Preparation、modification And Photocatalytic Activity Of Bi₂WO₆、BiVO₄ Photocatalysts

The use of light synergistic semiconductor catalysis technology can degrade pollutants in water into small molecules such as CO₂ and H₂O.This technology generally does not require the addition of other reagents.It has the advantages of high efficiency,energy saving,envi-ronmental friendliness,and no secondary pollution,but it also has short response wave-lengths.,Narrow scope and other shortcomings.How to modify and increase the photore-sponse range of the semiconductor photocatalyst and reduce the hole-electron recombination rate has become one of the hot issues in the research of semiconductor photocatalysis tech-nology in recent years.This paper mainly studies the preparation,modification,optimization of bismuth-based photocatalysts and the degradation of organic pollutants,and discusses the mechanism of photocatalysis.The specific results are as follows:（1）Using Bi（NO₃）₃·5H₂O and Na₂WO₄·2H₂O as precursors,Bi₂WO₆ was prepared by hydrothermal method,and on this basis,heterojunction Bi₂WO₆/Ti O₂ was prepared by gel sol method and butyl titanate Then load the rare earth metal La³⁺to prepare Bi₂WO₆/La₂WO₆/Ti O₂.It has higher photocatalytic activity than any single component under visible light,and the degradation rate reaches 96.62%under the experimental conditions.The reason is that the rare earth metal La³⁺is doped,which introduces La³⁺into the crystal lattice of Ti O₂.The SEM image presents a three-dimensional petal-like shape.UV-vis shows that the response light range of the composite photocatalyst has broadened to the visible light region.XRD shows that Bi₂WO₆ is an orthorhombic crystal system.The XPS spectrum confirmed that it contains Bi,W,O,Ti,La,and C elements.Infrared spectroscopy shows that it contains Bi-O,W-O,W-O-W,Ti-O,and La-O bonds.With Rh B as the target pollutant,the optimal conditions obtained by orthogonal experiments are 0.1 g catalyst,50 mg/L Rh B,and 200watts of visible light radiation,and the best degradation amount is 23.3 mg/g.（2）Use Na₂WO₄·2H₂O and Bi（NO₃）₃·5H₂O as raw materials to prepare Bi₂WO₆ hydro-thermally;use high-temperature calcined melamine as raw materials to prepare graphite phase g-C₃N₄;Na₂S and Cd Cl₂·2.5H₂O are reacted to form by one-step precipitation method Cd S:The three-complex Bi₂WO₆/Cd S/g-C₃N₄ was prepared by hydrothermal method,and the deg-radation rate reached 94.62%under the experimental conditions.Infrared characterization contains WO,WOW,CC,CN bonds;XPS analysis detects the specified elements and binding energy;SEM image presents a three-dimensional petal-like shape,and Rh B is used as the tar-get pollutant.The orthogonal experiment is designed and the optimized process is 0.1 g cata-lyst,50 mg/L Rh B,200W incandescent visible light radiation,the maximum degradation amount is 23.089 mg/g.（3）Using melamine,butyl titanate and Bi₂WO₆ prepared by hydrothermal method as precursors,uniformly mixed by gel sol method to prepare Bi₂WO₆/Ti O₂/g-C₃N₄.Under the experimental conditions,the degradation rate of Rh B reached 98.79%.The catalyst is charac-terized and analyzed by XRD,SEM,UV-Vis,XPS,IR and other characterization methods.XRD characterization can be explained by standard cards PDF#50-1250,PDF#12-2172,PDF#39-0256 Bi₂WO₆/Ti O₂/g-C₃N₄;XPS spectrum contains elements W,O,Bi,Ti,O,C,N;infrared spectrum shows stretching vibration and bending vibration containing Bi-O bond,including Bi-O,WO,WOW,Ti-O,CN bond;UV-vis indicates that the response range has been red-shifted,extending to the visible light region;the SEM image shows a white fun-gus-like structure.With the aid of response surface experiments,the optimized conditions are that the dosage of catalyst is 0.01 g,the initial concentration is 36.87 mg/L,the volume of H₂O₂（volume ratio is 1:100）is 1 m L,and the optimal degradation amount is 161.852 mg/g.The main active substances that degrade Rh B in the capture experiment are·OH,·O^2-,h⁺.Through the kinetic characteristics of Rh B degradation,the results show that different influ-encing factors have different rate constants,which can be described by first-order kinetic equations.（4）Using NH₄VO₃ and Bi（NO₃）₃.5H₂O as raw materials,adding KCl and KBr,the Bi-VO₄/BiOCl/BiOBr heterojunction was prepared by hydrothermal method,and the morpholo-gy,structure and performance of the sample were characterized.XRD proved that the water Thermally prepared BiVO₄ is a monoclinic phase;infrared spectroscopy has strong absorption in the range of 700-850cm^-1,which proves that it has VO bonds;SEM shows that Bi-VO₄/BiOCl/BiOBr is a nanosheet self-assembled into a spherical shape.With basic fuchsia green as the target pollutant,the screening of catalysts showed that BiVO₄/BiOCl/BiOBr has better photocatalyst performance than single-doped BiOCl,single-doped BiOBr and Bi-VO₄,and the degradation rate is 98.79 under the experimental conditions.%.The optimized conditions of the orthogonal experiment are 0.1 g of catalyst,initial concentration of 50 mg/L,visible light radiation power of 200 w,volume of H₂O₂（volume ratio 1:100）of 6 m L,and maximum degradation of 24.09 mg/g.With the help of capture experiments,the degradation mechanism of basic fuchsia green was explored.The study showed that the main active sub-stances that degrade basic fuchsia green are·OH,·O^2-,h⁺.