Cu2O Nanocrystal-Templated Growth of Cu2S Nanocages with Encapsulated Au Nanoparticles and In-Situ Transmission X-ray Microscopy Study

Cubic and octahedral Cu2O nanocrystals and Au-Cu2O core-shell heterostructures are used as sacrificial templates for the growth of Cu2S nanocages and Au-Cu2S core-cage structures. A rapid sulfidation process involving a surface reaction of Cu2O nanocrystals with Na2S, followed by etching of the Cu2O cores with HCl solution for approximate to 5 sec, results in the fabrication of Cu2S cages with a wall thickness of 10-20 nm. Transmission electron microscopy characterization reveals the formation of crystalline walls and the presence of ultrasmall pores with sizes of 1 nm or less. Formation of Cu2O-Cu2S core-shell structures and their conversion into Cu2S cages is verified by UV-vis absorption spectroscopy. X-ray photoelectron spectra further confirm the composition of the cages as Cu2S. The entire hollowing process via the Kirkendall effect is recorded using in-situ transmission X-ray microscopy. After shell formation, continuous ionic diffusion removes the interior Cu2O. Intermediate structures with remaining central Cu2O portions and bridging arms to the surrounding cages are observed. The nanocages are also shown to allow molecular transport: anthracene and pyrene penetration into the cages leads to enhanced fluorescence quenching immediately upon adsorption onto the surfaces of the encapsulated gold nanocrystals.