Study On The Defect Modulation And Light Absorption Property Change Of Transition Metal Oxides Induced By The Interfacial Reaction

Transition metal oxides（TMO）are widely used in the field of light-energy conversion and play important roles in solving the current energy shortage and environmental pollution problems.However,wide-bandgap TMO are only able to absorb UV light in the solar spectrum,which severely limits the utilization of solar energy.To broaden the absorbable spectral range of TMO materials,a solid-phase interfacial reaction-induced TMO defect modulation method is developed in this study to achieve the efficient preparation of multi-species and cross-scale modified TMO materials,and the method can broaden the absorbable spectral range of TMO to the visible and near-infrared regions,thus significantly improving the utilization of solar energy.Through the experimental characterization and simulation of the TMO/metal interfacial reaction process,the steps and laws of the interfacial reaction are clarified at the atomic scale,and the mechanism of TMO defect regulation induced by the interfacial reaction is revealed.By characterizing the crystal structure,electronic structure,and light absorption performance of modified TMO and simulating the interfacial reaction process,the correlation between interfacial reaction,crystal defect,electronic structure,and light absorption performance is explained,which provides the theoretical basis and technical guidance for the controllable preparation of modified TMO with excellent light absorption performance.The solid-solid and solid-liquid types of TMO/metal interfacial reaction experiments were designed to investigate the interfacial reaction-induced TMO defect modulation process.Firstly,the interfacial characteristics and interfacial reaction process between wide-bandgap ZrO₂ and active metal Tiwere investigated by first-principle calculations,and it was found that the ZrO₂/Tiinterfacial reaction process mainly consists of two steps,which are oxygen in ZrO₂ going through the interface and combining with metal to form compounds and oxygen in ZrO₂ migrating to the interface.Then,the interfacial reaction experiments of ZrO₂ with solid or liquid active metal were implemented.ZrO₂and metal remained separated from each other after the solid-solid interfacial reaction,which is more suitable for the engineering applications of TMO defect regulation.Based on the interfacial reaction simulation and experiments,it is found that two conditions are needed for the preparation of modified ZrO₂ using ZrO₂/Tiinterfacial reaction.One is establishing a contact ZrO₂/Tiinterface to provide a channel for oxygen transport,and the other is building a high-temperature vacuum environment to ensure the stability of active metal and modified ZrO₂ at high temperature and accelerate the interfacial reaction.Finally,the TMO/Tiinterfacial reaction was used to modify TiO₂,ZnO,MoO₃,WO₃,and CeO₂,achieving the strong absorption of visible and near-infrared light.The above results demonstrate that the defect modulation process induced by the interfacial reaction proposed in this paper has the advantages of high modification efficiency,simple process,and wide applicability.The defect modulation method based on TMO/Tiinterfacial reaction was used to modify ZrO₂ with wide-bandgap and high oxygen ion conductivity at high temperatures（900℃-1200℃）,and the results showed that the color of ZrO₂ gradually deepened and the light absorption performance gradually increased with the increase of reaction temperature.Black ZrO₂ was successfully prepared at 1100℃,and its band gap was reduced from 5.47 e V to 1.38 e V.Moreover,the black ZrO₂ particles have a core-shell structure with a high concentration of oxygen vacancy（V_O）and Zr³⁺defects in the core region.By comparing the calculation results of the defective ZrO₂ model with the characterized results of black ZrO₂,it is clear that black ZrO₂ contains not only high concentrations of V_O but also low concentrations of interstitial zirconium(I_Zr)defects,which lead to the generation of Zr³⁺.In addition,both V_O and I_Zr defects can narrow the bandgap of ZrO₂ and thus improve its light absorption performance.Moreover,V_Odefects in ZrO₂ play a dominant role in the absorption of short-band visible light,while I_Zr defects promote the absorption of long-band visible and near-infrared light.As a photothermal reagent,black ZrO₂ can kill more than 50%of He La cells after near-infrared light irradiation for 10 min,indicating that it has excellent photothermal therapeutic properties.The electrical and thermal conductivity of black ZrO₂ is lower than that of pristine ZrO₂,and it can remain stable in air or water at room temperature for a long time（400 days）.The modification of TiO₂ with wide-bandgap and low oxygen ion conductivity was also studied at high temperatures（900℃-1100℃）by a defect modulation method based on the TMO/Tiinterfacial reaction,and the results showed that the color gradually deepened and the light absorption performance gradually enhanced as the reaction temperature increased.The molecular dynamics simulation of the interfacial reaction of TiO₂/Tishows that only a few nanometers thick of TiO₂ immediately adjacent to the interface loses oxygen,forming a TiO₂ reduction region with high defect concentration.It infers that the modified TiO₂ produces crystal defects only in the surface region,resulting in a core-shell structure different from that of black ZrO₂.The experimental results show that the bandgap of TiO₂ can be reduced from 3.27 e V to 2.73 e V using the TiO₂/Tiinterfacial reaction,resulting in the preparation of blue TiO₂.Blue TiO₂contains higher concentrations of V_O and Ti³⁺defects,and its light absorption performance and photocatalytic activity for hydrogen evolution are significantly higher than that of pristine TiO₂.Additionally,blue TiO₂ can be stable in air or water at room temperature for a long time（400 days）.Based on the study of the defect regulation of the two types of wide-bandgap TMO,the interfacial reaction experiments and molecular dynamics simulations of different TMO/metal interfacial systems reveal the mechanism of interfacial reaction-induced TMO defect regulation.The interfacial reaction firstly causes TMO to lose oxygen as well as generate V_O defects,and then produces other types of crystal defects or even induces phase transitions as the concentration of V_O defects increases.The difference in oxygen ion conductivity of TMO leads to two reaction modes with the active metal.One is the TMO with high oxygen ion conductivity,such as ZrO₂,which loses oxygen in the whole lattice structure during the interfacial reaction.And the crystal defects are uniformly distributed in the modified TMO,in which the oxygen loss rate of modified ZrO₂ is about 5%.The other is the TMO with low oxygen ion conductivity,such as TiO₂,which only has an oxygen loss region with the thickness of a few nanometers during the interfacial reaction.And the modified TMO particles have a core-shell structure,in which the oxygen loss rate in the shell region of modified TiO₂ is about 40%.In addition,the modification effect of TMO not only depends on the number of crystal defects introduced by the TMO/metal interfacial reaction but is also affected by the distribution of crystal defects.The TMO/metal interfacial reaction method is more effective in modifying TMO when the oxygen density of the TMO is lower,and the V_O density and oxygen conductivity are higher.