Degradation Of Acid Red 73 By Activated Persulfate In Heat/Fe₃O₄@AC System With Ultrasound Intensification

Azo dyes account for more than 50%of the total production of dyes.The structure and properties of azo dyes are stable,and it is difficult to degrade with traditional biochemical methods.With the increasingly severe situation of environmental pollution,it is urgent to propose efficient degradation methods for dyeing wastewater.As a new wastewater treatment technology,persulfate advanced oxidation process has been paid much attention by researchers at home and abroad,but it is faced with the problems of high energy consumption and low efficiency.This work aims to solve the problems existing in advanced persulfate oxidation technology,such as low activation efficiency,difficult recovery of homogeneous catalyst,environmental pollution and poor economy.Based on the characteristics of high temperature discharge of printing and dyeing wastewater,an advanced oxidation technology of persulfate/heat/Fe₃O₄@AC/ultrasound was proposed for the treatment of Acid Red 73.Fe₃O₄@AC catalyst was prepared using coprecipitation and impregnation method and characterized by SEM,XRD and BET.It was found that the pore structure of activated carbon was filled with Fe₃O₄.The average particle diameter of Fe₃O₄ was22nm,the BET surface area of the catalyst was 715.5m²/g,and the pore volume was0.4354cm³/g.Reaction kinetics was studied by quasi-first-order kinetic fitting and the reaction activation energies of persulfate and Fe₃O₄@AC/persulfate were determined.Degradation of AR73 with thermal activatied（50℃）persulfate is relatively slow,the activation energy,enthalpy changeΔH and entropy changeΔS were determined to be143.02 k J·mol^-1,138.12k J·mol^-1 and 133.16J·mol^-1·K.When Fe₃O₄@AC was added to the system,the degradation rate was doubled and the reaction activation energy was reduced by about 56%compared with persulfate alone.The optimal conditions were determined to be AR73 50 mg/L,PS 7.5 mmol/L,dosage rate of catalyst and AR73 as4/1,ultrasound frequency 80 k Hz,ultrasound power 80 W,temperature 50℃and p H not adjusted.Nearly 100%decolorization was achieved within 10min under optimal condition.The prepared Fe₃O₄@AC catalyst had good magnetic recovery ability,and the recovery rate of catalyst was kept at 83%after 5 times of repeated reaction.UV-Vis spectrophotometer was used to measure the absorbance in a specific wavelength range.By observing the change of absorption peak reaction in the process,it is found that azo bond was rapidly destroyed in initial stage;more complex organic structures were also destroyed and the destruction of naphthalene ring structure was relatively thoroughly because less single ring structure was formed.Inhibitors were used to determine the active substances in the reaction system.The active substances involved in the reaction include not only free radicals such as HO·and SO₄^-·,but also singlet oxygen ¹O₂which is a non-free radical active substance.Moreover,¹O₂ produced by persulfate under the activation of AC plays a leading role in the reaction,indicating that the US/PS/heat/Fe₃O₄@AC system proposed in this paper has a wider application range and a broad prospect for the treatment of real printing and dyeing wastewater.