Yanting Zhao

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

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.

Tunable dielectric properties and excellent microwave absorbing properties of elliptical Fe3O4 nanorings

Elliptical Fe3O4 nanorings (NRs) with continuously tunable axes that range from 40 nm to 145 nm in length were prepared through a precursor-directed synthetic route to determine the electromagnetic responses generated at 2–18 GHz. The tunability of the dielectric properties of Fe3O4 NRs depends on the long axis rather than on the specific surface area, internal stress, and grain size. Elliptical Fe3O4 NRs exhibit the excellent microwave absorbing properties due to the unique ring-like configuration, which significantly enhances permittivity, multiple scattering, oscillation resonance absorption, microantenna radiation, and interference. These findings indicate that ring-like nanostructures are promising for devising effective microwave absorbers.

Controllable Synthesis of CuxFe3-xO4@Cu Core-Shell Hollow Spherical Chains for Broadband, Lightweight Microwave Absorption

CuxFe3−xO4@Cu (0

Polymorphous ZnO nanostructures: Zn polar surface‐guided size and shape evolution mechanism and enhanced photocatalytic activity

This study proposes a simple, low‐temperature chemical etching method for selective preparation of monodispersed, hexagonal, single‐crystal ZnO nanostructures. The morphological evolution from nanoplates (NPs) to nanoseals (NSs), nanobowls (NBs), and nanorings (NRs) is initiated by positively charged (0 0 0 1) Zn polar surface and driven by the principle of minimum energy. The relationship among the morphology, dimensions, and function of ZnO was determined by investigating polar planes, surface areas, energy bands, defects, optical properties, and catalytic activity for rhodamine B degradation. The ZnO NBs and ZnO NRs exhibit improved photocatalytic performance because of enhanced light harvesting and plasmonic resonance enhanced absorption. Surface recombination plays a key role in the apparent rate constant k for ZnO NBs with small size and those formed at low reaction temperatures. The photocatalytic activity of ZnO NBs formed at high reaction temperatures decreases with increasing size because of the decreased surface area.

Controllable synthesis, formation mechanism, and enhanced microwave absorption of dendritic AgFe alloy/Fe3O4 nanocomposites

Single-crystalline dendritic AgFe alloy/Fe3O4 nanocomposites were successfully synthesized through galvanic replacement using Fe nanofibers as reducers and templates. The molar ratio of Ag+/Fe2+ (δ) and the aspect ratio of Fe nanofibers influence the compositions and sizes of the nanocomposites, respectively. The selective attachment at the {220} planes and anisotropic growth along the (111) plane affect the growth of dendritic nanocomposites. The composition-dependent static magnetic and microwave electromagnetic characteristics were studied systematically. Dendritic nanocomposites are typically ferromagnetic. The Ms decreases and Hc increases with increasing δ because of the increased content of antiferromagnetic Ag. Nanocomposites with δ = 1 : 1 and 2 : 1 exhibit significantly stronger absorption, thinner sample thickness, and lower bandwidth than pure Ag nanoparticles because of enhanced dielectric loss, magnetic loss, resonance absorption, and impedance matching. The bandwidth (RL ≤ −10 dB) is 4.85 GHz, which corresponds to the minimum RL value of −43.5 dB, and the absorption frequency range (RL ≤ −20 dB) is 7.68 GHz. This work provides a general strategy for preparing dendritic Ag-based nanocomposites and a basis for further studies on using hierarchical heterostructures as microwave-absorbing materials.