Carbon nanocages with N-doped carbon inner shell and Co/N-doped carbon outer shell as electromagnetic wave absorption materials

Nitrogen-doped Co-C/MWCNTs nanocomposites derived from bimetallic metal–organic frameworks for electromagnetic wave absorption in the X-band

Lightweight and high-efficiency microwave attenuation are two major challenges in the exploration of carbon-based absorbers, which can be achieved simultaneously by manipulating their chemical composition, microstructure, or impedance matching. In this work, core-shell CoNi@graphitic carbon decorated on B,N-codoped hollow carbon polyhedrons has been constructed by a facile pyrolysis process using metal-organic frameworks as precursors. The B,N-codoped hollow carbon polyhedrons, originated from the calcination of Co-Ni-ZIF-67, are composed of carbon nanocages and BN domains, and CoNi alloy is encapsulated by graphitic carbon layers. With a filling loading of 30 wt %, the absorber exhibits a maximum RL of -62.8 dB at 7.2 GHz with 3 mm and the effective absorption bandwidth below -10 dB remarkably reaches as strong as 8 GHz when the thickness is only 2 mm. The outstanding microwave absorption performance stems from the hollow carbon polyhedrons and carbon nanocages with interior cavities, the synergistic coupling effect between the abundant B-C-N heteroatoms, the strong dipolar/interfacial polarizations, the multiple scatterings, and the improved impedance matching. This study demonstrates that the codoped strategy provides a new way for the rational design of carbon-based absorbers with lightweight and superior microwave attenuation.

Core-Shell CoNi@Graphitic Carbon Decorated on B,N-Codoped Hollow Carbon Polyhedrons toward Lightweight and High-Efficiency Microwave Attenuation.

Carbon-based composites have gained extensive attention as microwave absorbing materials due to the lighter weight compared with other materials. In this work, Co/C nanocomposites with Co nanoparticles uniformly distributed in amorphous carbon sheets are prepared by a freezing dry and carbothermic reduction process. Hierarchical porous microstructures (micropores, mesopores, macropores) are achieved by ice template and huge amounts of gas during carbothermal reduction. Excellent absorption performance is achieved at a very low Co/C content (10% and 15%), which is a great success to design ultralight absorbers. At 10% content level, the effective absorption bandwidth is 5.0 GHz with a thin thickness of 1.8 mm, while the absorption bandwidth is 4.7 GHz with a thin thickness of 1.5 mm at 15% Co/C content level. The excellent absorption performance is attributed to excellent impedance matching resulting from synergy of cobalt and carbon and strong interfacial polarization induced by the hierarchical porous microstructures. This work provides a new pathway of designing ultralight absorbers with the advantage of thin thickness and wide bandwidth. Excellent absorption performance is achieved at only 10% Co/C content level, a success to design ultralight absorbers.

Hierarchically porous Co/C nanocomposites for ultralight high-performance microwave absorption

Recent progress of nanomaterials for microwave absorption

Facile preparation and microwave absorption properties of RGO/MWCNTs/ZnFe2O4 hybrid nanocomposites

Fabrication of ferroferric oxide–carbon/reduced graphene oxide nanocomposites derived from Fe-based metal–organic frameworks for microwave absorption

Design and electromagnetic wave absorption properties of reduced graphene oxide/multi-walled carbon nanotubes/nickel ferrite ternary nanocomposites

Nowadays, developing novel microwave absorbers with thin matching thickness, strong absorption intensity, broad absorption bandwidth and low filler loading is of great importance for solving the increasingly serious problem of electromagnetic pollution. Herein, nitrogen-doped cobalt oxide/cobalt/carbon (CoO/Co/C) nanocomposites were fabricated by high-temperature pyrolysis of heterobimetallic zeolitic imidazolate frameworks (Co/Zn-ZIFs). Results demonstrated that the micromorphology and magnetic properties of as-prepared nanocomposites could be regulated by changing the molar ratios of Co to Zn in the ZIFs precursors. Moreover, the effects of molar ratios of Co to Zn and filler loadings on the microwave absorption properties of obtained nanocomposites were systematically investigated in the frequency range of 2–18 GHz. Remarkably, the as-prepared nanocomposites with a molar ratio of Co to Zn of 1:1 exhibited the best microwave absorption properties. The optimal minimum reflection loss reached −66.7 dB at 7.2 GHz with a thickness of 3.3 mm and effective absorption bandwidth (EAB) achieved 5.1 GHz (12.6–17.7 GHz) covering most of Ku-band for an ultrathin thickness of 1.8 mm and a low filler loading of 25 wt%. Furthermore, the EAB could reach 14.16 GHz (88.5% of 2–18 GHz) by facilely modulating the thicknesses from 1.5 to 5 mm, which spanned the whole C, X and Ku bands. In addition, the underlying microwave absorption mechanisms were carefully investigated and further proposed. Therefore, our results could be helpful for designing and fabricating the magnetic nanoparticles/carbon nanocomposites derived from ZIFs as lightweight and high-efficient microwave absorbers.

Fabrication of nitrogen-doped cobalt oxide/cobalt/carbon nanocomposites derived from heterobimetallic zeolitic imidazolate frameworks with superior microwave absorption properties

Weijie Li

Papers

Nitrogen-doped Co-C/MWCNTs nanocomposites derived from bimetallic metal–organic frameworks for electromagnetic wave absorption in the X-band

Facile preparation and microwave absorption properties of RGO/MWCNTs/ZnFe2O4 hybrid nanocomposites

Fabrication of ferroferric oxide–carbon/reduced graphene oxide nanocomposites derived from Fe-based metal–organic frameworks for microwave absorption

Design and electromagnetic wave absorption properties of reduced graphene oxide/multi-walled carbon nanotubes/nickel ferrite ternary nanocomposites

Fabrication of nitrogen-doped cobalt oxide/cobalt/carbon nanocomposites derived from heterobimetallic zeolitic imidazolate frameworks with superior microwave absorption properties