Adsorption and gas-sensing properties of formaldehyde on defective MoS[formula omitted] monolayers: A first-principles study

Abstract

Formaldehyde (CH2O) is an indoor hazardous gas and a respiratory marker for lung cancer patients, thus its adsorption and detection are of particular significance. 2H-MoS2 has a wide range of applications in gas sensors. However, its pristine form is chemically inert and not suitable for the adsorption and detection of CH2O. Here, we systematically investigated the adsorption and gas-sensing properties of defective 2H-MoS2 to CH2O based on first-principles calculations. The S vacancy, substitutional doping and adsorption of transition-metal (TM) atoms in the MoS2 monolayer are considered. We find that the S vacancy effectively enhances the adsorption of CH2O and results in significant charge transfer. The substitutional doping of TM atoms on both S and Mo sites is hard to form in equilibrium conditions for the high formation energy. The adsorption of TM atoms on MoS2 can easily occur for the rather low adsorption energy. Cr and Mn energetically prefer to be adsorbed above the S site, while V, Fe, Co, Ni and Cu energetically prefer to be adsorbed above the Mo site. The TM-adsorbed MoS2 can then strongly adsorb CH2O molecules and results in significant charge transfer, acting as a gas-sensing candidate material for the detection and adsorption of CH2O. The adsorption configurations, density of states, adsorption energy, charge transfer and charge density differences are calculated and discussed. These results are of significance to adsorb the toxic CH2O gas and design its gas sensors using MoS2.