Ultra-Fast NO₂ Detection by MoS₂ Nanoflakes at Room Temperature

Abstract

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 NO ₂ . Development of efficient sensor for the obnoxious gas is very crucial. This work presents the synthesis of MoS ₂ nanoflakes using liquid-phase exfoliation method and its application as NO ₂ sensor at room temperature. The synthesized MoS ₂ nanoflakes were characterized by atomic force microscope, 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 MoS ₂ was found to be 1.71 eV. The synthesized MoS ₂ was tested for NO ₂ , NH ₃ , 2NT, H ₂ O, CH ₃ OH, C ₂ H ₅ OH, and (CH ₃ ) ₂ CO at 25 °C. The sensor exhibited high selectivity towards NO ₂ and the response of MoS ₂ varied between 2.82–39.8 % for 3–150 ppm of NO ₂ . The response time and recovery time of the sensors were 9 s and 3 s for 3 ppm of NO ₂ . In an attempt to understand the detailed sensing mechanism of the MoS ₂ sensor, the adsorption characteristics of the seven vapors on MoS ₂ was theoretically studied using first principles studies. The role of defects in sensing performance of MoS ₂ was investigated theoretically. The findings of the theoretical studies were in excellent agreement with the experimental observations.