Construction Of Bismuth Oxide Halide Based Photocatalytic System And Its Performance Of Visible Light Driven Degradation Of Pollutants

With the rapid development of industry,water bodies have been seriously polluted.Semiconductor photocatalytic technology has attracted widespread attention because it does not need to add additional chemicals in the treatment of pollutants in water,has the advantages of green,efficient,simple operation,low cost and so on.As a new visible light driven bismuth based photocatalyst,bismuth halide oxide has positive valence band potential,non-toxic,good stability and other advantages,become a good candidate material for photocatalytic water treatment technology.However,pure BiOX（X=Cl,Br,I）limited its photocatalytic activity due to its shortcomings such as narrow visible light absorption range and low carrier separation efficiency.By constructing a new bismuth halogen-based photocatalytic system to improve these shortcomings,the research on improving the performance of visible light catalytic degradation of pollutants has become a hot spot.In this paper,BiOX was used as a photocatalytic material for water purification.Aiming at the key factors limiting the photocatalytic activity of BiOX,a variety of modification methods including bismuth enrichment strategy,defect engineering,heterojunction construction,solid solution formation,surface modification and internal electric field（IEF）tuning were adopted to improve the performance of BiOX for photocatalytic degradation of pollutants.At the same time,considering the design and synthesis of bismuth oxide halide based materials and the coordination of multiple modification,the main research contents are as follows:（1）Bi₅O₇I with rich oxygen vacancies was prepared by calcination-alcoholic thermal method and Perylene diimide（PDI）was prepared by substitution reaction.According to thermodynamic calculation and analysis,under inducing of acetic acid,PDI molecules were on the Bi₅O₇I surface successfully self-assembled through strongπ-πstacking with the form of face-to-face,and the structure of bismuth-rich Bi₅O₇I was maintained.The hybrid system of Bi₅O₇I-OVs/PDI was successfully constructed,and the self-assembly mechanism of PDI molecules on the surface of Bi₅O₇I induced by acetic acid was proposed.Under visible light irradiation,the degradation activity of Bi₅O₇I-OVs/PDI hybrid system to organic pollutants was significantly improved.The increased activity was attributed to the enhanced visible light absorption of Bi₅O₇I by the introduction of oxygen vacancy,and Bi₅O₇I-OVs/PDI hybrid system forms a traditional type I heterojunction,which improves the separation efficiency of photogenerated carriers.（2）First,the surface of carbon quantum dots（CQDs）was functionalized by nitrogen doping,and the introduced carboxyl group and amino group bonded with Bi atoms in the bismuth precursor to provide an in-situ growth site for BiOI_xBr_1-x,thus achieving the rapid synthesis of N-CQDs decorated BiOI_xBr_1-x solid solution layered microspheres.The strong binding between BiOI_xBr_1-x and N-CQDs is conducive to charge transfer.Under visible light irradiation,N-CQDs/BiOI_0.25Br_0.75 presented the remarkable photocatalytic activity when the loading amount of N-CQDs was 1.25 wt%.The removal rate of phenol and tetracycline hydrochloride was 98.7%within 3 h and 96.6%within 5min,respectively.The increased activity was attributed to the suitable energy band structure of the BiOI_0.25Br_0.75 solid solution,the multiple scattering absorption of light between the laminated nanosheets and the good electron collection ability of N-CQDs.（3）By designing the chemical reaction and analyzing the molten salt phase diagram,By designing the chemical reaction and analyzing the molten salt phase diagram,a solvothermal alkali assisted molten salt method was developed for the staged crystal reforming of BiOI,and the tetragonal BiOBr_xI_1-x,monoclinic Bi₄O₅Br_xI_2-x and Bi₄O₅Br_xI_2-xC_y solid solutions were obtained successively.The molten salt with the properties of engineering thermal conductivity fluid and ionic liquid promotes the synchronous bismuth-rich and carbon homogeneous doping of BiOBr_xI_1-x at low temperature.Due to the change of unit cell structure,the strong local dipoles were formed,the internal electric field between alternating atomic layers was significantly enhanced.The photogenerated electrons and holes of Bi_2.8C_1.2O₅Br_0.5I_1.5 were confined to the[Bi_2.8C_1.2O₅]²⁺layer and the double[Br_0.5I_1.5]-layer,respectively,and resulted to effective separation of charge carriers in the bulk.Under visible light irradiation,the removal rates of phenol,4-chlorophenol,resorcinol and hydroquinone were all 100%in 1h.Within 2h,the removal rates of p-nitrophenol,2,4-dinitrophenol and catechol were68.8%,83.3%and 96.1%,respectively.Photocatalytic degradation of phenol conforms to the"parallel"attack mechanism of·O₂^-and h⁺.