High-Response Room-Temperature NO2 Sensor and Ultrafast Humidity Sensor Based on SnO2 with Rich Oxygen Vacancy

SnO2 nanosheets with abundant vacancies (designated as SnO2–x) have been successfully prepared by annealing SnSe nanosheets in Argon. The transmission electron microscopy results of the prepared SnO2 nanosheets indicated that high-density SnO2–x nanoplates with the size of 5–10 nm were distributed on the surface of amorphous carbon. After annealing, the acquired SnO2–x/amorphous carbon retained the square morphology. The stoichiometric ratio of Sn/O = 1:1.55 confirmed that oxygen vacancies were abundant in SnO2 nanosheets. The prepared SnO2–x exhibited excellent performance of sensing NO2 at room temperature. The response of the SnO2–x-based sensor to 5 ppm NO2 was determined to be 16 with the response time and recovery time of 331 and 1057 s, respectively, which is superior to those of most reported room-temperature NO2 sensors based on SnO2 and other materials. When the humidity varied from 30 to 40%, ΔR/R was 0.025. The ultrafast humidity response (52 ms) and recovery (140 ms) are competitive compared with other state-of-art humidity sensors. According to the mechanistic study, the excellent sensing performance of SnO2–x is attributed to its special structure.