BCN nanosheets derived from coconut shells with outstanding microwave absorption and thermal conductive properties

[Display omitted] •BCN nanosheets were applied as an efficient heat-conduction microwave absorber.•Various building blocks integrated in BCN could provide multiple polarization loss mechanism.•Strong absorption and wide broadband were achieved for BCN with a thin coating thickness.•BCN nanosheets exhibited good thermal management performance. Multifunctional materials with high-efficiency microwave absorption properties and effective thermal conductivity are urgently required for modern electronic devices and systems. Herein, we successfully prepared biomass-derived borocarbonitride (BCN) nanosheets with excellent electromagnetic wave absorption and thermal management properties by a general, green and economical strategy using biomass coconut shell as carbon source, and explored the effect of the coconut-shell charcoal content on its performance. The as-prepared BCN nanosheets exhibit a large specific surface area, which is favorable to the formation of conductive network and multiple reflection and scattering, thus resulting in strong absorption. The results show that the minimum reflection loss value of −54.24 dB is obtained at 5.2 GHz, and the maximum effective absorption bandwidth reaches up to 4.16 GHz with a thickness of only 1.4 mm. Furthermore, the thermal diffusivities and conductivities of the BCN/natural rubber composites are significantly improved. Thus, this research offers an idea for exploring high-performance multifunctional absorbing materials.