Oriented adsorption and efficient sensing of NO2 on MoSe2 monolayer: a comparative study with WSe2 monolayer

Abstract

Oriented adsorption is very rare on two-dimensional inorganic thin layers. Based on preliminary study, density functional theory (DFT) was used to explore the adsorption and sensing behavior of NO2 on MoSe2 perfect and defective monolayers including selenium vacancy (VSe), molybdenum vacancy (VMo), and antisite defect of selenium on molybdenum site (SeMo) by large-scale sampling. The adsorption energy can reach 0.29 eV with 0.182 e charge transfer on the perfect monolayer. The adsorption ability is improved largely on VSe, VMo, and SeMo monolayers (3.27, 0.93, and 1.20 eV) with considerable charge transfer (0.583, 0.152, and 0.139 e, respectively), demonstrating the potential of MoSe2 monolayers as NO2 sensing materials. Meanwhile, similar to WSe2 monolayer, oriented adsorption of NO2 is disclosed. NO2 molecule extends mainly along the Se–Mo–Se trough and the Se–Mo bond on all the four MoSe2 monolayers. Whereas, the oriented adsorption ability is weaker than the WSe2 monolayer, which can be confirmed by the relatively small proportion of oriented adsorption conformations. This kind of double oriented adsorption behavior (vertical adsorption and adsorption along specific direction of the two-dimensional material) was considered to be due to the good polarity match between molecule and monolayer. Molecular dipole moment and material bond population are believed to be two important parameters that determine the oriented adsorption capacity of molecular-material systems. The successive discovery of the unique oriented adsorption and the deepening of understanding provide chance for molecular design of oriented adsorption of inorganic small molecules on two-dimensional layered materials. The strong dissociation ability of the anionic vacancy monolayer to NO2 molecule indicates that MoSe2 monolayer has a very high adsorption, capture, and activation potential for nitrogen oxides. Comparative study proved that the Mo site activity was less than the W site activity on the perfect monolayer, and defects could help the Mo site activity overtake. These findings provide pivotal guidance for creating advanced surface regulated electronic systems, such as sensors.