Crystal Plane-Dependent Compositional and Structural Evolution of Uniform Cu₂O Nanocrystals in Aqueous Ammonia Solutions

Abstract

The componential and morphological evolution of uniform Cu2O nanocrystals with different shapes in aqueous ammonia solutions has been comprehensively studied by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, and transmission electron microscopy. Cubic, octahedral, and rhombic dodecahedral Cu2O nanocrystals that, respectively, expose Cu2O {100}, {111}, and {110} crystal planes exhibit distinctly different reaction behaviors. The stability of various types of uniform Cu2O nanocrystals in the aqueous ammonia solution follows the order cubic Cu2O nanocrystals > octahedral Cu2O nanocrystals > rhombic dodecahedral Cu2O nanocrystals. The nucleation and growth of Cu(OH)2 and CuO precipitate also depend on the shape of Cu2O nanocrystals. The shape-dependent reaction behaviors of Cu2O nanocrystals were attributed to the type of crystal plane exposed on Cu2O nanocrystals that determines their surface structure and surface reactivity. Our results well exemplify the crystal plane-dependent reactivity of oxide nanocrystals and greatly deepen our fundamental understanding of complex chemical reactions occurring at the liquid–solid interface.