Preparation Of Bismuth Oxynitrate And Bismuth Molybdate And Regulation Of Photocatalytic Degradation Performance

The built-in electric field produced by Aurivillius layered bismuth oxynitrate and bismuth molybdate,which endows them with excellent photocatalytic performance.This electric field can effectively transfer and separate the charge.Therefore,both are widely used in the photodegradation of organic molecules in industrial sewage.However,the structure of bismuth oxynitrate,bismuth molybdate photodegradability tuning by surfactants and Nd³⁺-doped have not been studied yet.This work is based on the above research background,the photodegradation performance of bismuth oxynitrate and bismuth molybdate is tuned by hydrothermal method,experimental characterization and first-principles calculation.The main results are listed as below.（1）Bi₅O₇NO₃transformed from orthorhombic system Bi₅O₇Br into triclinic symmetry using nitrate radical（NO₃^-）to occupy Br sites.Negative formation enthalpy and positive phonon frequency denoted its structural stability.The substitution concentration of nitrate strongly affects the electronic structure of bismuth oxynitrate.Only when NO₃^-completely occupies the Br position can a wide and dispersed local band be produced.Double absorption edges are ascribed to electrons transition from valence band（VB）to local band and conduction band（CB）,not from local state of O-doped N sites to CB transfer.Experimentally,triphase heterojunction,pure Bi₅O₇NO₃,and?-Bi₂O₃were synthesized using Bi（NO₃）₃·5H₂O under acidic and alkaline conditions.Under the irradiation of a 250W mercury lamp,the degradation efficiency of the Rhodamine B by three-phase heterojunction and Bi₅O₇NO₃is98.1%and 89.9%,the corresponding reaction rates are higher than that of?-Bi₂O₃and?-Bi₂O₃.In addition,the methyl orange degradation rate of these two samples was about 90%,faster than 77%of?-Bi₂O₃and 86%of?-Bi₂O₃.The enhancement of photocatalysis is mainly attributed to the synergistic effect of morphology,heterojunction,and double absorption edges.Therefore,the in-situ growth method can be used to obtain a highly active bismuth oxynitrate-based photocatalyst,and the internal mechanism is given through first-principles calculation.（2）γ-bismuth molybdate is synthesized using hydrothermal method.Bismuth molybdate is synthesized by hydrothermal method,and the effects of sodium dodecylbenzene sulfonate（SDBS）cetyltrimethylammonium bromide（CTAB）polyethylene glycol（PEG）4000 and 6000surfactants on the crystal structure microstructure and photodegradation activity are studied The effect of surfactants on its crystal structure,microscopic morphology and photodegradation activity is investigated.The Rhodamine B of the samples with CTAB assistance preparation is completely degraded with photodcatalytic efficiency as 100%.The efficiency of the other four samples are 98.3%（no surfactant）,87.2%（PEG4000）,78.1%（PEG6000）,37.6%（SDBS）.The BET and morphology analysis show that the pure phase has the largest specific surface area.The optimal photocatalytic performance may be attributed to the acceleration separation of photogenerated electrons and holes by the heterojunction with the analysis of transmission electron microscopy,photocurrent,and impedance spectroscopy analysis.Thereby more superoxide and hydroxyl radicals are provided.（3）The above method was used to synthesize bismuth molybdate powders doped with different concentrations of neodymium.All samples were pure phase with X-ray diffraction characterization.When the neodymium concentration is 0.5at%,the sample possessed 100%photodegradation efficiency of Rhodamine B after 30 minutes.According to the analysis of morphology,element type,valence state,diffuse reflectance spectroscopy,and photoelectrochemical,the enhancement of photocatalytic performance is mainly attributed to the visible light absorption of neodymium ions and increment of electrons and holes numbers required for redox reaction.