Formation of Positively Charged Copper Hydroxide Nanostrands and Their Structural Characterization

Extremely narrow copper hydroxide nanostrands with a diameter of 2.5 nm were prepared by controlling the pH of an aqueous copper nitrate solution with weak bases. The nanostrands grew slowly from initially formed small particles of 2−6 nm. The growth was highly sensitive to the amount and types of weak bases. Long nanostrands were obtained in a range of pH 6.0−6.2 at a concentration of approximate 2 mM copper nitrate. The length reached several tens of micrometers after an aging time of a few days, giving an aspect ratio more than tens of thousands. Their structures were characterized by scanning electron microscopy, transmission electron microscopy (TEM), and electron diffraction. This nanostrand is composed of positively charged linear clusters, [Cu 8 (OH) 14 (H 2 O) 4 ] 2+, as judged from the results of high-resolution TEM, UV−vis titration experiments, and crystallographic considerations. We widely investigated the nanomorphologies of copper hydroxide and related compounds by changing the synthetic conditions and then proposed a unique growth mechanism for the nanostrands of orthorhombic copper hydroxide.