Direct Synthesis of Elastic and Stretchable Hierarchical Structured Fiber and Graphene-Based Sponges for Noise Reduction.

Noise pollution, as one of the three major pollutants in the world, has become a great burden on people's health and the global economy. Most present noise absorbers suffer large weight and inevitable compromise between good low-frequency (usually <1000 Hz) and high-frequency (typically >1000 Hz) noise reduction performance. This study presents a scalable strategy to directly synthesize ultrafine fiber sponges with ultrathin graphene-based vibrators by the synchronous occurrence of humidity-assisted electrospinning and electrospraying. The unique physical entanglements between reduced graphene oxide (rGO) nanosheets and ultrafine fibers endow hierarchical vibration structured fiber sponges (VSFSs) with excellent mechanical properties, which could withstand large shear strain (60%) and tensile stress (6000 times its weight) without damage and almost have no plastic deformation after 1000 compressions. Attribute to the vibration effect of ultrathin graphene-based vibrators and the viscous friction effect of porous fiber networks, the VSFSs achieve both good low-frequency (absorption coefficient of 0.98 in 680 Hz) and high-frequency sound absorption (absorption coefficients above 0.8 in 2000-6300 Hz) simultaneously. Furthermore, the noise reduction coefficient (NRC) of lightweight VSFSs (thickness of 30 mm) reaches 0.63, which could reduce high decibel noise by 24.4 dB, providing potential solutions for developing ideal noise-absorbing materials.

Heat-conducting elastic ultrafine fiber sponges with boron nitride networks for noise reduction.

Industrial and traffic noise has become increasingly serious with the progress of industrialization. Most existing noise-absorbing materials suffer from poor heat dissipation and insufficient low-frequency (<1000 Hz) noise absorption, which not only reduces working efficiency but also leads to safety risks. Herein, heat-conducting elastic ultrafine fiber sponges with boron nitride (BN) networks were prepared by integrating direct electrospinning and impregnation method. The large acoustic contact area of ultrafine fibers and the vibration effect of BN nanosheets in a three-dimensional direction endow fiber sponges with good noise reduction, which can reduce white noise by 28.3 dB with a high noise reduction coefficient of 0.64. Moreover, thanks to good heat-conducting networks composed of BN nanosheets and porous structures, the obtained sponges exhibit superior heat dissipation with thermal conductivity of 0.159 W m-1 K-1. Besides, the introduction of elastic polyurethane and following crosslinking endow the sponges with good mechanical properties, which have almost no plastic deformation after 1000 compressions, and the tensile strength and strain are as high as 0.28 MPa and 75%. The successful synthesis of heat-conducting elastic ultrafine fiber sponges overcomes poor heat dissipation and low-frequency noise reduction of noise absorbers.

Bubble Templated Flexible Ceramic Nanofiber Aerogels with Cascaded Resonant Cavities for High-Temperature Noise Absorption.

Aviation noise pollution has become a significant public health problem, especially with the endless improvement of flight speed and loading capacity. Existing aviation noise absorbers have fatal defects of large weight, weak high-temperature stability, and difficulty to achieve both good low-frequency (<1000 Hz) and high-frequency (up to 6000 Hz) noise absorption simultaneously. Herein, we report a robust strategy to create flexible ceramic nanofiber aerogels with cascaded resonant cavities by the air bubbles-assisted freeze-casting technology. The stable hinged resonance cavity structures coassembled by flexible ceramic nanofibers, soft montmorillonite nanosheets, and silica sol glue endow the aerogels with temperature-invariant compressibility (from -196 to 1100 °C) and bendability. Moreover, the comprehensive advantages of cascaded resonance cavities and interconnected fibrous networks enable flexible ceramic nanofiber aerogels to have temperature-invariant full-frequency noise absorption performance (noise reduction coefficient up to 0.66 in 63-6300 Hz). The synthesis of this flexible ceramic nanofiber aerogel provides a versatile platform for the design of high-efficiency noise-absorbing material for various fields.

Fire-Resistant and Hierarchically Structured Elastic Ceramic Nanofibrous Aerogels for Efficient Low-Frequency Noise Reduction.

Traffic noise has been regarded as one of the most annoying pollutions that induce severe hazards to human health, both physiological and psychological. The commonly used fibrous noise absorption materials are limited by their large density, poor sound absorption ability at low frequencies, and unsatisfactory fire-resistant ability. Here, we develop hierarchically structured elastic ceramic electrospun nanofibrous aerogels, which possess lightweight properties (density of 13.29 mg cm-3) and superior low-frequency sound absorption ability (NRC value of 0.59). Specifically, the obtained ceramic electrospun nanofibrous aerogel is nonflammable on exposure to fire and can be compressed and quickly recover to its original height without any visible damage. Moreover, the resultant aerogels could be facilely and efficiently manufactured into designed shapes on a large scale, demonstrating their potential for industrialization. The successful design of such ceramic-based bulk materials may provide new insights for the further development of the next-generation high-efficiency sound-absorbing products.

Flexible ceramic nanofibrous sponges with hierarchically entangled graphene networks enable noise absorption.

Traffic noise pollution has posed a huge burden to the global economy, ecological environment and human health. However, most present traffic noise reduction materials suffer from a narrow absorbing band, large weight and poor temperature resistance. Here, we demonstrate a facile strategy to create flexible ceramic nanofibrous sponges (FCNSs) with hierarchically entangled graphene networks, which integrate unique hierarchical structures of opened cells, closed-cell walls and entangled networks. Under the precondition of independent of chemical crosslinking, high enhancement in buckling and compression performances of FCNSs is achieved by forming hierarchically entangled structures in all three-dimensional space. Moreover, the FCNSs show enhanced broadband noise absorption performance (noise reduction coefficient of 0.56 in 63-6300 Hz) and lightweight feature (9.3 mg cm-3), together with robust temperature-invariant stability from -100 to 500 °C. This strategy paves the way for the design of advanced fibrous materials for highly efficient noise absorption.

Gradient structured micro/nanofibrous sponges with superior compressibility and stretchability for broadband sound absorption.

Ultrafine fibrous porous materials obtained by electrospinning technology have broad application prospects in the field of noise reduction. However, the two-dimensional fibrous membranes faced low thickness and dense structure, resulting in a single internal structure and narrow sound absorption band. Here, we report a simple and robust strategy to prepare gradient structured fiber sponges with superelasticity and stretchability by combining humidity-assisted multi-step electrospinning and a unique physical/chemical dual cross-linking method. The prepared gradient structured fibrous sponge has a maximum tensile strength of 169 kPa and can lift a weight 10,000 times its weight without breaking. Besides, the material can still maintain a stable structure after 500 compression cycles at 60% strain. Meantime, the material has lightweight properties (density of 13.8 mg cm-3) and hydrophobicity (water contact angle of 152°). More importantly, the gradient change of porosity and pore diameter in the Z direction endowed the fibrous sponge material with high-efficiency absorption of broadband sound waves (with a noise reduction coefficient up to 0.53). The design of this gradient structured fiber sponge opens a new way for the development of ideal sound-absorbing materials.

Biomimetic Multilayer Nanofibrous Membranes with Elaborated Superwettability for Effective Purification of Emulsified Oily Wastewater.

Creating a porous membrane to effectively separate the emulsified oil-in-water emulsions with energy-saving property is highly desired but remains a challenge. Herein, a multilayer nanofibrous membrane was developed with the inspiration of the natural architectures of earth for gravity-driven water purification. As a result, the obtained biomimetic multilayer nanofibrous membranes exhibited three individual layers with designed functions; they were the inorganic nanofibrous layer to block the serious intrusion of oil to prevent the destructive fouling of the polymeric matrix; the submicron porous layer with designed honeycomb-like cavities to catch the smaller oil droplets and ensures a satisfactory water permeability; and the high porous fibrous substrate with larger pore size provided a template support and allows water to pass through quickly. Consequently, with the cooperation of these three functional layers, the resultant composite membrane possessed superior anti-oil-fouling property and robust oil-in-water emulsion separation performance with good separation efficiency and competitive permeation flux solely under the drive of gravity. The permeation flux of the membrane for the emulsion was up to 5163 L m-2 h-1 with a separation efficiency of 99.5%. We anticipate that our strategy could provide a facile route for developing a new generation of specific membranes for oily wastewater remediation.