Constructing magnetic/dielectric dual loss and phonon/electron thermal carriers γ-Al2O3-based yolk-shell microspheres to collaboratively advance microwave absorption and heat conduction.

The severe electromagnetic (EM) interference and overheating issues in 5G/6G electric devices increasingly heighten the need for developing multifunctional materials with large heat conduction (HC) and high EM wave (EMW) absorption. Here, a series of γ-Al2O3-based yolk-shell microspheres (γ-AlOOH, γ-Al2O3, γ-Al2O3@C, γ-Al2O3@Fe3O4@C, and γ-Al2O3@FeAl2O4@Fe@C YSMSs) as multifunctional fillers are investigated for the simultaneous improvement in the HC and EMW absorption of γ-Al2O3-based composites. Using γ-AlOOH YSMSs as precursors produced from a hydrothermal method, the γ-Al2O3-based YSMSs were synthesized via an annealing route or soaking-annealing route; their phases, textures, and compositions were finely adjusted by changing the Al3+/Fe3+ molar ratio (ß) and annealing temperature (Ta). Results show that the thermal transfers in the γ-Al2O3-based YSMSs are promoted by the synergic effect of phonons and electrons when they are utilized as thermally conductive fillers. Comparatively, the γ-Al2O3@FeAl2O4@Fe@C YSMSs formed at ß = 8 : 2 and Ta = 700 °C exhibit a high HC of 1.84-3.29 W m-1 K-1 in a loading amount of 5-40%, exceeding those of not merely γ-Al2O3, γ-AlOOH, γ-Al2O3@C, and γ-Al2O3@Fe3O4@C YSMSs but also most previously reported fillers. Furthermore, the γ-Al2O3@Fe3O4@C YSMSs exhibit prominent EMW absorption properties with a large ABW/d of 4.49 GHz mm-1 (just 30% loading), superior to most other Al2O3-based absorbers. Such excellent EMW absorption could be explained by magnetic/dielectric dual loss and significant cavity and interfacial effects caused by yolk-shell structures. In conclusion, this work inspires the development of yolk-shell structures with magnetic/dielectric dual loss and phonon/electron thermal carriers as high-performance bifunctional materials with exceptional heat conduction and EMW absorption.

In situ generated gas bubble-directed self-assembly of multifunctional MgO-based hybrid foams for highly efficient thermal conduction, microwave absorption, and self-cleaning.

Developing multifunctional materials with superior thermal conductivity and microwave absorption is an effective means to address the increasingly serious electromagnetic (EM) compatibility and heat dissipation problems in modern electron devices. Here, multifunctional MgO/Mg(OH)2/C, MgO/M/C (M = Co, Ni, Cu), and MgO/NOx/C (N = Fe, Mn) hybrid foams were synthesized using a facile one-step gas-bubble-assisted combustion method, and their texture, composition, and properties were regulated by tuning salt type and feeding ratio. Our results show that the MgO/Co/C foams have high thermal conductivity (3.40-4.09 W m-1 K-1) with a filler load of 20-50 wt% at the Co2+ molar content of φ = 70 mol% and excellent EM wave absorption (EABW = 11.44 GHz), with a thickness of 2.1 mm and a minimal reflection loss of -59.42 dB at φ = 90 mol%. The enhanced properties are ascribed to the construction of foams with 3D interconnected networks and the synergistic effect of magnetic Co, insulating MgO, and dielectric C, which provide a continuous pathway for electron/phonon relay transmission and magnetic/dielectric dual losses. Moreover, the MgO/Co/C foams possess strong mechanical/hydrophobicity performance, tunable magnetic properties, and electrical conductivity, and can be applied in self-cleaning, electromagnetic interference, and heat management. Overall, this study offers a novel understanding of preparing multifunctional heat conductive-EM wave absorptive foam materials in modern electronic devices.

High-performance composite elastomers with abundant heterostructures for enhanced electromagnetic wave absorption with ultrabroad bandwidth.

Two-dimensional (2D) MXene has attracted vast attention in electromagnetic wave absorption (EWA), but there remains a contradiction between maintaining impedance matching and enhancing dielectric loss. Herein, the multi-scale architectures of ecoflex/2D MXene (Ti3C2Tx)@zero-dimensional CoNi sphere@one-dimensional carbon nanotube composite elastomers were successfully constructed by simple liquid-phase reduction and thermo-curing method. The binding between the hybrids as fillers and ecoflex as a matrix greatly enhanced the EWA capability of the obtained composite elastomer and improved its mechanical properties. Owing to its good impedance matching, abundant heterostructures, and synergistic electrical and magnetic losses, this elastomer exhibited an excellent minimum reflection loss of -67 dB at 9.46 GHz under a thickness of 2.98 mm. In addition, its ultrabroad effective absorption bandwidth reached 6.07 GHz. This achievement will pave the way for the exploitation of multi-dimensional heterostructures as high-performance electromagnetic absorbers with superior EWA ability.

Wheat-like Ni-coated core-shell silver nanowires for effective electromagnetic wave absorption.

Nowadays, developing high-performance electromagnetic functional materials to eliminate the ever-increasing electromagnetic pollution problem is necessary for the complex electromagnetic environment. However, the materials with high electrical conductivity are prone to secondary electromagnetic pollution due to interface impedance mismatching. Herein, the wheat-like electrically conductive and magnetic silver nanowire@nickle (AgNW@Ni) composites were fabricated via a one-pot in-situ growth method. The electromagnetic properties of the composites could be regulated by adjusting different ratios of precursors, resulting in various morphological features of the nanowire as the core with different Ni shell thicknesses. When the Ag and Ni molar ratio was 1:1.1, the AgNW@Ni composite exhibited the optimal minimum reflection loss (RLmin) of -61.1 dB with an adequate effective absorption bandwidth (EAB) of 4.06 GHz owing to good impedance matching, abundant heterostructures, and synergistic electrical and magnetic losses. Even after three months, it still maintained an acceptable RLmin value of -39.7 dB and similar EAB, demonstrating its long-term operational stability. This unique composite is expected to be applied in more actual electromagnetic protection occasions.

Synchronously boosting microwave-absorbing and heat-conducting capabilities in CeO2/Ce(OH)3 core-shell nanorods/nanofibers via Fe-doping amount control.

To address the electromagnetic interference (EMI) and heat dissipation issues in electronics, we pioneered the synthesis of Fe-doped CeO2/Ce(OH)3 core-shell nanorods/nanofibers (CSNRs/NFs) through a simple one-pot hydrothermal reaction. The growth of core-shell nanofibers was driven by the minimal surface free energy and vacancy formation energy. By controlling the amount of Fe-doping, not simply Fe0 content, crystallite size, defects, impurities, and length/diameter ratios could be modulated, but the electric, magnetic, thermal, and microwave absorption performance. The efficient 3D network constructed by 1D nanofibers in a silicone matrix offered a continuous pathway for electrons/phonon relay transmission, endowing the composites with exceptional heating conductance (3.442 W m-1 K-1) at 20%Fe-doping. An ultrawide absorption band (9.26 GHz) with intense absorption (-42.33 dB) and small thickness (1.7 mm) was achieved at 10%Fe-doping due to excellent matching performance, strong attenuation ability, and large EM parameters. Overall, Fe-doped CeO2/Ce(OH)3 CSNFs are a promising material for next-generation electronics with effective heat dissipation and EM wave absorption due to their straightforward process, mass production, and outstanding comprehensive performance. Beyond providing a deeper insight into the accurate defect modulation in magnetic-dielectric-double-loss absorbents by doping, this paper proposes an electron/phonon relay transmission strategy to improve heat conductance.

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 (RLm) 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.

Distinct plasmon resonance enhanced microwave absorption of strawberry-like Co/C/Fe/C core-shell hierarchical flowers via engineering the diameter and interparticle spacing of Fe/C nanoparticles.

Strawberry-like Co/C/Fe/C core-shell hierarchical flowers (CSHFs) consisting of separated Fe/C nanoparticles (NPs) anchoring on a Co HF surface were prepared by decomposing Fe(CO)5 in the presence of Co HFs. Changing the decomposition temperature (T d) and Fe(CO)5 volume (δ) could also facilely modulate the phase structure, surface morphology and composition of the products. The low T d and small δ helped form Co/C/Fe/C CSHFs with a strawberry-like plasmon surface. The diameter and interparticle spacing-dependent electromagnetic properties were investigated at 2-18 GHz. The interparticle-spacing-to-diameter ratio determines the plasmon resonance and coupling. The permittivity and permeability enhanced by strong plasmon resonance were exhibited by Co/C/Fe/C CSHFs formed at δ = 3-4 mL with the interparticle-spacing-to-diameter ratio of 1.36-0.76. The collective oscillation of the conduction band electrons and near field on the Co/C and Fe/C surfaces generated a surface plasmon resonance and coupling, which were responsible for significantly enhanced permittivity and permeability with negative values. In view of the synergistic effect of the enhanced permittivity and permeability, dual dielectric relaxations, dual magnetic resonances, high attenuation and good impedance matching, Co/C/Fe/C CSHFs with particle size of 110 ± 20-380 ± 100 nm and interparticle spacing of 150 ± 50 nm were excellent absorbers that feature strong absorption, broad bandwidth and light weight. An optimal reflection loss (R L) of -45.06 was found at 17.92 GHz for an absorber thickness of 1.6 mm, and the frequency range (R L ≤ -20 dB, 99% absorption) was over 2-18 GHz. Our findings demonstrated that optimally designed plasmonic heterostructures must be fabricated to improve microwave absorption performances for future applications.

Low-Cost Carbothermal Reduction Preparation of Monodisperse Fe3O4/C Core-Shell Nanosheets for Improved Microwave Absorption.

This paper demonstrates a facile and low-cost carbothermal reduction preparation of monodisperse Fe3O4/C core-shell nanosheets (NSs) for greatly improved microwave absorption. In this protocol, the redox reaction between sheet-like hematite (α-Fe2O3) precursors and acetone under inert atmosphere and elevated temperature generates Fe3O4/C core-shell NSs with the morphology inheriting from α-Fe2O3. Thus, Fe3O4/C core-shell NSs of different sizes ( a) and Fe3O4/C core-shell nanopolyhedrons are obtained by using different precursors. Benefited from the high crystallinity of the Fe3O4 core and the thin carbon layer, the resultant NSs exhibit high specific saturation magnetization larger than 82.51 emu·g-1. Simultaneously, the coercivity enhances with the increase of a, suggesting a strong shape anisotropy effect. Furthermore, because of the anisotropy structure and the complementary behavior between Fe3O4 and C, the as-obtained Fe3O4/C core-shell NSs exhibit strong natural magnetic resonance at a high frequency, enhanced interfacial polarization, and improved impedance matching, ensuring the enhancement of the microwave absorption. The 250 nm NSs-paraffin composites exhibit reflection loss (RL) lower than -20 dB (corresponding to 99% absorption) in a large frequency ( f) range of 2.08-16.40 GHz with a minimum RL of -43.95 dB at f = 3.92 GHz when the thickness is tuned from 7.0 to 1.4 mm, indicating that the Fe3O4/C core-shell NSs are a good candidate to manufacture high-performance microwave absorbers. Moreover, the as-developed carbothermal reduction method could be applied for the fabrication of other composites based on ferrites and carbon.

Excellent microwave-absorbing properties of elliptical Fe3O4 nanorings made by a rapid microwave-assisted hydrothermal approach.

High-quality elliptical polycrystalline Fe3O4 nanorings (NRs) with continuously tunable size have been synthesized in large amounts via a rapid microwave-assisted hydrothermal approach. The surface-protected glucose reducing/etching/Ostwald ripening mechanism is responsible for the formation of NRs. Ring size can be modulated by selecting iron glycolate nanosheets with various sizes as precursors. The size-dependent magnetic behavior of the NRs was observed. Our research gives insights into the understanding of the microwave absorption mechanism of elliptical Fe3O4 NRs. Owing to their large specific surface area, shape anisotropy, and closed ring-like configuration, elliptical polycrystalline Fe3O4 NRs exhibited significantly enhanced microwave absorption performance compared with Fe3O4 circular NRs, nanosheets, microspheres, nanospindles, and nanotubes. An optimal reflection loss value of -41.59 dB is achieved at 5.84 GHz and R(L) values (≤-20 dB) are observed at 3.2-10.4 GHz. Some new mechanisms including multiple scattering, oscillation resonance absorption, microantenna radiation, and interference are also crucial to the enhanced absorption properties of NRs. These findings indicate that ring-like nanostructures are a promising structure for devising new and effective microwave absorbers.

Facile Hydrothermal Synthesis of Fe3O4/C Core-Shell Nanorings for Efficient Low-Frequency Microwave Absorption.

Using elliptical iron glycolate nanosheets as precursors, elliptical Fe3O4/C core-shell nanorings (NRs) [25 ± 10 nm in wall thickness, 150 ± 40 nm in length, and 1.6 ± 0.3 in long/short axis ratio] are synthesized via a one-pot hydrothermal route. The surface-poly(vinylpyrrolidone) (PVP)-protected-glucose reduction/carbonization/Ostwald ripening mechanism is responsible for Fe3O4/C NR formation. Increasing the glucose/precursor molar ratio can enhance carbon contents, causing a linear decrease in saturation magnetization (Ms) and coercivity (Hc). The Fe3O4/C NRs reveal enhanced low-frequency microwave absorption because of improvements to their permittivity and impedance matching. A maximum RL value of -55.68 dB at 3.44 GHz is achieved by Fe3O4/C NRs with 11.95 wt % C content at a volume fraction of 17 vol %. Reflection loss (RL) values (≤-20 dB) are observed at 2.11-10.99 and 16.5-17.26 GHz. Our research provides insights into the microwave absorption mechanism of elliptical Fe3O4/C core-shell NRs. Findings indicate that ring-like and core-shell nanostructures are promising structures for devising new and effective microwave absorbers.

High-quality elliptical iron glycolate nanosheets: selective synthesis and chemical conversion into FexOy nanorings, porous nanosheets, and nanochains with enhanced visible-light photocatalytic activity.

This paper describes an original and facile polyol-mediated solvothermal synthesis of elliptical iron glycolate nanosheets (IGNSs) combined with precursor thermal conversion into γ-Fe2O3 and α-Fe2O3/γ-Fe2O3 porous nanosheets (PNSs), α-Fe2O3 nanochains (NCs), and elliptical Fe3O4 nanorings (NRs). The IGNSs were produced via the oxidation-reduction and co-precipitation reactions in the presence of iron(III) salts, ethylene glycol, polyethylene glycol, and ethylenediamine. Control over Fe(3+) concentration, temperature, and time can considerably modulate the size and phase of the products. The IGNSs can be transformed to γ-Fe2O3 and α-Fe2O3/γ-Fe2O3 PNSs, α-Fe2O3 NCs, and elliptical Fe3O4 NRs by heat treatment under various annealing temperatures and ambiences. The PNSs and NCs exhibited high soft magnetic properties and coercivity, respectively. Visible-light photocatalytic activity toward RhB in the presence of H2O2 by PNSs and NCs was phase-, SBET, size-, porosity-, and local structure-dependent, following the order: α-Fe2O3 NCs > α-Fe2O3/γ-Fe2O3 PNSs > γ-Fe2O3 PNSs > IGNSs. In particular, α-Fe2O3/γ-Fe2O3 PNSs possessed significantly enhanced photocatalytic activity with good recyclability and could be conveniently separated by an applied magnetic field because of high magnetization. We believe that the as-prepared α-Fe2O3/γ-Fe2O3 PNSs have potential practical use in waste water treatment and microwave absorption.

Generalized green synthesis and formation mechanism of sponge-like ferrite micro-polyhedra with tunable structure and composition.

This paper describes a green versatile glucose-engineered precipitation-sintering process that allows for the selective and mass preparation of spongy porous ferrite (M = Fe, Zn, Co, Ni, Mn, etc.) micro-polyhedra with tunable morphology, texture, and composition. Some kinetic factors, such as the molar ratio of glucose to metal nitrates, reaction temperature, sintering temperature and time, and type of metal nitrates, can be expediently employed to modulate their aspect ratio, shape, size, composition, and textural properties. In this protocol, glucose functions as a reductant, protecting agent, structure-directing agent, and a sacrificial template to guide the assembly of sheet-like nuclei into polyhedral precursors and the formation of spongy porous structures. Owing to larger EM parameters, multiresonant behavior, and dissipative current, spongy porous Fe3O4 polyhedra exhibited enhanced microwave-absorbing properties. This endows them with important potential applications in magnetic devices, catalysis, sorption, photoluminescence, electromagnetic wave absorbing materials, anode materials, and so on. Meanwhile, this general approach can be extended to synthesize other porous sponges with regular geometric configuration because it is simple, inexpensive, environmentally benign, and suitable for extensive production.

Polymorphous ZnO complex architectures: selective synthesis, mechanism, surface area and Zn-polar plane-codetermining antibacterial activity.

Complex ZnO architectures with tunable morphologies and structures were obtained by modulating only the base type and molar ratio of base to Zn2+ (α) using an easy one-pot hydrothermal approach without any template or organic additive. Characterizations by X-ray diffraction, Fourier-transform infrared spectrometry, scanning electron microscopy, transmission electron microscopy, and surface area analysis were performed. The effect of the base type and base/Zn2+ molar ratio on the morphology and corresponding mechanism were determined. The correlations between the microstructure and properties were established. The antibacterial effect of the ZnO samples was probably due to a combination of variable factors. Better antibacterial activity is derived from more effective antibacterial surfaces, which are mainly associated with the specific surface area and Zn-polar plane. Thus, flower-like architectures with larger specific surface areas and more highly exposed (0001) Zn-polar surfaces outwards are promising structures for ZnO antibacterial agents. This work provides a guide for devising and synthesizing highly efficient antibacterial materials.

Enhanced reactive oxygen species (ROS) yields and antibacterial activity of spongy ZnO/ZnFe2O4 hybrid micro-hexahedra selectively synthesized through a versatile glucose-engineered co-precipitation/annealing process.

In this study, sponge-like ZnO/ZnFe2O4 hybrid micro-hexahedra with diverse textures and compositions were fabricated by the thermal decomposition of hexahedral zinc/iron oxalate precursors, starting from a glucose-engineered co-precipitation process. The resulting ZnO/ZnFe2O4 micro-hexahedra were systematically characterized by X-ray powder diffraction, Fourier-transform infrared spectroscopy, scanning electronic microscopy, transmission electron microscopy (TEM), high-resolution TEM, and surface area analysis. Moreover, modulation in crystal size, composition, and textural properties of spongy ZnO/ZnFe2O4 micro-hexahedra was easily achieved by varying the Zn2+/Fe3+ feeding ratio and the annealing temperature. The antibacterial property of the products was analyzed by testing ATP (adenosine triphosphate) and inhibition zones. Results showed that oxidative stress was the governing mechanism for the antibacterial activity of ZnO/ZnFe2O4 hybrid materials. Moreover, we found that the higher reactive oxygen species yields and the resulting antibacterial activity were exhibited by the ZnO/ZnFe2O4 micro-hexahedra formed at lower sintering temperatures rather than the pure ZnO and Fe2O3. The enhanced antibacterial properties were likely caused by the spongy ZnO/ZnFe2O4 heterostructures, improving the probability of photoinduced charge separation and broadening the visible-light absorption.

Flower-like porous hematite nanoarchitectures achieved by complexation-mediated oxidation-hydrolysis reaction.

Flower-like porous hematite (α-Fe(2)O(3)) nanoarchitectures composed of ultra-thin nanoflakes were prepared by annealing the iron oxide precursor formed via the oxidation-hydrolysis reaction between Fe(II) ions and Tris(hydroxymethyl)aminomethane (abbreviated as Tris). The microstructure of the prepared FeOOH and hematite samples were fully characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, Fourier-transforming infrared spectra, thermogravimetric analysis, and nitrogen adsorption-desorption isotherm. Based on the influences of reactant concentrations, reaction time and reaction temperature on the morphologies of the resultant samples, a formation mechanism of etching was proposed, Fe(II)-Tris complexes were self-assembled via hydrogen bonds into brick-like building blocks, which then aggregated into rudimentary nanoparticles, and the synergistic effect between the crystallization of FeOOH and dissociation of Fe(II)-Tris complexes make the rudimentary nanoparticles evolve into the flower-like products. The as-prepared flower-like α-Fe(2)O(3) nanostructures possessed a Brunauer-Emmett-Teller specific surface area of 191.63 m(2)g(-1), hierarchical pore distribution ranging from micropores to macropores, and good crystallinity, and excellent visible photocatalysis in terms of removing chemical oxygen demand of dimethyl sulfoxide industrial wastewater. The current work provides a reliable approach for building functional hierarchical nanoarchitectures and the prepared iron oxide nanomaterials demonstrate an excellent ability to remove toxic pollutants in industrial wastewater.

One-pot synthesis of biocompatible Te@phenol formaldehyde resin core-shell nanowires with uniform size and unique fluorescent properties by a synergized soft-hard template process.

One-pot hydrothermal process has been developed to synthesize uniform Te@phenol formaldehyde resin core-shell nanowires with unique fluorescent properties. A synergistic soft-hard template mechanism has been proposed to explain the formation of the core-shell nanowires. The Te@phenol formaldehyde resin core-shell nanowires display unique fluorescent properties, which give strong luminescent emission in the blue-violet and green regions with excitation wavelengths of 270 nm and 402 nm, respectively.