First Principles Study On Modification Of ZnO And Surface Adsorption Of NO And CO

In recent years,serious accidents such as mine poisoning,explosions and fires caused by excessive concentrations of NO and CO gas in the process of coal mining.How to detect and monitor NO and CO gas with high sensitivity has become an increasingly concerned problem.In this paper,the Zn O gas-sensing materials are used as the research object,and the first principles are used as the calculation method to simulate the modified bulk phase of Zn O and the adsorption of NO and CO on the surface.The specific content are as follows:1.The crystal plane systems of Zn O（001）,Zn O（100）and Zn O（110）are established by cutting the plane of 2×2×1 Zn O supercell.Through structural relaxation of the three crystal planes,it is found that Zn O（001）is the most stable crystal plane.Then,Zn O（001）surface are selected to characterize the bulk phase of Zn O to explore the electronic properties and adsorption performance of NO and CO adsorbed at the three different sites（Zn,O,V）on the surface of Zn O（001）.After optimization calculation,it is found that the electronic structure of the system changes and the adsorption effect appeared.The best adsorption site for NO is O site and the minimum adsorption energy is-0.766 e V.The best adsorption site for CO is Zn site and the minimum adsorption energy is-0.647 e V.The adsorption energy of each adsorption system is negative for spontaneous adsorption,but the absolute value of adsorption energy is small that indicating poor sensitivity to NO and CO,which is also consistent with the situation that the sensitivity of single Zn O based gas sensor is poor in practical application.The adsorption energy of NO is smaller than CO system,indicating that NO is more easily adsorbed on the Zn O（001）crystal plane.2.The monolayer Mo S₂composite Zn O（001）material to establish Mo S₂-Zn O（001）system.It is found that electronic structure of the composite modified system is changed and the system stability is enhanced.The simulation calculation of the adsorption of NO and CO on its surface found that the stability of each adsorption system are improved compared with the control system Zn O（001）,the adsorption energy is negative and the value is small.This conclusion shows that the adsorption capacity of Zn O（001）on NO and CO is enhanced after being modified by Mo S₂.The V site of the Mo S₂-Zn O（001）system is the best adsorption site for NO,and the adsorption energy is-16.817 e V and the best adsorption site for CO is Zn site which the adsorption energy is-12.844 e V.Among them,the adsorption energy of NO system is smaller,indicating that NO is more easily adsorbed on the surface of the Mo S₂-Zn O（001）system.3.The rare earth element La doped Zn O（001）material to establish La/Zn O（001）system.By comparing the binding energy with the three doping models of La on the Zn site,O site and V site of the Zn O（001）crystal plane,it is found that the binding energy of La is the smallest when the Zn site is doped on the Zn O（001）crystal plane,which is-3.832 e V.On this basis,the adsorption performance of four different sites（Zn,O,V,La）on the surface of La/Zn O（001）_-Znsystem for NO and CO are further explored.It is found that the adsorption of NO on the La site of the La/Zn O（001）_-Znsystem is non-spontaneous adsorption.The adsorption energy of each point is negative when CO is adsorbed in the La/Zn O（001）_-Znsystem.The V site is the best adsorption site for NO,the adsorption energy is-2.132 e V,the O site is the best adsorption site for CO,which is-4.156 e V,and the value CO adsorption energy is smaller than that of the NO adsorption system.It shows that CO is more easily adsorbed on the surface of the La/Zn O（001）_-Znsystem.4.The rare earth element La doped Zn O（001）instead of Zn site and then composite with monolayer Mo S₂to establish Mo S₂-La/Zn O（001）system.It is found that electronic structure is changed and the system stability is enhanced.Afterwards,the adsorption performance of NO and CO on the surface are explored by selecting Zn site,O site,V site and La site as adsorption sites.Then,the adsorption performance of NO and CO on the surface are explored by selecting Zn site,O site,V site and La site as adsorption sites.After optimization calculations,it is found that the stability of each adsorption system is greatly improved compared with Zn O（001）,and the adsorption energy is negative indicating that it is spontaneous adsorption without external help.It shows that the Zn O（001）crystal plane is doped with La instead of Zn site and then composited with monolayer Mo S₂to improve the adsorption performance of NO and CO.The best adsorption site of NO is more inclined to be adsorbed at the V site and CO is more likely to be adsorbed at the La site as the best adsorption site with adsorption energy of-10.127 e V.Among them,the absolute value of the adsorption energy of the NO system is weaker than CO system,indicating that NO is more easily adsorbed on the surface of the Mo S₂-La/Zn O（001）system.There are 40 figures,14 tables and 98 references in this paper.