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 â 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. Cubic and octahedral Cu₂O nanocrystals and Au-Cu ₂O core-shell heterostructures are used as sacrificial templates for the growth of Cu₂S nanocages and Au-Cu₂S core-cage structures with excellent preservation of the template morphologies. The entire hollowing process via the Kirkendall effect is recorded using in-situ transmission X-ray microscopy. Intermediate structures with remaining central Cu₂O portions and bridging arms to the surrounding cages are observed.