The design of hierarchical structures from biomass has become one of the hottest subjects in the field of microwave absorption due to its low cost, vast availability and sustainability. A kapok-fiber-derived carbon microtube was prepared by facile carbonization, and the relation between the structure and properties of the carbonized kapok fiber (CKF) was systematically investigated. The hollow tubular structures afford the resulting CKF composites with excellent microwave-absorbing performance. The sample with a 30 wt.% loading of CKF in paraffin demonstrates the strongest microwave attenuation capacity, with a minimum reflection loss of −49.46 dB at 16.48 GHz and 2.3 mm, and an optimized effective absorption bandwidth of 7.12 GHz (10.64–17.76 GHz, 2.3 mm) that covers 34% of the X-band and 96% of the Ku-band. Further, more than 90% of the incident electromagnetic wave in the frequency from 4.48 GHz to 18.00 GHz can be attenuated via tuning the thickness of the CKF-based absorber. This study outlines a foundation for the development of lightweight and sustainable microwave absorbers with a high absorption capacity and broad effective absorption bandwidth.

Designing versatile rubber as a multifunctional elastomer is of great importance, incorporating it with biomass-derived nanoblocks will mitigate environmental challenges. Here biosynthesized natural rubber (NR) composites with CoFe2O4-immobilized biomass carbon (BC) derived from macadamia nutshells were fabricated by facile mechanical mixing. Morphological analysis indicates that CoFe2O4 nanoparticles are uniformly anchored on the surface of BC, forming intact electromagnetic loss networks in NR matrix. As a consequence, the as-fabricated NR/CoFe2O4@BC composites demonstrate enhanced mechanical, thermal, and electromagnetic performance. Particularly, NR/CoFe2O4@BC composite shows the best microwave attenuation capacity when CoFe2O4@BC loading is 40 phr, with the minimum reflection loss (RL) of −35.00 dB and effective absorption bandwidth (RL < −10 dB) of 1.60 GHz. All results indicate that this work open new paradigm for multiple applications based on biosynthetic elastomer with the sustainable biomass derived nanoblocks.

Increasingly severe electromagnetic pollution problem boosts the demand for light weight microwave absorbing materials with high absorption capacity over wide frequency range. Biomass-derived porous carbon has been regarded as one of the promising candidates for microwave attenuation as the biomaterials are vastly available and renewable. Here, macadamia nutshell derived porous carbon (MPC) was fabricated by activated carbonization. Evidenced by the morphological results, the resulted MPC demonstrates three-dimensional frameworks with tubular skeletons. Owing to such hierarchical structures, the resulted composite MPC-filled paraffin composites exhibit a minimum reflection loss of [Formula: see text]44.14[Formula: see text]dB and effective absorption bandwidth of 3.84[Formula: see text]GHz. Moreover, the resulted MPC can be explored as a practical absorber in a frequency range of 3.68–18.00[Formula: see text]GHz via tuning of the thickness. The analysis of microwave attenuation mechanism indicates that such outstanding microwave absorption capacity is attributed to hierarchical structure tuned impedance matching conditions and multiple attenuation mechanisms. All results in this work open the avenue for the development of nutshell derived sustainable microwave absorber with high absorption capacity as well as broad effective absorption bandwidth, boosting the utilizing of biomass resources.

Constructing hierarchical structures is indispensable to tuning the electromagnetic properties of carbon-based materials. Here, carbon microtubes with nanometer wall thickness and micrometer diameter were fabricated by a feasible approach with economical and sustainable kapok fiber. The carbonized kapok fiber (CKF) exhibits microscale pores from the inherent porous templates as well as pyrolysis-induced nanopores inside the wall, affording the hierarchical carbon microtube with excellent microwave absorbing performance over broad frequency. Particularly, CKF-650 exhibits an optimized reflection loss (RL) of −62.46 dB (10.32 GHz, 2.2 mm), while CKF-600 demonstrates an effective absorption bandwidth (RL < −10 dB) of 6.80 GHz (11.20–18.00 GHz, 2.8 mm). Moreover, more than 90% of the incident electromagnetic wave ranging from 2.88 GHz to 18.00 GHz can be dissipated by simply controlling the carbonization temperature of KF and/or the thickness of the carbon-microtube-based absorber. These encouraging findings provide a facile alternative route to fabricate microwave absorbers with broadband attenuation capacity by utilizing sustainable biomass.

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