The Effect Of Anatase Oxide XO₂(X=Ti,Sn,Zr,Ir) Surface On The Characteristics Of NH₃,HCL,CO Gas Optical Gas Sensing

HCl and CO are halides and carbon oxides produced by industrial production.NH₃ is a production raw material for many chemical products,and has wide application in the fields of chemical fertilizers,pharmaceutical,synthetic fibers.But they are also poisonous gases,and poisoning will endanger life when they are serious.Many scholars have a large number of studies on various harmful gas components and concentrations in the air.Semiconductor gas sensitive materials are widely used in the field of gas detection,as it has the advantages of stable performance,low cost,repetitiveness,and different materials often have different response sensitivity.The anatase phase TiO₂,SnO₂,ZrO₂ and IrO₂ are common optical gas sensitive materials,which have the same structural types of anatase.The optical gas sensing is an oxidative reaction when the gas sensitive material is contacted with the gas,causing electron transfer in the gas and material.When the number of electrons absorbs or releases the photon changes,the ingredients and concentrations of the gas are detected in the macroscopic representation of the optical properties.In order to find the relationship between the surface properties of optical gas-sensitive materials and the changes in their optical properties after interacting with gas molecules in the visible light range.This paper uses the crystal model of anatase TiO₂,SnO₂,ZrO₂,and IrO₂(101) surfaces to adsorb HCl,CO,NH₃,and the surface oxidization,adsorption energy,cjarge density,density of State and optical properties of anatase oxide XO₂(X=Ti,Sn,Zr,Ir)plane adsorbing HCl,CO and NH₃ are studied by using the plane-wave ultrasoft pseudopotential method under the first principle of density functional(DFT-D)system.The results showed that:The redox characteristics of surface oxygen vacancies are an important factor affecting the adsorption distance and adsorption energy of the system.By comparing the adsorption distance and energy of the four systems,it is found that the adsorption distance of IrO₂ is the largest,and the adsorption of SnO₂ is the largest.So the SnO₂ adsorption system is the most stable in the three adsorption.When ZrO₂ adsorbs CO,the adsorption distance is minimal,and the energy needs to be absorbed,indicating that the adsorption is unstable.When each system adsorb three gases,it was found that the adsorption energy of the material surface adsorbed NH₃ was the largest,indicating that the system was more stable after the oxide adsorbed NH₃.The density of states indicates the position of the transferred electron in the energy band.In this way,it is judged whether it is beneficial to the sensing adsorption and desorption.According to the number of the adsorbent molecule charge transfers,NH₃,CO and HCl lose most electrons in IrO₂ surface and the amount of charge is 0.042e,0.044e,0.041e,followed by the loss of the charge on the TiO₂ surface with 0.031e,0.033e and 0.024e.The number of charges obtained on the surface oxygen vacancies are more than that of the other two systems.The surface of ZrO₂ is only charged with CO molecules to achieve 0.023e.So the oxidation relationship is:IrO₂>TiO₂>SnO₂>ZrO₂?From the analysis of electronic density of state,The peaks of N2p,Cl 3p and O2p appear at the Fermi level with electron transfer after four materials adsorption NH₃,CO and HCl.Due to the band gap width(0e V),IrO₂ valence zone crossing the Fermi level makes IrO₂ show metal properties which is not conducive to the detection of gas.There is no electronic transfer with the surface of the material on ZrO₂ surface and the peak near the Fermi level is mainly due to the internal electron transfer of the adsorbed molecule.While the width of TiO₂ and SnO₂ is relatively small,and the electronic transfer occurred between the adsorption molecule and the surface of the material allows them to show good semiconductor properties.The electron transfer on the surface of the material is embodied in the macroscopically as a change in the optical properties of the material.In all four systems,TiO₂ and Sn O₂ have good optical gas sensitive sensitivity to gases.When the surface adsorbs NH₃,the SnO₂ has a maximum of 10675 cm^-1 near 400 nm,and the optical gas sensitive sensing of NH₃ is better in the range of 400?530 nm.TiO₂ peaks28000 cm^-1 near 750 nm,and the optical gas sensitive sensitivity of NH₃ is better in530?800 nm.When the surface adsorbs HCl and CO,the SnO₂ has a maximum of10713 cm^-1and 10770 cm^-1 in the absorption peak near 400 nm,and TiO₂ reached a peak 1200 cm^-1 and 14629 cm^-1 in the vicinity of 800 nm.TiO₂ and Sn O₂ have better optical gas sensitivity to HCl and CO in 550?800 nm and 400?550 nm bands of visible light.In the case of TiO₂ adsorption NH₃,HCl and CO gas,the optical gas sensing for NH₃ is the best,and the absorption coefficient reaches a maximum of 28000cm^-1near 750 nm.In the case of SnO₂ adsorb three gases,the optical gas sensing for CO is the best,and the absorption coefficient reaches a maximum of10770 cm^-1near 400 nm.In summary,IrO₂ show metal properties which is not conducive to the detection of gas.The oxygen-containing vacant defects on the surface of TiO₂ and SnO₂ are oxidative and exhibit good optical gas-sensitive sensing.Therefore,electron transfer is the root cause of the redox reaction,and the sensitivity of optical gas-sensitive materials to light is closely related to the redox characteristics of oxygen-containing vacancy defects on the surface.This also provides a reference for the study on the preparation and modification of NH₃,HCl and CO sensitive materials.