Synthesis of Nano sized Zinc-Doped Cobalt Oxyhydroxide Parties by a Dropping Method and Their Carbon Monoxide Gas Sensing Properties

Two nano structures of cobalt oxyhydroxide (CoOOH) and Zinc-(Zn-) doped CoOOH (1–4% Zn) are prepared from Co(NO₃)₂ solution via microtitration with NaOH and oxidation in air. The X-ray diffraction (XRD) analysis results show that a pure state of nano-CoOOH can be obtained at an alkalinity (OH−/Co⁺) of 5 with 40°C heat treatment after 6 h. The Zn ions preferentially substitute Co ions in the CoOOH structure, resulting in a decrease of its crystallinity. The disc-like CoOOH nano structure exhibits good sensitivity to carbon monoxide (CO) in a temperature range of 40–110°C with maximum sensitivity to CO at around 70–80°C. When CoOOH nano structure is doped with 1% Zn, its sensitivity and selectivity for CO gas are improved at 70–80°C; further Zn doping to 2% degraded the CO sensing properties of nano-CoOOH. The results of a cross-sensitivity investigation of the sensor to various gases coexisting at early stages of a fire show that the sensitivity of Zn-doped nano-CoOOH is the highest toward CO. Zn-doped nano-CoOOH film exhibits a high sensitivity to CO at room temperature, making it a promising sensor for early-stage fire detection.