The precise control architectures of Cu2O crystals are very crucial, which have a significant influence on their various performances. Herein, Cu2O crystals with diverse architectures were achieved via finely adjusting the concentration of NaOH. The intriguing results showed that the addition of specific amounts of OH− to the solution was crucial to tailor the morphology and size of the resulting microcrystals. We observed the evolution of the shapes of the Cu2O microcrystals, which change from a rhombic dodecahedron to spherical, octahedral-like and then to hexapod upon the increase in the NaOH concentration. Adjusting the volume of NaOH added provides a means to vary the particle size. Furthermore, density functional theory (DFT) may reveal that OH− ions serve as an efficient coordination agent selectively adsorbing onto different crystal faces of Cu2O crystals modifying the crystal energies, inducing the structure anisotropy on crystal growth. This work reveals that an effective and facile strategy has been developed for morphology-control of Cu2O crystals.
Previously, the formation of polyhedral Cu 2 O crystal is usually proposed like that the seed crystals grow outward following the relative growth rates (R values) along different directions ( Inside-out Pattern ) or that the surrounding building blocks aggregate toward the center followed by ripening ( Outside-in Pattern ). However, in this study, simply mixing aqueous Cu(CH 3 COO) 2 , NaOH, and D-(+)-glucose in the order listed at 70 °C for a period, a distinct growth manner of Cu 2 O polyhedron was observed based on carefully recording the solution color changes and the elaborate time-dependent SEM/TEM observations, which was referred to All-direction Pattern . More specifically, the initially formed Cu 2 O nanoshuttles first self-aggregated into porous braided structure with well-defined cubic framework and then condensed into solid cube from all direction via consuming the surrounding fragments everywhere possible, rather than in gradient densification from inside-out or outside-in. After that, the solid cube fell into the common Outside-in Pattern , i.e., adsorbing the surroundings followed by ripening. Although many complex polyhedral submicrostructures have been already reported, to our best knowledge, Cu 2 O crystal that grows in such manner is barely observed. It is believed that such interesting growth mechanism of polyhedral crystals could be general. What's more, the 30 min-Cu 2 O powder was made into a gas sensor towards ethanol, the performance of which has reached the level of application.
The novel ceria (CeO 2 ) hollow structures with uniform cubic, polyhedral and sphere shapes were successfully synthesized by template-engaged coordinating etching of shape-controlled Cu 2 O crystals. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microcopy (TEM), high resolution of transmission electron microcopy (HRTEM), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR) and photoluminescence spectroscopy (PL). The photocatalytic oxygen evolution via water oxidation was investigated for CeO 2 hollow structures with varied shapes under visible light irradiation. The photocatalytic results indicate that polyhedral CeO 2 nanocages show the highest photocatalytic activity, in contrast with spherical CeO 2 hollow structure and cubic CeO 2 hollow structure. The excellent catalytic activity can be attributed to the unique properties of the polyhedral CeO 2 nanocages, including efficient light refection through the inner shells, more active sites for enhancing separation efficiency of charge carriers. It is expected that this study could provide helpful results for designing and exploration of novel hollow structures with tunable photocatalytic performance.
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