Synthesis of hierarchical porous nitrogen-doped reduced graphene oxide/zinc ferrite composite foams as ultrathin and broadband microwave absorbers

Leaflet-heterostructures by MWCNT self-assembly following electrospinning

Electrospinning of nanocarbons such as graphene and carbon nanotubes typically produces mats composed of one-dimensional fibers where the carrier polymer encapsulates the nanocarbons. Recently it was found that decreasing the amount of carrier polymer in approaching the electrospinning-electrospray boundary for graphene suspensions resulted in retention of the graphene two-dimensional anisotropy with one-dimensional carrier polymer fibers connecting flakes. We explored a similar decrease in carrier polymer in MWCNT suspensions to investigate the network topology that might ensue. Unexpectedly, two-dimensional leaflet meso-networks were obtained wherein the leaflets comprise laterally aligned MWCNTs one to several nanotubes thick. A mechanism based on capillary force-driven MWCNT self-assembly activated by menisci formed during drying of electrospun fibers is presented. Such materials offer new approaches to producing high surface-area coatings for catalytic and energy applications and suggest ways of formulating two-dimensional MWCNT assemblies in metal foams and other open-cell porous materials.

Structurally Stable, High-Strength Graphene Oxide/Carbon Nanotube/Epoxy Resin Aerogels as Three-Dimensional Skeletal Precursors for Wave-Absorbing Materials

Three-dimensional (3D) graphene oxide aerogel (GOA) is one of the best fillers for composites for microwave absorption. However, its further development has been hindered by the poor mechanical properties. Methodology to improve the mechanical properties of the aerogel remains an urgent challenge. Herein, graphene oxide/carbon nanotube/epoxy resin composite aerogel (GCEA) was successfully prepared by a facile method. The results showed that the prepared GCEA with the hierarchical and 3D cross-linked structures exhibited excellent compression performance, structural and thermal stability, high hydrophilicity, and microwave absorption. The prepared GCEA recovered from multiple large strain cycles without significant permanent deformation. The minimum reflection loss (RL) was −39.60 dB and the maximum effective absorption bandwidth (EAB) was 2.48 GHz. The development of the enhanced GO aerogels will offer a new approach to the preparation of 3D microwave-absorbing skeletal materials with good mechanical properties.

Controllable Synthesis of Mo3C2 Encapsulated by N-Doped Carbon Microspheres to Achieve Highly Efficient Microwave Absorption at Full Wavebands: From Lemon-like to Fig-like Morphologies

Mo₃C₂@N-doped carbon microspheres (Mo₃C₂@NC) have been discovered to be a family of superior microwave absorbing materials. Herein, Mo₃C₂@NC was synthesized through a simple high-temperature carbonization process by evaporating a graphite anode and Mo wire in Ar and N₂ atmospheres with an N-doping content of 6.4 at. %. Attributing to the self-assembly mechanism, the number of Mo wires inserted into the graphite anode determined the morphologies of Mo₃C₂@NC, which were the unique lemon-like (1- and 2-Mo₃C₂@NC) and fig-like (3-, 4-, and 5-Mo₃C₂@NC) microstructures. 1- and 2-Mo₃C₂@NC exhibited powerful reflection losses (RLs) of -45.60, -45.59, and -47.11 dB at the S, C and X bands, respectively, which corresponded to thinner thicknesses. 3-, 4-, and 5-Mo₃C₂@NC showed outstanding absorption performance at the C, X, and Ku bands, respectively, with each value of a minimum RL less than -43.00 dB. In particular, the strongest RL (-43.56 dB) for 5-Mo₃C₂@NC corresponded to an ultrathin thickness of 1.3 mm. In addition, the maximum effective absorption bandwidth was 6.3 GHz for 4-Mo₃C₂@NC. After analysis, all Mo₃C₂@NC samples showed well-matched impedance due to the enhanced dielectric loss caused by the unique carbon structure and moderate magnetic loss derived from the weak magnetic property of Mo₃C₂. More importantly, the unique lemon-like and fig-like microstructures created sufficient interfaces and differentiated multiple reflection paths, which greatly contributed to the strong microwave absorptions at full wavebands. In full consideration of the simple preparation method and tunable absorption properties, Mo₃C₂@NC composites can be regarded as excellent electromagnetic wave absorption materials.

Graphene oxide supported Yolk - Shell ZnS/Ni3S4 with the adjustable air layer for high performance of electromagnetic wave absorber

Yolk-shell structure materials with the light weight, excellent impedance matching and electromagnetic wave (EMW) loss ability were widely used in the field of absorbing materials. However, the previous researches on this kind of structure always focused on the comparison between solid structure and empty structure. Different from previous studies, in this paper, the effect of yolk-shell structure with different air layer thickness on EMW absorption was studied for the first time. Graphene oxide (GO) supported yolk-shell ZnS/Ni₃S₄ absorbers with adjustable air layer were prepared by a simple two-step hydrothermal method. Through the equivalence of RLC resonant circuit and the elimination of the influence of polarization relaxation and conduction loss, it was found that yolk-shell structure with different air layer thickness will resonate with EMW of different frequencies, thus increasing the loss capacity of materials to EMW of this frequency. At the same time, Compared with the solid structure, the yolk-shell structure can not only make the material lighter, but also cause multiple reflections and scattering of EMW. Noteworthy, yolk-shell structure composite material exhibits the maximum reflection loss (RL) of -63.0 dB at 4.8 GHz and an effective absorption bandwidth (EAB) of 4.1 GHz at a thickness of 1.6 mm. This research provides an idea and basis for the design of absorbing materials that respond to different frequency EMW.