Study On Effect And Degradation Pathway Of Oxidizing Azo Dye AO₇ By H₂O₂-assisted Ultrasound-photocatalysis

Azo dye wastewater discharged from industry has characteristics of high chromaticity,high toxicity and refractory.It would threaten to the ecological security and human health serious if discharged into the environment directly.As a result,it is urgent to develop and improve wastewater treatment technology to alleviate the severe situation of water pollution.Ultrasonic-photocatalysis is a kind of advanced oxidation technology which is on the basise of free radical oxidation.It has both advantages of ultrasonic cavitation and photocatalytic oxidation,and can be applied alone or with other technologies flexibly.So the ultrasonic-photocatalysis is considered as a promising technology in refractory organic wastewater treatment.In this research,azo dye Acid Origin 7 was chosen as the target pollutant.The ultrasound?US?-ultraviolet?UV?system and the H₂O₂ assisted with US-UV/TiO₂ system were built to degrade AO7,and the effect of catalyst dosage,H₂O₂ dosage and initial pH value on AO7 degradation were investigated.Moreover,the factor of H₂O₂-US-UV/TiO₂ system were optimized by the response surface analysis,and the mechanism of AO7 degradation was explored.The main results were summarised as follows:?1?The ultrasound-assisted effect on the decolorization of AO7 in UV/TiO₂ system and UV/?-MnO₂ system were investigated,while TiO₂ and ?-MnO₂ were chosen as catalysts.The results demonstrated that the decolorization of AO7 could be improved in UV catalytic system by introducing ultrasound.When adding 2.5mmo//L catalysts,the decolorization of AO7 in UV/TiO₂ system was increased from 47.3% to 59.4% under ultrasonic assistance,and the decolorization of AO7 in UV/?-MnO₂ system was increased from 37.8% to 53.6% under ultrasonic assistance.It was indicated that with the increase of catalyst dosage,the decolorization of AO7 was presented a trend of increasing firstly and then decreasing,the optimum TiO₂ dosage was 0.5g/L and the optimum?-MnO₂ dosage was 0.2g/L.In addition,acidic initial pH was proved more propitious for the USUV /TiO₂ system to degrade AO7.?2?The H₂O₂-US-UV/TiO₂ synergetic system were built to treat the AO7 simulated wastewater.Under the condition of adding 0.5g/L TiO₂ and not adjusting the initial pH,the decolorization of AO7 in US-UV/TiO₂ system was increased from 59.4% to 70.6% when adding 1mmol/L H₂O₂,indicating that H₂O₂ had a synergistic effect on the AO7 degradation.The single factor experiment and response surface analysis method were used to invest the influence of main factors.The results demonstrated that the significance of influence factors in the synergistic system were ordered as H₂O₂ dosage,TiO₂ dosage and initial pH value.It was indicated that the decolorization of AO7 increased firstly and then decrease as the H₂O₂ dosage and the TiO₂ dosage increased,.In addition,acidic initial pH was proved more propitious for the US-UV /TiO₂ system to degrade AO7.Acid initial pH was more favorable for the synergetic system to degrade AO7,and it could reach 85% AO7 decolorization under the condition of initial pH<9.Considering both decolorization effect and economic cost,the optimal degradation conditions of the synergetic system were: TiO₂ dosage of 0.5g/L,H₂O₂ dosage of 4mmol/L and the initial pH value of 3.?3?Under the optimal degradation condition of H₂O₂-US-UV/TiO₂ synergetic system,tert-butanol was added to verify the hydroxyl radical oxidation in the system,and that was found in the synergetic system obviously.Uv-vis analysis showed that azo bond,naphthalene ring and benzene ring structures were destroyed accompanying by the degradation process of AO7.The salinity of AO7 was 23.3% after 60 min degradation under the synergistic system.Four major degradation products were detected by LC-MS,which were 2-naphthol,?S?-4-carboxyphenylglycine,cinnamic acid and 1,2-decanediol.