Controlled Synthesis, Mechanism and Degradation Property of Birnessite-MnO₂ Nanoflowers and Nanoflakes.

Birnessite-MnO₂ nanoflakes were synthesized via an aqueous oxidation method at 90 °C using Mn(CH₃COO)₂, NaOH, and KMnO₄. The samples' morphology, crystalline structure, and optical property were determined by field emission scanning electron microscopy, X-ray powder diffraction and UV-Vis spectrophotometry. The birnessite-MnO₂ nanoflakes were converted to KMnO and Mn suboxides following a decrease in the concentration of KMnO₄ in the reaction. The amount of NaOH in the reaction determined the type of precursor. Without NaOH, the precursor was converted from Mn(OH)₂ to Mn (from Mn(CH₃COO)₂), thereby enabling the synthesis of birnessite-MnO₂ nanoflowers. The formation mechanism of birnessite-MnO₂ nanoflowers and nanoflakes was clarified via the corresponding simulated crystal structures. Evaluation of the synthesized samples confirmed that the birnessite-MnO₂ nanoflakes and nanoflowers exhibited excellent degradation properties.