Ultrasonic Combined Catalyst CuO/AC Degradation Of Mixed Phenol

With the continuous development of industry,the discharge of industrial wastewater is increasing gradually.If the industrial wastewater can not meet the standard,it will not only pollute the surface water,but also result in underground water pollution.Among them,phenols in wastewater are difficult to be biodegraded with high toxicity and complex components,Which are listed as priority pollutants in many countries.In recent years,the degradation of phenols in wastewater by ultrasound has become a hot topic for many scholars,and achieved satisfactory achievements.In this paper,the degradation of mixed phenols by ultrasound combined with supported catalyst is studied.The main reason is that the supported catalyst has a large specific surface area.The ultrasound combined with the supported catalyst is used to achieve the synergetic degradation of mixed phenols in wastewater,which can significantly improve the degradation rate of mixed phenols.Meanwhile,the effects of catalyst preparation conditions,catalyst dosage,ultrasonic power,solution pH,initial concentration of the solution on the degradation rate of mixed phenols were investigated,thus providing a new idea for industrial wastewater treatment in the future.Three groups with mixed phenols were degraded by ultrasound combined with supported catalyst-copper oxide loaded on activated carbon?CuO/AC?,such as the first group with mixed phenols?o-chlorophenol,3-chlorophenol,2,5-xylenol?,the second group with mixed phenols?p-nitrophenol,o-nitrophenol,3,5-xylenol?and the third group of mixed phenols?4-chlororesorcinol,o-cresol,3,4-xylenol,2,4-xylenol?.The method can improve the degradation rate of mixed phenols by using the coupling technique,so as to give full play to the advantage of ultrasonic cavitation effect.?1?Preparation and characterization of supported catalyst?CuO/AC?The supported catalyst CuO/AC was prepared by multiple impregnation,and characterized by XRD and SEM.It was found that there were granular CuO on the surface and in the pores of CuO/AC catalyst,and strong and sharp CuO peak was observed.At the same time,the specific surface area,firmness and loading capacity of the supported catalyst were measured.It was found that the larger the specific surface area,firmness and loading capacity of the supported catalyst were,the better the ultrasonic degradation effect of the mixed phenols was.The optimum preparation conditions of the supported catalyst were as follows:the concentration of copper nitrate impregnating solution:for 0.01 mol·L^-1,calcination temperature:for 450?,catalyst dosage:for 3 g·L^-1?A₃B₁C₃?.?2?Establishment of liquid chromatographic conditionsThe separation conditions of three groups with mixed phenols by liquid chromatography were explored,including:detection wavelength,column temperature,mobile phase type and proportion,flow rate.It was found that the optimal chromatographic separation conditions for the first group of mixed phenols were as follows:detection wavelength for 275 nm,mobile phase ratio for V_acetonitrile:V_water=30:70,flow rate for 1.0 mL·min^-1,column temperature for25?;the optimal chromatographic separation conditions for the second group of mixed phenols were as follows:variable detection wavelength?0-5 min,?=317 nm;5-8 min,?=279nm;8-12 min,?=273 nm?,column temperature for 25?,mobile phase ratio for V_water:V_methanol=50:50,flow rate for 1.0 mL·min^-1;the optimal chromatographic separation conditions for the third group of mixed phenols were as follows:detection wavelength for277 nm,mobile phase ratio for V_water:V_methanol=50:50,flow rate for 1.0 mL·min^-1,column temperature for 25?.?3?Degradation of three groups of mixed phenols by ultrasound combined with supported catalystThree groups with mixed phenols were degraded by ultrasound combined with supported catalyst.The effects of catalyst preparation conditions,catalyst dosage,ultrasound power,solution pH and initial concentration on the degradation rate of mixed phenols were investigated.The results showed that the optimal degradation conditions of the first group of mixed phenols were as follows:the initial concentration for 100 mg·L^-1,the amount of catalyst for 1.8 g·L^-1,the ultrasonic power for 400 W,the original pH value.After ultrasonic degradation for 60 min,the degradation rates of o-chlorophenol,3-chlorophenol and2,5-xylenol were 92.5%,90.7%and 96.28%,respectively.The optimal degradation conditions of the second group of mixed phenols were as follows:the initial concentration for50 mg·L^-1,the amount of catalyst for 1.6 g·L^-1,the ultrasonic power for 400 W,and the original pH value.After ultrasonic degradation for 60 min,the degradation rates of p-nitrophenol,o-nitrophenol and 3,5-xylenol were 94.5%,93.56%and 96.28%,respectively.The optimal degradation conditions of the third group of mixed phenols were as follows:the initial concentration for 100 mg·L^-1,the amount of catalyst for 2.4·L^-1,the ultrasonic power for 500 W,and the original pH value.After ultrasonic degradation for 60 min,the degradation rates of 4-chlororesorcinol,o-cresol,3,4-xylenol and 2,4-Xylenol were 94.84%,85.16%,94.82%and 96.02%,respectively.?4?Exploration on degradation mechanism of mixed phenolsUnder the optimal degradation conditions of mixed phenols,three different radical scavenger?tert-butyl alcohol,isopropanol and n-butyl alcohol?were added,and the reaction types of mixed phenols during the degradation process were speculated by comparing the effects of the three radical scavenger?tert-butyl alcohol,isopropanol and n-butyl alcohol?on the degradation rate of mixed phenols before and after the addition of the scavenger.The degradation mechanism of mixed phenols was inferred by qualitative analysis of the intermediate products produced in the degradation process of mixed phenols by high performance liquid chromatography?HPLC?.It was found that o-chlorophenol generated catechol in the degradation process,further oxidized to o-quinone,and finally mineralized into pollution-free CO₂ and H₂O.Under the condition of high temperature and high pressure produced by ultrasonic cavitation effect,the C-Cl bond in 3-chlorophenol broke and was affected by the orientation effect of-OH,and 1,2,4-Benzenetriol is generated by electrophilic addition reaction.Finally,it was oxidized to open the ring,so as to form small molecules such as CO₂ and H₂O.During the degradation of 2,5-xylenol,2,5-toluenediol was produced,which was further oxidized to 2,5-Dimethyl-p-benzoquinone,and finally oxidized to open the ring,so as to form CO₂ and H₂O.In the degradation process of o-nitrophenol,1,2,4-Benzenetriol was formed under the influence of·OH orientation effect,and finally oxidized to form CO₂and H₂O.The C-NO₂ bond was broken by high temperature pyrolysis reaction of p-nitrophenol.At the same time,the hydroxyl radicals attack the free radicals to produce hydroquinone,which was oxidized to produce p-benzoquinone,and finally mineralized into CO₂ and H₂O.During the degradation process of 3,5-xylenol by ultrasound combined with supported catalyst,1,3-dimethylhydroquinone was formed,which was further oxidized to1,3-Dimethyl-p-benzoquinone,and finally mineralized into a large number of CO₂ and H₂O.In the degradation process of 4-chlororesorcinol,the attack of hydroxyl radical made the hydroxyl replace Cl to form 1,2,4-Benzenetriol,which was further oxidized to form small molecular substances such as CO₂ and H₂O.For 2,4-xylenol,no intermediates were detected in the degradation process.In the process of ultrasonic degradation of o-cresol,2-methyl-p-phenol was formed,which was further oxidized to 2-methyl-p-benzoquinone,and finally oxidized to form CO₂ and H₂O.During the degradation process of 3,4-xylenol by ultrasound combined with supported catalyst,4,5-dimethylphenol was formed,pyruvic acid was formed through a series of oxidation reactions,and finally was mineralized into CO₂,H₂O and other small molecular substances.