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.

Safety of water was for a long time and still is one of the most pressing needs for many countries and different communities. Despite the fact that there are potentially many methods to evaluate water safety, finding a simple, rapid, versatile, and inexpensive method for detection of toxins in everyday items is still a great challenge. In this study, we extend the concept of composites obtained impregnation of porous fibrous materials, such as fabrics and papers, by single walled carbonnanotubes (SWNTs) toward very simple but high-performance biosensors. They utilize the strong dependence of electrical conductivity through nanotubes percolation network on the width of nanotubes-nanotube tunneling gap and can potentially satisfy all the requirements outlined above for the routine toxin monitoring. An antibody to the microcystin-LR (MC-LR), one of the common culprits in mass poisonings, was dispersed together with SWNTs. This dispersion was used to dipcoat the paper rendering it conductive. The change in conductivity of the paper was used to sense the MC-LR in the water rapidly and accurately. The method has the linear detection range up to 10 nmol/L and non-linear detection up to 40 nmol/L. The limit of detection was found to be 0.6 nmol/ L (0.6 ng/mL), which satisfies the strictest World Health Organization standard for MC-LR content in drinking water (1 ng/mL), and is comparable to the detection limit of traditional ELISA method of MC-LR detection, while drastically reducing the time of analysis by more than an order of magnitude, which is one of the major hurdles in practical applications. Similar technology of sensor preparation can also be used for a variety of other rapid environmental sensors.

We report a highly effective growth of vertically aligned ZnO one-dimensional (1D) nanostructures on conducting alloy substrate (Fe−Co−Ni) in mild solutions (T ≤ 70 °C) in the absence of any seeds, catalysts, and surfactants. The growth conditions such as NH3·H2O concentration, temperature, and nature of the substrate are correlated to affect the nanostructure formation. Different ZnO single-crystal nanostructures including nanoneedles, hexagonal nanorods, and nanopencils oriented normal to the substrate can be selectively formed in high quantity. The ordered ZnO nanostructures show strong UV excitonic emissions and good field emission (FE) properties. Other metal substrates such as Ti and Ni are also proven to be effective for ZnO nanoarray growth. Since metal substrates are much more economical and scalable than Si, sapphire/Al2O3, GaN, etc., we believe that our approach presents a general economical route toward mass production of controllable ZnO arrays and will facilitate flexible design of device architectures for nanoelectronics.