Defective Cr2CTx-based sensors with high sensitivity for NO2 detection at room temperature

Abstract

Nitrogen dioxide (NO₂), a primary contributor to ozone depletion and acid rain, seriously threatens human health. However, the low response and slow dynamics derived from pristine MXenes remain a challenge to their real application in NO₂ detection. In this work, a novel hydrothermal approach was used to generate defective MXene-Cr₂CT_x nanosheets with outstanding NO₂ gas sensitivity, and first-principles calculations were used to analyze their gas sensing mechanism. The produced Cr₂CT_x nanosheets demonstrated rapid response/recovery durations (88 s/245 s), good selectivity, excellent stability, and durability (>30 days), and a high response rate (62.5%) to 10 ppm NO₂ at room temperature (RT). Furthermore, Cr₂CT_x nanosheets demonstrated a detection limit for NO₂ of less than 0.1 ppm. Utilizing density functional theory (DFT), the research explored the interplay between NO₂ and Cr₂CT_x nanosheets, unveiling the impact of surface oxygen functional groups and magnetic properties on the material's gas adsorption capabilities. The adsorption energy (E_ads) and Bader charge transfer measurements indicate that the Cr₂CT_x-based gas sensor exhibits a higher E_ads (−0.53 eV) and Bader charge transfer (0.122 e) for NO₂ compared to other gases, which are consistent with the experimental results. The research highlights the potential of Cr₂CT_x nanosheets in advancing the development of more effective and selective gas sensors.