Hopper-like framework growth evolution in a cubic system: a case study of Cu2O

Crystallization of hopper-like Cu2O cubes is demonstrated in alkaline citrate-copper solution upon the equilibrium between complexation, precipitation and redox reactions. The complexation reactions of Na(3)cit and NaOH with Cu2+ manipulate the current chemical reaction routes, phase transformation, and thus crystallization morphologies and compositions. During the crystallization of Cu2O variations of mother solution such as pH and the concentration of Cu2+ (Cu+) are monitored by ex situ pH measurement and UV-Vis absorption spectroscopy. The shape evolution of Cu2O hopper cubes is consistent with the chemical reaction routes, which demonstrates the interplay between chemical reactions and crystal growth. The appropriate reaction concentration, Na(3)cit:Cu2+ > 2 and 1 < NaOH:Cu2+ < 2, has been identified for the growth of these hopper cubes. The current reaction-controllable crystal growth may further the synthesis chemistry toward rational control over crystallization.