Study On The Degradation And Mechanism Of Contaminants In Water Based On ZnO Photocatalytic Composites Under Visible Light

For the problem of organic contamination in water,conventional methods of treatment include biological methods,chemical oxidation methods,and adsorption methods.Among these processing technologies,photocatalytic technology has the outstanding features of high efficiency,low energy consumption,easy operation,mild reaction conditions,wide application range,reusability,and secondary pollution reduction,and is favored by people in the aspect of environmental management.Photocatalytic degradation of organic contaminants under visible or ultraviolet light is a rapid and thorough method of eliminating contaminants.In most semiconductor materials,wide bandgap semiconductor materials such as titanium dioxide and zinc oxide are a promising class of photocatalysts.Zinc Oxide has proved to be a good photocatalyst due to its wide forbidden band?3.2eV?and strong excitation binding energy?⁶0 meV?,which has caused widespread concern.In this study,heterojunction photocatalysts were prepared using ZnO semiconductor photocatalysts as supporting materials on other narrow-gap semiconductors?Bi₂WO₆ and Bi₂O₄,two kinds of narrow-bandgap semiconductors used in this study?.Heterostructure photocatalyst promotes the separation of photo-excited electron-hole pairs and improves photocatalytic activity.With methylene blue and tetracycline as target organic contaminants,the photocatalytic properties of the composites were explored.In this study,advanced analytical instruments were used to systematically analyze the physical and chemical properties of the composite photocatalysts.?1?Photocatalytic properties of Bi₂WO₆/ZnO heterojunctionsIn this study,a flower-like Bi₂WO₆/ZnO heterojunction composite was synthesized by a two-step hydrothermal method.By degrading methylene blue?MB?and tetracycline,the basic photocatalytic properties of the composites were studied.The Bi₂WO₆/ZnO composite has excellent photocatalytic activity for methylene blue and tetracycline.The morphological structure,pore structure,chemical composition,valence state,light absorption properties and carrier recombination efficiency of the material were analyzed by XRD,TEM,SEM,UV-VisDRS,BET,XPS,PL and photocurrent.After being compounded,the morphology of Bi₂WO₆/ZnO is micro-sized and nano-structured flower-like pompoms,with a diameter of about 4?m,a band gap energy of 3.2 eV and a 2.6 eV.Bi₂WO₆/ZnO is a mesoporous structure,and the composite surface area is 4.98 times that of the original.The prepared Bi₂WO₆/ZnO photocatalyst has higher transient photocurrent density?about 4.5?A?than pure Bi₂WO₆ and ZnO particles.The results of active factor capture experiments showed that superoxide radicals played a major role in photocatalytic degradation,followed by hydroxyl radicals and photogenerated holes.The successful combination of Bi₂WO₆ and ZnO enhances the photocatalytic activity and reduces the band gap of ZnO,which can be attributed to the efficient separation of electrons and holes.?2?Photocatalytic properties of Bi₂O₄/ZnO heterojunctionsIn this study,Bi₂O₄/ZnO composites with heterostructures were successfully synthesized by hydrothermal method.The morphological structure,pore structure,chemical composition,valence state,light absorption properties and carrier recombination efficiency were studied by a series of methods.The photocatalytic properties of the composites were measured by XRD.The composites of hexagonal wurtzite ZnO and Biclinic Bi₂O₄ composites were synthesized.The XPS characterization shows that the materials contain Bi,O,Zn and no other impurities.Elements exist in two valence states(Bi³⁺and Bi⁵⁺),and O atoms exist in the form of O-Zn,O-Bi³⁺,and O-Bi⁵⁺.UV-vis diffuse reflectance spectra show that 1/3Bi₂O₄/ZnO is different.The band gap of the mass was1.53 eV.The N₂ adsorption and desorption isotherm was in line with the IV H3 hysteresis loop in the IUPAC classification,indicating that the material is mesoporous.The specific surface area and pore diameter of the Bi₂O₄/ZnO composite was approximately 9.693 m²/g and 3.108 nm,the specific surface area after recombination was 2.54 times that of the original.The transient photocurrent response plot shows that under visible light irradiation,the prepared Bi₂O₄/ZnO photocatalyst has higher photocurrent density of about 6.4?A than pure Bi₂O₄ and ZnO.Bi₂O₄/ZnO composites have excellent photocatalytic activity to degrade methylene blue and tetracycline.Active factor capture experiments show that superoxide radicals and holes play a major role in photocatalytic degradation,followed by hydroxyl radicals.The successful combination of Bi₂O₄ and ZnO enhances the photocatalytic activity and reduces the band gap of ZnO,which can be attributed to the effective separation of electrons and holes.Based on the experimental and characterization results,a highly efficient heterojunction photocatalyst Bi₂O₄/ZnO was successfully synthesized by a hydrothermal method.Due to the formation of a heterojunction at the interface of ZnO and Bi₂O₄,the separation efficiency of the photogenerated electron-hole pair is greatly increased,thereby increasing the Photocatalytic efficiency.