In the present work, we address the new route for the green synthesis of manganese dioxide (MnO2) by an innovative method named the solution plasma process (SPP). The reaction mechanism of both colloidal and nanostructured MnO2 was investigated. Firstly, colloidal MnO2 was synthesized by plasma discharging in KMnO4 aqueous solution without any additives such as reducing agents, acids, or base chemicals. As a function of the discharge time, the purple color solution of MnO4 - (oxidation state +7) was changed to the brown color of MnO2 (oxidation state +4) and then light yellow of Mn2+ (oxidation state +2). Based on the UV-vis analysis we found the optimal discharging time for the synthesis of stable colloidal MnO2 and also reaction mechanism was verified by optical emission spectroscopy (OES) analysis. Secondly, MnO2 nanoparticles were synthesized by SPP with a small amount of reducing sugar. The precipitation of brown color was observed after 8 min of plasma discharge and then completely separated into colorless solution and precipitation. It was confirmed layered type of nanoporous birnessite- MnO2 by X-ray powder diffraction (XRD), fourier-transform infrared spectroscopy (FT-IR), and electron microscopes. The most important merits of this approach are environmentally friendly process within a short time compared to the conventional method. Moreover, the morphology and the microstructure could be controllable by discharge conditions for the appropriate potential applications, such as secondary batteries, supercapacitors, adsorbents, and catalysts.

1. 서 론
2. 실험방법
    2.1. 합성방법
    2.2. 분석방법
3. 결과 및 고찰
    3.1. 용액 플라즈마 공정(solution plasma process,SPP)
    3.2. 콜로이드 MnO2 합성
    3.3. MnO2 나노 입자 합성
4. 결 론

• 김혜민(신슈대학 물질화학과) | Hyemin Kim (Department of Materials Chemistry, Shinshu University, Nagano 380-8553, Japan) Corresponding author