Synthesis Of Doped Manganese Oxide Micro/Nanostructures And Their Behaviors

Manganese oxides are of considerable interests because of their high applicability in various fields, like magnetic materials, energy device, catalysis, and battery materials. A class of manganese oxides, such as1D tunnel-based structure MnO2,2D birnessite-type Mn oxide and3D spinel Mn3O4, are possible by interlinking the basic MnO6octahedra via edges and vertices. Recently, most works about the tunnel-based structure MnO2have been reported. However, little research focused on the controlled synthesis and performance tuning of birnessite-type Mn oxide and spinel Mn3O4microstructures had been appeared in the papers. In addition, doping is an important way to tailor the physic-chemical properties of metal oxides. However, the optimization of doped Mn3O4with exceptional properties tuned conveniently by manipulating the synthetic conditions is still a challenge.In this work, manganese oxide micro/nanostructures with various shapes were successfully fabricated via redox reaction between organic reducing agent and potassium permanganate under hydrothermal condition. The doping effect of doped metal ions during the growth of Mn3O4microcrystals were discussed preliminaryly, and the properties of the obtained products were investiaged.Firstly, Mn3O4microcrystals and nanocrystals were achieved via controlling the proportion of the reducing agent and potassium permanganate. By using ethanol as reducing agent, the composition of the final products (MnOOH and Mn3O4) was only associated with the volume of ethanol in the reaction system. Single phase Mn3O4microcrystals were predictably prepared in higher ethanol volume (>1.5mL). The products were shaped in polyhedrons and sized in～1 μm. By using glucose as reducing agent, Mn3O4nano-octahedral sized in～50nm were achieved. Such results revealed that the content of reducing agent in the hydrothermal system played a decisive role in the formation of Mn3O4crystal.Secondly, the effects of doping ions on formation of Mn3O4microcrystals were investiaged by using ethanol as reducing agent. Metal ions Cr3+, Cu2+, Zn2+and Ni2+were selected as the dopant because of the comparable ionic radii of Mn3+/Mn2+. At low doping level, the introduction of divalent metal ions in place of Mn2+, or trivalent metal ions in place of Mn3+enhanced greatly the formation of single tetragonal phase doped Mn3O4microcrystals, revealing the match of ionic radius. Moreover, to meet the requirements of a stable lattice, the change in oxidation state of dopant for charge compensation was taken palce in the case of lagre mismatch of ionic radius.Further, energy bandgap and catalytic degradation activity of Mn3O4micro/nanocrystals were investigatived. The photon absorption of Mn3O4had a size effect, and the doping metal ions could be used to tune the bandgap of Mn3O4microcrystal. The catalytic activities of the as-obtained Mn3O4microcrystals for decomposition of methylene blue were also affected by the types of the doped ions.Finally, birnessite-type Mn oxide nanostructures with the high surface area (87m2/g) and the larger layer spacing (0.73nm) were synthesized via hydrothermal reduction of potassium permanganate with low content of glucose. The obtained birnessite-type Mn oxide had the appearance of20-50nm loosely packed nanoparticles formed by the large pieces of nanosheets. The capacitive characteristics of the birnessite-type Mn oxide nanoparticles electrode were investigated. The electrode exhibited a high mass-specific capacitance of542F/g at the lower loading, and the area-specific capacitance of2.39F/cm2at higher mass-loading were achieved.