Adsorption of gas molecules of CH₄, CO and H₂O on the vanadium dioxide monolayer: computational method and model

Inspired by the recent use of two-dimensional nanomaterials as gas sensors, we used density functional theory calculations to study the adsorption of gas molecules (CH₄, CO and H₂O) on sandwich vanadium dioxide tablets. The results showed that of all these gases, only the CH₄gas molecule was the electron acceptor with significant charge transfer on the VO₂sheet. The adsorption energies of CH₄, CO and H₂O are -229.5 meV, -239.1 meV and -388.3 meV, respectively. We have also compared the adsorption energy of three different gas molecules on the VO₂surface, our calculation results show that when the three kinds of gases are adsorbed on the VO₂surface, the order of the surface adsorption energy is H₂O > CO > CH₄. It is also found that after adsorption of CH₄, CO and H₂O molecules, the electronic properties of VO₂sheet changed obviously. However, due to the strong adsorption of H₂O molecule on VO₂sheet, it is difficult to desorption, which hinders its application in gas molecular sensors. The optical properties of VO₂sheet are further calculated. The absorption of CH₄, CO and H₂O molecules is introduced to red-shift the dielectric function of the thin film, which indicates that the optical properties of the thin film have changed significantly. According to the change of optical properties of VO₂sheet before and after molecular adsorption, VO₂can be used as a highly selective optical gas sensor for CH₄, CO and H₂O detection. These results provide a new approach for the potential application of VO₂based optical gas sensors.