Growth mechanism of SnC₂H₄O₂ nanowires prepared by the polyol process as SnO₂ precursor nanowires

Tin oxide (SnO₂) nanowires are produced by the calcination of tin glycolate (SnC₂H₄O₂) nanowires, which are synthesized with tin oxalate (SnC₂O₄) and ethylene glycol via the so-called polyol process. In this study, the growth mechanism of SnC₂H₄O₂ nanowires was investigated by monitoring the synthesis using scanning and transmission electron microscopy. The length and diameter of the nanowires were 9.25 μm and 0.37 μm, respectively; the former increased at a rate of 1.85 μm h^-1 but the latter did not increase over time. Fourier-transform IR spectroscopy showed that the nanowires were composed of SnC₂H₄O₂ instead of SnC₂O₄. Changes in the components of the reaction solution were also confirmed by ¹H NMR, ¹³C NMR, and high-performance liquid chromatography. SnC₂H₄O₂ was formed by the substitution of the oxalate coordinated to tin by ethylene glycolate, which was produced by the deprotonation of ethylene glycol. In this reaction, oxalate gradually changed to formic acid and carbon dioxide, and SnC₂H₄O₂ grew as a nanowire through O-Sn-O bond formation. In addition, when ethylene glycol was mixed with 1,2-propanediol, branched SnC₂H₄O₂ nanowires were formed. The branching was due to the interference of the methyl group of 1,2-propanediol with the growth of bundle-type nanowires. The branched nanowires had a higher surface area-to-mass ratio than the bundled ones based on dispersion measurements. Knowledge of the growth mechanism and reaction conditions that affect morphology would be valuable in modifying the physical and electrical properties of metal oxide nanowires.