Facile Hydrothermal Synthesis of Fe₃O₄/C Core–Shell Nanorings for Efficient Low-Frequency Microwave Absorption

TLDR

The study investigates the microwave absorption mechanism of elliptical Fe3O4/C core–shell nanorings. Elliptical Fe3O4/C core–shell nanorings were fabricated by a one‑pot hydrothermal method from iron glycolate nanosheets, where PVP‑protected glucose reduction, carbonization, and Ostwald ripening drive formation, and higher glucose ratios increase carbon content while reducing magnetization and coercivity. The Fe3O4/C nanorings exhibit strong low‑frequency microwave absorption, achieving a peak reflection loss of –55.68 dB at 3.44 GHz (11.95 wt % C, 17 vol %) and maintaining RL ≤ –20 dB across 2.11–10.99 GHz and 16.5–17.26 GHz, confirming their potential as effective microwave absorbers.

Abstract

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.