First Principles Study On The Adsorption Of CNCl,HCN,and NH₃ On Doped Graphene

Chemical toxic gases undoubtedly pose a great threat to the safety of humans and national regions.While there are fairly strict controls on highly toxic substances such as CNCl,HCN,and NH₃,more aggressive preventive measures must be taken to reduce their hazards.One of the effective ways is to explore a highly sensitive and specific gas-sensitive material to make sensing devices to be deployed in each possible place where toxic gas hazards may appear.Graphene’s high specific surface area and high carrier mobility properties make it very sensitive to gas molecules,capable of detecting very small gas changes,and naturally has potential as a gas-sensitive material.In this thesis,by using first-principles calculation method based on density functional theory（DFT）,The adsorption properties of three toxic and hazardous gases,CNCl,HCN,and NH₃,on the surface of different types of metal-doped graphene,including five metal elements,Au,Ag,Cu,Fe,and Ni,were investigated.The co-adsorption with oxygen on the surface of these substrates in an oxygen-containing environment was also studied.Based on these investigations,the modulation of the co-adsorption properties of CNCl,HCN,and NH₃with O₂on Au-doped graphene was studied by applying an electric field.The results are as follows:（1）Au G,Fe G and Ni G may have the possibility to be used as CNCl,HCN and NH₃adsorption and detection materials.Cu G has certain adsorption and detection effect on CNCl,and does not have detection ability on HCN and NH₃.While Ag G may not have the detection ability for all three gases.（2）After considering the presence of oxygen in the system,it was found that under oxygen-containing conditions,Au-doped graphene still maintained a certain adsorption detection ability for CNCl,HCN,and NH₃.Other systems showed certain adsorption effects on one or more gases under oxygen-containing conditions,but the conductivity of the system did not change significantly,and they did not have detection capability.（3）It was found that adding an electric field to the co-adsorption systems of CNCl,HCN,and NH₃with oxygen on Au-doped graphene under oxygen-containing conditions can enhance the adsorption between the three gases and the substrate while weakening the adsorption between O₂and the substrate when a positive electric field is applied,and the opposite effect is observed when a negative electric field is applied.Applying a positive electric field of 0.6V A^-1to the co-adsorption system of CNCl and O₂on Au G can result in the most significant change in electrical conductivity before and after CNCl adsorption,with the optimal modulation effect.Similarly,a positive electric field of 0.6V A^-1applied to the co-adsorption system of HCN and O₂on Au G results in the most significant change in electrical conductivity and the best modulation effect.A positive electric field of 0.4V A^-1or1.0V A^-1can effectively modulate the adsorption system of NH₃and O₂on Au G.In summary,Au G,Fe G and Ni G have potential as CNCl,HCN and NH₃detection materials,but the presence of O₂affects some properties of the adsorption system to some extent,and only Au G still maintains a certain detection capacity for CNCl,HCN and NH₃in the presence of O₂.In addition,the electrical properties of the system can be effectively regulated by applying a certain strength of external electric field.This thesis develops ideas for the research of the properties of gas sensor materials to cope with the complex environment.