KCS

We successfully control dimension and phase of manganese oxide by physico- chemical top-down method. The pristine layered K_0.5MnO₂ was prepared by conventional solid state reaction of K₂CO₃ and Mn₂O₃ at 800 ℃. Unilamellar manganese dioxide (MnO₂) nanosheets (two-dimensional) were obtained by intercalation and exfoliation reaction of the protonic manganese dioxide with tetrabutylammonium (TBA) cation. Because the suitable amount content of proton and organic material have key role in this physico-chemical top-down method, well-dispersed MnO₂ nanosheets were adjusted to pH 6 by addition of 1M HCl and removed excess TBA cation by washing. The phase transformation of layered MnO₂ nanosheets to Mn₃O₄ nanocrystals was successfully carried out by heat-treatment even at 150 ℃. And dimension of obtained particles was controlled as nanorods (one-dimensional) or nanoparticles (zero-dimensional) depending upon applied heat temperature (from 150 ℃ to 300 ℃). These nanocrystals have higher capacitance properties than that of the reference bulk Mn₃O₄ (Sigma Aldrich) powder due to their nano-size effect. Physicochemical characterization and transformation mechanism study were performed by using X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Dimensions of Mn₃O₄ nanocrystals were confirmed by high-resolution transmission electron microscopy (HR-TEM). The component and organic content of the sample were measured by Fourier transform infrared (FT-IR) spectroscopy, elemental analysis (EA) and thermal analysis, including thermogravimetry (TG) and differential thermal analysis (DTA). The capacitance properties of Mn₃O₄ nanocrystals investigated in 1M Na₂SO₄electrolyte showed maximum capacitance of 160 F/g at scan rate 2 mV/s.