Rapid Degradation And Degradation Mechanismof Typical Dyeunder UV/H₂O₂/Ferrioxalate System

With the characteristics of high color,high concentration,many suspended solids,fluctuation of water quality and water quantity,difficulty in biodegradation and so on,dye wastewater is one of the waste water which are difficult to treat and disposal.Therefore,dye waste water has a tremendous risk on human health,ecosystem and environment.Due to the simpleness in operation and high efficiency in treatment,advanced oxidation processes?AOPs?are commonly applied method for dyes wastewater treatment.However,the variety in species and polarity,the low residual concentration and unavailability in capturing of dye degradation products have increased the difficulties of this research filed.As a result,the effective treatment of organic pollutants,the identification of degradation products and degradation mechanism has become the hot topic of environmental chemistry.A simple and convenient AOPs method,UV/H₂O₂/ferrioxalate system was applied to degrade four dyes,namely,methylene blue?MB?,methyl orange?MO?,bromophenol blue?BPB?and rhodamine B?RB?,including the effect of single factor on the degradation rate and the kinetic process,and determine the optimal conditions of degradation.The degradation products of the dye were identified by GC-MS and derivatization GC-MS.The degradation mechanism and degradation mechanism were discussed.The results showed that:?1?The single factor experiment suggested that under UV,while the initial concentration of MB,concentration of H₂O₂,concentration of ferrioxalate and p H are 10mg/L,80mmol/L,0.5mmol/L and 11.0,respectively,much higher degradation efficiencies is observed.Compared to other systems,UV/H₂O₂/ferrioxalate system showed the highest degradation rate of MB,which can reached to 97.85%.The results of UV-Visible scanning also confirm that the degradation efficiency of MB in the UV/H₂O₂/ferrioxalate system is higher.6 kinds of products?such as benzothiazole and so on?were identified by GC-MS analysis,while the 12 kinds of degradation products?such as 2-hydroxy-4-methylbenzoic acid?by the derivative GC-MS method.Among them,the products 2-methyl-5-nitrophenyl methanimidothioate and1-Hydroxycyclohexyl phenyl ketone have not been reported other literatures.As·OH capture agent,tert-butyl alcohol effectively trapped·OH in UV/H₂O₂/ferrioxalate system and inhibited MB degradation.In addition,it can be concluded that there are other free radicals?·C₂O₄^-and·O₂^-?may be involved in the degradation reaction process.The degradation process of MB is suggested that firstly,·OH and other radicals attack MB molecules and cause band breakage?such as C-C,C-N,and C-O bond?,then formed degradation products,eventually,mineralize into NO₃^-,SO₄^2-,CO₂ and H₂O and so on.Therefore,the degradation mechanisms of MB can concluded that demethylation,oxidation,decarboxylation,opening ofbenzenering,mineralization.?2?The single factor experiment suggested that under UV,while the initial concentration of BPB,concentration of H₂O₂,concentration of ferrioxalate and p H are 10mg/L,80mmol/L,10mmol/L and 2.0,respectively,much higher degradation efficiencies is observed.Compared to other systems,UV/H₂O₂/ferrioxalate system showed the highest degradation rate of BPB,which can reached to 99.61%.The results of UV-Visible scanning also confirm that the degradation efficiency of BPB in the UV/H₂O₂/ferrioxalate system is higher.Non of products were identified by GC-MS analysis,while the 9 kinds of degradation products?such as phenol and so on?by the derivative GC-MS method.As·OH capture agent,tert-butyl alcohol effectively trapped·OH in UV/H₂O₂/ferrioxalate system and inhibited BPB degradation.The degradation process of BPB is suggested that firstly,·OH and other radicals attack BPB molecules and cause band breakage?such as S-O,S=O,C-C and C-Br bond?,then formed degradation products,eventually,mineralize into NO₃^-,SO₄^2-,CO₂ and H₂O and so on.Therefore,the degradation mechanisms of BPB can concluded that oxidation,substitution,opening of benzene ring,mineralization.?3?The single factor experiment suggested that under UV,while the initial concentration of MO,concentration of H₂O₂,concentration of ferrioxalate and p H are 10mg/L,80mmol/L,1.0mmol/L and 2.0,respectively,much higher degradation efficiencies is observed.Compared to other systems,UV/H₂O₂/ferrioxalate system showed the highest degradation rate of MO,which can reached to 99.80%.The results of UV-Visible scanning also confirm that the degradation efficiency of MO in the UV/H₂O₂/ferrioxalate system is higher.2 kinds of products?methyl benzene and so on?were identified by GC-MS analysis,while the 7 kinds of degradation products?such as aniline and so on?by the derivative GC-MS method.As·OH capture agent,tert-butyl alcohol effectively trapped·OH in UV/H₂O₂/ferrioxalate system and inhibited MO degradation.The degradation process of MO is suggested that firstly,·OH and other radicals attack MO molecules and cause azo band breakage,then formed degradation products,eventually,mineralize into NO₃^-,SO₄^2-,CO₂ and H₂O and so on.Therefore,the degradation mechanisms of MO can concluded that substitution,oxidation,opening of benzene ring,mineralization.?4?The single factor experiment suggested that under UV,while the initial concentration of RB,concentration of H₂O₂,concentration of ferrioxalate and p H are 10mg/L,40mmol/L,0.1mmol/L and 2.0,respectively,much higher degradation efficiencies is observed.Compared to other systems,UV/H₂O₂/ferrioxalate system showed the highest degradation rate of RB,which can reached to 100%.The results of UV-Visible scanning also confirm that the degradation efficiency of RB in the UV/H₂O₂/ferrioxalate system is higher.Non of products were identified by GC-MS analysis,while the 8 kinds of degradation products?such as benzophenone and so on?by the derivative GC-MS method.As·OH capture agent,tert-butyl alcohol effectively trapped·OH in UV/H₂O₂/ferrioxalate system and inhibited RB degradation.The degradation process of RB is suggested that firstly,·OH and other radicals attack RB molecules and cause band breakage?such as C-C?C=C?C-N and C-O bond?,then formed degradation products,eventually,mineralize into NO₃^-,SO₄^2-,CO₂ and H₂O and so on.Therefore,the degradation mechanisms of RB can concluded that oxidation,opening of benzene ring,mineralization.