General
Fabrication of 3D Hierarchically Structured
Bamboo-like Nitrogen-Doped Carbon Nanotube Arrays on 1D Nitrogen-Doped
Carbon Skeletons for Highly Efficient Electromagnetic Wave Energy
Attenuation
Hierarchically
three-dimensional (3D) micro-nanostructures have
promising applications in multifarious fields. Herein, we report a
general strategy, that is, in situ catalysis process, for fabrication
of nitrogen-doped carbon nanotube (NCNT) arrays on one-dimensional
(1D) nitrogen-doped carbon (NC) skeletons. The NCNT arrays branch
out from the 1D NC surfaces, resulting in the formation of hierarchically
3D micro-nanostructures. The strategy is involved in the pyrolysis
of M-precursor (M = Fe, Co, and Ni) nanowires with the assistance
of dicyandiamide. During the synthesis process, the metal components
in the precursors serve as catalysts for growing NCNTs, while dicyandiamide
provides carbon and nitrogen sources. With the ongoing reaction, the
NCNTs were catalytically grown and branched out from 1D NC skeletons.
Through the strategy, three kinds of hierarchically 3D structures
with encapsulated Fe/Fe3C, Co, and Ni nanoparticles, respectively,
were fabricated successfully. As functional materials for attenuating
electromagnetic wave energy, these hierarchically 3D structures exhibit
satisfactory performances even at a low matching thickness, exceeding
most of the carbon-based materials. Typically, the minimal reflection
losses of the 3D structures can reach −10.0 dB even as the
matching thickness is in the range of 1.4–2.0 mm. Experimental
results demonstrate that the excellent attenuation properties toward
electromagnetic wave energy are relative to high conduction loss at
a low frequency and high dielectric relaxations at a high frequency
as well as better impedance matching with the input impedance of the
free space. Our method presented here opens a general way for the
development of hierarchically 3D carbon-based micro-nanostructures
for their practical applications.