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.