Activated Carbon Supported Bariumcarbonate Combined With Ultrasound Degraded The Phenolic Mixture

Water is an important resource for our human beings to survive.With the rapid development of the economy and the advancement of industrialization,water pollution has increasingly exacerbated in the context of the growing demand for water.Solving water pollution problems becomes an urgent task.Phenolic compounds widely exist in industrial wastewater,which have been accepted as one of the hardest wastewaters to degrade due to their high toxicity and thermal stability.In recent years,the research on the removal of phenolic pollutants by ultrasonic degradation has been increasing.The paper introduces the method of activated carbon supported barium carbonate?BaCO₃/AC?as catalyst to degrade three groups of mixed phenols?p-cresol,o-chlorophenol,p-chlorophenol mixed phenol;a mixed phenol of 2,4,6-trinitrophenol,catechol and m-cresol;a mixed phenol of resorcinol,phenol and o-nitrophenol?,which exerts the advantage of uniting the two technologies.Besides the ultrasonic wave increases the superficial area of BaCO₃/AC by the shock wave generated from the bursting bubble in the liquid and improves the reactivity of the catalyst.The method is operated easily with strong degradation ability.?1?Preparation and characterization of BaCO₃/AC catalystBaCO₃/AC catalyst was prepared by multiple impregnation methods,and the three factors and threelevels experiments were designed according to the factors affecting the effect of the catalyst?concentration of the immersion liquid,calcination temperature,and amount of activated carbon?.The catalyst with the best degradation effect was characterized by X-ray diffraction?XRD?,scanning electron microscope?SEM?and brunauer emmett teller?BET?.It was found that the BaCO₃ particles were partially rod-shaped and partially spherical,and most of them were embedded in the macropores of activated carbon.?2?Separation and detection of mixed phenolsHigh performance liquid chromatography was used to separate and detect phenolic compounds.The optimum separation conditions of each group of mixed phenols were investigated from five aspects:detection wavelength,column temperature,flow ratio,flow?3?Ultrasonic catalytic degradation of mixed phenolsUltrasonic combined with BaCO₃/AC degraded phenolic compounds,and optimized the conditions for degrading phenolic compounds from catalyst preparation conditions,catalyst dosage,ultrasonic power,pH value and initial concentration.Under the optimal degradation conditions,the degradation rates of p-cresol,o-chlorophenol and p-chlorophenol in the first group of mixed phenols were 97.74%,98.01%,98.39%;The degradation rates of 2,4,6-trinitrophenol,catechol and m-cresol in the second group of mixed phenols were 94.91%,97.13%,97.34%.The degradation rates of resorcinol,phenol and o-nitrophenol in the third group of mixed phenols were 92.65%,87.89%,95.06%.?4?Presuming the degradation mechanism of mixed phenolsUnder the optimal degradation conditions of each group of mixed phenols,a radical scavenger is added,and the type of degradation reaction is judged according to the degree of inhibition of the degradation rate of each component.High performance liquid chromatography?HPLC?is used to detect the intermediate products in the process of mixed phenol degradation,and the mechanism of each group of mixed phenols in the degradation process is presumed.There are two kinds of reaction pathways for p-cresol.One reacts with a hydroxyl group to produce 4-methyl catechol,and the other methyl group on p-cresol is continuously oxidized,undergoing the process of changing the aldehyde to acid,the final oxidation product are water and carbon dioxide.O-chlorophenol undergoes high-temperature pyrolysis and undergoes C-Cl bond cleavage,and is attacked by hydroxyl radicals to form catechol,which is eventually oxidized to water and carbon dioxide.The p-chlorophenol undergoes high-temperature pyrolysis and undergoes free radical oxidation to form hydroquinone.A part of hydroquinone is electrophilically added to the hydroxyl group to form 1,2,4-benzenetriol,and the other part is continued oxidation to benzoquinone,the final two intermediates become water and carbon dioxide.The reaction pathway of catechol may be firstly attacked by hydroxyl radicals,and then hydroxyl is introduced into the ortho position to form pyrogallol.As the reaction progresses,the benzene ring is destroyed and produces acetic acid.The reaction eventually mineralizes to water and carbon dioxide.For the degradation of 2,4,6-trinitrophenol and m-cresol in mixed phenols,no intermediates are detected by high performance liquid chromatography.The ortho position of the phenolic hydroxyl group in resorcinol is attacked by a hydroxyl group to produce 1,2,4-benzenetriol,which is subjected to continuous oxidation to finally form water and carbon dioxide.The oxygen atom on the phenolic hydroxyl group in the phenol structure has a lone pair of electrons,which is p-?conjugated with the?-electron of the benzene ring,which increases the negative charge on the para-position of the phenolic hydroxyl group,and is attacked by the hydroxyl group to produce hydroquinone,which is oxidized again.P-benzoquinone is formed,which is ring-opened to produce a carboxylic acid.The reaction eventually mineralizes to water and carbon dioxide.Nitro in o-nitrophenol is attacked by hydroxyl groups to form catechol,and further oxidized to form ortho-benzoquinone,which is ring-opened to produce carboxylic acid.The reaction eventually mineralizes to water and carbon dioxide.