Selective preparation of SnO2 and SnO crystals with controlled morphologies in an aqueous solution system

The oxidation state of tin oxide crystals grown in an aqueous solution of Sn( II) was successfully controlled. Rutile-type SnO2 and tetragonal SnO were selectively produced under acidic conditions below pH 3.3 and alkaline conditions above pH 13.1, respectively. The nanostructures, including the grain size and shape, and the mesoscopic assembled states of the crystals were changed with the concentration of the Sn( II) species and a subtle variation of the pH. This versatile fabrication process for functional oxides is based on the difference in the stability of Sn( II) and Sn(IV) depending on the pH in an aqueous solution system.