The limited mechanical properties of carbon nanofibers (CNFs) have become a severe problem hindering their wide range applications. The restricting issues are found in the whole fabrication process, including the precursor design, spinning and collection techniques, post treatments like stretching and aligning, and complicated thermal treatments involving stabilization and carbonization. Here we access the CNF development by focusing on the mechanical properties, and systematically discuss the strengthening strategies during the different fabrication stages.
Twisted and coiled fiber-based actuators have drawn a great attention because their unique structure can provide mechanical response with the external thermal stimulus. Herein, an ultra-fast and light-weight twisted and coiled fiber-based actuator was designed based on a nature melanin/poly (vinyl alcohol-co-ethylene) (PVA-co-PE) nanofibers/PA6 composite fiber. In brief, PA6 was firstly coated by melanin/PVA-co-PE nanofibers using a spraying method, followed by the twisting and coating the composite fiber to obtain the actuator. The excellent photothermal property of melanin contributed to the superior performance of the actuator, whereas the PVA-co-PE nanofibers was responsible for the uniform distribution of melanin and the enhanced mechanical property of the prepared-actuator. This unique design has led to the high performance of the melanin/NFs/PA6 fiber-based actuator, whose torsion actuation can reach to 14,000 rpm, and maximum tensile actuation was − 6.36% at temperature difference of 40 ℃. In addition, the tensile stress of PA6/NFs/melanin fiber was about four times higher than PA6 filaments. Owing to the simple and environmental-benign preparation method, as well as the excellent efficiency of twisted and coiled melanin/NFs/PA6 fiber-based actuator, this study highlights the facile design of the composite fiber for high-performance fiber-based actuators. This fiber-based actuator is promising for application in energy generator.
The objective of this study was to convert biochar, a byproduct generated from the hydrothermal process (in oxygen-limited environment) of biomass (e.g., corn stover), into value-added product. In specific, three-dimensional (3D) biochar-containing precursor sponge, which was made by using electrospun polymer nanofibers as skeleton support, was fabricated via an innovative approach. The weight ratio of biochar to polymer (in the precursor sponge) was 2/1, and it appeared that the biochar weight ratio could be further increased. Upon heat treatments (i.e., stabilization in air and carbonization in argon), the precursor sponge was converted into carbon nanofibrous sponge that had the porosity of ~ 90 vol%, the BET surface area of ~ 51.7 m2 g− 1, and the carbon content of ~ 95 wt%; and it was mechanically elastic/resilient. The electrochemical study indicated that, the carbon nanofibrous sponge could be utilized for making supercapacitor electrode with excellent rate capability and high kinetic performance. This study would not only demonstrate a high-value application of hydrothermally generated biochar, but also provide a facile while novel approach for the fabrication of carbon nanofibrous sponge which could be potentially used for various applications (particularly the energy storage application).
Nanofibers with unique structures and multiple components have attracted more and more attention, which could combine multi-functions in one entity. Janus-type biphasic nanofibers with unique structure can be quickly obtained by electrospinning technology. We produced CoOx/C nanofibers with Janus structure by self-made side-by-side electrospinning spinneret, combined with electrospinning technology and heat treatment. CoOx/C nanofibers had a large amount of graphitic carbon distributed on one half of the Janus nanofiber, and CoOx/C nanoparticles were embedded in the other half of the Janus nanofiber and distributed uniformly. CoOx/C acted as ORR catalysis, and graphitic carbon, pridinc-N and CoOx in CoOx/C had a synergistic effect on their catalytic activity. The results confirmed that CoOx/C was dominated by four-electron pathway under alkaline conditions, and the Tafel slope was lower than that of commercial Pt/C catalysts. The preparation method of this work is simple and easy, the structure is controllable, and the composition is adjustable, which provides a feasible way for preparing Janus structure nanofibers with different functions.
Serious freshwater shortage and environmental pollution boost the rapid development of solar-driven water production. Although improved evaporation rate has achieved in recent years, undesirable impurity (e.g., pollutant components) can also be inevitably evaporated and collected as impurity in produced freshwater. This work reports new ultra-light three-dimensional (3D) aerogels assembled by hierarchical Al2O3/TiO2 nanofibers and reduced graphene oxide (RGO) for exciting synchronized solar-driven evaporation and water purification. Hydrophilic Al2O3/TiO2 fibrous channels linked up the graphene hot-spots and water body for sufficient water supply and bulk water insulation. Meanwhile, featured with thermal insulation effect, the Al2O3/TiO2 nanofibers effectively locked the converted heat with less energy loss from sunlight. The introducing of Al2O3/TiO2 nanofibers into RGO aerogel led to the effective interfacial evaporation for a more rapid water evaporation rate (2.19 kg · m−2 · h−1, normalized to evaporation area including both top and side surface), which was 36% higher than that of pristine RGO aerogel. Moreover, simultaneous with the strong steam generation, Al2O3/TiO2 nanofibers in situ removed the pollutants within steam by photodegradation, achieving polluted wastewater purification with high contaminant removal ratio of 91.3%. Our work on coupling Al2O3/TiO2 nanofibers into photothermal aerogel provides attractive solutions for the challenges of clean water scarcity and serious environmental pollution.
Biomimetic scaffolds made by synthetic materials are usually used to replace the natural tissues aimed at speeding up the skin regeneration. In this study, a flexible and cytocompatible poly(glycerol sebacate)@poly-l-lactic acid (PGS@PLLA) fibrous scaffold with a core–shell structure was fabricated by coaxial electrospinning, where the shell PLLA was used to be a skeleton with pores on the fibrous surface. The fibrous morphology with pores on the surface of the prepared fibers was observed by SEM. The core–shell microstructure of PGS@PLLA fibers was confirmed by TEM and Laser Scanning Confocal Microscopy (LSCM). In addition, the prepared fibers exhibited a strong ability to repair tissues of the skin wound, where the stability of cell security and proliferation, and the lower inflammatory response were all superior to those of pure PLLA scaffold. It’s worth noting that the percentage of skin tissue was regenerated by 95% within 14 days, which suggests the potential application for electrospun-based synthetic fibrous scaffolds on wound healing.
The improvement of the photocatalytic performance of TiO2 nanofibers (NFs), prepared by electrospinning, is achieved by surface modification with the rhodizonic acid (RhA). The condensation reaction between hydroxyl groups from TiO2 NFs and RhA is accompanied by the red-shift of optical absorption due to interfacial charge transfer (ICT) complex formation. Crystal structure, morphology, and optical properties of unmodified and surface-modified TiO2 NFs were analyzed. The photocatalytic performance of prepared samples has been examined through degradation of organic dye methylene blue. Superior photocatalytic activity of surface-modified TiO2 NFs with RhA is attributed to their enhanced optical properties, i.e., the ability to harvest the photon energy in the visible spectral range.