First-principles study of NO adsorption on S vacancy of MoS2 monolayer

Based on first-principles study in this research, a single-layer two-dimensional MoS2 model with intrinsic and a MoS2 with S-site vacancy defects (MoS2-V) were constructed. The adsorption behaviors of NO on the surface of the two models are calculated, and the electronic properties, adsorption energy, and optical properties of the adsorption systems are studied and analyzed. The results of placing NO in different positions of MoS2 show that the adsorption effect is related to the orientation of NO. The adsorption energy of the optimal model for NO adsorbed on intrinsic MoS2 is 0.009 eV, and the adsorption energy on MoS2-V is - 0.304 eV. The forbidden band gap of both adsorption systems are significantly reduced. After NO was adsorbed onto intrinsic MoS2, the forbidden band gap changed from 1.729 eV to 0.235 eV. When NO was adsorbed onto MoS2-V, the forbidden band gap changed from 0.938 eV to 0.201 eV. The band gap change caused by the S vacancy defect leads to the reduction of the electron hopping chance between energy levels. The electron density difference diagrams show that MoS2-V has a stronger adsorption effect on the NO. The total and partial density of states (DOS) of the NO adsorption system shifts to the lower energy region. The dielectric function diagram of the MoS2-V adsorption system is shifted to the low-energy region, and the peak intensity decrease. The reflective index of the MoS2-V adsorb NO system is higher than that of the intrinsic MoS2 in the 0 eV < E < 1 eV range, indicating that the MoS2-V material enhances the absorption of electromagnetic waves in low-frequency region. The reflective index tends toward zero in the high energy region of these two adsorption systems, indicating they all have strongly absorption of electromagnetic waves in high-frequency region. It is predicted that this material may be applied as a usable adsorption material or developed as a new type of gas material for early warning.