Novel multi-layered SnO2 nanoarray: self-sustained hydrothermal synthesis, structure, morphology dependence and growth mechanism

Abstract

Novel multi-layered well-oriented SnO₂ nanoarray assemblies have been successfully realized via a facile one-step self-sustained hydrothermal route. The morphology and phase structure of the multi-layered SnO₂ nanorod arrays were examined using X-ray powder diffraction spectroscopy, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy and Raman scattering spectroscopy. The results demonstrate that the multi-layered SnO₂ nanoarray structure consists of two storeys of rutile SnO₂ nanorods oriented in opposite directions with a diameter of 25 nm and a length of 200–400 nm. The dependence of the morphological evolution process of the layered SnO₂ nanorod arrays on the pH value, concentration, reaction temperature and reaction time were investigated. The results show that Sn(OH)₆²⁻ ions play a key role in the formation of the multi-layered SnO₂ nanorod array, and the pH value of the precursor solution is an important parameter for creating the multi-layered structure. A nonclassical crystallization process, i.e. an Ostwald ripening process followed by an in situ oriented growth mechanism, is proposed based on the detailed observations from the morphology dependent crystal evolution process.