Cu2O microcrystals: a versatile class of self-templates for the synthesis of porous Au nanocages with various morphologies

Design and synthesis of Au nanocages is one of the basic interests in the fabrication of nanoscale structures due to their attractive potentials in catalysis, medical science and so on. In most cases, spherical or cubic Au nanocages were fabricated using silica nanoparticles or Ag nanocubes as templates. In this article, another kind of versatile template, Cu2O microcrystals, has been employed to synthesize Au nanocages with various morphologies, such as cube, sphere, octahedron, truncated octahedron, cuboctahedron and concave cube morphologies. Surface modification of the templates, which is a necessary procedure in the synthesis of cage-shaped structures using a template-based strategy is avoided by this method because AuCl4- can be reduced spontaneously on the surfaces of the Cu2O microcrystals at room temperature. When the Cu2O microcrystals possess only one type of exposed planes, Au nanoparticles (NPs) are deposited homogeneously on the supports, etching out Cu2O portions in the as-prepared nanocomposites, with porous Au nanocages produced. However, if the Cu2O microcrystals have two kinds of exposed planes, such as (111) and (100), selective deposition of Au NPs was observed. Based on this phenomenon, cuboctahedral and truncated octahedral Au nanoframes were synthesized. Due to the porous structure of the as-prepared Au nanocages, the catalytic activity of cubic Au nanocages in the reduction of 4-nitrophenol by sodium borohydride is much higher than that of reported spongy Au nanocrystals.