Core-shell Octahedra Research Articles

Investigation of the Effects of Polyhedral Gold Nanocrystal Morphology and Facets on the Formation of Au–Cu2O Core–Shell Heterostructures

Rhombic dodecahedral and highly edge- and corner-truncated octahedral gold nanocrystal cores with entirely or significant {110} faces were employed to investigate the core–shell orientation relationship of Au–Cu2O core–shell heterostructures. By increasing the volume of reductant added, we synthesized Au–Cu2O face-raised cubes, cuboctahedra, and octahedra. TEM characterization indicates a fixed core–shell orientation relationship. The {100}, {110}, and {111} facets of the gold cores align parallel to the corresponding faces of the Cu2O shells. Structural requirements of the gold cores for the preparation of Au–Cu2O stellated icosahedra indicate that icosahedral gold nanocrystals are good candidates. Use of trisoctahedral nanocrystal cores cannot generate stellated icosahedra, but unusual face-raised octahedra with V-shaped {111} edges can be synthesized. Core–shell cubes, face-raised cubes, core–shell octahedra, and face-raised octahedra were examined for their comparative photocatalytic activity toward the photodegradation of methyl orange. Remarkably, all the cubes were found to be photocatalytically inactive because they are bounded by essentially {100} facets. Face-raised octahedra with more {111} facets showed significantly better photocatalytic performance than regular Au–Cu2O core–shell octahedra. The results reveal that gold nanocrystal-enhanced photocatalysis can be achieved only with Cu2O shells exposing proper facets.

A facile synthesis of Cu2O/SiO2 and Cu/SiO2 core–shell octahedral nanocomposites

We report here a simple approach to the synthesis ofCu2O/SiO2 core–shell nanocomposites in water solution. TheCu2O cores have a perfect octahedral structure with uniform size of about 200–300 nm. A compactSiO2 shell 9 nm in thickness is located at the surfaces ofCu2O octahedra, and itis composed of fine SiO2 nanoparticles. During the depositing of theSiO2 particles, as we presumed, dynamic absorbing and disengaging ofNa+ at theinterface of Cu2O octahedra and the solution made it possible for the formation of Cu–O–Si bondsbetween core and shell in the composites. The existence of Cu–O–Si bonds inour core–shell composite can be substantiated by peak changes at 1236 and1080 cm−1 in the FT-IR spectra. This is the reason why theSiO2 shell is so compact and uniform. Moreover, theseCu2O/SiO2 core–shell octahedra were further used as precursors, depending on a simple disproportionation reaction ofCu2O in acid, toeasily achieve Cu/SiO2 movable multicore–shell octahedral nanocomposites. In the finalCu/SiO2 core–shellcomposite, the thin SiO2 octahedral shell was held, inside of which formed several free Cu nanoparticles 50–80 nm in size. Studies on theCu2O/SiO2 core–shell octahedralcomposites and Cu/SiO2 movable multicore–shell octahedral nanocomposites would be a good thing not only forfundamental research but also for applications.