Cobalt nanoparticles embedded nitrogen-doped porous graphitized carbon composites with enhanced microwave absorption performance

Liquid metal derived MOF functionalized nanoarrays with ultra-wideband electromagnetic absorption

Low melting point liquid metal alloys are progressively utilized in different research fields due to their unique physicochemical properties. Among them, EGaIn is liquid at room temperature with an excellent solubility for reactive metal atoms such as Al. Combined with their characteristic flexible surface, large area and atomically flat interfaces, a library of two-dimensional materials can be generated. Liquid metal synthesis routes provide a highly reproducible thickness of nanosheets with fast, simple, scalable, inexpensive, high yield and non-toxic methods, especially for Al oxides and hydroxides. At the same time, Al-based heterojunction structure also shows a good application prospect in the field of electromagnetic wave absorption, therefore, the use of liquid metal synthesis methods to find the synthesis methods of Al-based layered double hydroxide (LDH) and its derivatives remains to be explored. In this work, EGaIn was used as an aluminum reservoir to prepare LDH and metal organic framework (MOFs) nano-arrays. The prepared CoAl-LDH@ZIF 67 can be transformed into CoAl-LDO@Co-C in the subsequent annealing process performed under nitrogen environments. Interestingly, a series of samples with different morphologies can be obtained by changing the synthesis parameters. The excellent electromagnetic wave interactions are fully characterized. It has an effective absorption bandwidth of 8.48 GHz at 2.6 mm. The findings demonstrated in this work pave the way for the application of lightwave and ductile complex nanoarrays obtained from liquid metals.

Superiority of graphite coated metallic-nanoparticles over graphite coated insulating-nanoparticles for enhancing EMI shielding

A superior EMI shielding effectiveness (SE) for composites with a metallic(Ni)@graphite core and lower SE for a dielectric(MnO)@graphitic core of carbonaceous materials.

Design of MOF-derived hierarchical Co@C@RGO composite with controllable heterogeneous interfaces as a high-efficiency microwave absorbent

Carbon-based composites have triggered tremendous attention in the development of high-efficiency microwave absorbers, due to their compatibility, light weight, and high microwave absorption. However, fabricating carbon-based absorbers with a strong absorption ability in a broad frequency range is challenging. Hence, a facile strategy was used to produce Co@C derived from a zeolitic imidazolate framework (ZIF)@ graphene. The Co@C@RGO composite was obtained by annealing the ZIF67/GO nanocomposite precursor at 650 °C in a nitrogen atmosphere. Due to the magnetic loss induced by the Co particles, the dielectric loss generated by the carbon skeletons and graphene, and the interfacial polarization between the components, the hierarchical composite exhibits superior electromagnetic (EM) wave absorption properties. The optimal reflection loss (R_L) of the Co@C@ RGO composite can be up to -67.5 dB at 2.6 mm, and the effective bandwidth (≥-10 dB) is 5.4 GHz (10-15.4 GHz) with a thickness of 2 mm at 20 wt% loading. The dipolar polarization caused by graphene, as well as enhanced impedance matching, synergistic effect and interfacial effect among the components, increase the microwave absorption performance of the composite. This work may open a new path to use the Co@C@RGO composite with its high-efficiency EM wave properties as an absorber.

Facile synthesis of reduced graphene oxide-wrapped CNFs with controllable chemical reduction degree for enhanced microwave absorption performance

The rGO-wrapped nanocomposites can be regarded as promising candidates for the development of advanced microwave absorbing materials. In this work, hierarchical rGO-wrapped CNFs were prepared via a two-step strategy, including a classical modified Hummers method and a green reduction reaction. Accompany with the chemical treatments, graphene oxide appears on the outer walls of carbon nanofibers. By modulating the addition amount of ascorbic acid, the outer graphene oxide can be controllably reduced. Moreover, the CNFs/rGO with proper reduction degree exhibits desirable microwave absorption performance, whose minimum RL and effective bandwidth are -38.1 dB (3.85 GHz, d = 5.0 mm) and 4.1 GHz (5.08-9.18 GHz, d = 3.5 mm). The superior microwave attenuation performance is attributed to the synergistic effects between the CNFs and rGO. While the nanofibers provide the obtained sample with an extremely long conductive network, rGO introduces a moderate amount of lattice defects and functional groups, resulting in desirable conductivity loss and multiple polarizations. The existence of rGO also endows CNFs/rGO with suitable dielectric values so that the absorber achieves well impedance matching. Considering the excellent microwave absorption performance, this research provides a new facile route to fabricate rGO-wrapped carbonaceous materials with proper oxygen-containing groups for MAMs.

Reflection phase modification by metamaterial interface: an understanding of design criteria for ultrathin multispectral absorber

We introduce a metasurface to modify the reflection phase for multispectral microwave absorbers. General quantitive design criteria are proposed by carrying out field analysis, so that design of multispectral microwave absorber can be effectively realized. Optimal design process is discussed to develop an understanding of the absorbing mechanism. Experiment results show that the absorber having only 0.015 times the wavelength at the center frequency can simultaneously achieve high absorption in the microwave, visible light and near-infrared light bands. Multispectral absorption comes with added features of flexibility, ultrathin thickness and a light weight that make it a powerful candidate in advanced stealth application.