Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made with regard to the development of electrospinning methods and engineering of electrospun nanofibers to suit or enable various applications. We aim to provide a comprehensive overview of electrospinning, including the principle, methods, materials, and applications. We begin with a brief introduction to the early history of electrospinning, followed by discussion of its principle and typical apparatus. We then discuss its renaissance over the past two decades as a powerful technology for the production of nanofibers with diversified compositions, structures, and properties. Afterward, we discuss the applications of electrospun nanofibers, including their use as “smart” mats, filtration membranes, catalytic supports, energy harvesting/conversion/storage components, and photonic and electronic devices, as well as biomedical scaffolds. We highlight the most relevant and recent advances related to the applications of electrospun nanofibers by focusing on the most representative examples. We also offer perspectives on the challenges, opportunities, and new directions for future development. At the end, we discuss approaches to the scale-up production of electrospun nanofibers and briefly discuss various types of commercial products based on electrospun nanofibers that have found widespread use in our everyday life.

Using elliptical iron glycolate nanosheets as precursors, elliptical Fe3O4/C core-shell nanorings (NRs) [25 ± 10 nm in wall thickness, 150 ± 40 nm in length, and 1.6 ± 0.3 in long/short axis ratio] are synthesized via a one-pot hydrothermal route. The surface-poly(vinylpyrrolidone) (PVP)-protected-glucose reduction/carbonization/Ostwald ripening mechanism is responsible for Fe3O4/C NR formation. Increasing the glucose/precursor molar ratio can enhance carbon contents, causing a linear decrease in saturation magnetization (Ms) and coercivity (Hc). The Fe3O4/C NRs reveal enhanced low-frequency microwave absorption because of improvements to their permittivity and impedance matching. A maximum RL value of -55.68 dB at 3.44 GHz is achieved by Fe3O4/C NRs with 11.95 wt % C content at a volume fraction of 17 vol %. Reflection loss (RL) values (≤-20 dB) are observed at 2.11-10.99 and 16.5-17.26 GHz. Our research provides insights into the microwave absorption mechanism of elliptical Fe3O4/C core-shell NRs. Findings indicate that ring-like and core-shell nanostructures are promising structures for devising new and effective microwave absorbers.

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