Electromagnetic Response and Energy Conversion for Functions and Devices in Low‐Dimensional Materials

Multifunctional Organic–Inorganic Hybrid Aerogel for Self‐Cleaning, Heat‐Insulating, and Highly Efficient Microwave Absorbing Material

With the rapid arising of information technology, microwave absorbing materials (MAMs) are playing an increasingly significant role in electronic reliability, healthcare, and national defense security. Hence, development of high performance MAMs with thin thickness, low density, wide bandwidth, and strong absorption has attracted great interests. Recently, taking graphene as MAMs for high-performance electromagnetic (EM) wave attenuation has grabbed considerable attention, owing to their low density, high specific surface area, strong dielectric loss, and high electronic conductivity. Furthermore, in order to address the interfacial impedance mismatching of the sole graphene materials, incorporation of other lossy materials has been widely studied as the imperative solution to improve its MA performance. In this review, we introduce the theory of microwave absorption and summarize recent advances in the fabrication of graphene-based MAMs, including rational design of the microstructure of pure graphene and tunable chemical integrations with polymers, magnetic metals, ferrites, ceramics, and multicomponents composites. The key point of enhancing MA in graphene-based MAMs is to regulate their EM properties, improve of impedance matching, and create diversified loss mechanisms. Furthermore, the shortcomings, challenges, and prospects of graphene-based MAMs are also put forward, which will be helpful to people working in the related fields.

Graphene-based microwave absorbing composites: A review and prospective

Carbon nanocages with N-doped carbon inner shell and Co/N-doped carbon outer shell as electromagnetic wave absorption materials

Lightweight absorption-dominated electromagnetic interference (EMI) shielding materials are more attractive than conventional reflection-dominated counterparts because they minimize the twice pollution of the reflected electromagnetic (EM) wave. Here, porous Ti2CT x MXene/poly(vinyl alcohol) composite foams constructed by few-layered Ti2CT x (f-Ti2CT x) MXene and poly(vinyl alcohol) (PVA) are fabricated via a facile freeze-drying method. As superior EMI shielding materials, their calculated specific shielding effectiveness reaches up to 5136 dB cm2 g-1 with an ultralow filler content of only 0.15 vol % and reflection effectiveness (SER) of less than 2 dB, representing the excellent absorption-dominated shielding performance. Contrast experiment reveals that the good impedance matching derived from the multiple porous structures, internal reflection, and polarization effect (dipole and interfacial polarization) plays a synergistic role in the improved absorption efficiency and superior EMI shielding performance. Consequently, this work provides a promising MXene-based EMI shielding candidate with lightweight and high strength features.

Lightweight Ti2CTx MXene/Poly(vinyl alcohol) Composite Foams for Electromagnetic Wave Shielding with Absorption-Dominated Feature

In this study, yolk–shell Ni@SnO2 composites with a designable interspace were successfully prepared by the simple acid etching hydrothermal method. The Ni@void@SnO2 composites were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The results indicate that interspaces exist between the Ni cores and SnO2 shells. Moreover, the void can be adjusted by controlling the hydrothermal reaction time. The unique yolk–shell Ni@void@SnO2 composites show outstanding electromagnetic wave absorption properties. A minimum reflection loss (RLmin) of −50.2 dB was obtained at 17.4 GHz with absorber thickness of 1.5 mm. In addition, considering the absorber thickness, minimal reflection loss, and effective bandwidth, a novel method to judge the effective microwave absorption properties is proposed. On the basis of this method, the best microwave absorption properties were obtained with a 1.7 mm th...

Yolk–Shell Ni@SnO2 Composites with a Designable Interspace To Improve the Electromagnetic Wave Absorption Properties

Yolk–shell ternary composites composed of a Ni sphere core and a SnO2(Ni3Sn2) shell were successfully prepared by a facile two-step method. The size, morphology, microstructure, and phase purity of the resulting composites were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy (TEM), high-resolution TEM, selected-area electron diffraction, and powder X-ray diffraction. The core sizes, interstitial void volumes, and constituents of the yolk–shell structures varied by varying the reaction time. A mechanism based on the time-dependent experiments was proposed for the formation of the yolk–shell structures. The yolk–shell structures were formed by a synergistic combination of an etching reaction, a galvanic replacement reaction, and the Kirkendall effect. The yolk–shell ternary SnO2 (Ni3Sn2)@Ni composites synthesized at a reaction time of 15 h showed excellent microwave absorption properties. The reflection loss was found to be as low as–43 dB at 6.1 GHz. The enhanced microwave absorption properties may be attributed to the good impedance match, multiple reflections, the scattering owing to the voids between the core and the shell, and the effective complementarities between the dielectric loss and the magnetic loss. Thus, the yolk–shell ternary composites are expected to be promising candidates for microwave absorption applications, lithium ion batteries, and photocatalysis.

Facile synthesis of yolk–shell Ni@void@SnO2(Ni3Sn2) ternary composites via galvanic replacement/Kirkendall effect and their enhanced microwave absorption properties

Lightweight graphene aerogels by decoration of 1D CoNi chains and CNTs to achieve ultra-wide microwave absorption

Exceptionally porous three-dimensional architectural nanostructure derived from CNTs/graphene aerogel towards the ultra-wideband EM absorption

In this study, hollow three-dimensional CuS hierarchical microspheres were prepared via a facile galvanic replacement reaction. The hollow flower-like CuS microspheres were characterized by XRD, Raman, XPS, SEM and TEM techniques, which revealed that numerous nanoflakes were self-assembled to construct hollow flowers. Based on time-dependent experiments, a plausible formation mechanism (galvanic replacement reaction) was proposed. Paraffin-based composites, containing 50 wt% hollow CuS, exhibited outstanding microwave absorption capabilities, which were attributed to the suitable impedance match and dielectric loss. The minimal reflection loss was −17.5 dB and the effective bandwidth was 3.0 GHz with thin absorber thickness of 1.1 mm. In addition, we put forward a novel solution to evaluate the microwave absorption efficiency. The high efficiency microwave absorption properties originate from the electric/dielectric polarization and unique hollow flower-like structure. The hollow structures can adjust the dielectric properties to obtain good impedance matching. Moreover, the two-dimensional flakes and hollow flowers can induce more multiple reflection and scattering, which consumes more microwave energy. This study has led to a novel useful method for the design of hollow structures used as high efficiency microwave absorbers.

Xiaoqin Guo

Papers

Yolk–Shell Ni@SnO2 Composites with a Designable Interspace To Improve the Electromagnetic Wave Absorption Properties

Facile synthesis of yolk–shell Ni@void@SnO2(Ni3Sn2) ternary composites via galvanic replacement/Kirkendall effect and their enhanced microwave absorption properties

Lightweight graphene aerogels by decoration of 1D CoNi chains and CNTs to achieve ultra-wide microwave absorption

Exceptionally porous three-dimensional architectural nanostructure derived from CNTs/graphene aerogel towards the ultra-wideband EM absorption

Constructing hierarchical hollow CuS microspheres via a galvanic replacement reaction and their use as wide-band microwave absorbers