Abstract
The effect of mechanical stirring on the morphology of hexagonal layer‐structure birnessite nanoparticles produced from decomposition of KMnO4 in dilute aqueous H2SO4 is investigated, with characterization by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA), and N2 adsorption (BET). Mechanical stirring during an initial stage of synthesis is shown to produce black birnessite containing nanofibers, whereas granular particulates of brown birnessite are produced without stirring. This is the first reduction synthesis of black birnessite nanoparticles with dendritic morphology without any use of organic reductant, and suggests that a particular morphology can arise from structural preferences of Mn in acidic conditions rather than particular organic reactants. These results enlighten the possibility of synthesizing nanoparticles with controlled size and morphology.
Highlights
There are increasing interests in layer-structure materials due to their potential applications in catalysis, ion-sieves, and rechargeable batteries [1,2,3]
To date synthesis of black birnessite nanoparticles, or nanofibers, with dendritic morphology by our direct method has not been reported, and it is speculated that dendritic structures produced by other methods are caused by either organic [19] or inorganic [20] reactants
Transmission electron microscopy (TEM) images were obtained with a Tecnai G2 F30 S-Twin transmission electron microscopy (TEM) instrument
Summary
There are increasing interests in layer-structure materials due to their potential applications in catalysis, ion-sieves, and rechargeable batteries [1,2,3]. The present study reports synthesis of birnessite nanoparticles with hexagonal layer structure, based on the reduction of KMnO4 in aqueous H2SO4, followed by wetaging time and air drying. This reaction has been studied intensively [15,16,17,18], the detailed synthetic conditions correlated with the structural parameters of birnessite. To date synthesis of black birnessite nanoparticles, or nanofibers, with dendritic morphology by our direct method (reduction of KMnO4 by H2SO4) has not been reported, and it is speculated that dendritic structures produced by other methods are caused by either organic [19] or inorganic [20] reactants. Discussions on the significance of the results and concluding remarks follow
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