A simple one step approach to preparation of γ-MnOOH multipods and β-MnO2 nanorods

Materials Letters (Impact Factor: 2.49). 03/2008; 62(8-9):1336-1338. DOI: 10.1016/j.matlet.2007.08.041


Multipod-like γ-MnOOH and rod-like β-MnO2 nanocrystals are synthesized by oxidization of manganese sulphate hydrate (MnSO4·H2O) using sodium chlorate (NaClO3) as an oxidizing agent in a simple hydrothermal reaction system in the absence of any templates, catalysts, or organic reagents. The powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) are used to characterize the as-prepared products. Based on the results of XRD and SEM, multipod-like γ-MnOOH can be transformed into rod-like β-MnO2 nanocrystals via one step synthetic route by simply increasing the reaction time while other conditions are kept constant. And a possible transfer mechanism via a nucleation–dissolution–anisotropic growth–recrystallization process is presented.

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    ABSTRACT: 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.
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    ABSTRACT: In the absence of extra surfactant or template, large-scale single-crystalline γ-MnOOH micro/nanorods were prepared directly via a hydrothermal method using Mn(NO3)2 aqueous solution as starting materials at 180 °C for 12 h. MnO2 could be obtained after calcining the γ-MnOOH precursor in air at 280 °C for 5 h and Mn3O4 could be synthesized via solvothermal treatment of γ-MnOOH in propylene glycol at 180 °C for 24 h. The products were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectrometer, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). It was found that the MnO2 and Mn3O4 products were both single crystalline and retained the similar morphologies of MnOOH micro/nanorods. Further experiments showed that the as-prepared MnO2 and Mn3O4 micro/nanorods had catalytic effect on the oxidation and decomposition of the methylene blue dye with the assistance of hydrogen peroxide.
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    ABSTRACT: Single crystal nanorods of γ-MnOOH with lengths up to hundreds of nanometers were successfully prepared employing a novel solvothermal process based on the redox reaction between potassium permanganate (KMnO(4)) and N, N-dimethyl ammonium formate (DMF) without extra surfactant or template. The as-prepared products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and Fourier transformed infrared spectroscopy (FTIR). The electrochemical properties of γ-MnOOH nanorods were investigated by cyclic voltammetry and galvanostatic charge-discharge performance measurements. Specific capacitance (C(s)) calculated from the galvanostatic discharge curve was 131.9 F g(-1) for γ-MnOOH nanorods at the current density of 0.5 A g(-1). The electrochemical experiment results demonstrate that γ-MnOOH nanorods should be a good candidate as electrode material for supercapacitor.
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