CuO Barrier Limited Corrosion of Solid Cu₂O Leading to Preferential Transport of Cu(I) Ion for Hollow Cu₇S₄ Cube Formation

Highly ordered, uniform Cu 7 S 4 hollow cubes have been successfully synthesized in a mild, low-temperature condition from freshly prepared solid Cu 2 O cubes. Cu 2 O cubes have been synthesized at ∼80 °C, exploiting the water-soluble Cu(II)–EDTA complex (λ max = 730 nm) as precursor and glucose as reducing agent under alkaline conditions. In the synthetic pathway, Cu 2 O solid cubes act as corrosion-prone, sacrificial templates. Kinetic parameters describe the corrosion of Cu 2 O solid cubes in the presence of sulfide ions, which is the product of hydrolysis of thioacetamide. Corrosion results in a nonstoichiometric hollow Cu 7 S 4 structure like a solid cubic template. Strong affinity of Cu(I) toward sulfide (“soft”–“soft” interaction) fetches Cu(I) from the central region of the solid Cu 2 O template, making hollow cubes of Cu 7 S 4 . Mechanistically, the thin film of the oxidized surface layer on Cu 2 O cubes protects the template. Then the oxidized layer offers resistance to the passage of sulfide ions for its inward transportation. Conversely, soft–soft affinity fetches Cu(I) ions from inside. Finally, hollow Cu 7 S 4 cubes are formed at the solid–liquid interface. The transformation process has been further examined and confirmed from UV–visible spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectra, and impedance measurement. Hollow Cu 7 S 4 cubes with increased surface area are generated from solid Cu 2 O cubes via Kirkendall diffusion.