Mechanistic Insight into the Conversion Chemistry between Au-CuO Heterostructured Nanocrystals Confined inside SiO2 Nanospheres

Abstract

By taking advantage of a nanospace-confined nanocrystal conversion protocol via high-temperature solid-state reaction within the SiO2 nanosphere, an in-depth study was conducted into the unique transformation behavior of the Au-CuO heterostructured nanocrystals (HNCs), which was discovered during the oxidative annealing of the embedded AuCu alloy nanocrystal (NC). The type of heterojuction structure of the oxidized AuCu NCs, between core(a)shell and heterodimer, could be determined by modulating either the annealing temperature (T-ann) or Cu contents (P-cu) in AuCu NCs; Au@CuO was generated only either at low temperature (T-ann <= 250 degrees C) or with very low Cu contents P-cu = 2.1), whereas the Au/CuO heterodimer was obtained as a major product in most of the cases at relatively high heat treatment (>250 degrees C). The systematic investigation of the conversion between HNCs could elucidate the distinct evolution pathway of the Au/CuO heterodimer via the kinetically accessed Au@CuO, revealing the escaping motion of the encapsulated Au core, which is more facilitated through a thicker CuO shell. This also demonstrated the high thermal stability of the Au@CuO with a very thin shell thickness due to the insufficient compressive lattice stain on the CuO shell to drive the morphological transformation into the heterodimer. Moreover, the higher operational stability could be detected for the Au@CuO with the lowest Cu content during catalytic CO oxidation, which correlates with its resistance against the thermal deformation.