Adsorption Of Nitrogen Oxides By H-BN Based On First-Principles Study

Gas-solid sensor is widely used in industry and environmental monitoring because of its good stability and high sensitivity.However,the sensitivity of most gas-solid sensors still cannot meet the requirements,especially for the detection of nitrogen oxides and other toxic gas molecules.Hexagonal boron nitride（h-BN）,a non-carbon nanomaterial with electronic structure and properties similar to or even better than graphene,has received considerable research attention due to its excellent specific surface area,flexibility and electrical conductivity,and these outstanding properties make it a research center for gas detection materials.In order to further explore the adsorption performance of h-BN,this paper,based on the calculation and analysis method of density functional theory,constructed B-vacancy defect boron nitride（V_B）,N-vacancy defect boron nitride（V_N）,Rh atom combined with B-vacancy h-BN(V_Rh-B),Rh atom combined with N-vacancy h-BN(V_Rh-N)and other structures as adsorption systems.The adsorption properties of nitric oxide（NO）,nitrogen dioxide（NO₂）and nitrous oxide（N₂O）gas molecules have been systematically studied and some meaningful results have been obtained.The main research content of this topic is roughly as follows:The first chapter is an introduction,taking the current research background and significance of two-dimensional materials as gas sensing materials as a starting point,and briefly introducing the research status of h-BN monolayer in recent years,including its structure and properties,application fields and doping status.Next,the main research content of this paper is introduced.The second chapter is the theoretical basis and calculation methods,including first-principles calculation methods,density functional theory,and software packages used in the calculation process of this topic.In the third chapter,a model of adsorption of NO,NO₂ and N₂O molecules in V_Band V_N systems is constructed,the most stable adsorption structure of the adsorption system is obtained through self-consistent calculation,and the non-self-consistent calculation is carried out on the basis of structural optimization to obtain the adsorption energy,charge density,state density and band structure of the adsorption system.The results show that the interaction of NO molecules on the V_B system is stronger than that in the V_N system,the adsorption of NO₂ and N₂O molecules on the V_N system is stronger,and the higher adsorption energy and the more charge transfer between the adsorption systems indicate that the adsorption system occurs chemical adsorption.In chapter 4,models for the adsorption of NO,NO₂ and N₂O molecules in V_Rh-B and V_Rh-N systems are constructed.The results show that defects and doping lead to the redistribution of electron density in the adsorption system,thus improving the adsorption energy of nitrogen oxide molecules.For NO molecules,the adsorption effect of V_Rh-Band V_Rh-N systems is better than that of V_B and V_Nsystems.For the other two gas molecules,the adsorption effect of V_N system on NO₂ and N₂O molecules is better than that of the other three systems,while the adsorption capacity of N₂O in the other systems is relatively weak.Therefore,V_Rh-B system and V_Rh-N system are suitable for detecting NO gas,and V_N system is suitable for detecting NO₂ and N₂O molecules.The electronic properties of the adsorption system show that the introduction of defect doping into h-BN can lead to changes in the band gap of adsorption,thus changing the conductivity and sensitivity of the adsorption system and improving its sensing ability to gas molecules.In chapter 5,based on the adsorption system established in Chapter 3 and Chapter 4,the influence of applied electric field on the adsorption system is also studied.The results show that the strong interaction of nitrogen oxides on the functional h-BN monolayer can be effectively avoided by applying the intensity and direction of the vertical electric field.To rationalize this finding,we also compared the net charge transfer values of gas molecules with and without an electric field.For example,for the adsorption of NO₂molecules,we found that the application of a negative electric field tends to prevent the transfer of electrons from the substrate to NO₂,resulting in a loss of electron density on the molecule,thus weakening the molecule-substrate interaction.The opposite is true for other adsorption systems.Therefore,when the applied electric field is applied,the direction of the electric field can be adjusted according to the direction of charge transfer of the adsorption system,so as to avoid the strong adsorption of gas molecules.In chapter 6,an overview of the full text,summarizes the topic and looks forward to future work.