Ultralight 3D-γ-MnOOH porous materials fabricated by hydrothermal treatment and freeze-drying

Creating three-dimensional (3D) ultralight metal oxide using cost-effective precursors and facile approaches is important. Here, shape-controlled γ-MnOOH (density lower than 0.078 g cm ⁻³ ) with a continuously 3D porous network (3D-γ-MnOOH) was successfully fabricated with KMnO ₄ , MnCl ₂ and NaOH via hydrothermal treatment and freeze-drying. The hydrothermal condition and the amount of reactants were systematically investigated, and the optimal procedure occurs at 180°C for 10 h with the molar ratios of NaOH/KMnO ₄ and MnCl ₂ /KMnO ₄ as 5.0 and 3.5, respectively. Owing to the low density, 3D network, and the filling of air inside the channel, the new γ-MnOOH can float on the water for at least 4 months with complete structure. The formation and floating mechanism of the 3D-γ-MnOOH were also explored. This new 3D-γ-MnOOH could be utilized in oil absorption.