Aerogels are commonly used in the fields of thermal insulation, sound insulation, adsorption, optical devices, and electrode materials. However, traditional aerogels suffer from poor structural ...stability and mechanical performance. Herein, we proposed a method in extracting fibers from hemp stems to prepare hydrophobic, thermal insulating and superelastic aerogels. The suspension of bleached hemp fibers (BHF), chitosan, and methyltrimethoxysilane (MTMS) is assembled into the network structure of aerogel by freeze-drying method. Because of the cross-linking between BHF, chitosan and MTMS, the material exhibited excellent properties. The aerogel demonstrated excellent compression performance, quickly recovering even when applied with 80 % compressive strain and maintaining 80 % of its original shape after 100 compression cycles. Furthermore, the aerogels demonstrated outstanding thermal insulation property; the thermal conductivity is only 0.01873 ± 0.0004 W/m·K. In addition, the aerogel exhibited excellent hydrophobic properties, with a water contact angle of approximately 130°. The superior properties of aerogel enable it to withstand complex external environments. In this study, we aim to provide new ideas and methods for resource reuse and the preparation of bio-based aerogels.
•Preparation of aerogels from fibers extracted from hemp stems.•One-step preparation of biomass aerogels by BHF, chitosan and MTMS.•Aerogels have low thermal conductivity(0.01873±0.0004 W/m·K).•Aerogels have good compression resilience.•Aerogels have excellent hydrophobicity(∼130°).
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•Superelastic and versatile cellulose aerogel was prepared by Schiff base cross-linking and freeze-drying assembly.•Porous water channels with reverse transportation achieved ...long-term desalination without salt accumulation.•This solar steam generator realized efficient purification of seawater and wastewater.•As a proof of concept, a simple device that can adsorb the dye pollutant was designed.
Solar steam generators (SSGs) that continuously supply clean water resources under solar radiation have been recognized as a sustainable approach to mitigate the global water and energy crisis. However, most SSGs currently face the accumulation of salt on the surface during long-term seawater desalination, which hinders the water supply and vapor escape and significantly reduces the evaporation efficiency. Inspired by the porous water channels of reverse transportation, the SSG (PPy@PEI@A-CNF aerogel) with superelastic and photothermal properties was obtained by the Schiff base reaction of aldehyde-based cellulose nanofibers (A-CNF) and polyethyleneimine (PEI) and freeze assembly, and further in-situ polymerized with polypyrrole (PPy). This aerogel with porous hierarchical structure performed outstanding mechanical robustness (89.9% strain remaining after 100 compress-release cycles), ultra-low density (0.021 g cm−3) and thermal conductivity (0.042 W m−1 K−1), high porosity (97.72%) and full spectrum solar energy absorption (98.4%). Moreover, the aerogel could be used for solar-driven water evaporation, and its evaporation rate and efficiency were as high as 1.66 kg m–2h−1 and 94.62% under 1.0 sun. Owing to the rapid re-dissolution of the salt in the reverse transport of macroporous structure, the aerogel exhibited excellent salt-resistant and self-desalting properties during long-term seawater desalination, and also showed superior purification effects and reusability. These findings provide a new method for designing reusable macroporous SSGs to meet eco-friendly, efficient and sustainable fresh water access.
In situ X-ray diffraction during loading and unloading is used to investigate the effects of grain size (GS) on the stress-induced nanoscale phase transition (PT) mechanism in polycrystalline ...superelastic NiTi. The average GS studied (10–1500nm) spans the range in which significant changes of macroscopic thermomechanical properties (due to GS reduction) have been observed. It is shown that when the GS⩾68nm, the evolution of the diffraction profiles (DPs) during loading and unloading exhibits well-defined distinct diffraction peaks with significant changes in their diffracted intensities corresponding to the nucleation and growth mechanism of B19′ martensite (high strain) phase. However, when GS<68nm, the evolution of DPs gradually degenerates from the multiple peaks mode to a continuous and reversible single peak shift mode. Measurements of the lattice parameters and the corresponding components of lattice strains show that such drastic changes in characteristics of DPs indicate a gradual change in the PT mechanism from traditional nucleation and growth mode in coarse-grained polycrystals to a continuous lattice deformation inside the nano-sized grains. Moreover, the middle eigenvalue (λ2) of the transformation matrix gradually approaches 1 with GS reduction, almost fulfilling the proposed λ2=1 condition in the literature for the vanishing of hysteresis in SMAs. The results provide lattice level scenarios for the understanding of GS effects on the change of PT type from first-order to continuous PT which brings significant changes in the macroscopic thermomechanical behavior and properties of the polycrystalline superelastic NiTi.
Elastocaloric cooling and heating is an alternative cooling technology that has the potential to be highly efficient and environmentally friendly. Experimental results are reported for two ...elastocaloric regenerators made of Ni-Ti alloys in the form of parallel plates in two plate thicknesses. For the regenerator made of 0.2 mm plates, a maximum no-load temperature span of 17.6 K was achieved for an applied strain of 4.3%. For the regenerator with 0.35 mm plates, a maximum temperature span of 19.9 K was reached for a strain of 3.5%. The 0.2 mm regenerator failed after approximately 5200 cycles and the 0.35 mm regenerator failed after approximately 5500 cycles.
Solar-driven vaporization devices are often hindered by complex fabrication process, low efficiency, poor durability, and non-reusability. Herein, based on the pre-pressed melamine foam (MF), we have ...fabricated a scalable, low cost, and durable bilayer polymer foam for efficient and stable solar steam generation. Making use of the bilayer structure, different functions are assigned to different layers, with polypyrrole (PPy) coating pre-pressed MF (PPy layer) for light absorption and water evaporation, and bottom pre-pressed MF layer for water transport and thermal insulation. A high average evaporation rate of 1.574 kg m−2 h−1 and a superb steam generation efficiency of 90.4% under 1 sun are achieved. Bilayer foam demonstrates remarkable robustness and stability under a series of severe conditions. Bilayer foam can keep its structural stability and evaporation performance in durability tests (over 30 days, with 60 min each day), exhibiting the long-term durability, excellent antifouling property, and good reusability. We have also demonstrated the potential practicability of two simple prototype devices for solar steam generation on land and water. The low cost, large-scale, and durable solar steam generation device is promising for highly efficient and stable generating fresh water under natural sunlight conditions, which is especially attractive for remote areas that lack of fresh water supply.
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•A scalable and low cost bilayer polymer foam is fabricated for solar steam generation.•A high evaporation rate of 1.574 kg m−2 h−1 and a superb steam generation efficiency of 90.4% under 1 sun are achieved.•Bilayer foam can keep its structural stability and evaporation performance in durability tests.
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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.
The creation of superelastic, flexible three-dimensional (3D) graphene-based architectures is still a great challenge due to structure collapse or significant plastic deformation. Herein, we report a ...facile approach of transforming the mechanically fragile reduced graphene oxide (rGO) aerogel into superflexible 3D architectures by introducing water-soluble polyimide (PI). The rGO/PI nanocomposites are fabricated using strategies of freeze casting and thermal annealing. The resulting monoliths exhibit low density, excellent flexibility, superelasticity with high recovery rate, and extraordinary reversible compressibility. The synergistic effect between rGO and PI endows the elastomer with desirable electrical conductivity, remarkable compression sensitivity, and excellent durable stability. The rGO/PI nanocomposites show potential applications in multifunctional strain sensors under the deformations of compression, bending, stretching, and torsion.
Superelastic and pressure‐sensitive carbonaceous nanofibrous aerogels with a honeycomb‐like structure are fabricated through the combination of sustainable konjac glucomannan biomass and flexible ...SiO2 nanofibers. The aerogels can detect dynamic pressure with a wide pressure range and high sensitivity, which enables real pressure signals, such as human blood pulses, to be monitored in real time and in situ.
Additively manufactured porous NiTi alloys hold unprecedented promise in metallic implants due to their low elastic modulus and superelastic behavior. Such porous structures are usually topologically ...ordered and designed with periodically-repeating unit cells. However, the superelastic behaviors of fractal porous structures have never been studied. The Menger sponge-like fractal structures consisting of non-periodic fractal pores mimick the architectures and biomechanical properties of human bone. In this investigation, porous NiTi alloys designed with Menger sponges were fabricated by additive manufacturing using selective laser melting technology, and their superelastic behaviors were systematically characterized for the first time. Additively manufactured bulk NiTi alloys exhibit fully recoverable superelastic responses with slim stress hysteresis. The mechanical properties of bulk NiTi alloys match the properties of human cortical bones. The Menger sponges display excellent superelastic recovery strain ratios even at high porosity levels. The mechanical properties of highly fractalized Menger sponges are almost identical to the properties of human cancellous bones. The deformation mechanism undergoes a transformation from bending-dominated to stretching-dominated mode when the porous structures are highly fractalized. The unique combination of fractal topology, nanostructured microstructure, highly controllable elastic modulus and large recoverable deformation make the NiTi Menger sponge a promising candidate for metallic implants.
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•Nanostructured NiTi alloys with slim stress hysteresis and nearly zero remnant strain were fabricated by additive manufacturing.•Porous NiTi alloys designed with Menger sponge-like fractal structures were fabricated with precise structural morphologies.•Highly controllable mechanical properties were realized and superelastic deformation mechanisms were systematically explored.•Structural hierarchy were found to significantly influence the superelastic behaviors and deformation mechanisms.•The highly fractalized structure undergoes a bending-dominated to stretching-dominated deformation mode transformation.
Many applications proposed for functional nanofibers require their assembly into a monolithic cellular structure. The ability to maintain structural integrity upon large deformation is essential to ...ensure a macroscopic cellular material that functions reliably. However, it remains a great challenge to achieve high elasticity in three-dimensional (3D) nanofibrous networks. Here, we report a strategy to create fibrous, isotropically bonded elastic reconstructed (FIBER) aerogels with a hierarchical cellular structure and superelasticity by combining electrospun nanofibers and the freeze-shaping technique. Our approach allows the intrinsically lamellar deposited electrospun nanofibers to assemble into elastic bulk aerogels with tunable porous structure and wettability on a large scale. The resulting FIBER aerogels exhibit the integrated properties of ultralow density (<30 mg cm–3), rapid recovery from 80% compression strain, superhydrophobic-superoleophilic wettability, and high pore tortuosity. More interestingly, the FIBER aerogels can effectively separate surfactant-stabilized water-in-oil emulsions, solely using gravity, with high flux (maximum of 8140 ± 220 L m–2 h–1) and high separation efficiency, which match well with the requirements for treating the real emulsions. The synthesis of FIBER aerogels also provides a versatile platform for exploring the applications of nanofibers in a self-supporting, structurally adaptive, and 3D macroscopic form.
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