Ultralight Cellular Foam from Cellulose Nanofiber/Carbon Nanotube Self-Assemblies for Ultrabroad-Band Microwave Absorption

Abstract

Microwave absorption materials (MAMs) with lightweight density and ultrabroad-band microwave absorption performance are urgently needed in advanced MAMs, which are still a big challenge and have been rarely achieved. Here, a new wide bandwidth absorption model was designed, which fuses the electromagnetic resonance loss ability of a periodic porous structure in the lowfrequency range and the dielectric loss ability of dielectric materials in the highfrequency range. Based on this model, a lightweight porous cellulose nanofiber (CNF)/carbon nanotube (CNT) foam consisting of a cellular vertical porous architecture with the macropore diameters between 30 and 90 μm and a nanoporous architecture at a scale of 1.7−50 nm was obtained by an ice-template method using CNTs and CNFs as "building blocks". Benefiting from the unique architecture, the effective absorption bandwidth reaches 29.7 GHz, and its specific microwave absorption performance exceeds 80,000 dB•cm −2 •g −1 , which far surpasses those of the MAMs previously reported, including all CNT-based composites. Moreover, the CNF/CNT foam possesses ultralow density (9.2 mg/cm 3 ) and strong fatigue resistance, all coming from the wellinterconnected porous structure and the strong hydrogen bonds among CNF−CNF and CNF−CNT molecular chains.

Facile Synthesis of Cobalt-Doped Porous Composites with Amorphous Carbon/Zn Shell for High-Performance Microwave Absorption

“…Nanomaterials 2020, 10 6 of 14 carbon crystal plane. With the increase of carbonization temperature, the graphite carbon peak intensity gradually increases from 700 °C to 900 °C, demonstrating that high temperature condition is beneficial to the graphitization of carbon.…”

“…Nanomaterials 2020, 10 10 of 14 Figure 6. Three-dimensional map reflection loss of (a) Co/C@C-700, (b) Co/C@C-800, and (c) Co/C@C- Figure 6e-f show the attenuation constant α and impedance matching ratio of the Co/C@C-700, Co/C@C-800, and Co/C@C-900 composites.…”

“…Among varieties of conventional absorbers-ferrite, carbonyl iron powder, magnetic metal nanoparticles, carbon materials, and conductive polymer, for instance-carbon composites absorbers are one of the most cost-effective microwave absorbers because of their chemical and thermal stability, low price, light weight, and controllable micro-structure [3][4][5]. In particularly, materials with a porous multi-interface structure have been considered as potential candidates in many fields owing to their multiple interfaces [6][7][8][9][10]. However, carbon materials' application is limited by the cumbersome multistep operations.…”

“…Transmission electron microscopy (TEM) image (e), HRTEM image (f), and element mapping analysis (g-j) of Co/C@C-800. CNTs, carbon nanotubes.Nanomaterials 2020,10 6 of 14…”

Carbon Nanofibers Propped Hierarchical Porous SiOC Ceramics Toward Efficient Microwave Absorption

“…Recently, porous structures have been proven to be favorable for prolonging propagation paths and then improving microwave scattering, thus leading to a better microwave absorption performance. For instances, Yin et al presented that the ultra-broad effective microwave band of cellular foam reached 29.7 GHz arising from the well-interconnected porous structure [4]. Li et al reported that porous carbon delivered a minimum reflection loss (RL min ) value of − 56.4 dB, which was owing to the improvement of polarization abilities and multiple reflections [5].…”