Reactive Species-Dependent Photocatalytic Activity Of Bismuthoxyhalides

Environmental pollution and resource shortage have become the main limiting factors for the development of today’s society,and the industrialization process is accelerating,resulting in increasingly severe problems.As a representative of new energy,solar energy has broad development space.Photocatalysts cleverly convert solar energy into chemical energy,which is not only safe and clean,but also cheap and efficient,gradually attracting the attention of researchers.As a unique photocatalyst,bismuth based catalyst material not only has a suitable band structure,but also stable and non-toxic physical and chemical properties,The influence of anisotropy makes layered structures more prone to the separation of photo generated electron holes.As of now,there is a lack of horizontal mechanism analysis on the differences in the performance of BiOX catalysts and their corresponding halogen rich bismuth catalyst materials in reducing activated CO₂.This article uses hydrothermal and ionic liquid combustion methods to synthesize nano BiOCl photocatalysts,and ionic liquid combustion methods to synthesize Bi₃O₄Cl,Bi₂₄O₃₁Cl₁₀,and BiOCl photocatalysts.Various factors affecting reduction ability and CO₂activation are studied,and their photocatalytic mechanisms are obtained through comparison.In this work,BiOCl（O-BiOCl）prepared by ionic liquid combustion and BiOCl（S-BiOCl）prepared by hydrothermal method were used for CO₂reduction tests,and a series of characterization comparisons showed that the CO₂reduction activity of BiOCl by ionic liquid combustion was stronger,and the O-BiOCl catalyst showed a significant upward shift of conduction band sites and valence band sites,and the forbidden band width decreased.BiOCl showed 1.4 times higher CO₂reduction performance than that of S-BiOCl,and it was determined that the current separation efficiency and the conduction band position were the determining factors for CO₂reduction.The higher the photogenerated carrier separation efficiency,the higher the conduction band position and the more negative the potential,the higher its CO₂reduction activity.Based on the first experiment,the variables were controlled and the bismuth-rich materials with higher carrier separation efficiency were compared with BiOCl,and Bi₃O₄Cl,Bi₂₄O₃₁Cl₁₀and BiOCl were prepared by ionic liquid combustion method to continue the in-depth study of the factors affecting the CO₂reduction activity.Through a series of tests,it was concluded that the photogenerated electron-hole separation efficiency:Bi₂₄O₃₁Cl₁₀>Bi₃O₄Cl>BiOCl;conduction band position:BiOCl>Bi₂₄O₃₁Cl₁₀>Bi₃O₄Cl;forbidden band width:BiOCl>Bi₃O₄Cl>Bi₂₄O₃₁Cl₁₀;activity of reducing CO₂:BiOCl>Bi₂₄O₃₁Cl₁₀>Bi₃O₄Cl.The rate of CO₂reduction by BiOCl is 3.44 and 1.93 times higher than that of Bi₃O₄Cl and Bi₂₄O₃₁Cl₁₀,respectively,which proves that the determining factor affecting the activity of CO₂reduction is the conduction band position,and the higher the conduction band position,the more negative the potential,the higher the rate of CO₂reduction.To further investigate the mechanism of the three catalysts Bi₃O₄Cl,Bi₂₄O₃₁Cl₁₀and BiOCl in the degradation of Rh B,experiments were carried out and it was concluded that the active species affecting their rate of Rh B degradation were superoxide radicals（·O₂^-）and vacancies（h⁺）,and the most dominant active species of BiOCl was vacancies,and the oxygen vacancies contributed to the·O₂^-formation.Based on the characteristics of BiOCl,such as the lowest photoelectron-hole separation efficiency,the least·O₂^-,the least oxygen vacancies,the higher degradation performance,and the low position of the valence band,it was concluded that the lower the valence band position,the more positive the value,the higher the oxidation capacity of the cavities.