A simple one step approach to preparation of γ-MnOOH multipods and β-MnO2 nanorods
ABSTRACT 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.
SourceAvailable from: M. Saiful Islam[Show abstract] [Hide abstract]
ABSTRACT: MnO2 is a technologically important material for energy storage and catalysis. Recent investigations have demonstrated the success of nanostructuring for improving the performance of rutile MnO2 in Li-ion batteries and supercapacitors and as a catalyst. Motivated by this we have investigated the stability and electronic structure of rutile (β-)MnO2 surfaces using density functional theory. A Wulff construction from relaxed surface energies indicates a rod-like equilibrium morphology that is elongated along the c-axis, and is consistent with the large number of nanowire-type structures that are obtainable experimentally. The (110) surface dominates the crystallite surface area. Moreover, higher index surfaces than considered in previous work, for instance the (211) and (311) surfaces, are also expressed to cap the rod-like morphology. Broken coordinations at the surface result in enhanced magnetic moments at Mn sites that may play a role in catalytic activity. The calculated formation energies of oxygen vacancy defects and Mn reduction at key surfaces indicate facile formation at surfaces expressed in the equilibrium morphology. The formation energies are considerably lower than for comparable structures such as rutile TiO2 and are likely to be important to the high catalytic activity of rutile MnO2.Journal of the American Chemical Society 01/2014; 136(4). DOI:10.1021/ja4092962 · 11.44 Impact Factor
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ABSTRACT: Branchy structures of β-MnO2 were prepared through a two-step process including MnO2 nanosheet-assisted hydrothermal synthesis of branchy γ-MnOOH precursor and followed by calcination of the obtained precursor. After the calcination, the branchy feature was retained for β-MnO2 with two types of the end structures, i.e., pyramidate ends and opened ends. The assembly and shedding mechanism was proposed to explain the formation of the branchy structure. This nanosheet-assisted hydrothermal method studied here offers a new approach for synthesis of other layered materials. Furthermore, the decolorization experiments of methyl blue (MB) showed that the obtained β-MnO2 exhibited excellent ability to remove the MB dye with the assistance of hydrogen peroxide.Materials Letters 07/2012; 79:288–291. DOI:10.1016/j.matlet.2012.04.055 · 2.27 Impact Factor
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ABSTRACT: Formation and conversion mechanisms between single-crystal gamma-MnOOH and manganese oxides had investigated systematically. Without extra surfactant or template, α-MnO2 nanorods and prismatic single crystalline γ-MnOOH rods had been synthesized under hydrothermal treatment in this study. The formation and conversion mechanisms of prismatic γ-MnOOH rod were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that the formation process includes three evolution stages: (1) formation of α-MnO2 nanorods whiskers; (2) transformation from α-MnO2 nanorods to prismatic γ-MnOOH rods by a dissolution-growth-recrystallization process; and (3) preferred growth on (1 1 1¯) crystal plane. In addition, β-MnO2, Mn2O3 or Mn3O4 rods could be obtained by calcination of the γ-MnOOH rods at different temperatures, which indicated that γ-MnOOH is an important precursor for preparing manganese oxides. The morphology and dimension of γ-MnOOH rods remained unchanged after converted to β-MnO2, Mn2O3 and Mn3O4.Materials Research Bulletin 07/2012; 47(7):1740–1746. DOI:10.1016/j.materresbull.2012.03.041 · 1.97 Impact Factor