Toxic gas molecules adsorbed on intrinsic and defective WS2: gas sensing and detection

The magnetic and electronic behaviors of four toxic gas molecules (CO, NH3, NO, and NO2) adsorbed on intrinsic and defective (VW/WS2 or VS/WS2) WS2 are systematically discussed using density functional theory. The adsorption energy of NO-VW/WS2 is reduced more compared to that of NO adsorbed on intrinsic WS2, indicating that VW/WS2 can be used to capture NO. The adsorption of the four toxic gas molecules shortens the band gap of the defective WS2. The introduction of the S defect changes the type of band gap of the system. More interest-ingly, the adsorption of NO2 (NO) changes the system from a direct bandgap for intrinsic WS2 (VW/WS2) to an indirect bandgap, while the introduction of NO2 changes the system from an indirect bandgap for VS/WS2 to a direct bandgap. Finally, the shorter recovery times for CO and NH3-VW/WS2 compared to CO and NH3 adsorbed on intrinsic WS2 suggest that VW/WS2 makes an ideal reversible sensor for detecting CO and NH3. In conclusion, the adsorption of gas molecules and the defect can modulate the magnetic and electronic properties of WS2. Importantly, intrinsic and defective WS2 will facilitate gas sensing and detection of toxic gases.