First-principles Study On Adsorption Of Gas Molecules By Metal-modified Molybdenum Distelluride

The increasingly severe environmental problems make the development of high performance gas sensing materials become one of the most popular research topics in the field of gas sensing.MoTe₂monolayer has a large specific surface area,high surface activity and toughness,so it can be used as a gas sensor material with high sensitivity and fast response,and has a wide prospect in the practical application of gas sensors in the future.In this paper,the adsorption properties of nitrite gases（NO、NO₂and NH₃）and sulfide gases（SO₂and H₂S）on the intrinsic MoTe₂monolayer are systematically investigated by using the first-principles calculation method based on density functional theory.Through the comprehensive analysis of the adsorption energy,band structure,state density and differential charge density of the most stable adsorption configuration,the gas-sensitive mechanism between gas molecules and MoTe₂monolayer was clarified.In addition,in order to improve the gas sensitivity of MoTe₂to gas molecules,transition metal atoms（Fe、Co and Ni）and precious metal atoms（Au、Ag、Pd and Pt）were introduced into the MoTe₂monolayer for modification and doping.The results show that the interaction between NO、NO₂and NH₃molecules and the intrinsic MoTe₂monolayer is very weak.The small adsorption energy,large adsorption distance and small charge transfer all indicate that the three gas molecules are not conducive to being captured by the MoTe₂monolayer.In order to enhance the adsorption capacity of MoTe₂for three nitride gases,the MoTe₂monolayer was modified with transition metal atoms Fe、Co and Ni.It was found that the transition metal modification significantly improved the adsorption capacity of NO、NO₂and NH₃molecules on MoTe₂.The analysis of state density diagram shows that the strong orbital hybridization between transition metal atoms and gas molecules is the main reason for the increase of adsorption energy.The differential charge density diagram shows that there are charge dissipation and accumulation behaviors between the gas molecules and the modified system.These behaviors are consistent with the direction of charge transfer calculated by Bader charge.The work function changes obviously before and after gas adsorption.The recovery time indicates that the modified system and gas molecules can be desorbed at room temperature or above 398 K.The optical properties show that the spectral peaks of the modified system shift before and after gas adsorption.These results indicate that MoTe₂monolayer modified by transition metal atoms（Fe、Co and Ni）can be used as sensing or adsorption materials for nitride gases（NO、NO₂and NH₃）.The sensitivity of SO₂and H₂S molecules to the intrinsic MoTe₂monolayer was found to be very weak.In order to improve the gas sensitivity between them,and further expand the use of MoTe₂monolayer in the field of gas sensing,noble metal atoms Au、Ag、Pd and Pt are used to substitute doping the single Te atom in MoTe₂.The doped structure can be used for gas adsorption due to its high formation energy and small deformation.The results show that the doping of noble metal atoms greatly improves the interaction between gas molecules and MoTe₂.The adsorption energy and charge transfer of SO₂molecules in the doping system of Au、Ag、Pd and Pt are greater than that of H₂S molecules,which indicates that SO₂is more sensitive to doping substrate.The sensitivity of MoTe₂to SO₂and H₂S was enhanced by the introduction of noble metal atoms which reduced the band gap of the adsorption system.The interaction between gas molecules and doped substrate was analyzed by state density and differential charge density.The strong orbital hybridization between gas molecules and doped substrate was the main reason for the enhanced adsorption capacity.The variation of work function is closely related to the direction of charge transfer in adsorption system.Bader charge analysis shows that SO₂gas is an electron acceptor in the four doping systems,and the work function increases.H₂S is the electron donor,so the work function decreases.The electron local function shows that the ionic bond between the two gas molecules and the doped substrate is formed by electrostatic interaction.The results show that the MoTe₂monolayer doped by noble metal atoms（Au、Ag、Pd and Pt）can be used as the sensing material for SO₂and H₂S gas molecules.