs) and modify their morphology. Here, the utilization of biomineralized bovine serum albumin (BSA) protein as a template for synthesizing Mil-100 with superior microwave absorption (MA) properties is investigated. The multi-dimensional structure and abundant functional groups of biomineralized BSA protein make it an ideal candidate for guiding the synthesis of Mil-100 with intricate network structures. The BSA@Mil-100 synthesized using this method exhibits exceptional uniformity and monodispersity of nanocrystals. The findings suggest that the BSA protein template significantly influences the regulation of nanocrystal and microstructure formation of Mil-100, resulting in a highly uniform and monodisperse structure. Notably, the synthesized 2-BSA@Mil-100 demonstrates a high reflection loss value of -58dB at 8.85GHz, along with a maximum effective absorption bandwidth value of 6.79GHz, spanning from 6.01 to 12.8GHz. Overall, this study highlights the potential of utilizing BSA protein as a template for MOF synthesis, offering an effective strategy for the design and development of high-performance MA materials.

Controllable synthesis and enhanced microwave absorption properties of hexagonal boron nitride@polyaniline composite

Nowadays, electromagnetic pollution caused by electronic devices is gradually becoming a concern. Moreover, as the frequency of electromagnetic pollution from electronic devices is mainly in the range of 2–10 GHz, the design of microwave-absorbing materials for this frequency range has become a hot issue. To tackle the issue, core-shell structured hexagonal boron nitride (h-BN) @polyaniline (PAn) composites have been proposed to construct heterogeneous microwave-absorbing materials. Firstly, the h-BN is exfoliated, and hydroxyl functionalized to produce hydroxy boron nitride (OH-BN), which enhances its polarization ability by structuring defects and adding functional groups to improve its microwave absorption efficiency. Afterward, PAn was grafted on the OH-BN surface by in situ polymerization. The microwave absorption properties of OH-BN@PAn composites can be tuned by modulating the doping of PAn. As expected, the OH-BN@PAn composite exhibits superior microwave absorption properties with the minimum reflection loss (RLmin) value of −38.60 dB at 3.5 mm and an effective absorption bandwidth (EAB) of 3.4 GHz (6.24–8.64 GHz) at pH = 2. Also, the composite achieves effective microwave absorption at 3.76–18 GHz by adjusting the matching thickness. Notably, the RLmin value of OH-BN@PAn was successfully tuned from the high-frequency region (12.4 GHz, pH = 0) to the low-frequency region (7.28 GHz, pH = 2) by adjusting the doping degree. In addition, the RL value and EAB width have been increased due to the increased impedance matching and polarization capability. This work can provide a reference for constructing composite microwave-absorbing materials and regulating microwave absorption performance.

Detailed microwave loss mechanisms for nanocomposites of La-doped BaFe12O19 and polyaniline

To mitigate the undesirable effects of electromagnetic pollution on the precise instrument, biological health, and human life, high-efficiency microwave-absorbing materials (MAMs) have been pursued by the scientific community. MAMs also have important potential for information security, 5G, energy harvesting, reduced radar cross-section, and military stealth technology. In this work, magnetic/dielectric composites of La-doped BaFe12O19 (La-BaM) and polyaniline (PANI) were developed to be MAMs. Composites with no and 30% of La concentration (named M0-C and M3-C, respectively) showed poor microwave absorption performance with reflection loss (RL) values of about −20 dB, meaning 99% of the incident microwave was absorbed. The effective absorption bandwidths (EABs) were narrow, with values of 0.70 and 1.55 GHz, respectively. In contrast, the microwave absorption performance of composites with 10% and 50% of La concentration (named M1-C and M5-C, respectively), reached excellent values in both RL and EAB of −47.83 and −43.53 dB and 3.98 and 3.43 GHz, respectively. These RL values implied that 99.99% of the incident microwave could be absorbed. The superior microwave absorption properties of M1-C and M5-C composites could be attributed to their excellent impedance matching, better natural ferromagnetic resonance, exchange resonance, and better attenuation constant. The loss mechanism of microwave energy in La-BaM/PANI composites could be attributed to interfacial polarization at the interfaces of two phases, dipole polarization and micro-current and conductive loss (from PANI), eddy current (from La-BaM), multiple reflection and scattering (from the dispersion of PANI into La-BaM), as well as thermal energy dissipation (from embedding La-BaM/PANI into the epoxy matrix).

Facile synthesis of 2D MoS2/reduced graphene oxide hybrids with excellent microwave absorption

High-performance microwave absorption materials with tunable electromagnetic properties have long been the goal of researchers. It is still a challenge to achieve broad band absorption and lightweight performance by simply optimizing the chemical composition of absorbers. Molybdenum disulfide (MoS2) belongs to the two-dimensional transition metal disulfide with a layered structure similar to graphene. In this work, two-dimensional MoS2/reduced graphene oxide (MS/RGO) hybrids have been constructed through a convenient self-assembled hydrothermal method, in which MoS2 ultrathin nanosheets in-situ grow uniformly on the surface of RGO, constructing a unique hierarchical microstructure. Electromagnetic parameter measurements display that the dielectric behaviors of MS/RGO composites are optimized via changing the content of RGO, and meanwhile the superior microwave absorption properties are achieved with the filler-loading ratio of only 20 wt%. The widest effective absorption bandwidths (RL<−10 dB) of 5.68 GHz (12.32–18 GHz) and 6.32 GHz (11.20–17.52 GHz) are observed at a thickness of 2.0 mm for MS/RGO-10 and MS/RGO-15, respectively. When the thickness is raised to 5.0 mm, the reflection loss value of MS/RGO-10 composites reaches the minimum value of − 39.8 dB at 4.96 GHz. The improved performance can be explained by the strong interfacial polarization loss due to abundant heterogeneous interfaces, defect dipole polarization, conduction loss, and multiple reflections and scattering. The results indicate that the light-weight MS/RGO composite is considered as a promising candidate for high-performance microwave absorbers with an adequate absorption bandwidth.

Broadband electromagnetic dissipation superiority of hierarchical ZnO flakes co-decorated with CoFe/CoFe2O4 and rGO

Currently, in order to solve the increasing issues caused by the electromagnetic radiation pollution and broadened radar detection bandwidth, electromagnetic wave dissipating materials with high performance of broadband absorption are desired urgently. Herein, the CoFe/CoFe2O4/ZnO/rGO composites composed of hierarchical ZnO flakes with anchored CoFe/CoFe2O4 and rGO-doping were synthesized via a facile aging approach and subsequent calcination process under vacuum atmosphere. The constituents and electromagnetic parameters of absorbers could be efficiently modulated through tuning the additive amount of raw GO. Notably, the composite with GO additive amount of 0.025 g exhibits a prominent broadband electromagnetic wave absorbing capacity. In detail, the widest effective absorption bandwidth reaches 7.66 GHz with thin thickness of just 2.5 mm. This superior broadband microwave absorption property is owing to the synergistic effect of hierarchical nanostructure and well-matched impedance, as well as enhanced interfacial polarization, conduction loss, eddy current, natural and exchange magnetic resonances. The investigation demonstrates the specific CoFe/CoFe2O4/ZnO/rGO composite is a potential candidate to be applied for broadband military radar stealth and serious electromagnetic radiation contamination.

Construction of multi-dimensional NiCo/C/CNT/rGO aerogel by MOF derivative for efficient microwave absorption

The development of high-performance microwave absorption materials is currently imperative in order to solve the problem of electromagnetic pollution. Herein, we successfully obtained a multi-dimensional graphene-based aerogel (NiCo/C/CNT/rGO aerogel) decorated with one-dimensional carbon nanotubes (CNTs) and metal-organic framework (MOF) derivatives. The introduction of rGO aerogel significantly modifies the phase composition (NiCo/C/CNT and rGO) and hierarchical structure (1D CNT, 3D NiCo/C/CNT and rGO aerogel) of the composite, resulting in a multi-dimensional gradient, defects, heterogeneous interfaces, and superior microwave absorption properties. The optimum electromagnetic wave absorption performance of −58.8 dB is achieved at a filler loading of 20 wt%, with a thickness of 1.8 mm and an effective absorption bandwidth of 7.6 GHz, covering the entire Ku-band. The excellent electromagnetic wave absorption performance can be attributed to the synergistic effect of impedance matching, electromagnetic attenuation capability, unique multi-dimensional porous structure, abundant defects and interfaces. In summary, the present work provides a novel approach for the synthesis of multi-dimensional lightweight magnetic/dielectric microwave absorbers.

Core–shell-like nanocrystalline FeSiB/amorphous carbon composite powder with remarkable and tunable microwave absorption properties

Micron-sized Fe90Si7B3/carbon composite powder with 8–15 wt% C has been synthesized by ball milling. The powder possesses a core–shell-like structure, in which the Fe90Si7B3 core is composed of α-Fe nanocrystalline/amorphous dual phases, and the carbon shell is amorphous. The composites exhibit high permeability, matchable permittivity, and excellent microwave absorption properties including strong reflection loss of −54.8 dB at 12.7 GHz and large effective absorption bandwidth of 6.5 GHz with 1.9 mm in absorber thickness. The superior microwave absorption properties are benefited from the enhanced impedance matching and synergistic effect of strong magnetic and dielectric losses as contributed by the nature resonance and eddy current effect of the nanocrystalline Fe90Si7B3 core, and multiple polarizations and conduction loss between the Fe90Si7B3/carbon components, respectively. The microwave absorption performance can be tuned by changing carbon content and/or annealing. The Fe90Si7B3/carbon composites are promising as a new type of high-performance microwave absorbers.

Structural Defects in Phase‐Regulated High‐Entropy Oxides toward Superior Microwave Absorption Properties

AbstractHigh‐entropy (HE) oxides have become increasingly popular as electromagnetic wave‐absorbing materials owing to their customizable structure and unique HE effects. However, the weak loss property of single‐phase HE ceramics and the approaches implemented to improve them based on semi‐empirical rules severely limit their development. Herein, two biphasic HE oxides are prepared by simple sintering to realize accurate regulation of crystal phases and structural defects. It is verified that HE effects cause various defects that are beneficial for microwave dissipation within complex‐phase ceramics. In spinel/perovskite HE oxides, around the interface of spinel (111) and perovskite (110) planes, notable stress concentrations and lattice distortions are directly observed, inducing numerous point defects and stacking faults. Interestingly, besides the existing heterogeneous interface of rock salt (220)/spinel (220) plane and defects, rock salt/spinel HE oxides enabled synergistic effects via the precise regulation of components’ phase. Driven by structural defects and multi‐phases in HE complexes, the intense polarization is evidently found, confirmed by the first‐principles calculations. Accordingly, the two complex‐phase HE oxides demonstrate excellent microwave absorption performance, and the minimal reflection loss of −54.5 dB is achieved. Therefore, this study provides valuable guidelines for the design of microwave absorbers using HE oxides.

Lightweight and Compression-Resistant Carbon-Based Sandwich Honeycomb Absorber with Excellent Electromagnetic Wave Absorption.

Honeycomb (HC) composites were fabricated by impregnating an aramid paper HC core with carbon nanotubes/carbon black/reduced graphene oxide (CNTs/CB/RGO) and polyurethane resin (PU). The sandwich HC (SHC) absorber containing HC composites with superior microwave-absorption properties were fabricated using the vacuum bagging method. Through the absorption performance of the SHC absorber, it can be concluded that the triple-layer SHC absorber has the best absorbing performance. The effective bandwidth (reflection loss < 10 dB) can be achieved in the entire frequency range of 2.2–18 GHz, and the minimum RL value is −35 dB. Furthermore, the compressive stress of the triple-layer SHC absorber reached 3.71 MPa, which is similar to the compressive stress of aluminum HC panels for aviation. Benefiting from the excellent integration of absorption and mechanical performance, the SHC has significant potential in the stealth-technology field.

Nano-SiC-decorated Y2Si2O7 ceramic for enhancing electromagnetic waves absorption performance

To improve the electromagnetic (EM) wave absorption performance of rare earth silicate in harsh environments, this work synthesized dense SiC–Y2Si2O7 composite ceramics with excellent EM wave absorption properties by using the polymer permeation pyrolysis (PIP) process, which introduced carbon and SiC into a porous Y2Si2O7 matrix to form novel composite ceramics. SiC–Y2Si2O7 composite ceramics with different numbers of PIP cycles were tested and analysed. The results show that the as-prepared composites exhibit different microstructures, porosities, dielectric properties and EM wave absorption properties. On the whole, the SiC–Y2Si2O7 composite ceramics (with a SiC/C content of 29.88 wt%) show superior microwave absorption properties. The minimum reflection loss (RLmin) reaches −16.1 dB when the thickness is 3.9 mm at 9.8 GHz. Moreover, the effective absorption bandwidth (EAB) included a broad frequency from 8.2 GHz to 12.4 GHz as the absorbent thickness varied from 3.15 mm to 4.6 mm. In addition, the EM wave absorption mechanism was analysed profoundly, which ascribed to the multiple mediums of nanocrystalline, amorphous phases and turbostratic carbon distributed in the Y2Si2O7 matrix. Therefore, SiC–Y2Si2O7 composite ceramics with high-efficiency EM wave absorption performance promise to be a novel wave absorbing material for applications in harsh environments.

Rational design of hierarchical structure of carbon@polyaniline composite with enhanced microwave absorption properties

Reasonable combination of components and ingenious structure design are effective strategies to achieve superior microwave absorption (MA). In this work, polyaniline was grown in situ on hollow porous carbon microspheres prepared by polymerization and pyrolysis-etching processes. The synthesized hollow porous carbon@polyaniline (HPC@PANI) shows a specific hierarchical structure and possesses extraordinary MA properties. The optimal minimum reflection loss (RL) of HPC@PANI is as high as −64.31 dB at 13.80 GHz with a thin thickness of 1.86 mm, and the corresponding effective absorption bandwidth (EAB, RL ≤ −10 dB) is as wide as 4.85 GHz (11.90 GHz–16.75 GHz). The mechanism of such superior MA properties is associated with well impedance matching, strong loss capabilities and well-defined structural characteristics. It is expected that the design of HPC@PANI with hierarchical structures in this work could provide ideas for the structural design of efficient MA materials.

The microwave-absorption properties and mechanism of phenyl silicone rubber/CIPs/graphene composites after thermal-aging in an elevated temperature

Recently, the application and development of flexible microwave-absorption composites based on silicone rubber have gradually become a research hot spot. In this study, methyl vinyl phenyl silicone rubber (MPVQ)/carbonyl iron particles (CIPs)/graphene (GR) composites were prepared by mechanical blending, and the effects of thermal-ageing temperature on the microwave-absorption properties of the composites were investigated. The mechanism of the thermal-ageing temperature’s effects on microwave-absorption behaviour was identified. The results show that unaged composites have superior microwave-absorption properties, with a minimum reflection loss (RLmin) of − 87.73 dB, a lowest thickness of 1.46 mm, and an effective absorption bandwidth (EAB, RL < − 10 dB) reaching 5.8 GHz (9.9–15.7 GHz). With ageing at 240 °C for 24 h, the RLmin at a frequency of 5.48 GHz is − 45.55 dB with a thickness of 2.55 mm, and the EAB value reaches 2 GHz (range 4.6–6.6 GHz). In the thermal-ageing process, a crosslinking reaction occurs in MPVQ with an increase in crosslinking density from 5.88 × 10−5 mol g−1 (unaged) to 4.69 × 10−4 mol g−1 (aged at 240 °C). Simultaneously, thermal degradation of the composites leads to a reduction in the rubber concentration. In addition, a small amount of CIPs are oxidized to Fe3O4, and the remaining CIPs aggregate to generate more electrically conductive pathways. Consequently, the dielectric loss of the composites will be significantly improved, resulting in poor impedance matching. The microwave-absorption properties of the composites gradually decrease with increasing thermal-ageing temperature from 200 to 240 °C.

Carbon aerogel based composite phase change material derived from kapok fiber: Exceptional microwave absorbility and efficient solar/magnetic to thermal energy storage performance

Herein, we report a facile yet efficient strategy for fabricating a carbonized kapok fiber aerogel (CKF) based composite PCM , by incorporating magnetic guest of Fe 3 O 4 nanoparticles and encapsulating thermal energy guest of lauric acid (LA). The obtained LA/CKF@Fe 3 O 4 composite PCMs (CPM) shows an ultrahigh latent heat of 97.5% that of LA. Besides, the integration of Fe 3 O 4 contributes to the CPM with excellent microwave absorption performance by achieving an optimal balance between the impedance matching and the high loss characteristics. The minimum reflection loss for CPM-30 is −17.3 dB at 8.4 GHz within thickness of 5.5 mm, far exceeding the practical demand of −10 dB. Furthermore, the CPM can also realize efficient solar/magnetic to thermal conversion . To the best of our knowledge, this is the first example of carbon aerogel based composite PCM prepared by facile yet renewable method that also exhibits ultrahigh thermal energy capacity, enhanced thermal conductivity , superior microwave absorption property and efficient solar/magnetic to thermal conversion performance. This study paves a way for designing of high-performance composite PCMs with numerous energy storage forms and functions by extending the reported system to other natural microtubules and functional guests. In addition to the highly efficient utilization of solar irradiation, the composite PCM is also able to convert magnetic energy into thermal energy. Similarly, the CPMs were subjected to an alternating magnetic field to estimate the magnetic to thermal energy conversion performance. The temperature evolutions were detected using an infrared thermometer in real-time, as illustrated in Fig. 7d. Upon electromagnetic excitation, the temperatures of the CPMs increase rapidly owing to the magnetothermal effect of the Fe 3 O 4 nanoparticles. It is clear that the heating rate of the CPMs increase gradually with increasing Fe 3 O 4 contents. As excitation time increases, an inflection point is observed in the temperature-time curve, demonstrating that the harvested magnetic energy is converted into thermal energy and stored in the form of latent heat. The higher magnetic to thermal conversion efficiency of sample with high Fe 3 O 4 content may be attributed to the synergistic effect of their relatively low latent heat, large thermal conductivity, optimal impedance matching, and high loss characteristics. Upon the excitation being switched off, the temperatures of CPMs drop immediately to the freezing point of LA, and an obvious freezing plateau appears between 41 and 37 °C, indicating that the stored latent heat is released due to the normal crystallization of LA. These results reveal that the novel CKF@Fe 3 O 4 host matrix can effectively absorb solar and electromagnetic energy, thereby convert them into thermal energy, then dispatch this energy to the surroundings through the interpenetrating 3D network of carbon microtubules, and successfully store it in the form of latent heat through the phase transition of embedded PCM. Thus, the novel carbon aerogel based CPMs in this study is a multifunctional energy harvester and is expected to have broad application in solar/magnetic energy conversion and storage.

Porous cobalt ferrite microspheres decorated two-dimensional MoS2 as an efficient and wideband microwave absorber

In this article, the CoFe2O4/MoS2 composites have been well constructed via a facial hydrothermal method, from which the porous CoFe2O4 microspheres were embedded into MoS2 ultrathin nanosheets. As a typical two-dimensional transition metal sulfide, MoS2 with high electrical conductivity and flexible properties is expected to exhibit high dielectric loss and magnetic loss when combined with magnetic material CoFe2O4. Meanwhile, the unique hierarchical structure of as-synthesized MoS2 nanoflowers is conducive to scattering and reflection of electromagnetic waves, and endows designed composites with competitive microwave absorption properties. Notably, although the saturation magnetization of MoS2/CoFe2O4 composites is significantly decreased compared to pure CoFe2O4 microspheres, the coercivity still maintains a high value of 626.1 Oe. As expected, the results demonstrate that as-fabricated MoS2/CoFe2O4 composites do have superior microwave absorption properties in comparison with CoFe2O4 and MoS2. It is found that the complex permittivity is enhanced with increasing filling ratio from 45 wt% to 60 wt%, which is helpful for obtaining a moderate permittivity value. When the filling ratio is 50 wt%, the MoS2/CoFe2O4 composites exhibit a minimum reflection loss (RLmin) of − 53.1 dB at 12.08 GHz when the thickness is 2.5 mm. An effective absorption bandwidth less than − 10 dB of 6.61 GHz from 11.28 to 17.89 GHz is achieved with a thin thickness of 2.2 mm, almost covering the whole Ku-band. The improvement in microwave absorption properties can be ascribed to the synergistic effect of the magnetic CoFe2O4 and dielectric MoS2. The impedance matching characteristic and interfacial polarization are significantly optimized by inserting CoFe2O4 spheres onto the surface of MoS2 nanosheets. Considering the excellent performance of as-fabricated MoS2/CoFe2O4 composites, it is believed that the MoS2-based composites can be applied as a promising candidate of highly effective microwave absorbers with strong absorption intensity and broad absorption frequency.

Morphology optimization strategy of flower-like CoNi2S4/Co9S8@MoS2 core@shell nanocomposites to achieve extraordinary microwave absorption performances

Morphology optimization is an effective strategy to take full advantage of interface polarization for the improvement of electromagnetic wave attenuation capability. Herein, a general route was proposed to produce the flower-like core@shell structured MoS2-based nanocomposites through a simple hydrothermal process. Through the in-situ hydrothermal reaction between the Mo and S sources on the surface of CoNi nanoparticles, flower-like core@shell structured CoNi2S4/Co9S8@MoS2 nanocomposites could be successfully synthesized. By regulating the hydrothermal temperature, the flower-like geometrical morphology of samples could be effectively optimized, and the as-prepared sample (S2) synthesized at 200 °C displayed very excellent flower-like morphology compared to the samples (S1 and S3) obtained at 180 and 220 °C. Owing to the excellent interface polarization effect, the as-prepared S2 presented the evidently superior comprehensive microwave absorption properties in terms of strong aborption capability, wide absorption bandwidth and thin matching thicknesses compared to those of S1 and S3. The as-prepared core@shell structured CoNi2S4/Co9S8@MoS2 sample with very excellent flower-like morphology simultaneously displayed the minimal reflection loss of −50.61 dB with the matching thickness of 2.98 mm, and the effective absorption bandwidth of 8.40 GHz with the matching thickness of 2.36 mm. Therefore, we provided a general route for the production of flower-like core@shell structured MoS2-based nanocomposites, which could make the best of interface polarization to develop high-efficiency microwave absorbers.