Heterojunctions of ZnO-Nanorod-Decorated WO3 Nanosheets Coated with ZIF-71 for Humidity-Independent NO2 Sensing

NO2 is a very dangerous and toxic gas and is prone to cause acid rain in high humidity environments, so it is essential to prepare a real-time monitoring and humidity immunity NO2 sensor. WO3 nanomaterials are commonly applied to detect NO2, but their poor immunity to humidity is still a critical limitation for the application. ZnO-nanorod-decorated WO3 nanosheets coated with ZIF-71 (ZnO@ZIF-71/WO3) composites prepared by an in situ growth method displayed excellent gas sensing performance and good humidity immunity to detect NO2. Compared to WO3 nanosheets and ZnO-nanorod-decorated WO3 nanosheets (ZnO/WO3) heterojunction composites grown on ceramic substrates in situ, ZnO@ZIF-71/WO3 presented excellent selectivity, good long-term stability, and a remarkably high response of about 947.96 to 100 ppm NO2 at 180 °C, which is 3.07 times higher than that of the ZnO/WO3 sensor and 4.59 times higher than that of the pure WO3 sensor. Even at a relative humidity of 85%, the response of ZnO@ZIF-71/WO3 to NO2 remained essentially constant. The functional ZIF-71 layer not only improved the humidity immunity of ZnO@ZIF-71/WO3 but also enhanced the sensitivity and selectivity performance to NO2 at low operating temperatures. The ZnO@ZIF-71/WO3 sensor still provided a response of 88.41 to 100 ppm NO2 at room temperature.