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

NO 2 is a common air pollution gas, which can cause acid rain and photochemical smog. Accordingly, NO 2 gas sensors with high sensitivity, selectivity, and real-time monitoring for detecting low concentration of NO 2 are urgently needed. NiO and NiO-based nanomaterials have attracted more attention in the field of NO 2 sensing, whereas the low response and sensitivity to NO 2 limit the application of NiO in the field of gas sensors. In this work, flower-like NiO modified with WO 3 nanoparticles with different W/Ni ratios were successfully prepared by a two-step hydrothermal process. The excellent sensing performance of NiO modified with WO 3 to NO 2 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 NO 2 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 NO 2 with 20–1000 ppb, the response time and recovery time of WN-3 are still within 30 s. Moreover, the prepared NO 2 sensor still retained more than 80% of its original response after 90 days. The sensing mechanism is also discussed, and the construction of the WO 3 /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 WO 3 for NO 2 gas sensors is a promising approach to optimize the NO 2 sensing performance of pure NiO.