N-/S- dual doped C@ZnO: An excellent material for highly selective and responsive NO₂ sensing at ambient temperatures

Nitrogen dioxide (NO₂) is an extremely toxic gas and harmful to human health and the environment. Inhalation of NO₂ reduces immunity to lung infections and causes respiratory problems such as wheezing, coughing, colds, flu, and bronchitis. To date, several sensors have been developed for the detection of NO₂. Indeed, the development of highly sensitive and selective room temperature sensor with rapid response and recovery time could be called an “innovation” for metal oxide-based gas sensors for environmental remedy applications. Herein, we prepared ZnO nanospheres (ZNS), nitrogen-doped carbon-coated ZnO spheres (NC@ZNS), sulfur-doped carbon-coated ZnO spheres (SC@ZNS), and nitrogen-sulfur dual doped carbon-coated ZnO spheres (NSC@ZNS) for NO₂ sensing. Among them, the NSC@ZNS exhibits excellent NO₂ sensing characteristics with the sensor response (S_R = R_g/R_a) of 730.4 and 31.2 at 100 and 25 °C, respectively. The limit of detection (LOD) of the NSC@ZNS sensor is ~21 ppb at ambient temperature. The NSC@ZNS hybrid nanocomposite sensor exhibits ultrafast response and recovery times of ~88 s and 305 s to 500 ppb of NO₂ at 25 °C. Besides, the NSC@ZNS sensor shows excellent selectivity to NO₂, which is ~31 times higher than other interfering gases. The enhanced sensing characteristics of the NSC@ZNS sensor is attributed to the synergy between the nitrogen-sulfur dual doped carbon and hierarchical mesoporous ZnO. The selective detection of NO₂ with significantly rapid response and recovery time at 25 °C makes for intriguing the promising practical applications of our proposed NSC@ZNS sensor.