| With the development of modern industry,the hydrogen chloride gas produced during the production process of chlorinated paraffin has become an important cause of air pollution.Therefore,it is particularly important to use a gas sensor to detect the concentration of hydrogen chloride gas in the air.Common gas sensors are divided into resistance type and optical type.High precision,good selectivity,and wide gas sensitivity range are the advantages of optical gas sensors,so they have become the current research hotspot.Rutile metal oxides are a kind of materials commonly used in optical gas sensors to detect gas concentration and types.In this paper,the first-principles plane wave super-soft pseudopotential method based on density functional theory is used to study Oxidation performance,adsorption energy,density of state,charge population distribution and optical properties of（undoped,Ru single doped,N-Ru co-doped）oxygen-containing vacancy rutile metal oxide XO2（X=Ti,Mo,Sn）（110）surface adsorbed by HCl gas.Explore the microscopic mechanism of the change of the macroscopic optical properties of the system caused by electron transfer after the target gas is adsorbed on the surface of the material.The results show:1.Redox characteristics and electron transferAfter adsorbing the same kind of gas,the amount of electrons gained or lost by different materials reflects the strength of the gas’s oxidation-reduction ability,and the size of the adsorption energy and adsorption distance reflects the strength and difficulty of the material’s adsorption of gas.Comparing the adsorption energy and adsorption distance characteristics of the three materials,it can be seen that Ti O2 is the most easily adsorbed HCl gas when it is not doped,and the adsorption distance is 0.311（?）.After adsorption,the adsorption energy of the system（0.477e V）is the largest and the adsorption is the most stable;When Ru and N-Ru are co-doped,HCl gas is most easily adsorbed on the surface of Sn O2（110）,and the corresponding adsorption distance is 0.695（?）,0.732（?）,the adsorption energy（0.831e V,0.884e V）is the largest,and the stability is the strongest.From the electron transfer,it can be seen that both single-doped Ru and co-doped N-Ru enhance the oxidation of oxygen vacancies on the surface of the three systems,and the（110）surface adsorption of pure rutile oxide XO2（X=Ti,Mo,Sn）When HCl gas is mixed with Ru alone and N-Ru co-doped,the charge transfer number changes to Mo O2（0.02e→0.03e→0.03e）,Sn O2（0.01e→0.05e→0.06e）,Ti O2（0.03e→0.04e→0.04e）.Sn O2 oxygen vacancy oxidation changes the most after doping,which is stronger than the other two doping systems.The doping effect of N in Ti O2 and Mo O2 is not obvious.N-Ru co-doped oxygen-containing vacancy rutile metal oxide XO2（X=Ti,Mo,Sn）and the relationship between the oxidation properties of the three surface oxygen vacancies is consistent with that of Ru single doping.2.Density of statesBy analyzing the density of states,it is possible to more accurately find the specific transfer situation of the microscopic electrons and the position in the energy band.It can be obtained from the density of states of the three systems.When undoped,Sn O2 is the largest among the three materials due to its own band gap value,and the total density of states does not change significantly after absorbing HCl gas;when single-doped Ru and co-doped with N-Ru After the three materials adsorb HCl gas,the forbidden band width is narrowed,and the band gap changes the most when Ru is doped with Sn O2 alone.This is not only because the distance between the top of the valence band and the bottom of the conduction band becomes smaller,but also a strong phenomenon appears on the Fermi surface.The impurity peak,the peak value is about 2.6e V.The narrowing of the band gap（2.4e V）of Ru-doped Mo O2 significantly exceeds the change of Ru-doped Ti O2,which is different from the downward shift of the conduction band of Ru-doped Mo O2 and Sn O2.Ru-doped Ti O2 has an impurity peak near the Fermi level,thus Reduce the band gap and increase the transition probability of photogenerated electrons.Single-doped Ru and co-doped N-Ru,and Ru4d electrons in the density of states map have higher peaks near the Fermi surface,and the effect of doping is obvious.In the Sn O2 system,the density of states has a continuous peak near the Fermi level,and the maximum peak is Increased from 2.6e V in single doping to about 4.8e V,introducing impurity levels.The doping effect of N2p electrons is only more obvious in Sn O2 materials.A peak of about 3.0 e V appears at the Fermi level,which promotes the incorporation of Ru4d.Therefore,the N-Ru co-doped Sn O2 exhibits strong metallic properties.Sex is weakened.After N-Ru co-doping,Mo O2 also has a metallization trend.3.Optical propertiesThe surface of the material undergoes an oxidation-reduction reaction with gas molecules,electrons are transferred,and the density of states changes,which is reflected in a macroscopic change in optical properties.When undoped,in the visible light range of 400-760nm,the imaginary part of the dielectric function of the（110）surface of Ti O2and Mo O2 after adsorbing HCl gas shows an increasing trend,and the increase of Mo O2is more than that of Ti O2,at 760nm A peak of 4.0 is reached.After HCl gas is adsorbed on the（110）surface of Mo O2,the absorption coefficient shows an increasing trend in the entire visible light range.In the blue-violet light range,it increases from 25,000 to 50,000.The increase is more obvious than that of Ti O2.It has better properties as a gas sensor substrate.Great.In the range of 500-760nm,the reflectance before and after Ti O2 adsorbs HCl gas changes significantly,and the maximum value changes from 0.1 to about 0.3.After Ti O2 adsorbs HCl gas,it shows good responsiveness to red-orange light.After single Ru doping,in the light wave range of 400-760nm,the imaginary part of the dielectric function of Ru doped Mo O2（110）surface after adsorption of HCl gas shows an increasing trend,and the increase rate is faster than that of undoped,The peak value is larger,from the original about 4 to about 40,the sensitivity to blue-violet light is better than that when it is not doped.After Ru-doped Sn O2 adsorbs HCl gas in the range of 500-760nm,its reflectivity changes from a stable below 0.1 to an increase from 0.1 to 0.4,and the growth rate is obvious,and it stabilizes at about 0.4 in the range of 600nm-760nm.Although the co-doping of N-Ru makes Mo O2 and Sn O2 show better optical properties,the surface of Mo O2 and Sn O2 on the density of states diagram of the two have metallization characteristics,and they are no longer suitable as gas-sensitive sensing materials.In summary,（1）Mo O2 system has better sensing performance to blue-violet light after HCl is adsorbed on undoped and Ru single-doped;（2）Ru single-doped Sn O2 has the best response to red-orange light after HCl is adsorbed（3）N-Ru co-doped Mo O2 and Sn O2 show strong metallicity,and the semiconductivity is weakened.It is not suitable as a gas-sensing material for HCl.N-Ru co-doped Ti O2 exhibits high absorption and low reflection characteristics for visible light as a whole.The best sensing performance. |
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