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 mull-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 mull-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 mull-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.