Lightweight Porous Aerogels Comprising Nanofibrillated Cellulose and MXene Nanosheets for Simultaneous Microwave and Sound Absorption Applications

Designing a material with simultaneous microwave and sound absorption abilities is highly desired to mitigate electromagnetic radiation and noise pollution. However, their further development is highly challenging due to their totally different mechanisms of energy conversion. Here, we fabricate an ultralight and porous composite aerogel composed of cotton-derived nanofibrillated cellulose and MXene (f-Ti₃C₂T_X) nanosheets by directional freeze-drying technology, toward simultaneous microwave and sound absorption. The honeycomb-like biomimetic microstructure of obtained composite aerogel not only allows unidirectional transmission for incident microwaves and sound waves but also induces strong energy attenuation and high conductive loss due to assembled f-Ti₃C₂T_X nanosheets. Moreover, the f-Ti₃C₂T_X content and density of the composite aerogel are further regulated to enable precise tunability of the microstructure and dielectric properties, contributing to optimal microwave absorption ability and high sound absorption capacity at the same time. The high-efficiency absorption covers the whole X band with a RC_min of −44.9 dB at a thickness of 6.35 mm, while the average sound absorption coefficient reaches 0.82 at a thickness of 30 mm in the frequency range from 1000 to 6300 Hz. This study offers a facile and sustainable approach to achieving controllable microwave and sound absorption for the targeted applications.