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HighlightsBenefiting from the possible “seed-germination” effect, the “seeds” Ni2+ grow into “buds” Ni nanoparticles and “stem” carbon nanotubes (CNTs) from the enlarged “soil” of MXene skeleton.Compared with the traditional magnetic agglomeration, the MXene-CNTs/Ni hybrids exhibit the highly spatial dispersed magnetic architecture.3D MXene-CNTs/Ni composites hold excellent microwave absorption performance (−56.4 dB at only 2.4 mm).Ti3C2Tx MXene is widely regarded as a potential microwave absorber due to its dielectric multi-layered structure. However, missing magnetic loss capability of pure MXene leads to the unmatched electromagnetic parameters and unsatisfied impedance matching condition. Herein, with the inspiration from dielectric-magnetic synergy, this obstruction is solved by fabricating magnetic CNTs/Ni hetero-structure decorated MXene substrate via a facile in situ induced growth method. Ni2+ ions are successfully attached on the surface and interlamination of each MXene unit by intensive electrostatic adsorption. Benefiting from the possible “seed-germination” effect, the “seeds” Ni2+ grow into “buds” Ni nanoparticles and “stem” carbon nanotubes (CNTs) from the enlarged “soil” of MXene skeleton. Due to the improved impedance matching condition, the MXene-CNTs/Ni hybrid holds a superior microwave absorption performance of − 56.4 dB at only 2.4 mm thickness. Such a distinctive 3D architecture endows the hybrids: (i) a large-scale 3D magnetic coupling network in each dielectric unit that leading to the enhanced magnetic loss capability, (ii) a massive multi-heterojunction interface structure that resulting in the reinforced polarization loss capability, confirmed by the off-axis electron holography. These outstanding results provide novel ideas for developing magnetic MXene-based absorbers.

As pioneering Fe 3 O 4 nanozymes, their explicit peroxidase (POD)-like catalytic mechanism remains elusive. Although many studies have proposed surface Fe 2+ -induced Fenton-like reactions accounting for their POD-like activity, few have focused on the internal atomic changes and their contribution to the catalytic reaction. Here we report that Fe 2+ within Fe 3 O 4 can transfer electrons to the surface via the Fe 2+ -O-Fe 3+ chain, regenerating the surface Fe 2+ and enabling a sustained POD-like catalytic reaction. This process usually occurs with the outward migration of excess oxidized Fe 3+ from the lattice, which is a rate-limiting step. After prolonged catalysis, Fe 3 O 4 nanozymes suffer the phase transformation to γ-Fe 2 O 3 with depletable POD-like activity. This self-depleting characteristic of nanozymes with internal atoms involved in electron transfer and ion migration is well validated on lithium iron phosphate nanoparticles. We reveal a neglected issue concerning the necessity of considering both surface and internal atoms when designing, modulating, and applying nanozymes. The mechanism of peroxidase-like Fe 3 O 4 nanozymes remains elusive. Here, the authors show the electron transfer mechanism of Fe(II) ions to regenerate surface Fe(II) and the related phase transformation and depletion of activity.

HighlightsMo–MXene/Mo–metal sulfides with semiconductor junctions and Mott–Schottky junctions are designed.Built-in electric field are constructed in semiconductor–semiconductor–metal heterostructure, enhancing dielectric polarization and impedance matching.Density functional theory calculations and Radar cross-section simulations confirmed the excellent electromagnetic wave absorption ability of heterostructures.The exploration of novel multivariate heterostructures has emerged as a pivotal strategy for developing high-performance electromagnetic wave (EMW) absorption materials. However, the loss mechanism in traditional heterostructures is relatively simple, guided by empirical observations, and is not monotonous. In this work, we presented a novel semiconductor–semiconductor–metal heterostructure system, Mo–MXene/Mo–metal sulfides (metal = Sn, Fe, Mn, Co, Ni, Zn, and Cu), including semiconductor junctions and Mott–Schottky junctions. By skillfully combining these distinct functional components (Mo–MXene, MoS2, metal sulfides), we can engineer a multiple heterogeneous interface with superior absorption capabilities, broad effective absorption bandwidths, and ultrathin matching thickness. The successful establishment of semiconductor–semiconductor–metal heterostructures gives rise to a built-in electric field that intensifies electron transfer, as confirmed by density functional theory, which collaborates with multiple dielectric polarization mechanisms to substantially amplify EMW absorption. We detailed a successful synthesis of a series of Mo–MXene/Mo–metal sulfides featuring both semiconductor–semiconductor and semiconductor–metal interfaces. The achievements were most pronounced in Mo–MXene/Mo–Sn sulfide, which achieved remarkable reflection loss values of − 70.6 dB at a matching thickness of only 1.885 mm. Radar cross-section calculations indicate that these MXene/Mo–metal sulfides have tremendous potential in practical military stealth technology. This work marks a departure from conventional component design limitations and presents a novel pathway for the creation of advanced MXene-based composites with potent EMW absorption capabilities.

HighlightsThe rGO/CoNi nanosheets embedded between the MXene layers can continue to serve as a conductive channel, ensuring carrier migration and proper conductive loss capability.Owing to the strong magnetic coupling between the magnetic FeCo alloy nanoparticles on the rGO substrate, the entire MXene-rGO/CoNi film exhibits a strong magnetic loss capability.Self-assembly MXene-rGO/CoNi films hold excellent microwave absorption performance − 54.1 dB at 13.28 GHz.MXene, as a rising star of two-dimensional (2D) materials, has been widely applied in fields of microwave absorption and electromagnetic shielding to cope with the arrival of the 5G era. However, challenges arise due to the excessively high permittivity and the difficulty of surface modification of few-layered MXenes severely, which infect the microwave absorption performance. Herein, for the first time, a carefully designed and optimized electrostatic self-assembly strategy to fabricate magnetized MXene-rGO/CoNi film was reported. Inside the synthesized composite film, rGO nanosheets decorated with highly dispersed CoNi nanoparticles are interclacted into MXene layers, which effectively suppresses the originally self-restacked of MXene nanosheets, resulting in a reduction of high permittivity. In addition, owing to the strong magnetic coupling between the magnetic FeCo alloy nanoparticles on the rGO substrate, the entire MXene-rGO/CoNi film exhibits a strong magnetic loss capability. Moreover, the local dielectric polarized fields exist at the continuous hetero-interfaces between 2D MXene and rGO further improve the capacity of microwave loss. Hence, the synthesized composite film exhibits excellent microwave absorption property with a maximum reflection loss value of − 54.1 dB at 13.28 GHz. The electromagnetic synergy strategy is expected to guide future exploration of high-efficiency MXene-based microwave absorption materials.

HighlightsThree-dimension hierarchical core–shell Mo2N@CoFe@C/CNT composites were successfully constructed via a fast MOF-based ligand exchange strategy.Abundant magnetic CoFe nanoparticles suspended within “nanotubes on microrods” matrix exhibited strong magnetic loss capability, confirmed by off-axis electron holography.Hierarchical Mo2N@CoFe@C/CNT composites displayed remarkable microwave absorption value of − 53.5 dB.Hierarchical magnetic-dielectric composites are promising functional materials with prospective applications in microwave absorption (MA) field. Herein, a three-dimension hierarchical “nanotubes on microrods,” core–shell magnetic metal–carbon composite is rationally constructed for the first time via a fast metal–organic frameworks-based ligand exchange strategy followed by a carbonization treatment with melamine. Abundant magnetic CoFe nanoparticles are embedded within one-dimensional graphitized carbon/carbon nanotubes supported on micro-scale Mo2N rod (Mo2N@CoFe@C/CNT), constructing a special multi-dimension hierarchical MA material. Ligand exchange reaction is found to determine the formation of hierarchical magnetic-dielectric composite, which is assembled by dielectric Mo2N as core and spatially dispersed CoFe nanoparticles within C/CNTs as shell. Mo2N@CoFe@C/CNT composites exhibit superior MA performance with maximum reflection loss of − 53.5 dB at 2 mm thickness and show a broad effective absorption bandwidth of 5.0 GHz. The Mo2N@CoFe@C/CNT composites hold the following advantages: (1) hierarchical core–shell structure offers plentiful of heterojunction interfaces and triggers interfacial polarization, (2) unique electronic migration/hop paths in the graphitized C/CNTs and Mo2N rod facilitate conductive loss, (3) highly dispersed magnetic CoFe nanoparticles within “tubes on rods” matrix build multi-scale magnetic coupling network and reinforce magnetic response capability, confirmed by the off-axis electron holography.

HighlightsMOF-derived porous Ni1−xCox@Carbon composites with tuning nano-micro structure were successfully synthesized.Magnetic-dielectric synergy effect among the Ni1−xCox@Carbon microspheres was confirmed by the off-axis electron holography technology.MOF-derived Ni@C microspheres displayed strong microwave absorption value of − 59.5 dB..Intrinsic electric-magnetic property and special nano-micro architecture of functional materials have a significant effect on its electromagnetic wave energy conversion, especially in the microwave absorption (MA) field. Herein, porous Ni1−xCox@Carbon composites derived from metal-organic framework (MOF) were successfully synthesized via solvothermal reaction and subsequent annealing treatments. Benefiting from the coordination, carbonized bimetallic Ni-Co-MOF maintained its initial skeleton and transformed into magnetic-carbon composites with tunable nano-micro structure. During the thermal decomposition, generated magnetic particles/clusters acted as a catalyst to promote the carbon sp2 arrangement, forming special core-shell architecture. Therefore, pure Ni@C microspheres displayed strong MA behaviors than other Ni1−xCox@Carbon composites. Surprisingly, magnetic-dielectric Ni@C composites possessed the strongest reflection loss value − 59.5 dB and the effective absorption frequency covered as wide as 4.7 GHz. Meanwhile, the MA capacity also can be boosted by adjusting the absorber content from 25% to 40%. Magnetic–dielectric synergy effect of MOF-derived Ni1−xCox@Carbon microspheres was confirmed by the off-axis electron holography technology making a thorough inquiry in the MA mechanism.

HighlightsA novel FeCoNi carbon fiber (FeCoNi/CF) is obtained through an improved electrospinning technology, which greatly endows the fiber with strong magnetic property.The FeCoNi/CF exhibits an enhanced electromagnetic loss capability due to the construction of one-dimensional magnetic FeCoNi alloy.The designed one-dimensional FeCoNi/CF exhibits excellent performance, with a broad effective absorption band of 1.3 GHz in the low-frequency electromagnetic field at an ultrathin thickness of 2 mm, which provides a great potential for practical application in the future.Rational designing of one-dimensional (1D) magnetic alloy to facilitate electromagnetic (EM) wave attenuation capability in low-frequency (2–6 GHz) microwave absorption field is highly desired but remains a significant challenge. In this study, a composite EM wave absorber made of a FeCoNi medium-entropy alloy embedded in a 1D carbon matrix framework is rationally designed through an improved electrospinning method. The 1D-shaped FeCoNi alloy embedded composite demonstrates the high-density and continuous magnetic network using off-axis electronic holography technique, indicating the excellent magnetic loss ability under an external EM field. Then, the in-depth analysis shows that many factors, including 1D anisotropy and intrinsic physical features of the magnetic medium-entropy alloy, primarily contribute to the enhanced EM wave absorption performance. Therefore, the fabricated EM wave absorber shows an increasing effective absorption band of 1.3 GHz in the low-frequency electromagnetic field at an ultrathin thickness of 2 mm. Thus, this study opens up a new method for the design and preparation of high-performance 1D magnetic EM absorbers.

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

HighlightsFe3+, Co2+, H3BTC, and collagen peptide are used to achieve a one-step assembly of stable FeCo-MOG/CP by manipulating the complexation effect and solution polarity.By optimizing pyrolysis, two kinds of nitrogen-doped carbon aerogels loaded with virus-shaped and nanospherical magnetic particles are obtained.FeCo/Fe3O4/NC and FeCo/NC aerogels exhibit excellent electromagnetic wave absorbing and radar stealth performances.Metal–organic gel (MOG) derived composites are promising multi-functional materials due to their alterable composition, identifiable chemical homogeneity, tunable shape, and porous structure. Herein, stable metal–organic hydrogels are prepared by regulating the complexation effect, solution polarity and curing speed. Meanwhile, collagen peptide is used to facilitate the fabrication of a porous aerogel with excellent physical properties as well as the homogeneous dispersion of magnetic particles during calcination. Subsequently, two kinds of heterometallic magnetic coupling systems are obtained through the application of Kirkendall effect. FeCo/nitrogen-doped carbon (NC) aerogel demonstrates an ultra-strong microwave absorption of − 85 dB at an ultra-low loading of 5%. After reducing the time taken by atom shifting, a FeCo/Fe3O4/NC aerogel containing virus-shaped particles is obtained, which achieves an ultra-broad absorption of 7.44 GHz at an ultra-thin thickness of 1.59 mm due to the coupling effect offered by dual-soft-magnetic particles. Furthermore, both aerogels show excellent thermal insulation property, and their outstanding radar stealth performances in J-20 aircraft are confirmed by computer simulation technology. The formation mechanism of MOG is also discussed along with the thermal insulation and electromagnetic wave absorption mechanism of the aerogels, which will enable the development and application of novel and lightweight stealth coatings.

Harvesting largely ignored and wasted electromagnetic (EM) energy released by electronic devices and converting it into direct current (DC) electricity is an attractive strategy not only to reduce EM pollution but also address the ever-increasing energy crisis. Here we report the synthesis of nanoparticle-templated graphene with monodisperse and staggered circular nanopores enabling an EM–heat–DC conversion pathway. We experimentally and theoretically demonstrate that this staggered nanoporous structure alters graphene’s electronic and phononic properties by synergistically manipulating its intralayer nanostructures and interlayer interactions. The staggered circular nanoporous graphene exhibits an anomalous combination of properties, which lead to an efficient absorption and conversion of EM waves into heat and in turn an output of DC electricity through the thermoelectric effect. Overall, our results advance the fundamental understanding of the structure–property relationships of ordered nanoporous graphene, providing an effective strategy to reduce EM pollution and generate electric energy. The electromagnetic (EM) energy released by electronic devices in the environment is largely wasted and contributes to EM pollution. Here, the authors report the synthesis of staggered circular nanoporous graphene enabling the absorption and conversion of EM waves into electricity via the thermoelectric effect.