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 ≈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.