Ultra-Fast NO2 Detection by MoS2 Nanoflakes at Room Temperature

Air pollution is posing a serious threat to mankind lately which in turn, makes continuous air quality monitoring imperative. One of the pollutants that has harmful effect on human health, as identified by World Health Organization is NO2. Development of efficient sensor for the obnoxious gas is very crucial. This work presents the synthesis of MoS2 nanoflakes using liquid-phase exfoliation method and its application as NO2 sensor at room temperature. The synthesized MoS2 nanoflakes were characterized by atomic forcemicroscope, field emission scanning electron microscope, ultraviolet-visible spectroscope, Fourier transform infrared spectroscope, and high-resolution transmission electron microscope. The thickness of the nanoflakes varied from 4-20 nm and the lateral dimensions ranged from hundreds of nm to few microns. HOMO-LUMO gap of synthesized MoS2 was found to be 1.71 eV. The synthesized MoS2 was tested for NO2, NH3, 2NT, H2O, CH3OH, C2H5OH, and (CH3)(2)CO at 25 degrees C. The sensor exhibited high selectivity towards NO2 and the response of MoS2 varied between 2.82-39.8 % for 3-150 ppm of NO2. The response time and recovery time of the sensors were 9 s and 3 s for 3 ppm of NO2. In an attempt to understand the detailed sensing mechanism of the MoS2 sensor, the adsorption characteristics of the seven vapors on MoS2 was theoretically studied using first principles studies. The role of defects in sensing performance of MoS2 was investigated theoretically. The findings of the theoretical studies were in excellent agreement with the experimental observations.