Micro-nanospheres assembled with helically coiled nitrogen-doped carbon nanotubes: Fabrication and microwave absorption properties.

Micro-nanospheres assembled with helically coiled nitrogen-doped carbon nanotube (HNCNT) are successfully fabricated using CoZn double hydroxide nanosheets as substrates and catalytic precursors and dicyandiamide as carbon and nitrogen sources. The micro-nanospheres have diameters of 3–5 μm, composed of helically coiled NCNTs with diameters of 40–100 nm. The metallic Co NPs covered with graphene shell were encapsulated in HNCNTs. Experimental results demonstrate that both Co and Zn are important to the formation of the specially coiled NCNTs. The optimized micro-nanostructures exhibit excellent microwave absorption property with a minimal reflection loss of −44.2 dB at the thickness of absorber film (d) of only 1.7 mm, and efficient absorption bandwidth (reflection loss less than −10 dB) of 4.8 GHz at d of 2.0 mm. Furthermore, even at a thin thickness (1.5–2.0 mm) the minimal reflection losses of the optimized micro-nanostructures can reach −10 dB. The enhanced microwave absorption property can be explained by increased dielectric loss caused by defects and N dopants, better impedance matching characteristic, and the unique helically coiled structure. Image 1 • Micro-nanospheres assembled with helically coiled carbon nanotube are designed. • Both cobalt and zinc are important to produce the coiled carbon nanotubes. • Nitrogen-doping, single atom sites and defects are formed in carbon nanotubes. • The micro-nanospheres have excellent microwave absorption property. [ABSTRACT FROM AUTHOR]