从Mn3O4前驱体到MnO2纳米结构的形貌和结构变化

锰氧化物是一类重要的且具有广泛应用背景的材料, 控制合成不同形貌和组成的锰氧化物纳米结构将有助于拓宽其应用领域. 本文报道了以Mn3O4为前驱体, 通过水热法控制合成MnO2纳米结构的方法. 用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)等手段对产物进行表征. 在硫酸体系中,当反应温度为80 和180 ℃时, 所得产物分别为γ-MnO2海胆结构和β-MnO2单晶纳米棒. 此外, MnOOH纳米线可以在稀酸溶液中合成. 考察了反应温度、溶液酸度、反应时间对产物结构的影响, 并提出了基于γ-MnO2为中间产物的反应机理. 实验结果表明, 水热体系促进了产物的各向异性生长并最终形成不同形貌和结构的锰氧化物.

Structural and Morphological Transformation of MnO2 Nanostructures from Mn3O4 Precursor

Manganese oxides show huge structural flexibility and appear in various crystallographic polymorphs. Hence, morphological and phase control of desired manganese oxide nanostructures could enable their properties to be tuned with a greater versatility, and endow them with potential applications. Herein, we report a simple hydrothermal route for the synthesis of various MnO2 nanostructures using Mn3O4 powder as raw material. The obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Results show that in H2SO4 solution, urchin-like γ-MnO2 nanostructures and single-crystal β-MnO2 nanorods are obtained at 80 and 180 ℃, respectively. In addition, MnOOH nanowires were obtained in a dilute acid solution. The influence of synthetic parameters including temperature, acidity, and reaction time are discussed. The γ-MnO2 intermediate might play an important role in the formation of nanorods. The evolution of phases and morphologies in the reaction process suggested the anisotropic crystal growth for the formation of nanostructures under acidic conditions.