Preparation And Recombination Of BiOX（X=NO₃、I、Cl） Semiconductor Photocatalytic Materials And Their Photocatalytic Performance Semiconductor Photocatalytic

As a novel photocatalyst photocatalytic material,the valence band of bismuth-based photocatalysts is formed by the hybridization of O2p orbitals and Bi6s orbitals.This hybrid orbital is beneficial to enhance the oxidation performance of the catalyst and effectively reduce the width of its forbidden band.In addition,its unique layered structure also improves photogenerated electron–hole separation efficiency.However,bismuth-based semiconductors still have many problems,such as:low visible light utilization rate,high electron-hole recombination rate,immature synthesis method,etc.This article combines the advantages of the precipitation method and the molten salt method to prepare BiOX（X=NO3,I,Cl）and its composite photocatalyst with excellent performance by improving the synthesis method,and using a variety of test methods to characterize the photocatalytic performance and catalytic mechanism of the sample.The conclusions are as follows:（1）Using Bi（NO₃）₃·5H₂O and KNO₃ as raw materials,a sheet-shaped Bi₅O₇NO₃photocatalyst was prepared by precipitation-molten salt method.The effects of precipitation reaction pH,calcination temperature,precursor/molten salt ratio on sample performance were studied.The results show that the high-temperature liquid phase environment provided by the molten salt is beneficial to the uniformity of the reaction and makes the particle size distribution of the sample uniform.At 350℃⁴00℃,the obtained sample was flaky Bi₅O₇NO₃ at about 200 nm;the sample synthesized at 400℃degraded 97.4%of RhB in 20 minutes,which was 1.2 times the photocatalytic degradation efficiency of TiO₂ and 2.46 the degradation rate of TiO₂Times.After five cycles of use,the degradation efficiency of the sample was basically unchanged,showing excellent stability.As the reaction temperature increases,due to the loss of NO and O₂,part of Bi₅O₇NO₃ is converted to Bi₂O₃.The size of the sample also increased sharply.The particle size of the sample increased to about 500 nm at500℃,which caused the photocatalytic performance of the sample to decrease sharply and the degradation rate to drop to 85%.This novel strategy may readily be used to prepare other catalyst materials.（2）In this paper,the photocatalytic performance of Bi₅O₇NO₃/BiOI composite was synthesized and studied for the first time.Based on the preparation of Bi₅O₇NO₃ by the molten salt method,Bi₅O₇NO₃/BiOI composites were formed by controlling the amount of HI solution and reacting with Bi₅O₇NO₃.The samples were characterized by XRD,XPS,EDS and HTEM.The results showed that the Bi₅O₇NO₃/BiOI composite was successfully synthesized.The generated BiOI greatly improves the Bi₅O₇NO₃ light absorption range and reduces the Bi₅O₇NO₃band gap,and BiON_0.4I_0.6 complex has the highest photocatalytic activity.After 120 minutes of light irradiation,its degradation RhB reached 99.4%,and its cycle performance was stable.The Bi₅O₇NO₃/BiOI composite material forms a heterojunction,which can quickly and effectively separate photogenerated electrons and holes,which is the main reason for enhancing the photocatalytic activity of pure phase Bi₅O₇NO₃ and BiOI.（3）Although the photocatalytic performance of Bi5O7NO3/BiOI composite materials is good,the relative specific surface area is not large enough to achieve applicable performance.Based on this,nano-microsphere composites composed of BiOI/BiOCl nano-sheets with high-efficiency visible light catalytic effect were successfully synthesized by a simple one-pot,template-free,hydrothermal method.Among them,in BiOI_XCl_Y,the closer the I:Cl ratio is to 1:1,the thinner and looser the nanosheets in the formed microspheres,the larger the aperture,the more the number of times the light is refracted between the sheets,and the sample is exposed The more active sites in visible light,the better its photocatalytic performance.The widest band gap of BiOCl is 3.27 eV,which makes it difficult for visible light to undergo electronic transitions.With the increase of I^-ions,the band gap of BiOI_XCl_Y gradually decreases,BiOI_0.2Cl_0.8,BiOI_0.4Cl_0.6,and BiOI_0.5Cl_0.5,BiOI_0.6Cl_0.4,BiOI_0.8Cl_0.2 and BiOI have band gaps of 2.26 eV,1.91 eV,1.81 eV,1.77 eV,1.75 eV,and 1.71 eV,respectively.The results show that BiOI/BiOCl recombination will greatly reduce the band gap of BiOCl.After 30 minutes of visible light irradiation,the degradation rate of RhB by BiOI_0.5Cl_0.5 exceeded 97%.After five cycles,the degradation efficiency was still maintained at 94%,and the stability was good.And the photodegradation rate of BiOI_0.5Cl_0.5 is 4.3 times that of pure BiOCl.It is even more surprising that the degradation rate of BiOI_0.5Cl_0.5 is 155times that of pure BiOI/BiOCl composite materials form a heterojunction,which can quickly and effectively separate photogenerated electrons and holes,greatly enhancing the photocatalytic activity of BiOI and BiOCl.