Controllable Synthesis Of Two-dimension Bismuth Oxyhalides Photocatalysts And Study Of Photocatalytic Phenolic Pollutants Abatement Performance

Northern region of Shaanxi is rich in coal resources,and the semi-coke industry,which relies on coal resources,has become the pillar-industry of the economy.The wastewater produced by this process poses a threat to the safety of fresh water resources because of its toxic and harmful components and high concentration.Compared to the traditional methods,photocatalytic oxidation technology has the advantages of low cost,mild reaction conditions and relatively thorough reaction.Photocatalytic degradation and removal of harmful phenolic substances from semi-coke has become a hot topic in the field of environment and catalysis.In this paper,a controlled preparation of two-dimensional bismuth oxide-based photocatalysts was used to degrade phenol-containing wastewater.The catalytic activity of bismuth oxyhalide based materials were enhanced by means of composition control,transition metal phosphide（TMPs）loading and oxygen vacancy modification.The enhancement mechanism of multi-effect synergistic effect and catalytic reaction mechanism of the modified systems were revealed by means of surface spectroscopy,photoelectrochemical characterizations and experimental testing.The main contents of this dissertation are summarized as follow:（1）BiOCl,BiOBr,BiOI,Bi₄O₅Br₂,Bi₂₄O₃₁Br₁₀ and Bi₃O₄Br photocatalysts with the same two-dimensional nanosheet structure were prepared based on the composition control strategy of halogen species and stoichiometric ratio of bismuth oxyhalide.The results show that the chemical composition of catalysts can significantly affect the absorption range,redox potential and charge separation characteristics of bismuth oxyhalide material,and then affect its photocatalytic activity.Among them,Bi₄O₅Br₂ and Bi₃O₄Br showed better catalytic degradation of bisphenol A under visible light due to their relatively narrow band gap,higher oxidation capacity and putstanding charge separation performance.（2）A series of different concentrations of TMPs/Bi₄O₅Br₂（TMPs:Ni₂P,Co₂P,Ni Co P）composite photocatalytic materials were prepared by liquid phase assembly method,which can effectively enhance the oxidation and degradation efficiency of wastewater such as bisphenol A,phenol and p-nitrophenol,etc.The degradation rate of bisphenol A was 86.1%over 15%Ni Co P/Bi₄O₅Br₂ under visible light for 60 min,and the reaction constant rate was 3.11 times higher than that of Bi₄O₅Br₂.It was found that TMPs loading significantly enhanced the light absorption and charge separation efficiency of the catalyst.In addition,the captured experiments,ESR test and NBT degradation showed that the main active species of pure Bi₄O₅Br₂ in the reaction was photogenerated hole（h⁺）,and the active species of TMPs/Bi₄O₅Br₂ composite system were h⁺andsuperoxide radical（·O₂^-）,and the concentration was significantly higher than that of monomer.Binding band structure and XPS charge transfer analysis showed that TMPs/Bi₄O₅Br₂ exhibits a particular Z-scheme charge transfer mechanism.Therefore,the photocatalytic activity can be effectively enhanced by utilizing the multi-functional promoting effect of TMPs:broadening the range of light utilization,enhancing the utilization efficiency of photogenerated charge separation,and increasing the concentration of active species.（3）In order to enhance the activation and utilization efficiency of oxygen in the aerobic oxidation degradation process of phenol-containing wastewater,Bi₃O₄Br-OVs photocatalysts with different oxygen vacancies（OVs）concentration were prepared by hydrothermal method using glycerol（GLY）and polyvinylpyrrolidone（PVP）as surfactants.Furthermore,Ni₂P/Bi₃O₄Br-OVs composite was obtained by the combination of transition metal phosphates.The synergistic effect of Ni₂P and OVs was used to enhance the photocatalytic activity of the materials.The main mechanisms of reaction are as follows:（1）The introduction of OVs can reduce the band gap energy of Bi₃O₄Br,and Ni₂P can broaden the spectral response range of the composite material.The synergistic effect of the two parts can improve the absorption and utilization of visible light.（2）The defect level of oxygen vacancy can be used as electron capture center to effectively inhibit photogenerated charge recombination,and the Z-scheme charge transport mechanism formed by Ni₂P/Bi₃O₄Br-OVs composite system is more conducive to promote the system charge separation,thus improving the utilization efficiency of photogenerated electrons and holes of the catalyst.（3）Both OVs and Ni₂P can be used as oxygen activation sites to form a"two-channel"·O₂^-generation pathway.Combined with the Z-scheme charge separation mechanism,the concentration of·O₂^-and h⁺can be greatly promoted,and the visible light degradation efficiency of phenolic pollutants can be synergistically enhanced.