Carbon nanofibers prepared from electrospun polyimide, polysulfone and polyacrylonitrile nanofibers by ion-beam irradiation

Polyimide-derived carbon nanofiber membranes as free-standing anodes for lithium-ion batteries

Free-standing and flexible carbon nanofiber membranes (CNMs) with a three-dimensional network structure were fabricated based on PMDA/ODA polyimide by combining electrospinning, imidization, and carbonization strategies. The influence of carbonization temperature on the physical-chemical characteristics of CNMs was investigated in detail. The electrochemical performances of CNMs as free-standing electrodes without any binder or conducting materials for lithium-ion batteries were also discussed. Furthermore, the surface state and internal carbon structure had an important effect on the nitrogen state, electrical conductivity, and wettability of CNMs, and then further affected the electrochemical performances. The CNMs/Li metal half-cells exhibited a satisfying charge–discharge cycle performance and excellent rate performance. They showed that the reversible specific capacity of CNMs carbonized at 700 °C could reach as high as 430 mA h g⁻¹ at 50 mA g⁻¹, and the value of the specific capacity remained at 206 mA h g⁻¹ after 500 cycles at a high current density of 1 A g⁻¹. Overall, the newly developed carbon nanofiber membranes will be a promising candidate for flexible electrodes used in high-power lithium-ion batteries, supercapacitors and sodium-ion batteries.

Free-standing and flexible carbon nanofiber membranes (CNMs) with a three-dimensional network structure were fabricated based on PMDA/ODA polyimide by combining electrospinning, imidization, and carbonization strategies.

A comprehensive study on the effect of carbonization temperature on the physical and chemical properties of carbon fibers

Carbon fibers were successfully fabricated via the electrospinning technique, followed by stabilizing and carbonizing electrospun PAN fibers. A wide range of analytical techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL), vibrating sample magnetometer (VSM) techniques, and Hall effect were performed to study of the effect of carbonization temperature on the physical and chemical characterization of carbon fibers. The SEM images of the PAN precursor exhibit a smooth outer surface, after the stabilization and carbonization process, along with a broken fiber at higher carbonization temperature about 1400 °C. Morphological characterization based on the recorded TEM images of carbonized fibers at 1000 °C and 1400 °C, showed that the obtained morphology can be classified as fiber structures, where their diameters ranged from 196 to 331 nm. The XRD patterns of PAN-based carbon fibers confirm the structural changes from linear structure into a graphite-like structure. The DRS study indicates the possible π–π*/σ–π* and n–π* transitions. The presence of the surface functional groups and different trapped radiative recombination on the emission bands is confirmed by the PL. VSM results shows the weak ferromagnetic nature of the carbon fibers.

Anti-oil-fouling hydrophobic-superoleophobic composite membranes for robust membrane distillation performance

As a promising thermally driven separation process, membrane distillation (MD) is capable of treating challenging wastewaters. However, the traditional hydrophobic membranes are vulnerable to fouling by non-polar contaminants owing to the strong hydrophobic-hydrophobic interactions. To address this problem, we developed novel anti-oil-fouling MD membranes in this study. The composite membranes with asymmetric wettability were fabricated through electrospinning polyacrylonitrile (PAN) fibrous coating on a hydrophobic polytetrafluoroethylene (PTFE) membrane, followed by hydrolyzing the PAN coating with ethylenediamine (EDA) and NaOH, respectively. These two composite membranes exhibited excellent underwater superoleophobicity, with the underwater oil contact angle >150°, which can be attributed to the fibrous and re-entrant surface structure and the optimized surface hydrophilicity of the electrospun coating. During MD process using saline and oily emulsion as feed, the composite membranes presented robust anti-oil-fouling performance, indicating by stable permeate flux and salt rejection. A novel oil-droplet adhesion force probe was introduced to quasi-quantitatively elucidate oil-membrane interaction and evaluate membrane fouling propensity, the force spectroscopy indicated that the fabricated composite membranes had fairly less attractive to crude oil compared with the PTFE membrane. Our research results suggest that the novel composite membranes with asymmetric wettability were competent to serve as an anti-oil-fouling MD membrane for desalinating challenging saline and oily wastewaters.

Functional Polyimide-Based Electrospun Fibers for Biomedical Application

The current study focuses on the application of cytotoxicity tests upon one membrane matrix based on electrospun polyimide fibers, appealing for biomedical application, such as scaffolds for cell growth, patches or meshes for wound healing, etc. Assays were performed in order to determine the viability and proliferation of L929 murine fibroblasts after they were kept in direct contact with the studied electrospun polyimide fibers. Increased cell viability and proliferation were detected for cells seeded on electrospun polyimide fibers membrane, in comparison with the control system, either after two or six days of evaluation. The number of live cells was higher on the studied material compared to the control, after two and six days of cell seeding. The tendency of the cells to proliferate on the electrospun polyimide fibers was revealed by confocal microscopy. The morphological stability of electrospun polyimide membrane was evaluated by SEM observation, after immersion of the samples in phosphate buffer saline solution (PBS, 7.4 at 37 °C) at various time intervals. Additionally, the easy production of electrospun polyimide fibers can facilitate the development of these types of matrices into specific biomedical applications in the future.

Fabrication and electrolyte characterization of uniaxially-aligned anion conductive polymer nanofibers

We report the anion transport properties of anion conductive polymer nanofibers fabricated using an electrospinning method. The aligned nanofibers were prepared to evaluate the anion conductivity of the nanofibers. The aligned nanofibers had 10-15 times higher conductivity (up to 160 mS cm^-1 at 90 °C and 95%RH) and lower activation energy (23-25 kJ mol^-1) than the corresponding membranes, even though the nanofibers showed lower water uptake than the corresponding membranes. The anion conductivity measurement of nanofibers with different IEC values and anion species revealed that the dependency of anion conductivity on these factors was smaller in the nanofibers than in the corresponding membranes. These results indicate that effective ion transport pathways were formed in the nanofibers due to the phase separation and the polymer chain orientation along the nanofiber axis. These nanofibers are expected to be useful for future applications in alkaline fuel cells, air batteries, and other energy- and environment-related devices regardless of the ion species.

Graphene/polypyrrole-coated carbon nanofiber core–shell architecture electrode for electrochemical capacitors

In this study, a two-step electrospinning and potentiostatic electrodeposition method was used to fabricate the graphene/polypyrrole-coated carbon nanofiber core–shell architecture electrode for supercapacitor applications.