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Ringent hollow carbons synthesised by CDs through controllable reaction temperatures show great absorbing values and absorbing bands as well as relative compression ratios of radar cross section. Finite element simulation demonstrats that unique structure of ringent hollow carbons can lower normal reflected wave and promote energy attenuation which provides a new direction for the structural design of absorbers. [Display omitted] • A high-yield of carbon quantum dots derived ringent hollow carbon spheres (RHCs) for efficient microwave absorber has been proposed. • Outstanding microwave absorbing performance with optimal reflection loss of −67 dB as well as superior absorbing bandwidth (covering C, X and Ku band) could be achieved. • A relative compression ratio of 56.7 % of of RHCs loaded coating could be achieved due to ringent hollow structure and intrinsic nanosheets attenuation. Carbon nanomaterials have steadily grown into a class of composite absorbers with remarkable properties due to their unique structure, low density, high specific surface area, strong electrical conductivity, and substantial dielectric losses. In this paper, a facile strategy with low-cost, high-efficiency, and scalable strategy for carbon dots-derived ringent hollow carbon (RHC) for superior microwave absorption is proposed. Controllable structures ranging from amorphous carbon to ringent hollow carbon are well performed through simple heat-treated temperature. In addition, an optimal absorption value of −67 dB and a superior absorption band width covering the C, X, and Ku bands, as well as a relative compression ratio of 56.7 percent in the case of perpendicular incidence, have been achieved. Further, finite element simulations have demonstrated that the unique structure of partially ringent hollow carbon is considered as an effective way to lower normal reflected wave and promote energy attenuation. New applications of carbon dots-derived RHC as superior microwave absorbers are opening up, and the scalable strategy may pave a solid foundation for rapid applications. [ABSTRACT FROM AUTHOR]

The development of wide-band microwave absorbing materials based on carbonaceous fillers remains a great challenge. In this study, carbon nanotubes (CNT) assembled coronal hollow clusters with efficient microwave absorbing performance have been obtained through successive hydrothermal and calcination process. Microstructural analysis reveals the distinct features of multiple assembly structures in the fabricated materials. The electromagnetic responses of Ni/CNT assembled clusters were examined across a frequency range of 2–18 GHz. Results demonstrate that the microwave frequency dispersion of electromagnetic parameters and reflection loss of Ni/CNT clusters are strongly influenced by weight loading. Multi-absorbing peaks with reflection loss better than − 40 dB could be achieved, while the equivalent absorbing band for RL < −10 dB covers 3.2–18 GHz, which account for 92.5% of the whole evaluated frequency range, and 62.5% for condition of RL < −20 dB. Furthermore, intrinsic attenuation beyond thickness derived semi-wavelength resonant absorption makes a major contribution to this superior performance. The underlying mechanism of dielectric response was investigated through Cole-Cole analysis and finite element simulation. 'Micro-dipoles' relaxation and hopping relaxation originated from defects within CNT and barrier between CNT, while the high magnetic dissipation capability of Ni nanoparticles make a major contribution to overall absorbing performance. All these are beneficial to regulation and optimization of microwave absorption performance of novel Ni/ CNT functionalized multistage architecture. [Display omitted] • Ni/CNT clusters were prepared through a sample solvothermal method; • Carbon nanotubes were assembled in situ into coronal hollow spherical multilayer carbon nanotube clusters; • The absorption efficiency of CNT is improved by anisotropic strong dielectric loss and multi-layer structure. • The microwave absorption of the new Ni/ CNT functionalized multistage structure greatly improves the performance. [ABSTRACT FROM AUTHOR]