N-doped branched metal–organic framework derivatives to boost multiband microwave absorption with ultrathin thickness

Abstract

Although multiband compatible electromagnetic wave absorption (EMWA) materials are in demand, easy fabrication of lightweight and thin EMWA materials is challenging. Herein, rod-like CoNi-MOF-74 precursors were prepared, and then a melamine-assisted chemical vapor deposition pyrolysis technique was employed to fabricate magnetic CoNi nanoalloys@N-doped porous carbon/N-doped carbon nanotubes (CoNi@NPC/NCNTs) composites. Benefiting from the nitrogen and carbon sources supplied by melamine during the pyrolysis, N-doped carbon matrices with rich assembly of branching structures were obtained, and the magnetic nanoalloys homogeneously dispersed in the carbon matrix. Because of these features, CoNi@NPC/NCNTs exhibited superior dual-band EMWA properties with increased polarization relaxation losses, an excellent dielectric/magnetic synergistic effect, and good impedance matching. In the 2–18 GHz band, the minimum reflection loss (RL_min) value of CoNi@NPC/NCNTs is −54.8 dB at 1.6 mm thickness, and the maximum effective absorption bandwidth (EAB_max) is 4.7 GHz at 1.5 mm thickness. In the 26.5–40 GHz band, the RL_min value of the sample is −49.5 dB and EAB_max is 9.7 GHz at a thickness of only 0.7 mm. The superb microwave attenuation capability with dual frequency bands is verified by radar cross-section simulations. This work provides valuable guidance for fabricating ultrathin, and lightweight multiband absorbing materials.