Room temperature NO₂ sensor with rapid recovery based on ZnO/In₂O₃ heterojunction

Metal oxides have been widely used in gas sensors. Metal oxides have the advantages of low cost, easy preparation and stable performance. However, the disadvantage of their high operating temperature limits their wider application. In this paper, a simple method based on hydrothermal reaction was developed to prepare ZnO/In₂O₃ composites with high response values capable of fast recovery. The chemical composition, microscopic morphology and structure of the ZnO/In₂O₃ composites were investigated by various characterization methods to determine the formation of ZnO/In₂O₃ heterojunction. The gas-sensitive properties of pure In₂O₃ and ZnO/In₂O₃ composites were tested at room temperature. The results showed that ZnO/In₂O₃ composites with different Zn/In molar ratios had short recovery time and high response value to NO₂ at room temperature. Among them, the ZnO/In₂O₃ with Zn/In molar ratio of 2:1 showed the best gas-sensitive performance to NO₂ at room temperature. The response values to NO₂ were measured at concentrations of 5, 10, 20, and 30 ppm, resulting in values of 2.70, 3.26, 4.80, and 5.25, respectively. The response time to NO₂ at 30 ppm was 267 s, with a recovery time of 7 s. In addition, ZnO/In₂O₃ composites have good long-term stability and selectivity to NO₂ at room temperature.