Preparation And Microwave Absorbing Properties Of Manganese Dioxide Nanomaterials With Different Morphology

As the rapid development of information technology,all kinds of electronic equipment and small portable electronic products gradually infiltrate into all aspects of our life,the problems of electromagnetic wave pollution and electromagnetic interference have become more and more serious.Therefore,it is urgent to exploit absorbing materials with light weight,thin coating,strong absorption in a wide range,simple preparation process and low cost.In this paper,the hydrothermal method is mainly used to obtain the one-dimensional rod-shaped（α-MnO₂,β-MnO₂）,three-dimensional core-shell structure（δ-MnO₂,α-MnO₂,dual-phase δ/a MnO₂）and three-dimensional hollow porous structure（γ-MnO₂）of MnO₂ nanomaterials by changing the experimental materials and preparation process.Furthermore,we studied the microwave absorption properties of MnO₂ nanomaterials separately,discussed the structure-microwave absorption performance relationship of the MnO₂,and explored the possible electromagnetic absorption mechanisms in MnO₂ nanomaterials with different crystal phases and morphology.The specific research contents are as follows:（1）Three kinds of rod-shaped MnO₂ with different crystal phases and sizes were obtained using KMnO₄ and MnSO₄.H₂O as raw materials at different hydrothermal temperatures,and their absorption properties were further explored.The results show that the absorption properties of P-MnO₂ with one-dimensional rod structure are better than α-MnO₂,and the sample’s crystallinity is higher,the absorbing performance is better.The β-MnO₂ prepared at 220 ℃ exhibited the best absorbing properties,at a test frequency of 4.7 GHz and a coating thickness of 1.5 mm,the minimum reflection loss is-25.5 dB and the effective absorbing bandwidth is 5.0 GHz（13-18.0 GHz）.（2）Three kinds of 3D core-shell MnO₂ nanomaterials were obtained using KMnO₄and dilute HCl as raw materials at different hydrothermal temperatures for 1 h.By analyzing the growth mechanism of three kinds of MnO₂,it was found that the layered-oriented adhesion growth mechanism and the Ostwald ripening process are important for the formation of 3D structure and crystal transformation of MnO₂ nanomaterials.By studying its electromagnetic absorption performance,it was found that the dual-phase core-shell composite material prepared at 150 ℃,with δ-MnO₂ microspheres as the core and a-MnO₂ nanorods as the outer shell exhibited excellent microwave absorption properties.With a thickness of 3.9 mm and a test frequency of 4.5 GHz,the minimum reflection loss is-45.2 dB.The excellent microwave absorption properties of the composite are attributed to the good impedance matching properties of the two-phase core-shell heterostructure and the strong interfacial polarization between the 8-MnO₂ microspheres and the a-MnO₂ nanorods.（3）A three-dimensional hollow porous structure of y-MnO₂ nanospheres with layered particles was prepared using MnSO₄·H₂O and NH₄HCO₃ as raw materials by two-step method.By analyzing the formation process and pore size distribution of the hollow porous structure,it was found that the release of CO₂ during the calcination of the precursor has an important influence on the microstructure of the sample.In the subsequent electromagnetic microwave absorption performance test,it was found that the y-MnO₂ microspheres of the three-dimensional hollow porous structure exhibited excellent absorbing properties.When the test frequency is 4.9 GHz and the coating thickness is 3.5 mm,the minimum reflection loss is-51.3 dB and the effective absorbing bandwidth is 3 GHz（3.5～6.5 GHz）.Its excellent absorbing properties are mainly attributed to the various polarization behaviors in the electromagnetic microwave environment,the multiple reflection and scattering of the incident electromagnetic microwaves by the porous sheet particles and the hollow porous structure of the materials.