Supramolecular self-assembly of nickel (Ⅱ)-substituted α-Keggin-type polyoxometalate and polyaniline coated Fe2O3 hollow nanospindle for microwave absorption application
Progress in Natural Science , Volume 31, pp 387-397; doi:10.1016/j.pnsc.2021.04.007
Abstract: A general strategy has been developed here to supramolecular self-assembly of nickel (Ⅱ)-substituted α-Keggin-type polyoxometalate and polyaniline coated Fe2O3 hollow nanospindle (Fe2O3 hollow [email protected]/α-SiW11Ni composites) via electrostatic attraction and hydrothermal method. Fe3+ was first hydrolyzed and polymerized into Fe2O3, then dissolved into [Fe(H2PO4)x]3−x, resulting in hollow structure. The polyoxometalate existed in polyaniline as a proton-doped counter-ion form, rather than as a separate crystalline state. The protons and anions entered the PANI main chain and combined with N atoms of amines and imines on the PANI chain ((-NH‧+ = )/α-[SiW11Ni(H2O)O39]6-) to form poles and bipolar delocalization into π bonds of the whole polyaniline molecular chain, which leaded to conductance and polarization. The Fe2O3 hollow [email protected]/α-SiW11Ni composites were proven to be excellent microwave absorber in terms of reflection loss (RL) and bandwidth. The maximum RL value was up to −53.6 dB at 3.5 mm and 6.9 GHz. The broadest absorption bandwidth exceeding −10 dB was 6.3 GHz at a thickness of only 1.9 mm. Moreover, the ternary composites presented obvious multi-band absorption with the matching thickness range of 1.5–5 mm. The absorption peaks bandwidth reached as wide as 14.3 GHz, which included all C-Ku bands. The hollow and core-shell structures could provide non-uniform interface for the induced polarization loss and space for the reflecting and scattering of microwave. The carrier, pair-ion carrier and hydrogen bond network could lead to conduction loss. The magnetic losses were caused by eddy current effect and natural resonance. This work can lay a theoretical foundation for the design and performance regulation of new absorbing materials.
Keywords: Microwave absorption / Electrostatic attraction / Conduction loss / Impedance matching / Attenuation
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