Synthesis and microwave absorbing properties of quasione-dimensional mesoporous NiCo2O4 nanostructure

doi:10.1016/j.jallcom.2013.09.091

Journal of Alloys and Compounds

Volume 585, 5 February 2014, Pages 240-244

https://doi.org/10.1016/j.jallcom.2013.09.091 Get rights and content

Highlights

•
A quasione-dimensional mesoporous NiCo₂O₄ nanostructure was synthesized.
•
The NiCo₂O₄ was used as microwave absorber for the first time.
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The NiCo₂O₄/paraffin composite shows excellent microwave absorbing property.
•
The microwave absorbing mechanism was discussed.

Abstract

Quasione-dimensional NiCo₂O₄ nanostructure was synthesized by a precipitation-thermal decomposition process. The diameters and special ratios of the NiCo₂O₄ fibers are 0.2–0.5 μm and 20–50, respectively. The mesoporous structure with a surface area of 54.47 m² g⁻¹ and average pore-size of 12.5 nm for the NiCo₂O₄ was obtained. The relative complex permittivity and permeability of paraffin/50 wt.% NiCo₂O₄ composite were measured in the frequency range of 2–18 GHz, and the microwave absorbing property of the composite was evaluated. An excellent reflection loss (RL) of −35.76 dB at 14.86 GHz with a composite thickness of 1.50 mm and effective bandwidth (RL < −10 dB) of 11.18 GHz were obtained, which is related to the thickness, impedance matching and morphology of the absorber.

Introduction

Recently, the electromagnetic (EM) pollution has become a serious social problem due to the development of wireless communication and the wide application of electronic devices. To overcome this problem, EM shielding and absorbing materials as EM protection roles have attracted considerable attention [1], [2]. However, the EM shielding materials cannot eliminate EM wave radically. Therefore, the microwave absorbing materials with the capability of absorbing and attenuating EM energy have become the focus of attention. Among the microwave absorbing materials, ferrite was most studied in experiment and applied in both military and civil fields for its large saturation magnetization, superior antioxidation and corrosion resistance, and easy preparation [3]. However, the permeability of ferrite will decrease rapidly in high frequency owing to the Snoek’s limit which leads to a weak magnetic loss [4]. What is more, the thickness of ferrite has to be thick for an efficient EM wave absorption [5]. Therefore, it is difficult for the traditional ferrite absorber to meet the requirement of wide bandwidth, thin thickness, lightweight and strong absorption for modern microwave absorber.

Previous studies about various morphologies of microwave absorbers indicate that the geometrical shape and size of the absorbers play a key role in the microwave absorbing properties [6]. One-dimensional (1D) or quasione-dimensional (Q1D) nanostructure seems to be a potential choice for enhancing the microwave absorbing properties because of its typical shape anisotropy and tunable electromagnetic parameters [7], [8]. On the other hand, it was found that a porous structure is beneficial to a good absorbing performance due to its large specific surface area and favorable impedance matching [9]. As mentioned above, it is a feasible approach to obtain a satisfactory absorption by modifying the morphology and architectural structure of the ferrite, which already has been partly confirmed [10], [11].

To date, a number of spinel ferrites with various compositions have been synthesized and used as microwave absorbing materials [12], [13], [14]. However, as an important spinel structure, NiCo₂O₄ was mainly used in electrochemistry field [15], [16], [17], and to the best of our knowledge, there has been no report about the microwave absorbing property of NiCo₂O₄ so far. In our previous work, an oxalate precursor structured as Ni_1/3Co_2/3(NH₃)_xC₂O₄·yH₂O has been successfully synthesized by a coordination–precipitation process [18]. In this study, the Q1D mesoporous NiCo₂O₄ nanostructure was first synthesized by a thermal decomposition of the precursor and used as a microwave absorber. The microwave absorbing properties of the as-prepared samples were investigated in the frequency range of 2.0–18.0 GHz and the microwave absorbing mechanism was discussed.

Section snippets

Preparation

All the chemicals are analytical grade and were used without further purification. All solutions were freshly prepared before each reaction. The Ni_1/3Co_2/3(NH₃)_xC₂O₄·yH₂O precursors were synthesized by a coordination–precipitation process. First, 0.2 mol NiCl₂·6H₂O and 0.4 mol CoCl₂·6H₂O were dissolved in 100 mL deionized water labeled as solution I, and 0.72 mol H₂C₂O₄·2H₂O was dissolved in 100 mL water/ethanol mixture solvent (1:1, volume ratio) labeled as solution II. Then, solution I was dropped

Results and discussion

XRD pattern of the as-synthesized thermal decomposition product is shown in Fig. 1(a). The distinct peaks observed at 2θ values of 18.9°, 31.2°, 36.7°, 44.6°, 55.4°, 59.1°, 65.0°, and 77.0° can be assigned to (1 1 1), (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1), (4 4 0) and (5 3 3) plane reflections of the face-centered cubic structure NiCo₂O₄ (JCPDS Card No. 73-1702; space group Fd3m), respectively. No diffraction peaks from impurity component can be detected, indicating the formation of pure NiCo₂O₄ product.

Conclusion

In summary, Q1D mesoporous NiCo₂O₄ nanostructure was synthesized by a thermal decomposition of oxalate precursor fiber. The paraffin/50 wt.% NiCo₂O₄ composites with the thickness of 1.25–3.00 mm exhibit excellent microwave absorbing properties (RL < −10 dB) in the frequency range of 6.82–18 GHz. The minimum reflection loss of −35.76 dB was obtained at 14.86 GHz with a composite thickness of 1.50 mm. The excellent microwave absorbing property comes from the quarter-wavelength absorbing mechanism,

Acknowledgments

This work was supported by Hunan Provincial Innovation Foundation for Postgraduate (CX2012B046) and Program of Science and Technology of Hunan Province (2010FJ3012).

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View full text

Synthesis and microwave absorbing properties of quasione-dimensional mesoporous NiCo2O4 nanostructure

Highlights

Abstract

Introduction

Section snippets

Preparation

Results and discussion

Conclusion

Acknowledgments

Mater. Lett.

J. Alloys Comp.

Appl. Surf. Sci.

Trans. Nonferr. Metal Soc. China

Physica B

J. Alloys Comp.

Mater. Lett.

Nano Lett.

J. Phys. Chem. C

Nanoscale

J. Appl. Phys.

Appl. Phys. Lett.

Appl. Phys. Lett.

Synthesis and microwave absorbing properties of quasione-dimensional mesoporous NiCo₂O₄ nanostructure