八面體氧化錳奈米粒子的合成與特性分析

Synthesis and Characterization of Octahedral Manganese Oxide Nanoparticles

本研究利用熱裂解法合成單一分佈的氧化錳MnO奈米粒子。實驗以市售氧化錳粉末為起始材料，利用油酸作為溶劑，溶解形成油酸錳錯化合物，再以熱注入(Hot-injection)方式注入界面活性劑油胺與三正辛胺，熱裂解形成單一分佈奈米氧化錳粒子。藉由不同的界面活性劑與不同濃度控制氧化錳奈米粒子的大小與均一性。經由X-光繞射儀(XRD)鑑定，所合成的粉末為岩鹽結構的MnO奈米晶體，經掃瞄式電子顯微鏡(SEM)、穿透式電子顯微鏡 (TEM)分析結果顯示此氧化錳奈米粒子型態為八面體結構。在氬 (Ar) 氣氛下，三正辛胺濃度為2 mmol、4 mmol、8 mmol ，合成出的氧化錳奈米粒子平均粒徑分別為12 nm、15 nm、20 nm，三正辛胺濃度也會影響氧化錳粒子的粒徑分佈。磁性質分析顯示氧化錳奈米粒子為反鐵磁性，隨著粒徑減少，反鐵磁性與飽和磁化量有減少的趨勢。藉由電泳披覆的方法將氧化錳奈米粒子披覆在石墨電極上，三種粒徑MnO電極其第50次循環伏安法所量測的比電容值分別為73.57、58.70與45.64 F/g，充放電行為穩定且具有再現性，顯示MnO奈米粒子具有應用在超級電容器上的潛力。

In this study, different types of monodispesed manganese oxide nanoparticles have been synthesized by thermal decomposition of Mn-oleate (MnO) complex, which is prepared from dissolving the commercial manganese oxide powder in oleic acid. The size and uniformity of the manganese oxide nanoparticle are controlled by surfactants and concentration of the precursors. An XRD (Shimadzu XRD-6000) analysis shows that the synthesized powder is MnO crystals with rock-salt structure. SEM and TEM micrographs indicate that the MnO is monodispersed and octahedral. In an Ar atmosphere, the particle size can be controlled to 12, 15 and 20 nm with respect to the variation of tri-n-octylamine concentration i.e. 2 mmol, 4 mmol, and 8 mmol, respectively. Magnetic properties of manganese oxide exhibit anti-ferromagnetic behavior. When the particle size of manganese oxide decreases from 20 nm to 12 nm, the Curie-Weiss temperature increases, which implies that the anti-ferromagnetic phase slightly shifts to the paramagnetic phase. The graphite electrode coated with the MnO film prepared by electrophoresis deposition exhibits a capacitance of 73.57, 58.70, 45.64 F/g at scan rate of 25 mV/s, 50 mV/s, 100 mV/s, and possesses regular capacitive behaviors along with good cycling stabilities. This result implies that MnO nanoparticles have the potential to be implemented in supercapacitors.