A low-cost hierarchical FeBTC/PI composite with gradient pore structure for broadband noise reduction and efficient thermal insulation

Porous materials are widely used for sound attenuation, but achieving broadband absorption remains challenging. Under the guidance of finite element simulations, this study designed and fabricated a gradient porous sound-absorbing material via the air bubble method and freeze-casting technique. The gradient pore structure, constructed via a dual-templating approach using ice crystals and air bubbles, dissipates sound waves in a stepwise manner, thereby enhancing the sound absorption performance of traditional PI aerogels. Subsequently, iron-trimesic metal organic framework (FeBTC), as an acoustic metamaterial, was introduced into foam aerogel through the liquid diffusion method to form a hierarchical sound-absorbing composite structure. The synergistic effect of the hierarchical composite structure significantly improves the sound absorption and insulation performance of foam aerogels. The FF 2 P composite aerogel exhibits an average sound absorption coefficient (ASAC) of 0.82 and an average sound transmission loss (ASTL) of 26.6 dB across the broad frequency range of 500–6300 Hz. Meanwhile, the small-pore layer with ice crystal pores enables composite aerogels to retain excellent thermal insulation performance (0.04 W/m·K). Besides, the introduction of a foam gradient structure enables foamed aerogels to achieve excellent mechanical durability. The successful development of the gradient hierarchical composite aerogel provides a novel approach for designing high-performance, low-cost noise absorbers.