Carbonized fibers with multi-elemental doping and hollow architecture derived from natural cotton for tunable microwave absorption properties

The exploration of bio-derived materials for various applications has attracted considerable attention due to the global challenges of elemental sustainability. Herein, we report the synthesis of hollow-structure carbon fibers by carbonizing natural cotton at different temperatures. The microwave absorption properties are investigated, and the dielectric loss mechanism is studied furtherly. During the pyrolysis process, multi-elements such as oxygen, sulfur, and nitrogen existing in natural cotton can remain and in-situ doped into the carbonized fibers. And a high-concentration atomic-scale substitute is realized, which becomes the dielectric polarization site for microwave attenuation due to the symmetry breaking of localized charge. Moreover, the pyrolysis process results in forming a hollow structure of carbonized fibers, implying an ultra-low density of the resultant fibers. In the present study, it is found that the sample carbonized at 700 °C for 120 min (denoted as S_700-120) exhibits the minimum reflection loss (RL_min) of − 51.9 dB at 12.1 GHz with the absorption bandwidth (f_b) of 5.5 GHz when the thickness is 1.96 mm. The RL_min and f_b for S_700-80, S_800-40, S_800-80, and S_800-120 are − 47.0 dB and 3.9 GHz, − 57.3 dB and 3.1 GHz, − 42.7 dB and 2.1 GHz, − 44.2 dB and 1.8 GHz, respectively, demonstrating a significant tunability of microwave absorption performances. Our work provides an alternative for the development of high-performance microwave absorbents from bio-sources.