Green Wood Aerogels for Ultrabroadband Near-Perfect Acoustic Absorption

Noise ranks as the world's second-largest environmental risk factor according to the WHO. The simultaneous achievement of ultrabroadband and perfect or near-perfect noise absorption is a quite significant yet long-standing challenge. Here, we propose a "gradient pore circulation (GPC)" strategy for building a hierarchical ordered architecture of green aerogels by using highly active microfibers precisely dissociated from a wood S₂ sublayer as basic units. The aerogels comprise anisotropic, parallelly layered microchannels enriched with multilevel pores within each layer, alongside abundant spring-shaped strips bridging these adjacent layers. Under the "GPC" strategy, the soundwaves effortlessly enter the parallelly layered microchannels possessing moderate flow resistance, while the synergy of long microchannels, multilevel pores, and abundant interlayer strips creates plentiful closed loops, fostering a repetitive cyclic reflection-friction-dissipation of soundwaves. Under these synergies, the aerogels achieve near-perfect acoustic absorption properties, with a sound-absorption coefficient (SAC) of 0.95 to 1 across an ultrabroad frequency range of 520 to 6300 Hz and a superb noise-reduction coefficient of 0.82, the highest recorded to date. More significantly, the aerogels retain excellent sound absorption (SAC > 0.85) even under extreme temperatures (-196 to +80 °C), and high humidities (up to 98%) and salt spray environments with mild modifications. Moreover, the aerogels are biodegradable, superelastic, and have strong compression fatigue resistance over 1000 cycles, manifesting great potential as sustainable sound absorption materials for diverse applications.