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.
The effective utilization of sound-absorbing materials is the primary approach to treat noise pollution, which represents a principal public health and environmental issue. However, current research on acoustic absorption materials has several drawbacks, including narrow sound absorption frequency bands, low sound absorption coefficients, and excessive material thickness. Herein, we propose a facile sound-enhanced strategy that integrates a micro-sized polyimide (PI) membrane network and nanoscale FeBTC metal-organic frameworks into a submillimeter porous ceramic with high open porosity and multiscale pore structure. The enhancement of broadband sound absorption performance can be achieved by adjusting the freeze-casting temperature and precursor solution concentration to regulate the distribution density of the PI membrane network. Furthermore, the med-low frequency acoustic performance was further enhanced by in-situ growth of FeBTC within the fabricated organic-inorganic composites featuring a dual network structure. Across a broadband frequency range of 500 Hz to 6300 Hz, the composites exhibited an average sound absorption coefficient (SAC) of 0.64 and an average sound transmission loss (STL) of 20.5 dB at a thickness of 15 mm, which was significantly higher than that of commonly available noise reduction products and advanced sound absorbers ever achieved. The synergistic sound absorption effects of the hierarchical structure play a significant role in achieving a remarkable noise reduction ability. Moreover, the low thermal conductivity and excellent environmental stability of this composite material make it suitable for a wide range of applications requiring broadband noise control, including building design, transportation, and precision instruments.
At present, over 95 % of H 2 O 2 is produced via the anthraquinone process that requires large infrastructure, generates organic pollution, and poses safety issues. Electrochemical H 2 O 2 generation through oxygen reduction can serve as an alternative, reliable, and decentralized production method if affordable and high-performance electrocatalysts can be developed. Herein, a two-step process is used to prepare an Fe-based complex as a non-precious metal electrocatalyst to facilitate oxygen reduction reaction (ORR) and produce an alkaline H 2 O 2 solution. The Fe complex of benzene-1,3,5-tricarboxylate (FeBTC) is first synthesized using a hydrothermal method and then activated via a pulsed laser treatment process that is optimized via the Taguchi method. The pulse-laser-treated FeBTC (PL-FeBTC) lowers the H 2 O 2 electrosynthesis overpotential by 50 mV at −0.1 mA/cm 2 and exhibits a 25 % increase in H 2 O 2 product selectivity at 0.4 V vs. RHE. The experimental results indicate that the O 2 -to-H 2 O 2 turnover frequency and electrocatalytic yield of the Fe-based metal–organic framework are enhanced simultaneously through solid-to-solid pulsed laser conversion. Through a series of X-ray photoelectron spectroscopy, elemental analysis, Raman spectroscopy, X-ray absorption spectroscopy, and control atmospheric experiments, the origin of the improvement in catalytic performance is rationalized through the formation of an oxo-bridge across the di–Fe active site via an oxygen-doping mechanism, thus providing a systematic laser methodology for precise structure-performance tuning. Beyond H 2 O 2 generation, this study further lays the foundation for the development of cost-effective and scalable electrocatalysts that are central to other commodity manufacturing and sustainable resourcification processes.
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