The Effect Of TiO₂ Surface And Surface Impurity On CO Gas Sensing Characteristics

At present,a variety of technologies have emerged,and there is still a lot of room for development in gas detection technology.This detection method has become an important gas detection technology,which is favored by the majority of researchers.The absorption of gaseous molecules on the surface of the material changes its optical properties.Therefore,the sensing properties of materials for environmental gas analysis can be reflected by the changes of optical properties,which is called optical gas sensing characteristics.At present,semiconductor materials such as TiO₂,SnO₂and ZnO are mainly used as optical gas sensing materials.Among them,ZnO is one of the earliest semiconductor gas sensitive materials.Because of its cheapness,non-toxicity and high temperature resistance,It is mainly used in air purification,sewage treatment and gas sensors.However,because the band gap of TiO₂ is relatively wide and only absorbs ultraviolet light with a wavelength of less than 400nm,researchers have changed its activity by doping materials to expand the light response range and make it redshift.For example,when nonmetallic N is doped,the hybrid of N2p orbital electrons and O2p orbital electrons narrows the bandgap and enlarges the absorption of visible light.In addition,the doping of metal ions(such as Fe³⁺)can introduce defect sites on the surface of materials.The energy of impurity electron transition under light is less than the band gap of TiO₂,and the concentration of impurity electron is more red-shifted than that of TiO₂.In order to further explore the surface properties of TiO₂ materials,In this paper,the rutile TiO₂?110?and anatase TiO₂?101?surfaces are calculated by plane wave ultra-soft pseudopotential method based on density functional theory.The main calculation contents are as follows:?1??1?The electronic structure of rutile TiO₂?110?surface is studied.The rutile?2 x 1?supercell model is established in MS software.Surface energy and optical properties were calculated respectively after structural optimization.?2?he optical properties of rutile TiO₂?110?were calculated.Establishment of?3 x 3 x 2?supercell model and cut out?110?surface.C-terminal adsorption of CO molecule was carried out by introducing oxygen vacancies of different concentrations on the surface.The intrinsic surface adsorption energy,fractional density of states,charge population and optical properties were calculated.Results show the defect of oxygen vacancy on the surface makes the optical properties of the material surface change.The CO gas is adsorbed to a certain extent.?3?Comparing the characteristics of rutile TiO₂?110?surface,The surface binding energy,surface adsorption energy,charge distribution,differential charge density,electronic fractional density of States and optical properties of CO molecule adsorbed on anatase TiO₂?101?surface have also been calculated.The results show that the optical properties of anatase TiO₂?101?surface for CO adsorption are better than rutile TiO₂?110?surface.?4?In order to further optimize the adsorption characteristics of anatase TiO₂?101?surface,The adsorptive properties of the surface were changed by doping transition metals.Considering that the radius of Cu,Sc,Cr and V atoms is close to that of Ti atoms and the electron instability of 4S¹ atoms of Cu and Cr atoms,impurity atoms are selected.The results show that anatase TiO₂?101?surface is more stable than rutile TiO₂?110?surface.After doping metal Cu,Sc,Cr and V on the surface of oxygen vacancy and the surface of oxygen vacancy,By calculating and comparing the surface energy,The doping of impurities reduces the band gap of the surface and improves the CO adsorption of the material,and the doping of Cu and Cr is the most stable.From the analysis of charge transfer,the contribution of impurities to oxygen vacancy oxidation of the substrate is as follows:Cu>Cr;By means of density of States and optical properties analysis,CO molecule adsorbed on the surface of oxygen-containing vacancy TiO₂?101?doped with Cu and Cr improves the response of the material in visible light range compared with the surface of oxygen-free vacancy TiO₂?101?.The doping of Cu and Cr improves the optical gas sensing performance of CO adsorbed by materials obviously.It is a good method to improve the optical gas sensing performance of materials.