ZnO1− coatings deposited by atmospheric plasma spraying for room temperature ppb-level NO2 detection

Abstract NO2 is one of the main pollutants that affect air quality, and the use of ZnO as a gas-sensitive material to prepare sensors for NO2 detection has broad prospects. Wide bandgap semiconductor ZnO requires a high-temperature or ultraviolet-light illumination condition for excitation, and the high temperature or ultraviolet light will increase energy consumption and accelerate component aging. This paper reports the method of deposition of ZnO1−x gas-sensitive coatings by atmospheric plasma spraying. With the optimization of hydrogen flow rate in plasma forming gas, the ZnO1−x coatings can be directly deposited by a typical atmospheric plasma spraying process. Under the illumination of visible light, the as-sprayed ZnO1−x gas sensors achieved room temperature responses to ppb-level NO2. The best hydrogen flow rate for atmospheric plasma sprayed ZnO1−x coatings was found to be 7 L/min, and the H-7 ZnO1−x sensor exhibited the best gas sensing performance under blue light illumination. In addition, the enhanced effects of oxygen vacancies on optical and gas sensing properties were also discussed.