Rambutan-like heterostructures consisting of Ni microspheres coated with oriented multiwall carbon nanotubes (MWCNTs) were synthesized by the one-pot thermal decomposition of a mixture of organic matter and Ni precursors. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy were used to reveal the formation mechanism. The growth of MWCNTs capped by Ni nanoparticles on the surface of the Ni nanoparticle-built microspheres followed a tip-growth mode. The composition and morphology of the rambutan-like heterostructures were easily controlled by changing the reaction time, mass ratio δ of polyethylene glycol (PEG) 20 000 to NiO, as well as type of C source and Ni precursor. Increasing the δ favored not only the increased C mass fraction but also the morphological conversion from Ni/C film core–shell structures to rambutan-like Ni/MWCNT heterostructures. Such changes caused the decreased saturation magnetization and enhanced permittivity properties with δ. Owing to intensive eddy current loss and multiresonance behaviors, rambutan-like Ni/MWCNT heterostructures with long MWCNTs exhibited significantly improved complex permeability and magnetic loss. Ni/MWCNT heterostructures coated by short MWCNTs showed an optimal microwave absorption property with a minimum R_L value of −37.9 dB occurring at 12.8 GHz. This work provides effective guidelines for devising and synthesizing highly efficient microwave-absorbing materials.

Fe ₃ O ₄ @C and Fe ₃ O ₄ /Fe@C core–shell nanorings (NRs) with enhanced microwave absorption properties were synthesized by a simple and controllable two-step process.

A facile template-free and one-pot thermal decomposition approach was used for the mass preparation of submicrometer-sized NiO octahedra. Ni octahedra with tailored crystallization and texture characteristics are easily achieved through H₂-annealing of NiO octahedra at various temperatures. The good morphology retention of Ni octahedra is due to the principle of minimum surface free energy as well as the similar crystallographic system to that of NiO. Studies on static magnetic and microwave electromagnetic properties reveal the relationships among the reactivity, shape, and resultant properties of the nanomaterials. Because of their high BET specific surface area and favorable crystal size, porous Ni octahedra produced at 300 °C exhibit excellent matching and absorbing properties with a minimum R_L value of −37.93 dB at 12.80 GHz and 11.60 GHz bandwidth (below −20 dB). Thus the Ni octahedra described here are believed to have a wide range of applications, including catalysis, electromagnetic shielding, and absorption.

Complex ZnO architectures with tunable morphologies and structures were obtained by modulating only the base type and molar ratio of base to Zn²⁺ (α) using an easy one-pot hydrothermal approach without any template or organic additive. Characterizations by X-ray diffraction, Fourier-transform infrared spectrometry, scanning electron microscopy, transmission electron microscopy, and surface area analysis were performed. The effect of the base type and base/Zn²⁺ molar ratio on the morphology and corresponding mechanism were determined. The correlations between the microstructure and properties were established. The antibacterial effect of the ZnO samples was probably due to a combination of variable factors. Better antibacterial activity is derived from more effective antibacterial surfaces, which are mainly associated with the specific surface area and Zn-polar plane. Thus, flower-like architectures with larger specific surface areas and more highly exposed (0001) Zn-polar surfaces outwards are promising structures for ZnO antibacterial agents. This work provides a guide for devising and synthesizing highly efficient antibacterial materials.

Flower-like Co superstructures composed of leaf-like flakes were synthesized via a facile hydrothermal approach independent of surfactants or complex precursors. The evolution of the morphology and crystal phase was closely related to the variation of the electrode potentials, in which NaOH and hydrazine hydrate played crucial roles. The microwave electromagnetic and absorbing properties of the flower-like Co/wax composites varied strongly with the mass ratios (λ) of Co powder to wax. At the low λ of Co powder to wax, flower-like Co superstructures functioned as the random distributed patches in wax matrix and, therefore composites exhibited frequency selective surface (FSS) behaviors. Owing to high conductance and eddy current losses, however, composites with high λ showed excellent microwave absorption performances, with a minimum reflection loss (R_L) of −40.25 dB observed at 6.08 GHz, corresponding to a matching thickness of 2.5 mm. In particular, the absorption bandwidth (R_L ≤ −20 dB) was 13.28 GHz. The current work provides insights into the absorption mechanism of flower-like complex absorption materials.