Two-dimensional (2D) CuO layered oval nanosheets and three-dimensional (3D) nanoellipsoids were grown on a large scale at ∼65 °C by a facile template-free method. Shape and dimensionality control of well-defined CuO single crystals could be achieved by simple variations of pH value. At pH 8.5, CuO nanosheets were obtained, whereas at pH 7.5, CuO nanoellipsoids were formed. XRD, SEM, TEM, and HRTEM were used to characterize the products. The growth mechanisms were discussed by monitoring the early growth stages. It was shown that the CuO nanoarchitectures were formed through oriented attachment of tiny single-crystal nanoribbons and nanoparticles. UV−vis spectra were employed to estimate the band gap energies of the nanosized semiconductors. Further control experiments involving changing the growth temperature and alkaline reactant were also carried out to prepare other ultrafine nanoarchitectures. Our work demonstrates the growth of single-crystal CuO architectures built from 0D and 1D nanocrystals through a one-step solution-phase chemical route under controlled conditions.

We have demonstrated a facile fabrication of CuO hierarchical nanostructures on copper substrates by the oxidation of copper in alkaline conditions at 60 uC. CuO flowerlike structures composed of hierarchical two-dimensional (2D) nanosheets and spherical architectures constructed by ultrathin nanowalls of y10 nm in thickness could be selectively generated by simply immersing a copper substrate into different alkaline solutions (NaOH and NH 3 ?H 2 O). The continuous supply of Cu 2+ from the substrate, as well as the reaction temperature, has shown its importance for the self-assembled growth of tiny 2D nanosheets and nanowalls into intricate hierarchical nanostructures. Optical absorption was used to determine the band gap energies of the nanostructures. Stable superhydrophobicity was firstly observed for these nanostructured films after modification. When the concentration of solution was changed, well-defined 2D nanosheet and nanowall arrays can accordingly be fabricated on a large scale. Our method might provide a general route towards the preparation of novel hierarchical films on metal substrates (Cu, Al, Zn, etc.), for which a number of promising applications in various fields can be envisioned.

ZnO/Zn-Al layered double hydroxide (ZnO/Zn-Al LDH) hierarchical architecture, a new type of ZnO-based heterostructure, has been synthesized directly on an Al substrate via a facile solution phase process. The firecracker-like heterostructures consist of uniform ZnO nanorods orderly standing at the edges of two-dimensional (2D) surfaces of Zn-Al LDH nanoplatelets. Experimental result obtained from the early growth stage indicates that the underlying Zn-Al LDH nanoplatelet arrays are well constructed with their (00l) planes perpendicular to the surface of Al substrate. We propose that the "edge effect" of Zn-Al LDH and the "lattice match" between ZnO and Zn-Al LDH are vital to the growth of such heterostructures. The effects of total solution volume and NH3.H2O concentration on the formation of heterostructures are investigated. It is found that other LDH-based complex structures can also be achieved controllably by varying the mentioned experimental factors. Our work is the first demonstration of fabricating intricate ZnO/Zn-Al LDH heterostructures as well as well-defined Zn-Al LDH arrays on an Al substrate, for which several promising applications such as optoelectronics, biosensors, and catalysis can be envisioned.

Self-assembled unusual ZnO ellipsoids have been grown by a facile low-temperature (60 degrees C) solution process on a large scale. FESEM and TEM reveal that these ellipsoids have an average horizontal axis of 1.5 microm and a longitudinal axis of 0.6 microm. Experimental results obtained from the early growth stage demonstrate that the ZnO ellipsoidal structures are single crystals and formed from direct "oriented attachment" of two types of building blocks, that is, nanorods and nanoparticles. It is further found that the existence of poly(ethylene glycol) (PEG-10 000) is vital to the formation of the complex microparticles. Raman spectrum, room-temperature photoluminescence, and UV-vis absorption spectra are also discussed. This work presents a simple and effective route for large-scale fabrication of single-crystal ZnO ellipsoids with micrometer-scale sizes and 3D self-assembled structures.