| The increasingly severe environmental pollution has caused an immeasurable impact on life and production,especially water pollution.In order to solve these problems,green pollution treatment technology has attracted much attention,and photocatalytic technology has been extensively studied.Among many photocatalytic materials,titanium dioxide has become the most popular photocatalytic material due to its non-toxic,stable,readily available and inexpensive advantages.Ti O2exists mainly in three polymorphs in nature,anatase,rutile,brookite,and Ti O2（B）,among which the anatase phase has good photocatalytic properties.In subsequent studies,it was found that the composite phase structure of anatase and Ti O2（B）is better photocatalytic than anatase,but the absorption of visible light by dual-phase Ti O2is as bad as that of anatase,and the carrier problems such as compounding speed are yet to be resolved.Due to the lack of theoretical research on dual-phase titania materials,this paper studies the optoelectronic properties,interface properties and catalytic mechanism of dual-phase titania through first-principles,and through the dual-phase titanium dioxide composite metal to reduce the carrier recombination,increase its photocatalytic properties.（1）Calculate the optoelectronic properties of the anatase（space group I41/amd）and the Ti O2（B）（space group C2/m）,and calculate the energy band structure and optical properties of the two materials,which are consistent with the previous calculation results,and it is concluded that the calculation method is feasible.Then take the vacuum layer calculation for the single cell material,and then take the vacuum layer calculation for the single supercell,which provides a single-phase model for the study of dual-phase titanium dioxide.It was found that after the material changed from three-dimensional to two-dimensional,there is some decrease in the absorption index due to material thickness,etc.The overall absorption of single-phase titanium dioxide is not very good,at the wavelength of 370nm-700nm,anatase has a stronger ability to absorb light,and at a wavelength of 100nm-370nm,Ti O2（B）has a better relative light absorption ability.From the distribution of sunlight energy,it can be found that anatase is naturally The environment is a better photocatalytic material.（2）A dual-phase titania structure composed of anatase and Ti O2（B）was constructed,and it was found that the material structure was the most stable when the distance between the two phases was 4.0（?）,and the band gap was 1.83 e V.And calculated its optoelectronic properties,it is found that the optical absorption peak of dual-phase titanium dioxide at100nm-780nm is 58%higher than that of the single phase,and no significant increase in visible light region compared to single phase.Through the analysis of the two-phase interface,it is found that a small amount of electrons are transferred from the anatase phase to the Ti O2（B）phase.In the anatase phase,the charge density at the interface is small,and the charge density is large away from the interface,while the charge distribution in the Ti O2（B）phase is uniform.In the dual-phase titanium dioxide structure,there is interphase charge transfer,which makes the recombination of holes and electrons slow down,and the carriers can stay on the surface of the material for a longer time to generate redox reactions and catalyze the decomposition of organic pollutants.（3）By combining metal Pt,Ag,and Au atomic chains in the dual-phase titanium dioxide,the carrier transmission path is changed,the time of the carriers staying on the surface of the material is prolonged,and the optoelectronic properties of the composite metal titanium dioxide material are calculated.First,the spatial position of the atomic chain was studied,and it was found that the material was the most stable when the atomic chain was in the middle of the two phases and at the phase interface.Next,we explored the optimal distance between the metal and the interface and found that the Pt atomic chain was closest to（2.1（?））,while the Ag atomic chain was the farthest（3.3（?））.The charge density of anatase O atoms at the two-phase interface becomes smaller after the metal atom chain is placed,and the charge is transferred to the metal atom chain at the interface.From the density of states,it is found that there is an electronic transition from the anatase phase to the metal at the interface.In the optical calculation,it is found that the absorption effect of the dual-phase titanium dioxide composite metal material has more than doubled in the visible light region,and has increased dozens of times in the 500nm-780nm region,and also has a certain absorption in the infrared region.Among the three metal composites,the Pt composite works best in the visible light region.After the composite metal material,the photocatalytic efficiency of the material has been significantly improved,and the disadvantage of poor absorption in the visible light region of titanium dioxide has been improved. |
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