Density Functional Theory Study On Adsorption Properties Of Transition Metal Supported On Nitrogen-Doped Graphene

Graphene,a two-dimensional nanomaterial with unique monatomic layer structure,has entered a stage of rapid development and has been research focus in basic science and advanced technology in the past two decades.Due to the fact that its long-rangeπconjugated bond provide graphene with extraordinary thermal,mechanical and electrical properties,ultra-thin two-dimensional graphene nanomaterials have potential application in many fields,such as electronics,photoelectronics,electrocatalysis,biological nanotechnology,composites,photocatalysis,new energy and sensor.However,zero band gap of graphene has limited its applications in electronic devices,which is the main problem in the specific application of graphene.In this paper,the calculations are performed using the first principle method based on the density functional theory.We have theoretically studied the electronic structure characteristics and adsorption properties of the nitrogen（n）and transition metal doped graphene system,which provides theoretical guidance in the fields of nano electronic devices and new sensors.The main contents and results are summarized as follow:（1）The adsorption behavior of C₂H₂,CO,CO₂,NO₂and SO₂gas molecules on nitrogen-containing graphene system doped with transition element Co in single vacancy（SVN₃Co-GP）was studied by density functional theory.The adsorption structure,electronic density of states,charge density difference,spin density and adsorption energy of the adsorption system were systematically calculated.The results showed that the strongest adsorption(E_ads=-3.32e V)occurred between NO₂ molecule and SVN₃Co-GP graphene.The adsorption between C₂H₂,CO,SO₂ and SVN₃Co-GP is weaker than that of NO₂molecule,but it shows chemical adsorption.But for CO₂ adsorption,it shows physical adsorption and the adsorption is the weakest,which hardly affects the electronic structure of SVN₃Co-GP.From the diagram of DOS,it can be observed that the magnetism of the system is effectively changed by the adsorption of NO₂ and SO₂ molecules.The stable SVN₃Co-GP material is more likely to become a magnetic gas sensor for detecting NO₂ and SO₂gas molecules.（2）The changes of structure,charge density and spin state of C₂H₂,H₂S,SO₂,SO₃and O₂ molecules adsorbed on Fe N₃-GP substrate were analyzed.The results show that charge density of each of five gas molecules overlapped strongly with Fe N₃-GP graphene,and the adsorption energy is relatively large,which shows chemical adsorption.Based on the density of states,Fe N₃-GN graphene has high sensitivity to detect these molecules.N atoms replace C atoms in graphene,so that the adsorption energy of Fe N₃-GP is significantly greater than that of single hole graphene doped with Fe（Fe SV-GP）after adsorbing SO₂,SO₃ and O₂ gas molecules,and the conductivity of the system was changed obviously.Thus,Fe N₃-GP graphene will be a good candidate material for detecting gas.（3）The adsorption behaviors of gas molecules,including CH₂O,CO,N₂O,SO₂ and NH₃,on Mn SV-GP and Mn N₃-GP which has been replaced C atoms with N atoms were thoroughly studied.It is found that the interaction adsorption energy of CH₂O,CO,N₂O,SO₂ and NH₃molecules with Mn N₃-GP is greater than that of Mn SV-GP.The adsorption of these two substrates is chemical adsorption.From the point of view of density of states,the total density of states of Mn N₃-GP adsorbed five molecules near the Fermi level is greater than that of Mn SV-GP.At room temperature（298K）,the recovery time of Mn SV-GP sensor for N₂O gas molecules is about 1.1 s.Therefore,Mn SV-GP system with high selectivity and sensitivity can be predicted as a promising magnetic gas sensor for repeatable detection of N₂O.（4）The adsorption structure,electronic structure,magnetism and adsorption energy of three graphene substrates for CH₂O,H₂S and HCN gas molecules were studied by density functional theory（DFT）.The order of adsorption energy of CH₂O,H₂S and HCN molecules on the three substrates is Mn SV-GP>Mn DV-GP>Mn N₄-GP.The order of adsorption height is Mn SV-GP<Mn DV-GP<Mn N₄-GP.The order of the integral values of the integrated projected crystal overlap Hamiltonian population（-Ip COHP）is Mn SV-GP>Mn DV-GP>Mn N₄-GN.The adsorption energy and adsorption height are correlated with the-Ip COHP,and the values of-Ip COHP are correlated with Fermi softness.The change near the Fermi level in the-p COHP curve can be used as a descriptor for magnetic field.Fermi softness,height change of modified atoms and-Ip COHP values can be used as important indicators of adsorption activity.These results can provide feasible basis for promoting manganese doped graphene to become an effective material and improving the design of graphene substrate.