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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.
Liu et al. (Sun,) studied this question.