Theoretical Study Of BaTiO₃ Piezoelectric Photocatalytic Degradation Of Volatile Organic Compounds

With the acceleration of urbanization,the consumption of natural resources has caused many environmental problems while people’s living quality has been improved.As an essential environmental factor for human survival,the pollution of the atmosphere has seriously harmed human health.Volatile organic pollutants（VOCs）in the atmosphere have attracted much attention because of their toxicity and volatility.Therefore,it is urgent to develop new and efficient pollution control technology.Photocatalytic technology can use solar energy to decompose various organic pollutants at room temperature,and can play a role in the field of environmental pollution,but the relatively low quantum efficiency limits the development of this technology.Many methods have been used to improve the quantum efficiency of photocatalysis.The piezoelectric effect can form an internal electric field in the material due to its principle of action,thus enhancing the separation and migration efficiency of charge carriers in the process of photocatalysis,which has a good application prospect for the improvement of photocatalysis.As a typical lead-free piezoelectric material,barium titanate has attracted wide attention due to its excellent piezoelectric properties and similar photocatalytic properties to titanium dioxide,which may have a good development prospect in photopiezoelectric co-catalysis.In this paper,Density Functional Theory（DFT）was used to study the influence of CASTEP module on the piezoelectric effect in the photocatalytic process of barium titanate,as well as the piezoelectric performance and photocatalytic performance after doping.（1）It is of great significance to explore the microscopic mechanism of photopiezoelectric synergy.Therefore,barium titanate,a typical material,was selected to study its structure and electronic properties under different strains in order to understand its synergistic mechanism.It is found by calculation that the variation trend of Ti O₂bond length and band gap is the same under the compressive strain condition,but opposite under the tensile strain condition,and there is a turning point between 6%and 7%.Subsequently,the effect of the piezoelectric process on the adsorption efficiency of volatile organic compounds（VOCs）on the surface of BaTiO₃was measured,and it was found that the optimum strain range for formaldehyde,oxygen,acetone and hydroxyl was the same.In addition,in the range of deformation rate of7%～12%,the relationship of deformation rate,electronic structure and adsorption energy was studied,and the best catalytic effect was obtained.The results of charge density difference and Born effective charge reveal the synergistic mechanism of piezoelectric photocatalysis.The internal electric field generated by polarization enhances the separation of charge and the aggregation of surface charge,which enhances the adsorption of VOCs on the surface of piezoelectric materials,and is conducive to the subsequent photocatalytic degradation.（2）Considering that the piezoelectric effect on the band gap adjustment range of the material is limited,we modified the material by doping substitution method.In this part,we first studied the influence of different metal elements on the change of band gap,the change of piezoelectric properties and the adsorption performance of formaldehyde molecules after the adulteration of titanium atoms in tetragonal barium titanate.Secondly,we studied the influence of stress changes on the formaldehyde adsorption performance of the system under different doping systems.The results show that the doping of V,Mn,Fe,Co and Ni can effectively reduce the band gap and improve the photoelectron absorption range of the material.Doped with different elements,the oxygen octahedron of barium titanate is distorted in different degrees and directions.The doping of Fe can enhance the adsorption of formaldehyde,and under the tensile strain condition,compared with other element doping,the doping of Fe can significantly enhance the adsorption of formaldehyde molecules,and the adsorption of formaldehyde molecules is weakened under the compressive strain.In addition,the doping of Fe can enhance the polarization intensity of the system.Therefore,the doping of Fe can be used to improve the photocatalytic band gap of materials and enhance the piezoelectric properties of materials,and further enhance the photopiezoelectric synergistic effect,which can further improve the catalytic performance of materials for VOCs.