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

SnO₂ nanosheets with abundant vacancies (designated as SnO_{2- 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 SnO_{2- x} nanoplates with the size of 5-10 nm were distributed on the surface of amorphous carbon. After annealing, the acquired SnO_{2- 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 SnO_{2- x} exhibited excellent performance of sensing NO₂ at room temperature. The response of the SnO_{2- 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%, Δ R/ 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 SnO_{2- x} is attributed to its special structure.