Novel flame-gradient method for synthesis of metal-oxide channels, nanowires and nanorods

Abstract

The formation of 1D and 3D transition metal oxide (TMO) nano- and micron- size structures on molybdenum, iron and tungsten probes inserted in a counter- flow flame is studied experimentally. The unique thermal profile and chemical composition of the generated flame tends to convert almost pure bulk (99.9%) transition metal materials into 1D and 3D architectures. The synthesised Mo-, Fe- and W-oxide structures exhibit unique morphological characteristics. The application of Mo probes results in the formation of micron-size hollow and solid Mo-oxide channels. The formation of solid iron oxide nanorods is observed on iron probes. The use of W probes results in the synthesis of 1D solid carbon/metal oxide nanowires. This study confirms the existence of a common generic mechanism controlling the growth of the structures on the high-temperature probes. Metal oxide/hydroxides are formed on the probe surface exposed to the high-temperature oxidative environment. These oxides/hydroxides are further evaporated and transported by the gas flow to the low-temperature side where they are reduced to other oxide forms and deposited in the form of 1D or 3D TMO materials. This study reveals that a preferential growth at the edges of the MoO2 whisker tips leads to the development of hollow structures. © 2010 Taylor & Francis.