Gas Sensor Based on Flower-like NiO Modified with WO3 Nanoparticles for NO2 Detection

NO2 is a common air pollution gas, which can cause acid rain and photochemical smog. Accordingly, NO2 gas sensors with high sensitivity, selectivity, and real-time monitoring for detecting low concentration of NO2 are urgently needed. NiO and NiO-based nanomaterials have attracted more attention in the field of NO2 sensing, whereas the low response and sensitivity to NO2 limit the application of NiO in the field of gas sensors. In this work, flower-like NiO modified with WO3 nanoparticles with different W/Ni ratios were successfully prepared by a two-step hydrothermal process. The excellent sensing performance of NiO modified with WO3 to NO2 gas detection was tested, including ultrahigh response, ultralow detection limit, excellent selectivity, and rapid response time as well as recovery time. At an operating temperature of 200 °C, the response of WN-3 to 10 ppm of NO2 is as high as 16.06, which is 8.11 times higher than that of pure NiO, and also the low detection limit of the sensor can reach 20 ppb. For NO2 with 20–1000 ppb, the response time and recovery time of WN-3 are still within 30 s. Moreover, the prepared NO2 sensor still retained more than 80% of its original response after 90 days. The sensing mechanism is also discussed, and the construction of the WO3/NiO heterojunction and the change of the oxygen component distribution are the dominating reasons for excellent sensing performance of the product. All of these advantages indicate that NiO modified with WO3 for NO2 gas sensors is a promising approach to optimize the NO2 sensing performance of pure NiO.