Ultrasonication-switched formation of dice- and cubic-shaped fullerene crystals and their applications as catalyst supports for methanol oxidation

Abstract

Three-dimensional (3D) nanostructures of an endohedral fullerene, Sc₃N@C₈₀ (I_h), including both cubic-shaped and unprecedented dice-shaped crystals, have been successfully prepared for the first time via a modified liquid–liquid interfacial precipitation (LLIP) method integrating ultrasonication. By simply switching ultrasonication on/off upon mixing the good/poor (mesitylene/isopropanol) solvents, the dice- and cubic-shaped Sc₃N@C₈₀ crystals have been selectively prepared, and their size can be readily controlled by varying the concentration of the starting Sc₃N@C₈₀ solution in mesitylene. The growth mechanism of the cubic- and dice-shaped Sc₃N@C₈₀ crystals has been proposed, highlighting the formation of local mesitylene cavities which lead to the nucleation and growth of Sc₃N@C₈₀ molecules, while the formation of the dice structure. i.e., a hole in each facet of the cube, was primarily due to the hindered diffusion of Sc₃N@C₈₀ solutes by ultrasonication-generated gas microbubbles. The crystal structure of the Sc₃N@C₈₀ cubes has been determined as a simple cubic unit cell with a lattice constant of a = 10.8 Å. Finally the dice-shaped Sc₃N@C₈₀ crystals were applied as a Pt catalyst support for the methanol oxidation reaction (MOR), revealing the improved MOR activity compared to the cubic-shaped Sc₃N@C₈₀ crystals due to its larger surface area resulting from the dice (hole) structure.