| The printing and dyeing industry produces a large number of wastewater,which contains high strength organic compounds and salt.Due to the high concentration of COD,dark colour and high variability in composition,the printing and dyeing wastewater presents a great challenge for its treatment.The triphenylmethane dyes-containing of rhodamine B(Rh B)effluent is one of the most difficult treatment of printing and dyeing wastewater,which is a kind of compounds which have some benzene rings,and is widely used in textile,leather products and staining agent.This kind of dye is carcinogenic,teratogenic and mutagenic.Its emission by producing,transporting and applying,leads to environmental pollution.Due to the traditional biochemical treatment effect is not obvious,therefore based on the advanced oxidation technology is currently one of the hotspots in the field of water treatment.Therefore,in this study,RhB,which is categorized into triphenylmethane dye,was selected as the target pollutants and treated with advanced oxidation in quinone-containing reaction systems by oxidative degradation of RhB.RhB is taken as model compound,and the degradation conditions of the model dye is studied with the oxidation of quinones(AQS,AQDS,HQ).The optimal conditions such as pH,degradation time,quinones’ s concentration and oxygen’s concentration for degradation process were investigated based on degradation rate.And the kinetic characteristics of pH,quinones’ s concentration and oxygen’s concentration were analyzed.The results showed that with the decrease of pH value,or the increase of concentration of quinones,or the increase of oxygen’s concentration,the degradation efficiency of Rh B was elevated and the degradation rate was faster.Therein,in the reaction systems containing 0.10 m M AQS and AQDS,nearly 100% of RhB were degradated within 30 min when pH decreased to 2,while the percentage of Rh B degradation were not more than 10% when the initial pH were above 4.In the reaction systems containing 0.10 mM HQ,however,the extents of RhB degradation were slim and all kept within 10% among the wide range of pH values(2-10).And in the reaction systems of aerobic containing 0.10 mM AQS,nearly 100% of RhB were degradated within 30 min,but in the reaction systems of aerobic,above 90% of RhB were degradated within 30 min when AQDS concentration is 0.03 mM.Under the same conditions,the degradation rate of the anaerobic system is significantly reduced,and slow down.In the HQ reaction system,the degradation rate was less than 10% under both aerobic and anaerobic conditions.The degradation mechanism of a model compound is studied by the changes of their UV-visible spectra,the determination of TOC,the quenching experiment and the change of electron paramagnetic resonance spectrum(EPR)after adding quinones solution.The experimental results showed that this method was suitable for the degradation of cationic triphenylmethane dyes.Under the condition of light,dye becomes excited state.Dyes of excited state as electron acceptor,while the quinones as the electron donor,generate semiquinone radical by the interaction between of them.And semiquinone radical induced oxygen to produce superoxide radical.When AQS concentration was 0.10 mol/L and pH = 2,20 μmol/L Rh B was 100% degraded within 25 min and reached complete mineralization.It was found that persulfate inhibited the degradation of RhB,and AQS was the main reason for the degradation of RhB,compared with the addition of persulfate.The lower the initial pH value,the higher the protonation degree of the dye during the whole process of oxidative degradation,which result in more producing a carbon-centered radical.Superoxide radicals could attack a carbon-centered radical,leading to rupture of conjugated structure of the dye,and the maximum absorption peak gradually disappeared.At the same time,there is the N-dealkylation reaction which can be characterized by the blue-shift at the maximum absorption peak. |
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