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

Three-dimensional reduced graphene oxide foam modified with ZnO nanowires for enhanced microwave absorption properties

Graphene has been long sought-after over the past few decades because of its multiple functions and broad applications in various fields, such as energy, information, medicine, military equipments, and aerospace. In particular, it has been significantly reported in electromagnetic wave absorbing and shielding fields, promoting it as the most cutting-edge topic. Herein, we systematically comb the structures and electromagnetic functions of graphene hybrids. We demonstrate the advances in the microwave response mechanism, including relaxation, charge transport, magnetic resonance, and eddy currents, as well as magnetic-dielectric synergistic effects. Furthermore, our review mainly focuses on graphene-dispersed systems, flexible graphene papers, graphene hybrids, and 3D graphene architectures.

Graphene nanohybrids: excellent electromagnetic properties for the absorbing and shielding of electromagnetic waves

Flower-like CuS hollow microspheres composed of nanoflakes have been successfully prepared via a facile solvothermal method. The crystal structure, morphology and microwave absorption properties of the as-synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and a network analyser. The effects of reaction temperature, concentration of the reagents and reaction time on the structures and morphologies of the CuS products were investigated using XRD and SEM techniques. A plausible mechanism for the formation of hollow architectures related to Ostwald ripening was proposed. The CuS/paraffin composite containing 30 wt% CuS hollow microspheres shows the best microwave absorption properties compared with other CuS/paraffin composites. The minimum reflection loss of −31.5 dB can be observed at 16.7 GHz and reflection loss below −10 dB is 3.6 GHz (14.4–18.0 GHz) with a thickness of only 1.8 mm. The effective absorption (below −10 dB, 90% microwave absorption) bandwidth can be tuned between 6.2 GHz and 18.0 GHz for the absorber with a thin thickness in the range 1.5–4.0 mm. The results indicate that the microwave absorption properties of flower-like CuS hollow microspheres possess the advantages of broad bandwidth, strong absorption, lightweight and thin thickness are superior to those of other absorbing materials.

Synthesis of flower-like CuS hollow microspheres based on nanoflakes self-assembly and their microwave absorption properties

High-performance graphene microwave absorption materials are highly desirable in daily life and some extreme situations. A simple technique for the direct growth of graphene as absorption fillers in wave-transmitting matrices is of paramount importance to bring it to real-world application. Herein, a simple chemical vapor deposition (CVD) route for the direct growth of edge-rich graphene (ERG) with tailored structures and tunable dielectric properties in porous Si3N4 ceramics using only methyl alcohol (CH3OH) as precursor is reported. The large O/C atomic ratio of CH3OH helps to build a mild oxidizing atmosphere and leads to a unique structure featuring open graphite nanosteps and freestanding nanoplanes, endowing the ERG/Si3N4 hybrid with an appropriate balance between good impedance matching and strong loss capacity. Accordingly, the prepared materials exhibit superior electromagnetic wave absorption, far surpassing that of traditional CVD graphene and reduced graphene oxide-based materials, achieving an effective absorption bandwidth of 4.2 GHz covering the entire X band, with a thickness of 3.75 mm and a negligibly low loading content of absorbents. The results provide new insights for developing novel microwave absorption materials with strong reflection loss and wide absorption frequency range.

Direct Growth of Edge-Rich Graphene with Tunable Dielectric Properties in Porous Si3N4 Ceramic for Broadband High-Performance Microwave Absorption

A new method is introduced for the preparation of graphene/polyaniline hybrids using a one-step intercalation polymerization of aniline inside the expanded graphite. The structural and morphological characterizations were performed by X-ray diffraction analysis, transmission electron microscopy and field emission scanning electron microscopy. Both the experimental and first-principles simulated results show that the aniline cation formed by aniline and H+ tends to be drawn towards the electron-enriched zone and to intercalate into the interlayer of graphite. Subsequently, an in situ polymerization leads to the separation of graphite into graphene sheet, resulting from the exothermic effect and more vigorous movements of the chain molecules of polyaniline. The interactions between polyaniline and graphene were confirmed by Fourier transform infrared spectroscopy and Raman spectra. In addition, the graphene/polyaniline hybrid exhibited a breakthrough in the improvement of microwave absorption.

One-step synthesis of graphene/polyaniline hybrids by in situ intercalation polymerization and their electromagnetic properties

The facile preparation of high-purity carbon nanofibers (CNFs) remains challenging due to the high complexity and low controllability in reaction. A novel approach using gas-induced formation of Cu crystals to control the growth of CNFs is developed in this study. By adjusting the atmospheric composition, controllable preparation of Cu nanoparticles (NPs) with specific size and shape is achieved, and they are further used as a catalyst for the growth of straight or helical CNFs with good selectivity and high yield. The preparation of Cu NPs and the formation of CNFs are completed by a one-step process. The inducing effect of N2, Ar, H2, and C2H2 on the formation of Cu NPs is systematically investigated through a combined experimental and computational approach. The morphology of CNFs obtained under different conditions is rationalized in terms of Cu NP and CNF growth models. The results suggest that the shapes of CNFs, namely, straight or helical, depend closely on the size, shape, and facet activity of C...

Gas-induced formation of Cu nanoparticle as catalyst for high-purity straight and helical carbon nanofibers.

Preparation of high purity helical carbon nanofibers by the catalytic decomposition of acetylene and their growth mechanism

A simple approach using ∼90 nm Ni nanoparticles to tune the growth of carbon fibers is developed basing on the bottom-up regulation in this study. By adjusting the preparing temperature and atmospheric composition, the nickel-containing catalysts with specific sizes and shapes are alternately prepared from 90 nm to 500 nm. The straight carbon nanofibers and three kinds of carbon coils (single-helix carbon nanocoils, single-helix carbon microcoils and twinning double-helix carbon microcoils) with the coil diameter ranging from 150 nm to 3 μm are achieved by using the as-prepared catalyst. The relationship between the carbon coil and catalyst particle, and the growth mechanism for different kinds of helices are discussed in details. The results suggest that catalytic anisotropy come from growing tendency and rate of carbon deposition on the facets, edges and vertices of catalyst grain. The twinning structure exists in each fiber of the double-helix carbon microcoils regardless of circular or flat fiber, which is separated by the tip of the catalyst particle due to the different rate of carbon deposition at edge and vertex.

https://site.icce-nano.org/Clients/iccenanoorg/2013%20controllable%20synthesis%20of%20carbon%20coils%20and%20growth%20mechanism%20for%20twinning%20double-helix%20catalyzed%20by%20ni%20nanoparticle.pdf

Jun Lu

Papers

One-step synthesis of graphene/polyaniline hybrids by in situ intercalation polymerization and their electromagnetic properties

Gas-induced formation of Cu nanoparticle as catalyst for high-purity straight and helical carbon nanofibers.

Preparation of high purity helical carbon nanofibers by the catalytic decomposition of acetylene and their growth mechanism

Controllable synthesis of carbon coils and growth mechanism for twinning double-helix catalyzed by Ni nanoparticle