Dual-template hydrothermal synthesis of multi-channel porous NiCo₂O₄ hollow spheres as high-performance electromagnetic wave absorber

Dual-template hydrothermal method was adopted for the synthesis of NiCo₂O₄ materials. The D-glucose acted as the hard template and the three kinds of soft templates, i.e., nonionic polyvinylpyrrolidone (PVP), anionic sodium dodecyl benzene sulfonate (SDBS) and cationic hexadecyl trimethyl ammonium bromide (CTAB) were selected to synthesize NiCo₂O₄ materials. We found that the species of the soft templates play significant role in the determination of products’ morphologies. Flower-like, flower-like spherical and multi-channel porous hollow spheres structured NiCo₂O₄ could be obtained by utilization of PVP, CTAB and SDBS, respectively. When employed as the electromagnetic (EM) wave absorbers, the multi-channel porous NiCo₂O₄ hollow spheres possessed the best EM wave absorption performance. The reflection loss (RL) value lower than −10 dB was up to 5.44 GHz and could be achieved at thin thickness of 1.8 mm. The minimum RL value corresponding to this thickness reached to −31.1 dB as well. The outstanding EM wave absorption performance was ascribed to the unique multi-channel porous hollow spheres structure, which could provide abundant interfaces between absorbers-air thus promoting the interfacial polarization. Additionally, the multiple reflections and scattering, dipole polarization and eddy current loss conjointly accounted for the superior attenuation behavior. The facile synthetic route and the high EM wave absorption performance of multi-channel porous NiCo₂O₄ hollow spheres may offer a novel strategy for the preparation of high-performance ferrite EM wave absorbers.