In this work, the adsorption of toxic gaseous NO2 and other gas molecules (NO, CO, CO2, N2, O2, SO2) on pristine and X-doped (X = Si, P, S, Te, As) two-dimensional (2D) WSe2 have been detailed studied by performing density functional theory (DFT) calculations. Calculation results of adsorption energies and adsorption distances demonstrate that As-doped 2D WSe2 (As-WSe2) exhibits high selectivity not only towards NO2, but also towards NO and SO2. However, the charge transfer between NO and the substrate is too small to detect, and chemical bond forms between SO2 and the substrate; both phenomena make As-WSe2 substrate more suitable as a substrate material of the NO2 sensor. To eliminate the interference of SO2 on the adsorption of NO2, coexistence of NO2 and SO2 is simulated. Results reveal that although the interaction between SO2 and the As-WSe2 substrate is stronger than that between NO2 and the substrate, SO2 molecule hardly interacts with the substrate when co-adsorbed with NO2. Besides, calculation results of DOS and PDOS further confirm the sensitivity of As-WSe2 towards NO2; and those of the recovery time also highlight the extremely fast recovery rate of As-WSe2 after adsorbing NO2. The present findings make As-WSe2 monolayer a potential substrate material of NO2 gas sensors used in the atmospheric environment.@en

For the relevant properties of pristine and doped (Si, P, Se, Te, As) monolayer WS2 before and after the adsorption of CO, CO2, N2, NO, NO2 and O2, density functional theory (DFT) calculations are made. Calculation results reveal that the monolayer WS2 doped with P and As atoms can be substrate materials for NO and NO2 gas sensors. However, after the subsequent CDD and ELF calculations, it is found that P-doped monolayer WS2 adsorbs NO and NO2 in a chemical way, while As-doped monolayer WS2 adsorbs NO and NO2 in a physical way. Also, the charge transfer between As-doped monolayer WS2 and NO is relatively small and not easily detected. Besides, As-doped monolayer WS2 system exhibits greater differences in optical properties (the imaginary part of reflectivity and dielectric function) before and after the adsorption of NO2 gas than before and after adsorption of NO gas. These differences in optical properties assist sensor devices in making gas adsorption-related judgments. Through the analysis of the recovery time, DOS and PDOS, As-doped monolayer WS2 is also verified to be a promising NO2 sensing material, whose recovery time is calculated to be as short as 0.169 ms at 300 K.@en