The Catalytic Effect Of Nano-Fe₃O₄ On Decolorization Of Rhodamine B

With the characters of high organics residual concentration,complex constituents and difficult to be biodegraded,the dye wastewater has been paid much attention.Advanced oxidation processes?AOPs?such as Fenton reaction and Fenton-like reactions are one of the most effective chemical methods in dye wastewater treatment.Solid catalysts are introduced to the Fenton-like reactions,avoiding secondary pollution caused by adding chemical reagents.In this paper,Rhodamine B?RhB?was selected as a typical pollutant to study the catalytic effect of nano-Fe₃O₄ in heterogeneous Fenton reaction,ultrasound-Fenton reaction and the contact glow discharge electrolysis?CGDE?.In this work,nano-Fe₃O₄ was prepared by coprecipitation.The effects of experiment factors in the preparation of nano-Fe₃O₄ on RhB decolorization efficiency during catalyzing the decomposition of H₂O₂ were investigated.The experiment factors include:temperature,reaction time,precipitant type and adding order,the ultrasound environment during preparation process,et.al.Nano-Fe₃O₄ productions prepared under different conditions were with the peroxidase catalytic activity.By means of both formal and reverse synthesis,using NH₃·H₂O and NaOH as precipitant,the nano-Fe₃O₄ productions were prepared with the peroxidase catalytic activity.The ingredients of the production prepared through the formal coprecipitation were more closed to the theoretical ratio.The ultrasound environment during preparation process not only can help to obtain the productions with smaller particle size,but also lead to the closer ratio of Fe²⁺/Fe³⁺to the theoretical product.The decolorization efficiencies of RhB by catalyzing heterogeneous Fenton reaction and ultrasound-Fenton reaction were investigated in this work.The effects of the experimental factors were similar in both heterogeneous Fenton reactions and ultrasound-Fenton catalyzing by nano-Fe₃O₄.For 10 mg/L RhB,in acid environment both of these two Fenton-like reactions showed high decolorization efficiency.High temperature was beneficial for the decolorization of RhB.With the increasing dosage of nano-Fe₃O₄,the decolorization efficiency increased.Nevertheless,the effect of the concentration of H₂O₂ seemed little.Compared with other experimental factors.High efficiencies were obtained both in heterogeneous Fenton reactions and ultrasound-Fenton reactions catalyzed by nano-Fe₃O₄.Under the same conditions,the decolorization efficiency of RhB can be increased from 56.1%to 63.0%in 30 min due to the addition of ultrasound.The decolorization efficiency in the combined process of CGDE and nano-Fe₃O₄ was observed,the decolorization efficiency improved with the higher temperature or the dosage of nano-Fe₃O₄.The pH value has very little effect on the decolorization efficiency when the pH value was changed from 4.0 to 7.0.The decolorization efficiency decreased with the increasing initial concentration of RhB.Nano-Fe₃O₄ showed a good reusability with the decolorization efficiency of RhB achieved at the third cycle of 55%.42.8%,33.7%and 94.7%of the decolorization efficiency were obtained in 20 min CGDE processes catalyzed by Fe²⁺,Fe³⁺and nano-Fe₃O₄,respectively.The results indicated that the active sites on the surface of nano-Fe₃O₄ played an important role in the catalysis.In conclusion,as a heterogeneous catalyst,nano-Fe₃O₄ showed good catalytic effect due to the active sites on its surface.Beyond that,it can be easily separated by magnetism and can be reused,which can be expected to apply for dye wastewater treatment.