The electronic and optical properties, gas sensor and NO removal application investigations of noble metal-adsorbed MoSi2N4

In this paper, the electronic and optical properties, gas sensor behavior and photocatalytic nitric oxide (NO) removal applications of noble metal-adsorbed MoSi2N4 (NMs-MSN, NMs = Au, Ag, Cu, Pd and Pt) are investigated and screened based on first-principles calculations. The band gaps of MoSi2N4 decrease to different degrees after noble metals are adsorbed, especially when the band gap changes from intrinsic MoSi2N4 of 1.89 eV to Pd-MoSi2N4 of 1.59 eV. Based on density of states (DOS) analysis, new degenerate energy bands formed and combined with the valence band after Pd adsorbed, which resulted in a band gap decrease. The optical property calculations show that the light absorption range and coefficient of NMs-MSN significantly increase. Then, the sensor behaviors are investigated and screened based on the adsorption and recovery behaviors of gas molecules (including NO, CO, O-2, CO2, NO2, H2O, H2S and NH3) on NMs-MSN. Based on the adsorption energy, recovery time and band gap changes after gas adsorption, it can be concluded that Ag-MSN is suitable for sensing SO2 molecules, that Au-MSN is suitable for sensing SO2, CO and O-2 molecules, and that Pd-MSN is suitable for sensing N-2, NO and NO2 molecules. The most suitable noble-metal atoms for the photocatalytic removal of NO are calculated and screened, and the Pd-MSN is determined to be most suitable for NO removal. The introduction of a Pd atom inhibits desorption of the toxic product nitrogen dioxide (NO2), inducing the main product to become a nitrate ion (NO3). The mechanism indicates that the potential barrier is greatly reduced because electron-hole complexation is suppressed. In general, noble metal atom-adsorbed MoSi2N4 can effectively change the band gap, improve the light absorption coefficient, adjust the gas sensor behavior, and enhance the photocatalytic ability for NO removal.