Sequential control of catalyst alloying and oxygen-mediated nucleation for continuous synthesis of SnO nanowires floating in the gas phase

Abstract

In floating catalyst chemical vapour deposition (FCCVD), nanotubes or nanowires grow suspended in a gas stream using a catalyst aerosol as they travel through a tubular reactor and are collected at the outlet as macroscopic paper-like networks. The method is continuous, removes the need for substrates and reduces the reaction time to seconds. Herein, we demonstrate the fast growth of SnO nanowires with high selectivity through sequential injection of precursors and carrier gases in order to separately control the stages of precursor decomposition, alloying of Au and Sn, and nucleation and growth of SnO as nanowires instead of alloy encapsulation by SnO_x, all occurring within 10 seconds under continuous flow at atmospheric pressure. Reaction selectivity is monitored in situ through the measurement of nanoparticle mobility in the gas phase to discriminate undesired homogeneous precursor decomposition as quasi-spherical particles from heterogeneous nanowire growth via the vapour–liquid–solid route, offering a tool to accelerate the synthesis of new nanowires by FCCVD. The nanowires have a log–normal diameter and length distributions, with means of 11.4 nm and 257 nm, respectively. A mean growth rate of 40 nm s⁻¹ (max. 107 nm s⁻¹) was obtained, which is substantially higher than that for substrate growth and is limited by precursor incorporation into the catalyst.