Light-assisted recovery of reacted MoS₂ for reversible NO₂ sensing at room temperature

Two-dimensional (2D) nanomaterials have been extensively explored as promising candidates for gas sensing due to their high surface-to-volume ratio. Among many 2D nanomaterials, molybdenum disulfide (MoS₂) is known to be functional in detecting harmful gases at room temperature; therefore, it has been actively studied as a gas sensing material. However, there has been a limitation in recovering the original signal from reacted MoS₂ after exposure to the target gas. This work demonstrates the recovery of the initial resistance of reacted chemical vapor deposition-grown MoS₂ by illuminating it with a UV light-emitting diode (LED). A novel mechanism involving photo-generated electron-hole pairs in MoS₂ is proposed and experimentally verified. The fabricated sensor detects nitrogen dioxide (NO₂) and distinguishes between concentrations from 1 to 10 ppm with the proposed recovery process. Reversible detection after repeated exposure to 5 ppm NO₂ over eight cycles is achieved through UV-LED illumination for a short time during the recovery process, while the identical sensor without UV illumination shows a transitional response at each cycle. To apply a low cost gas sensing solution at room temperature, visible light LEDs are also used to recover the resistance of the reacted MoS₂.