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

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 (NO 2 ) gas in the mixture of ammonia (NH 3 ) and NO 2 gases. In this work, the CuO x octahedrons sensing layer derived from the metal-organic frameworks (MOFs) is synthesized via self-assembly and calcination route. The gas sensing performance of CuO x sensor to ppb-level NO 2 at different temperatures is systematically investigated. Interestingly, the CuO x sensor manifests the intrinsic p-type behavior in the temperature range from room temperature (RT, i.e. 25 ℃) to 180 °C and n-type behavior above 200 °C. This tunable sensing behavior with switching from p-type to n-type ensures that the CuO x sensor accurately identifies a specific gas without considering the relative intensity of responses between target gas and interference gases. Moreover, the CuO x sensor exhibits high response of 76.69% at 25 ℃ and superior repeatability. The mechanism of p-n sensing behavior transition for NO 2 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 NO 2 gas sensors and exhibits potential applications for the environment monitoring. • MOFs-derived CuO x was synthesized by combining self-assembly and calcination route. • CuO x sensor exhibits temperature-dependent p-n behavior transition for 500 ppb NO 2 . • Qualitative analysis of selectivity by comparing the sensing behavior at RT and 200 ℃. • Superior sensitivity benefits from large specific surface area and porous feature.