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

Abstract

Abstract Cubic and octahedral Cu 2 O nanocrystals and Au–Cu 2 O core–shell heterostructures are used as sacrificial templates for the growth of Cu 2 S nanocages and Au–Cu 2 S core–cage structures. A rapid sulfidation process involving a surface reaction of Cu 2 O nanocrystals with Na 2 S, followed by etching of the Cu 2 O cores with HCl solution for ≈5 sec, results in the fabrication of Cu 2 S 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 Cu 2 O–Cu 2 S core–shell structures and their conversion into Cu 2 S cages is verified by UV–vis absorption spectroscopy. X‐ray photoelectron spectra further confirm the composition of the cages as Cu 2 S. 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 Cu 2 O. Intermediate structures with remaining central Cu 2 O 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.