Low-temperature synthesis of manganese oxide-carbon nanotube-enhanced microwave-absorbing nanocomposites

摘要

Noting that the dielectric properties of manganese oxide make it a promising microwave-absorbing material, a low-temperature method to deposit crystalline MnO2 over carbon nanotubes (CNTs) is developed. Adjusting the pH of the precursor solution allows control over the phases and morphologies of the synthesized manganese oxides MnO2 and Mn3O4 that have minimum reflection losses of -11dB and -6dB, respectively. The synthesized CNT-MnO2 and CNT-Mn3O4 nanocomposites are superior microwave absorbers than simpler physical mixtures of CNTs and manganese oxides, with reflection losses as high as -19dB at 9.5GHz and -34dB at 4GHz, and have wider absorption bands than pure manganese oxides. Coating CNTs with manganese oxide not only increases dielectric and magnetic losses, but also improves the impedance match between free space and the absorber. The addition of CNTs to pure MnO2 and Mn3O4 improves impedance matching by enhancing the relaxation polarization and conductivity losses, magnetic loss, including contributions form eddy current and natural resonance. This facile, low-cost, scalable, high-yield method produces an enhanced microwave-absorbing nanocomposite.