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Optical microscopy images of the as obtained hollow particles (a) SSHPs, (b) ASHPs, (c) DSCHPs; (d) SEM image of DSCHPs
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Double shell composite hollow particles (DSCHPs) with silica (inner shell) and magnetic metal (outer shell) shells are prepared on a large scale through a novel cost effective strategy involving spray drying, simultaneous silicification and surface decoration with active sites, and finally directed growth of magnetic metal shells. The silica shell...
Citations
... Readers interested in these cases are encouraged to refer to the specific examples. 122 ...
Multishelled hollow nanostructures have attracted considerable research interest owing to their unique structural features, promising properties, and fascinating performances in relevant applications. During the past few decades, considerable progress has been made in the synthesis of multishelled hollow nanostructures by accurately controlling their geometric morphology, chemical composition, thickness, number of shells, and their applications in various fields. In this review, we present a comprehensive overview on the recently used synthesis approaches for fabricating multishelled hollow nanostructures. For a comprehensive review, the synthesis approaches have been classified into four categories, namely, hard template, soft template, self-template, and template-free approaches based on the template/structure-directing agent used. The advantages and disadvantages of each approach are discussed by comparing with each other. Furthermore, the fascinating performances of multishelled hollow nanostructures, application in energy conversion and storage, environment remediation, chemical catalysis, and biomedicine are comprehensively summarized. Combining certain typical examples and related theoretical analysis, the relationship between the structure of multishelled hollow nanomaterials and their specific application performances in the related areas is highlighted. Finally, the emerging challenges and future prospects of multishelled hollow nanostructures in the research and development for the future are outlined. This journal is
... Rational structure design is a powerful method to prepare ideal EM absorbers besides raw materials selection. A variety of micro/ nano structures have been designed and fabricated, including spheres [4][5][6][7][8][9], rods [10], nanotubes [11], nanowires [12,13], flakes [14], and foam [15]. Spherical absorbers integrate the advantages of raw materials with spherical colloids, which give them several favorable features, such as regular geometry, good liquidity, tunable porosity, and controllable particle size distribution. ...
In this study, mesoporous carbon hollow spheres (PCHMs) with tunable textural properties have been prepared through a facile hard template etching method. The PCHMs were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), Raman, and nitrogen adsorption and desorption system. The uniform PCHMs with shell thickness ranges from 23 nm to 55 nm is realized. PCHMs with different textural properties can regulate dielectric and electromagnetic wave absorption effectively. The composite of paraffin wax mixed with 10 wt % PCHMs (the shell thickness of PCHMs is 23 nm and 35 nm) exhibits a minimum coefficient value of -53.8 dB at 8.8 GHz with a thickness of 3.4 mm. Besides, it is remarkable that the effective absorption bandwidth covers all the X band with as low as 10 wt % filler ratio, compared with other spherical electromagnetic wave absorbers. The excellent electromagnetic wave absorption capability of PCHMs can be ascribed to the better impendence matching and strong EM wave attenuation constant based on tunable textural properties. Our results provide a facile strategy to tune dielectric properties of spherical carbon absorbers based on textural properties, and which can be extend to other spherical absorbers.
Ferromagnetic metal/alloy particles are widely used in the field of electromagnetic wave absorption. Doping is an effective means of modulating the electromagnetic properties of magnetic metals and alloys. In this study, (Fe3Co7)1-xRux nanoparticles with different Ru doping contents are prepared using a polyvinylpyrrolidone (PVP)-assisted liquid-phase reduction process. First-principles calculations reveal that strong electron-orbit hybridization occurs between Ru-4d and Fe/Co-3d owing to the strong spin-orbit coupling effect of Ru-4d orbital electrons. This generates a space charge distribution and carries a magnetic moment of 1.80 hbar/2. The use of Ru doping results in a reduction in FeCo alloy particle size from 1.5 μm to 200 nm, slight decrease in the saturation magnetization from 179 to 152 emu/g, and increase in the electrical conductivity from 2.79 × 10⁻⁴ to 6.62 × 10-4 S·cm⁻¹. The dielectric and magnetic loss values vary from 0.22 to 0.95 and 0.06 to 0.37, respectively, in the 2-18 GHz frequency range. Ru doping-induced dipole polarization relaxation, exchange resonance, and increased conductivity loss are the primary reasons for the enhanced electromagnetic loss of the material. When the level of Ru doping x reaches 0.10, the minimum reflection loss (RLmin) increases from -21.5 to -41.9 dB. Thus, (Fe3Co7)1-xRux is a promising material for electromagnetic loss due to its tunable composition, size, conductivity, magnetic properties, and excellent electromagnetic loss capability.
P-doped FeCo microcubes are fabricated through a facile solvothermal method using sodiumphosphinate (NaH2PO2·H2O) as assisted agent. The morphology and particle size of FeCo alloy can be well controlled by tuning the NaH2PO2·H2O amount. Benefitting from the unique morphology and the incorporation of P dopants, P-doped FeCo microcubes exhibit outstanding electromagnetic wave absorption performance with reflection loss of −51.67 dB at a very thin layer thickness of 1.60 mm, which is superior to the previously reported FeCo-based absorbers. The radar cross section (RCS) of FeCo as an absorber is simulated in the frequency of 2.0–18.0 GHz for the first time, which indicates that the RCS reduction effect is evident in a wide band, and the most significant decline in RCS is from −2.67 to −16.53 dBm² for horizontal polarization, and from −2.51 to −15.67 dBm² for vertical polarization. This work presents an outstanding electromagnetic wave absorbing material, and systematically analyzes the contribution of magnetic absorber to the reduction of RCS, which provides a reference for the practical application of magnetic absorbing materials.
Dopamine-derived cavities/Fe3O4 nanoparticles-encapsulated carbonaceous composites with self-generating three-dimensional (3D) network structure were successfully fabricated by a facile synthetic method, in which sodium alginate provided carbon matrix pores and excellent microwave absorption performance was established. The hollow cavities derived from the core-shell-like CaCO3@polydopamine were creatively introduced into the 3D absorber to significantly improve the absorption performance. The sample calcined at 700 °C exhibited the most outstanding microwave absorption performance, with minimal reflection loss up to −50.80 dB at 17.52 GHz with a rare thickness of only 1.5 mm when filler loading was 35% in paraffin matrix. The effective absorption bandwidth of reflection loss < −10 dB reached 3.52 GHz from 14.48 GHz to 18 GHz, corresponding to the same thickness of 1.5 mm. In contrast, the sample without hollow dopamine-derived cavities showed poor performance due to poor impedance matching, and this highlights the role of hollow cavities brought into the 3D structure, which led to a difference in interfacial polarization, multiple reflections and scattering. The novel dopamine-derived cavities/Fe3O4 nanoparticles-encapsulated carbonaceous composites with 3D network structure can be regarded as a promising candidate for application as a microwave absorber with strong absorption.
