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

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 − 11 dB and − 6 dB, 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 − 19 dB at 9.5 GHz and − 34 dB at 4 GHz, 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.