Enhancing NO₂ Gas Sensing: The Dual Impact of UV and Thermal Activation on Vertically Aligned Nb-MoS₂ for Superior Response and Selectivity

Nitrogen dioxide (NO2) is considered to be a highly hazardous gas found in combustion engine exhaust, which causes several diseases at a young age. To detect NO2 at room temperature (RT), two-dimensional transition metal dichalcogenides play an essential role because of their greater surface-to-volume ratio. However, their higher limit of detection (LOD), slow response, and incomplete recovery kinetics hinder their use in efficient gas sensors. To mitigate these issues, we fabricate a facile and robust niobium (Nb)-doped molybdenum disulfide (MoS2) sensor using low-pressure chemical vapor deposition on a SiO2/Si substrate. Doping is confirmed through various characterization techniques. As compared to pristine MoS2, three batches of sensors are prepared with different weight percentages of Nb (8, 16, and 24%). Out of these, the 16% Nb-MoS2 sensor gives a greatly enhanced relative response of ∼30% for 500 ppb NO2 at 100 °C with an LOD of 489 ppt. Also, the sensor gives an ultrahigh response of ∼39% (18%) for 50 ppm (500 ppb) NO2 under 0.4 mW/cm2 intensity of UV light and exhibits a lower LOD of 117 ppt at RT. In addition, the 16% Nb-MoS2 sensor shows impressive selectivity toward NO2 against a range of reducing and oxidizing gases, along with exceptional long-term durability and stability. Based on density functional theory calculations, a comprehensive gas sensing mechanism is proposed. The calculations focus on identifying the favorable sites for NO2 adsorption on 16% Nb-MoS2 nanoflakes. This study offers a compelling and practical approach to boosting the efficiency of Nb-MoS2-based NO2 gas sensors.