Large-scale synthesis and gas sensing application of vertically aligned and double-sided tungsten oxide nanorod arrays

Large-scale vertically aligned and double-sided Co-doped hexagonal tungsten oxide nanorod arrays have been successfully synthesized by a facile hydrothermal method without using any template, catalyst, or substrate. Scanning electron microscopy and transmission electron microscopy analyses reveal an interesting three-order hierarchical nanostructure from small, single-crystalline nanorods via nanorod bundles to double-sided nanorod arrays. The optical absorption properties of the Co-doped WO3 samples were investigated by ultraviolet–visible spectroscopy, and the results indicate that the Co-doped WO3 nanostructures are semiconducting with direct band gaps of 2.26 eV and 2.77 eV. The gas sensing performance of the as-prepared Co-doped WO3 double-sided nanorod arrays was tested towards a series of typical organic solvents and fuels. The sample shows excellent gas sensing performance towards 1-butanol vapor, with rapid response and high sensitivity. We propose that the double-sided nanorod arrays are formed from urchin-like microspheres via a self-assembly and fusion process. This new synthesis strategy could be extended to prepare other well-aligned nanorod arrays for many functional applications.