Synthesis, Characterization, and Gas Sensing Properties of Porous Nickel Oxide Nanotubes

Abstract

A novel approach was employed to synthesize porous NiO nanotubes with controllable interior voids based on an effective interplay of Kirkendall effect and volume change upon phase transformation. For this purpose, nickel nanowires were chemically converted into Ni₃S₂/Ni core–shell structures, followed by a controlled oxidation, whereby the associated volume change (Ni → NiO conversion) resulted in 1D porous structure with voids. The voids between the Ni core and Ni₃S₂ shell could be controlled by adjusting the oxidation conditions that enabled fabrication of hollow and double-walled morphologies. Phase composition, morphological evolution, and porosity of double-walled NiO nanotubes were analyzed by X-ray diffraction, scanning and transmission electron microscopy, and N₂ adsorption–desorption studies. Gaseous sulfur oxides formed during the oxidation of Ni₃S₂/Ni structures resulted in a perforated structure with multiple voids with pores ranging between 1 and 14 nm. The unique complex structure with the interpenetrating voids and the surface porosity resulted in a high specific surface area of 161.6 m²·g^–1. The gas sensing property of such double-walled structure was found to vary as a function of the concentric void between the core and the shell. Gas-sensing measurements in hollow porous core–shell NiO nanotubes exhibited excellent sensitivity toward ethanol, originating from efficient adsorption of target molecules in the interior voids and their rapid diffusion and transport through the porous structures.