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: Materials International
A B S T R A C T A general strategy has been developed here to supramolecular self-assembly of nickel (II)-substituted α-Keggintype polyoxometalate and polyaniline coated Fe 2 O 3 hollow nanospindle (Fe 2 O 3 hollow nanospindle@PANI/ α-SiW 11 Ni composites) via electrostatic attraction and hydrothermal method. Fe 3þ was first hydrolyzed and polymerized into Fe 2 O 3 , then dissolved into [Fe(H 2 PO 4 ) x ] 3Àx , resulting in hollow structure. The polyoxometalate existed in polyaniline as a
... yaniline 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 to form poles and bipolar delocalization into π bonds of the whole polyaniline molecular chain, which leaded to conductance and polarization. The Fe 2 O 3 hollow nanospindle@PANI/ α-SiW 11 Ni composites were proven to be excellent microwave absorber in terms of reflection loss (R L ) and bandwidth. The maximum R L value was up to À53.6 dB at 3.5 mm and 6.9 GHz. The broadest absorption bandwidth exceeding À10 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.