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

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 low-frequency range and the dielectric loss ability of dielectric materials in the high-frequency 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·g, 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) and strong fatigue resistance, all coming from the well-interconnected porous structure and the strong hydrogen bonds among CNF-CNF and CNF-CNT molecular chains.