Gradient Pore Structured Elastic Ceramic Nanofiber Aerogels with Cellulose Nanonets for Noise Absorption.

The expeditious growth of modern transportation and industrialization has given rise to serious noise pollution, which has brought disaster to the world economy and human health. Most existing sound‐absorber with single pore structures suffer from large weight and the incidence and dissipation of noise that are difficult to be enhanced simultaneously. Herein, gradient‐structured elastic ceramic nanofiber aerogels with cellulose nano‐nets are successfully structured through step‐by‐step directional freeze‐casting technology, which has a gradient structure of "larger pore‐middle pore‐smaller pore" in the propagation direction of sound waves and dual nanofiber networks perpendicular to the direction of sound waves. The integration of gradient pore structures and dual nanofiber networks effectively improves the acoustic contact area of aerogels while increasing the acoustic incidence. The noise reduction coefficient of the obtained lightweight gradient aerogels (average density only 9 mg cm−3) reaches 0.58, and the low‐frequency air compressor noise can be reduced by 23.1 dB. Besides, the silica sol with hydrophobic groups endows gradient aerogels with good mechanics (plastic deformation only 5.7% after 1000 compressions) and superhydrophobic properties (water contact angle of ≈150°). The successful construction of gradient‐structured dual network nanofiber aerogels will offer new horizons for the upgrading of nextgen noise absorbers. [ABSTRACT FROM AUTHOR]