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

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.

Synthesis and Potential Adsorption of Fe3O4@C Core-Shell Nanoparticles for to Removal of Pollutants in Aqueous Solutions: A Brief Review.

“…Another approach to synthesize the Fe 3 O 4 @C core-shell was proposed by Wu et al [55]. This strategy is a combination of two reactions: solvothermic and hydro thermic.…”

“…This strategy is a combination of two reactions: solvothermic and hydro thermic. However, the crucial step to the formation of Fe 3 O 4 @C core-shell is the hydrothermic reaction [55]. The synthesis of Fe 3 O 4 @C core-shell was basically carried out via polyvinylpyrrolidone-protected glucose reduction/carbonization/ Ostwald ripening.…”

“…Depending on the synthesis techniques, a variety of scales and shapes can be synthesized, such as sphere, cube, prism, platelets, wire, rod, tube, etc. In order to synthesize Fe 3 O 4 @C core-shell nanostructures at different scales and shapes, several methodologies have been developed [34,37,[47][48][49][50][51][52][53][54][55].…”

“…Therefore, there are several studies addressing the use of different coating materials for magnetic nanoparticles, such as silicon [66], polyanile [67], chitosan [68], carbon [35,52,53,55], among others. A comparison between silicone and carbon as a coating material for metallic particles shows that carbon presents a much greater stability in various types of environments and conditions, both for acid and basic media, and high temperatures and pressure [34].…”

“…Several different methodologies are found in the literature for the synthesis of core-shell Fe 3 O 4 @C nanoparticles, such as solvothermal [49], chemical vapour decomposition [48], hydrothermal coprecipitation [34], pyrolysis [55,53], combustion waves [69] and synthesis by microwave [55], as well as the combination of two or more methods.…”