Controllable synthesis of α- and β-MnO₂: cationic effect on hydrothermal crystallization

Abstract

α- and β-MnO(2) were controllably synthesized by hydrothermally treating amorphous MnO(2) obtained via a reaction between Mn(2+) and MnO(4)(-), and cationic effects on the hydrothermal crystallization of MnO(2) were investigated systematically. The crystallization is believed to proceed by a dissolution-recrystallization mechanism; i.e. amorphous MnO(2) dissolves first under hydrothermal conditions, then condenses to recrystallize, and the polymorphs formed are significantly affected by added cations such as K(+), NH(4)(+) and H(+) in the hydrothermal systems. The experimental results showed that K(+)/NH(4)(+) were in competition with H(+) to form polymorphs of α- and β-MnO(2), i.e., higher relative K(+)/NH(4)(+) concentration favoured α-MnO(2), while higher relative H(+) concentration favoured β-MnO(2).

Water–Gas Shift on Pd/α-MnO2 and Pt/α-MnO2

“…XRD of the as-synthesized aMnO 2 nanorods (Fig. 1a) clearly shows crystallization of the a phase of MnO 2 (JCPDS 41-1348) [39]. Upon anchoring 1 wt% Pd or 1 wt% Pt on nanorod surface, XRD pattern of a-MnO 2 is preserved (not shown here), suggesting that an introduction of 1 wt% Pd or Pt through deposition precipitation does not alter the structure of aMnO 2 support.…”

The Use of C-MnO2 as Hybrid Precursor Support for a Pt/C-MnxO1+x Catalyst with Enhanced Activity for the Methanol Oxidation Reaction (MOR)

“…No peaks were observed for other types of crystals or amorphous MnO2 which confirmed the purity of the prepared sample. The intensive diffraction peaks appeared at 12.46°, 18.08°, 28.83°, 37.00°, 37.66°, 41.95°, 50.13°, 60.36°, 66.30°, 72.87°, respectively, which are characteristic peaks of α-MnO2 with the major peaks intensity at 18.08° [15,16]. α-MnO2 is constructed from the double chains of edge-sharing MnO6 octahedra, which are linked at the corners to form tunnel structures [17].…”

Green synthesis of nanosized manganese dioxide as positive electrode for lithium-ion batteries using lemon juice and citrus peel

“…KMnO 4 is one of the main starting materials for synthesis of α-MnO 2 as it is not only a suitable Mn source, but it can also stabilize the crystallographic structure of MnO 2 by the presence of K + cations located in the cavities [12]. Based on redox reactions between MnO 4 -and Mn +2 species, MnO 2 nanomaterials have been successfully prepared by several methods, such as sol-gel, solid state reaction, electrochemical deposition, refluxing, hydrothermal and solvothermal routes [13][14][15][16][17][18][19].…”