Building of zinc borate@bamboo cellulose composite aerogels with excellent acoustic performance and thermal insulation inspired by breakwater.

The noise pollution and climate warming have attracted more and more attention due to the rapid development of urbanization and industry. The preparation of lightweight aerogels with excellent acoustic performance, thermal insulation, and flame retardancy can quickly adapt to practical environments. Inspired by the breakwater, ZB@BC aerogels were successfully synthesized by sol-gel process, freeze-drying, and adsorption and precipitation. Noise reduction coefficient (NRC) value of ZB@BC composite aerogels is 0.48 and average sound absorption coefficient is 0.72 in 800-6300 Hz. Average transmission loss is 30.31 dB in 50-6300 Hz when the volume of sound source is 85 dB. In addition, ZB@BC composite aerogels exhibit excellent thermal conductivity (0.053 W/mK at 25 °C). The surface temperature is only 42.1 °C when the ZB@BC aerogel is placed on hot stage (100 °C), which proves its thermal insulation performance. Specifically, ZB@BC composite aerogels are flame-retardant with the limit oxygen index (LOI) value of 30.6 %. ZB@BC composite aerogels show compressive strength of 0.28 MPa and Young's modulus of 2.79 MPa. ZB@BC composite aerogels exhibit the advantages of low density, excellent acoustic performance, thermal insulation, flame retardancy, and mechanical strength compared with commercial acoustic and thermal insulation materials.