Both oxygen vacancies defects and porosity facilitated NO2 gas sensing response in 2D ZnO nanowalls at room temperature

In this report, NO2 gas sensing properties of ZnO nanowalls fabricated by facial solution method under subsequent various annealing temperatures ranging from 350 °C to 750 °C in air have been investigated. Upon annealing in air, significant porosity and oxygen vacancies modification of the ZnO nanowalls has been observed through SEM and photoluminescence spectroscopy. The gas sensing behaviors of the fabricated sensors are systematically investigated. The ZnO nanowalls annealed at 450 °C exhibit excellent NO2 gas response magnitude and fast response and recovery time (23 s, 11 s) at room temperature. The results reveal that, for their good sensing properties, there is a delicate balance between oxygen vacancies defects and porosity dependent on the annealing temperature.