Temperature modulated p-n transition NO2 sensor in metal-organic framework-derived CuOx

The wide reactivity of metal oxide semiconductor sensors to different gases leads to poor selectivity of the devices, which seriously hinders their practical application. Herein, a qualitative method for analyzing selectivity is proposed by modulating the working temperature to realize p-n response conversion. This method is independent of the response values and can identify the nitrogen dioxide (NO2) gas in the mixture of ammonia (NH3) and NO2 gases. In this work, the CuOx octahedrons sensing layer derived from the metal-organic frameworks (MOFs) is synthesized via self-assembly and calcination route. The gas sensing performance of CuOx sensor to ppb-level NO2 at different temperatures is systematically investigated. Interestingly, the CuOx sensor manifests the intrinsic p-type behavior in the temperature range from room temperature (RT, i.e. 25 ?) to 180 ? and n-type behavior above 200 ?. This tunable sensing behavior with switching from p-type to n-type ensures that the CuOx sensor accurately identifies a specific gas without considering the relative intensity of responses between target gas and interference gases. Moreover, the CuOx sensor exhibits high response of 76.69% at 25 ? and superior repeatability. The mechanism of p-n sensing behavior transition for NO2 is proposed based on content of adsorbed oxygen and surface reactions at different temperatures. This work provides a novel approach for tailoring the selectivity of ppb-level NO2 gas sensors and exhibits potential applications for the environment monitoring.