Controlled Synthesis And Characterization Of Manganese Oxide Nanomaterials

As one of the most important transition metal oxides, manganese oxides have attracted considerable interest due to their unique physical and chemical properties, which provide wide-spread applications in catalysts, batteries, magnetic materials, ion exchange, etc. Nanostructured manganese oxides exhibit the superior properties compared with their bulk counterparts. Thus, many works have been carried out to study the synthesis and novel properties of manganese oxide nanostructures. Selective synthesis of nanomaterials with controllable compositions and morphologies represents an increasingly important research direction in nanosciences and nanotechnologies because the intrinsic properties of nanostructures depend on their shape, phase, and size. Currently, controlled synthesis of manganese oxide nanomaterials is still a challenge.We have developed a facile hydrothermal method for the preparation of γ-MnOOH nanorods with the use of potassium permanganate (KMnO4) and ethylene glycol (EG) as raw materials. We noted that the reaction time and temperature make important effects on the formation of the γ-MnOOH nanorods. Based on the experimental results, the formation mechanism of γ-MnOOH nanorods through a lamellar growth, assembly and ripening process was proposed. Calcination of the γ-MnOOH under different heat treatment conditions leads to the formation of MnO2, Mn2O3, and Mn3O4 nanorods, which indicates that γ-MnOOH is an ideal precursor for further synthesis of various manganese oxide nanostructures.The single-crystalline α-MnO2 and γ-MnOOH nanorods were prepared through a hydrothermal route by the direct reaction between the KMnO4 and NaHSO3. We investigated the impacts of experimental environments including reactant concentration and reaction temperature on the size, shape, and structure of manganese oxide nanostructures. Selective preparation of α-MnO2 and γ-MnOOH nanorods was achieved just by adjusting the concentration of NaHSO3. The temperature also has important effects on the morphologies of the final products. Our. results show the a-MnO2 nanorods are formed through the particles, fibres, and rods by improving the hydrothermal temperature. Vibrating sample magnetometer (VSM) analyses indicate that the a-MnO2 nanorods are paramagnetic at room temperature.We developed a facile, high-yield and low-temperature synthetic route for the preparation of various nanostructured MnOx with crystalline phases of y-MnOOH, δ-MnO2, α-Mn2O3, and Mn3O4 as well as the shapes of the rods, sheets, cubes, and particles just by adjusting the amount of H2O2 or reactant concentration. We systematically investigated the impacts of experimental environments including reaction time, reaction temperature, reactant concentration, the amount of H2O2, and the source of caustic alkalis on the size, shape, and structure of manganese oxide nanostructures. Based on the transmission electron microscope (TEM) results, the formation mechanism of bundle-like y-MnOOH nanorods through a lamellar growth, dissolution-recrystallization and oriented attachment process was proposed. Furthermore, the bundle-like MnO2, Mn2O3, and Mn3O4 nanorods are synthesized by calcining the γ-MnOOH precursors under different heat treatment conditions.