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

Crystallization of hopper-like Cu 2 O 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 Cu 2+ manipulate the current chemical reaction routes, phase transformation, and thus crystallization morphologies and compositions. During the crystallization of Cu 2 O variations of mother solution such as pH and the concentration of Cu 2+ (Cu + ) are monitored by ex situ pH measurement and UV–Vis absorption spectroscopy. The shape evolution of Cu 2 O 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:Cu 2+ > 2 and 1 < NaOH:Cu 2+ < 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.