Facile synthesis and enhanced microwave absorption properties of novel hierarchical heterostructures based on a Ni microsphere–CuO nano-rice core–shell composite

A novel hierarchical heterostructure of Ni microspheres–CuO nano-rices was fabricated using a simple two-step process. The CuO rices were densely deposited on the surfaces of Ni microspheres. The phase purity, morphology, and structure of composite heterostructures are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). Different structured Ni–CuO composite heterostructures are also investigated by adjusting the volume ratio of the reactants. The core–shell rice-like CuO-coated Ni exhibits better antioxidation capability than pure Ni due to the presence of the barrier effect of the CuO shell, which is revealed by the thermogravimetric analysis (TGA). In comparison with pristine Ni microspheres and CuO nanoflakes, the Ni–CuO composites exhibit excellent microwave absorption properties. Moreover, the amount of CuO plays a vital role in the microwave attenuation of Ni–CuO composites. The Ni–CuO heterostructures prepared at 0.017 M Cu2+ exhibit the best electromagnetic wave absorption capabilities. A minimum reflection loss reaches −62.2 dB (>99.9999% microwave absorption) at 13.8 GHz with the thickness of only 1.7 mm. The effective absorption (below −10 dB) bandwidth can be tuned between 6.4 GHz and 18.0 GHz by tuning the absorber thickness of 1.3–3.0 mm. Thus, the Ni–CuO composite possesses a fascinating microwave absorption performance as a novel absorbing material with strong absorption, wide-band gap and thin thickness.