Nanoparticle Shape Conservation in the Conversion of MnO Nanocrosses into Mn₃O₄

Abstract

The conversion of hexagonal-, square-, and cross-shaped MnO nanoparticles into mixed MnO-Mn 3 O 4 nanoparticles occurs with retention of the nanoparticle shape. Upon aging, extra diffraction spots appear in the TEM analyses of both hexagonal-and cross-shaped nanoparticles (NPs). These extra diffraction spots can be assigned to the spinel form of Mn 3 O 4 (s-Mn 3 O 4 ) and exhibit moiré interference patterns arising from the presence of two closely aligned, crystallographically similar phases. Examination of a variety of reaction conditions showed that the transformation of MnO into MnO/Mn 3 O 4 occurred while the particles are suspended in hexane at ambient temperature, by refluxing in hexadecane for 36 h, by heating to 200°C in air, and by irradiating the NPs with a Raman laser beam. The crystal phase development and shape retention can be observed by using transmission electron microscopy (TEM). Single-crystal and polycrystalline selected area electron diffraction (SAED) patterns and dark-field TEM images confirm the coexistence of both MnO and s-Mn 3 O 4 phases. Evaluation of the polycrystalline SAED patterns after irradiation in the Raman spectrometer indicated the presence of rings assignable to the tetragonal phase of Mn 3 O 4 (t-Mn 3 O 4 ) as well as MnO and s-Mn 3 O 4 . The growth of the tetragonal phase by laser heating in the Raman experiment was confirmed by powder X-ray diffraction.

Shape control of new FexO–Fe3O4and Fe1–yMnyO–Fe3–zMnzO4 nanostructures

“…Samples of both FeOX and FeMnOX NPs were successfully oxidized under relatively mild conditions, by heating and stirring in a high boiling point solvent (hexadecane; boiling point 287 8C) for approximately 36 h (under air). [23,35] (Fig. 10).…”

“…In general, results indicate that a very delicate balance exists between the surfactant concentration and the amount of water needed in order to obtain the right dissolution-crystallization process that will tune the shape of the NPs. [17,23,35] Shapes of FeMnOX NPs were also tuned by using different ratios of iron to manganese precursors Fe II (HCOO) 2 :Mn II (H-COO) 2 (Fig. 9).…”

“…This metal deficiency may provide a facile pathway for rearrangement of the lattice without causing too much strain on the unit cell and the NP itself. [35] In fact, rearrangement from wü stite to magnetite, for example, may be facilitated because both are in cubic space groups and the unit cell of the latter is almost double that of the former (vide supra). The same principles explained here apply to the mixed-metal phase.…”

Mn2O3 Nanoparticles Synthesized from Thermal Decomposition of Manganese(II) Schiff Base Complexes

“…Among the transition metals, manganese exhibits several oxidation state and forms different oxides such as MnO [8,9], Mn 2 O 3 [10,11], Mn 3 O 4 [8][9][10][11], and MnO 2 [8]. Manganese oxides are an important class of transition metal oxide family due to unique chemical and physical properties [8][9][10][11].…”

“…Among the transition metals, manganese exhibits several oxidation state and forms different oxides such as MnO [8,9], Mn 2 O 3 [10,11], Mn 3 O 4 [8][9][10][11], and MnO 2 [8]. Manganese oxides are an important class of transition metal oxide family due to unique chemical and physical properties [8][9][10][11]. Among the different oxidation state of manganese oxides, Mn 2 O 3 nanoparticles are well-known as non-toxic, cheap, environmentally friendly and abundant and widely investigated as anode materials for lithium ion batteries because of their large theoretical specific capacities [12][13][14], catalyst [15,16] and hydrazine electrochemical sensing [17].…”