Abstract
The controlled synthesis of oneβdimensional, two dimensional, and threeβdimensional CuO nanostructures has been achieved by a hydrothermal process in the presence of sodium citrate (SC) by simply controlling the reaction conditions. When the molar ratio of sodium citrate to CuSO~4~**Β·**5H~2~O (represented by SC/Cu^2+^) is below 1.0, 1D CuO nanorods with 30β40 nm diameters and 100β200 nm lengths are formed. In the absence of citrate, 2D flakelike CuO nanostructures with 150β200 nm widths and 300β400 nm lengths are obtained. When the SC/Cu^2+^ ratio is more than 1.0, 3D branchlike CuO nanostructures with lengths of hundreds of nanometers and diameters of 20β100 nm are attained. On the basis of the morphology and Xβray diffraction patterns of the samples, a possible growth mechanism for the CuO nanostructures is proposed. Moreover, it is shown that the optical bandgap energy (E~g~) of resulting CuO nanostructures can be tuned through morphological control of the CuO nanostructures. Ultraviolet absorption measurements reveal that the estimated bandgap energy of the 1D rodlike, 2D flakelike, and 3D branchlike CuO nanostructures is 2.36, 1.60, and 1.40 eV, respectively.(Β© WileyβVCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)