Mechanochemical Preparation Of Bismuth Oxyhalide Materials And Research On Photocatalytic Properties Of Materials

In recent years,photocatalytic technology has achieved rapid development,and has been well applied to the degradation of pollutants in water and the conversion of clean energy.The development potential of this technology is mainly due to the cleanliness of solar energy,abundant reserves and can be used on-site.It is worth noting that,compared with traditional wastewater treatment methods and energy conversion methods,the emerging photocatalytic technology has shown positive industrialization effects and economic effects.As we all know,as a semiconductor material first used in the development of photocatalysis technology,Ti O₂ has two obvious defects:low quantum yield and low energy（solar）utilization rate.The defects limit the practical application range of Ti O₂,and it is necessary to develop a semiconductor catalyst that can have a light response effect in the visible light range.As a new type of bismuth-based semiconductor,bismuth oxyhalide BiOX has caused extensive research due to its suitable band position and special layered structure.Moreover,ternary oxide semiconductors such as BiOX provide favorable conditions for the effective separation of photogenerated electron-hole pairs and the effective transfer of electric charges in the field due to the electric field force of the bismuth-oxygen double layer and the interlayer halogen atoms.In addition to enhancing the activity of the catalyst itself,this advantage provides a prerequisite for the preparation of novel bismuth-rich bismuth oxyhalides.The mechanochemical method provides a new way to prepare bismuth oxyhalide photocatalytic materials with excellent photocatalytic performance.For the preparation of photocatalyst materials,the advantages of this new method are mainly simple operation,short synthesis time,no solvents especially organic solvents,no emissions of pollutants and a high degree of homogeneity of the obtained product particles.Based on the application potential of the above photocatalytic materials,this paper systematically studied photocatalytic performance of bismuth oxyhalide BiOX（X=F,Cl,Br,I）and bismuth-rich bismuth oxyhalide Bi_xO_yX_z（X=Cl,Br）prepared by mechanochemical method in the degradation of organic matter in sewage and energy production,the specific research content is as follows:1.The preparation of pure phase bismuth oxyhalides BiOX（X=F,Cl,Br,I）and bismuth-rich bismuth oxyhalides Bi_xO_yX_z（X=Cl,Br）were studied.Using Bi₂O₃ and Bi X₃（X=F,Cl,Br,I）as raw materials,the optimal preparation conditions were determined to be 700rpm,2h by changing the ball milling time and ball milling,and combining with X-ray diffraction（XRD）pattern.At present,photocatalysts BiOF,BiOCl,BiOBr,BiOI,Bi₁₂O₁₅Cl₆,Bi₁₂O₁₇Cl₂,Bi₄O₅Br₂ and Bi₂₄O₃₁Br₁₀ have been successfully prepared by one-step ball milling using mechanochemical method.Then,the above prepared samples are analyzed by various characterization tests and demonstrated the accuracy of samples components.The tests included scanning electron microscopy（SEM）,X-ray photoelectron spectroscopy（XPS）,ultraviolet-visible diffuse reflectance（UV-vis）,photoluminescence（PL）and electrochemical impedance spectroscopy（EIS）.2.The photocatalytic degradation of organic pollutants in pure phase bismuth oxyhalides and bismuth-rich bismuth oxyhalides were studied and analyzed.The sample degraded the organic compounds ciprofloxacin（CIP）and bisphenol A（BPA）under the excitation of visible light,and combined with active species capture experiments and spin capture-electron spin resonance（ESR）to determine main types of free radicals in the photocatalytic reaction process.According to the results of total organic carbon（TOC）,the organic matter was gradually mineralized,and the photodegradation effect of the photocatalyst on the organic matter was confirmed.The degradation rate of Bi₁₂O₁₇Cl₂ to CIP（10ppm,200m L）reached 83% after photoreaction for 120min,and the degradation rate of Bi₂₄O₃₁Br₁₀ to BPA（20ppm,200m L）to 100%after photoreaction 300min.3.The photocatalytic nitrogen fixation properties of pure phase bismuth oxyhalides and bismuth-rich bismuth oxyhalides were studied and analyzed.It was judged by Nessler’s reagent spectrophotometry whether the sample can convert N₂ in solution into NH₄⁺under the excitation of visible light,The experimental test results showed that the bismuth-rich bismuth oxyhalides had a good effect on nitrogen fixation under visible light.In contrast,the reason why the pure phase of BiOX（X=F,Cl,Br,I）does not have nitrogen fixation ability is due to the difference in the band gap structure of the sample.After 2.5h photoreaction,the concentration of NH₄⁺in the photocatalyst Bi₁₂O₁₇Cl₂ solution reached 45μmol/L.