3D halos assembled from FeO/Au NPs with enhanced catalytic and optical properties.

3D structures assembled from multiple components have attracted increasing research interest based on their enriched functionalities and broadened applications. Here, we report a bottom-up strategy to fabricate 3D halos through the co-assembly of FeO and Au nanoparticles (NPs). Typically, FeO NPs assemble into a 3D core (size around 500 nm) with simultaneous growth of Au NPs on the 3D surface during the assembly process.