Selective Growth and Structural Analysis of Regular MnO Nanooctapods Bearing Multiple High‐Index Surface Facets

Abstract

Although numerous morphologies of MnO nanostructures have been reported, an exact structural analysis and mechanistic study has been lacking. In the present study, the formation of regular MnO octapods was demonstrated in a simple procedure, comprising the thermal decomposition of manganese oleate. Because of their structural uniformity, an ideal three-dimensional model was successfully constructed. The eight arms protruded from the cubic center with tip angles of 38° and surface facets of {311} and {533} with rounded edges. The concentrations of oleate and chloride ions were the determining factors for the octapod formation. Selective coordination of the oleate ions to the {100} faces led to edge growth along the <111> direction, which was then limited by the chloride ions bound to the high-index surface facets. These structural and mechanistic analyses should be helpful for understanding the complex nanostructures and for tuning their structure-related properties.

Chemistry of Shape-Controlled Iron Oxide Nanocrystal Formation

“…Interestingly, we observe that metamorphism of SPIONs is similar to the processes, well-described for metallic NPs (Au, Pt, and Pd), as well as MnO 2 . 47,48 Gold, platinum, palladium, and manganese oxide form a cubic face centered crystal lattice, and the formation of special shapes such as octapods is explained as a result of high coverage of the {100} side facets of a cuboctahedral core under the influence of atom deposition and surface diffusion.…”

Selective formation of Ag domains on MnO nanooctapods for potential dual imaging probes

“…The average diameter of the Ag particles was 29 ± 3 nm. As we previously reported, 21 in the MnO domain, the boundaries of the arms on the tetrapod projection were identified as the ( 21) planes, and more specifically, a combination of ( 31) and (53) planes. 21 Interestingly, the Ag domains are not formed at the tips or at the centre of the concave faces, but are attached on the arm sides covered with high index facets.…”

“…As we previously reported, 21 in the MnO domain, the boundaries of the arms on the tetrapod projection were identified as the ( 21) planes, and more specifically, a combination of ( 31) and (53) planes. 21 Interestingly, the Ag domains are not formed at the tips or at the centre of the concave faces, but are attached on the arm sides covered with high index facets. In particular, the Ag domains are dominantly located on the surface close to the tips, which is assigned as (53) in the two dimensional projection (Fig.…”

“…MnO nanooctapods were synthesized through thermal decomposition of a manganese oleate complex according to a procedure reported in the literature. 21,22 Oleic acid was used as a surfactant, and the MnO octapods were dispersed well in toluene by the aid of long alkyl chains in the surfactant anchored on the surface. Ag ions were transferred from ethanol into toluene by the addition of dodecylamine as a phase transfer agent.…”

“…1c. 21 Based on this model, the region where the Ag domain is dominantly attached can be assigned as (53) in the two dimensional projection and (533) in the three dimensional structure. This indicates that the Ag domains were selectively grown on the most high index surface of the MnO octapod structure during the reaction.…”