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Fabrication of electromagnetic wave-absorbing materials derived from biomass have aroused great attention due to their special structures, eco-friendly and economical qualities. Herein, ultralight hierarchical porous carbon (UHPC) is successfully prepared through simple swelling-freeze drying and pyrolysis. UHPC possesses hierarchical porous architecture, which is inherited and expanded from but greater than the inherent unique macro/microporous structures of tremella. The hierarchical porous architecture derived from tremella provides a long conductive path and more interfaces to form conductance loss and polarization loss. It causes multiple reflections and scattering of electromagnetic waves, as well. The swelling process of tremella can offer dipole polarization and defect polarization. As a bio-derived microwave-absorbing carbon material, it holds good impedance matching and high attenuation constant. Particularly, the minimum reflection loss (RL) value of UHPC750-3 (obtained at 750 °C) can be reached at −48.57 dB with a small matching thickness of 1.7 mm. Remarkably, the effective absorption bandwidth is up to 4.55 GHz at 2.5 mm. The results show that absorbing properties of UHPC can be adjusted by changing pyrolysis temperature and swelling rate. The corresponding absorption mechanism is discussed as well. This method provides an effective strategy to prepare biomass-derived microwave absorbents which show great potential for practical applications. • The inherent hierarchical and nanopore structures of tremella can be retain using the freeze-drying method. • The regulation of microstructure of porous carbon materials could be synchronously fulfilled by controlling swelling rate. • The performance with RL min of −48.57 dB and effective absorption bandwidth of 4.55 GHz were achieved at only 1.7 mm. [ABSTRACT FROM AUTHOR]

Biomass derived porous carbon has attracted extensive attention in microwave absorption and shielding due to its unique structure and low cost. However, it is a great challenge to improve the impedance matching of electromagnetic wave absorbers by adjusting the distribution of magnetic particles and pore structure. In this research, Fe 3 C/Fe@N-doped biomass-derived porous carbon composites (Fe 3 C/Fe@NBPC) is successfully prepared by swelling-freeze-drying and carbonizing. It is worth noting that the uniform distribution of magnetic particles is achieved through the swelling process. The impedance matching performance of Fe 3 C/Fe@NBPC is effectively improved by adjusting the aperture and doping magnetic particles. The heterogeneous magnetic/dielectric multi-component benefit to superior EMW absorption performance through forming multiple polarizations, magnetic loss, and dielectric loss effects. The optimal Fe 3 C/Fe@NBPC composites exhibits superior electromagnetic wave (EMW) absorption performance with the minimum reflection loss value of − 52.25 dB and wide effective absorbing bandwidth of 3.06 GHz at 2.71 mm matching thickness. This work provides guidance for designing an efficient biomass derived EMW absorber with low cost, light weight and strong absorption. [Display omitted] • Fe 3 C/Fe@N-doped biomass-derived porous carbon is synthesized by simple swelling-freeze drying and pyrolysis process. • The uniform distribution of Fe 3 C/Fe and construction of porous structure are beneficial to microwave absorption. • The maximum reflection loss and effective absorption bandwidth of Fe 3 C/Fe@NBPC can reach − 52.25 dB and 3.06 GHz. [ABSTRACT FROM AUTHOR]

• A unique pod-like macroporous carbon nanofibers are prepared by Electrospinning-etching strategy. • The pod-like macroporous carbon nanofibers achieve an ultra-wide absorption bandwidth of 7.6 GHz. • It also exhibits self-cleaning property and radar wave attenuation feature. Constructing multiple polarization losses and improving impedance matching in carbon materials is essential for improving electromagnetic wave absorption performance of carbon materials. Meanwhile, surface contamination of electromagnetic wave absorbers has a significant impact on their absorption performance. Herein, a pod-like macroporous carbon nanofibers with self-cleaning function are successfully prepared by Electrospinning-etching strategy. Through the adjustment of SiO 2 and pore structure, conduction loss, dipole polarization loss, interface polarization loss, and impedance matching of carbon nanofibers are optimized simultaneously. The optimized a pod-like macroporous carbon nanofibers has strong absorption and wide effective absorption bandwidth. With a cavity content of 4 %, the minimum reflection loss at 2.29 mm is -49.36 dB, and the effective absorption bandwidth is 7.6 GHz and the matched thickness is 2.16 mm. This result indicates that cavity and pod-like structure can significantly improve dielectric properties and enhance interface polarization loss and conductivity loss. The simulation results verify that the pod structure has a greater impact on surface electric field distribution, which shows that interface polarization is caused by the cavity structure. In addition, the contact angle of absorber is 105 °, which proves its self-cleaning ability. This functional absorbing material has potential to meet future practical applications. [Display omitted] [ABSTRACT FROM AUTHOR]