Construction Of Defective Perovskite-BiOCl Heterojunctions And Their Photocatalytic Nitrogen Fixation Performance

Photocatalytic technology can make full use of solar energy to reduce nitrogen to ammonia.Common photocatalysts such as Ag₂CO₃,Cd S,which had showed shortcomings such as decomposition and toxicity.Perovskite with high stable structure and excellent dielectric properties had become one of the hot spots.The crystal structure of CaTiO₃is similar to that of typical perovskite crystals.Eight regular octahedral TiO₆units surround calcium ions to keep it chemical bonds in a stable state.La₂TiO₅is a typical perovskite-like mineral possessed not only the structure and advantages of perovskite,but also more reactive sites.However,the wide bandgap values of the above two materials(Eg_（CaTiO3）=3.62 e V,Eg_{（La2TiO5）}=3.87 e V)brought a negative impact on the efficiency of photocatalytic ammonia synthesis.For this reason,the modification treatment of perovskite is particularly important.Defect engineering can effectively broaden its spectral response range,construction of heterojunctions can easily help the electron transitions.The synergistic effect of the above two is of great significance for the improvement of photocatalytic nitrogen fixation activity.In this paper,the heterojunction was constructed after defect engineering of CaTiO₃and La₂TiO₅nanomaterials,which not only successfully regulated the energy band position,but also inhibited the recombination of photogenerated electrons and holes.The research contents are as following:1.Construction of defective CaTiO₃-BiOCl heterostructures and research on photocatalytic nitrogen fixation performance:CaTiO₃（CTO）was prepared by sol-gel method,which were mixed with Na BH₄in Ar atmosphere to obtain defective CaTiO₃（R-CTO）.Then defective CaTiO₃-BiOCl heterojunction was obtained via hydrothermal method.The photocatalytic test results showed that the photocatalytic nitrogen fixation efficiency of R-CTO after the defect was significantly improved,and the efficiency of the sample（CTO-60-B-2）was about 1.43 times that of defective CaTiO₃（CTO-60）.This study demonstrated that the presence of defects and the formation of heterojunctions enhanced the photocatalytic nitrogen fixation activity of CaTiO₃.2.Construction of defective La₂TiO₅-BiOCl heterojunctions and study on photocatalytic nitrogen fixation performance:Defective La₂TiO₅（R-LTO）and defective La₂TiO₅-BiOCl heterojunctions（LTO-400-B）were obtained by sol gel method and hydrothermal method.The photocatalytic experimental results indicated that LTO-400 showed the best photocatalytic activity in the defective La₂TiO₅（R-LTO）,with ammonia production rate of158.13μmol·g^-1·h^-1.The photocatalytic nitrogen fixation performance of heterojunction（LTO-400-B-4）was also slightly improved compared with LTO-400,which suggested that either surface defects or the formation of heterojunctions could improve the efficiency of La₂TiO₅photocatalytic synthesis of ammonia.In this work,we constructed heterogeneous photocatalysts with surface defects by using defective CaTiO₃,defective La₂TiO₅and BiOCl to obtain LTO-400-B-4 and CTO-60-B-2.Without the addition of cocatalysts,LTO-400-B-4 and CTO-60-B-2 already possessed efficient photocatalytic nitrogen fixation performance,which laid an experimental foundation for developing the new application of modified perovskite-based materials.