Morphology control technique of ZnO by hydroxide ion supply rate and its effect on the ppt-level gas sensors

The sensitivity of the metal–oxide–semiconductor-type gas sensors has been improved typically using novel metal catalysts, such as Pt, Ru, and Pd. However, the sensing performance could be enhanced by only controlling the nanostructure. Herein, we introduce fabrication methods for ZnO nanobelt by changing the supply rate of hydroxide ions. Hexamethylenetetramine (HMT) and potassium hydroxide were used to generate hydroxide ions, and their rate to reach the maximum pH was different by more than twofold. The supply rate of hydroxide ions caused the different morphology of ZnO nanomaterial due to the change in the seed of material formation. Although both samples could detect acetone gas up to 100 ppt, ZnO nanobelts synthesized by HMT exhibited higher sensitivity. The ZnO morphology influenced the exposed surface area, and a larger specific surface area could facilitate the generation of pre-adsorbed oxygen species that are the main factor for sensitivity.