Study On Preparation Of BiOBr/TiO₂ Nanotube Arrays And Photocatalytic Degradation Of Trace Bisphenol A In Water

Bisphenol A（BPA）is a typical endocrine disruptor,which is widely used in the synthesis of polycarbonate,epoxy resin and other industrial materials.Due to the wide application and unreasonable disposal of BPA,it will enter the water environment through various ways,thus posing a potential threat to human life and health.BPA is stable in structure and properties,while has poor biodegradability and a low concentration in water.Therefore,conventional physical,chemical and biological treatment processes have limited removal effects on BPA in water.As a green and efficient water treatment technology,TiO₂ photocatalysis technology has great application prospects in the treatment of trace BPA pollution in water.However,the utilization rate for visible light of TiO₂ is low,the photogenerated carriers are easy to recombine,and the powder TiO₂ is difficult to recycle after use,which is easy to cause secondary pollution.In response to the above problems,BiOBr-doped TiO₂ nanotube arrays（BiOBr/TNTAs）were prepared in this study to investigate their removal performance of trace BPA in water under visible light.The specific research contents and results are as follows:（1）BiOBr/TNTAs were prepared in situ on titanium sheets by anodization and cyclic impregnation,and the preparation conditions of BiOBr/TNTAs were optimized.The BiOBr/TNTAs prepared under the conditions of water bath temperature of 45°C,immersion time of 1 min,and immersion times of 7,Bi（NO₃）₃ and Na Br concentrations of 50 m M had the highest photocatalytic activity.The degradation efficiency of Rhodamine B by BiOBr/TNTAs prepared under optimal conditions was 74.7±2.8%,which was significantly higher than that of TNTAs（18.9±1.8%）.The analysis results of SEM,XRD,Raman and XPS indicated that BiOBr was introduced on the surface of TNTAs by cyclic impregnation method,and a tight heterojunction was formed between TiO₂ and BiOBr.Cyclic degradation experiments showed that the prepared BiOBr/TNTAs have excellent photocatalytic stability.（2）UV-Vis diffuse reflectance spectroscopy results indicated that the introduction of BiOBr enhanced the absorption performance of TNTAs for visible light.Fluorescence spectroscopy results showed that the formation of BiOBr/TiO₂ heterojunction can effectively promote the separation of photogenerated carriers.The photoelectrochemical performance results showed that appropriate amount of BiOBr doping can reduce the charge transport resistance of TNTAs,improve their carrier separation efficiency and photoelectric conversion efficiency,thereby improving the photocatalytic performance.However,excessive BiOBr loading will block the TiO₂ nanotubes,affecting their absorption of visible light,and the photocatalytic performance will decrease instead.（3）The BiOBr/TNTAs prepared under the above optimal conditions had a degradation rate of 81.2±1.5%for trace BPA in water under visible light,which was much higher than that of TNTAs（24.6±0.6%）,indicated that the doping of BiOBr also improved the removal of BPA by TNTAs.The effects of different water quality parameters on the photocatalytic degradation of BPA by BiOBr/TNTAs were discussed.The results showed that the removal rate of BPA was higher under alkaline conditions,and BiOBr/TNTAs had good degradation ability to 0.5-3 mg/L BPA.Inorganic anions that coexisting in water were able to capture photogenerated holes（h⁺）and hydroxyl radicals（·OH）,thereby reducing the photocatalytic removal rate of BPA in water by BiOBr/TNTAs.The effects of different inorganic ions on the degradation efficiency of BPA were as follows:HPO₄^2->HCO₃^->NO₃^->Cl^->SO₄^2-.Natural organic matter existing in water can compete with BPA for active sites,affect light absorption and act as an active free radical scavenger,thus adversely affecting the removal effect of BPA.Under visible light irradiation,due to the difference in the energy band structure of BiOBr and TiO₂,the holes on the valence band of BiOBr transferred to the valence band of TiO₂,and the electrons on the conduction band of TiO₂ transferred to the conduction band of BiOBr,which promotes the separation of photogenerated carriers.Radical trapping experiments demonstrate that h⁺and·OH play major roles in the photocatalytic degradation of BPA by BiOBr/TNTAs.