In Situ Synthesis Of Fluorine Modified Fe₃O₄ And Their Degradation Of Dye Wastewater

With the rapid development of the dyeing and printing industry,the treatment of dye wastewater has become an important issue in environmental issues.As one of the most widely used advanced oxidation processes,Fenton reaction has its own unique advantages including strong oxidation,high degradation efficiency,and general applicability.However,the homogeneous Fenton still has many drawbacks,such as low utilization of hydroxyl radicals,easy formation of secondary pollution,narrow pH range（³）,and loss of iron ions,making the catalyst unreusable.The study found that the use of Fe₃O₄ as a heterogeneous Fenton catalyst can not only broaden the pH range of the system,but also avoid the production of iron solids,and the catalyst after the reaction is easy to magnetic recovery.However,the single Fe₃O₄ MNPs（magnetic nanoparticles）have limited ability to activate H₂O₂ and produce insufficient·OH,making the degradation of organic pollutants less efficient than Fenton reaction.In recent years,studies have found that doping Fe₃O₄ with metal ions can increase its catalytic degradation activity.Most of the cations used are rarely reported using anion doping,such as fluoride ion（F^-）.Therefore,in this thesis,fluorine modified Fe₃O₄particles were synthesized in situ by solvothermal method and ionothermal method for the first time.The degradation effects of catalysts on anionic dyestuff Orange G and cationic dye Rhodamine B dyestuff wastewater were studied.The main results and conclusions are as follows:1.In-situ synthesis of fluorine modified Fe₃O₄ catalyst by solvothermal method,and a series of catalysts F-Fe₃O₄-rp-MEG（R_F=0.1,1,2,3,R_F was atomic ratio of F to Fe,rp was the reduction precipitation method,and MEG was the reaction solvent ethylene glycol）were synthesized by changing fluorine doping amount.The XRD,SEM characterization showed that with the increase of the fluorine doping amount,the product of the synthesis appears to be pure Fe₃O₄→fluorine doped Fe₃O₄→fluorine doped Fe₃O₄ and Na₃FeF₆ blending process.The XPS test shows that the fluorine in the fluorine-modified Fe₃O₄ is in the form of surface fluorine and lattice fluorine.2.In-situ synthesis of fluorine modified Fe₃O₄ by solvothermal method for the catalytic degradation of orange G by Fenton-like reaction,and the most suitable catalyst F-Fe₃O₄-rp-MEG（R_F=1）with fluorine doping content was selected when the reaction conditions were:0.1 mM OG,volume 50 mL,pH 6.5,temperature 40 ^oC,Fe₃O₄ concentration 0.5 g/L,40 mM of H₂O₂,degradation time 2 h,the decolorization rate was 96.8%,the reaction rate was 0.0284 min^-1,and the salinity was 83.2%.The study found that catalytic decomposition of F^-and Fe ions in the system was rarely,the degradation of orange G is mainly attributed to the oxidation of F-Fe₃O₄-rp-MEG（R_F=1）surface with H₂O₂.The effects of dissolved traces of F^-（0.65mg of/L）and Fe ions（0.15 mg/L）were negligible.Experiments with tert-butanol by the addition of a free-radical trapping agent showed that hydroxy radical（·OH）was the active free radical that plays a leading role in the degradation process.F-Fe₃O₄-rp-MEG（R_F=1）still has high catalytic activity and stability after 8cycles of catalytic cycling and can be repeatedly recycled.Although the in situ synthesis of fluorine modified Fe₃O₄ by solvothermal method can effectively degrade the anionic dye Orange G,the degradation of cationic dyes Rhodamine B and methylene blue was very limited.3.In order to improve the catalytic degradation of Fe₃O₄ particles,a fluorine modified Fe₃O₄ catalyst was successfully prepared by ionothermal method,and two kinds of samples were prepared by changing the fluorine addition method.The XRD,TEM characterization method indicated that the synthesized samples were Fe₃O₄MNPs（particle size 10 nm）.Synthetic fluorine modified Fe₃O₄ was used to decompose Rhodamine B in a heterogeneous Fenton reaction,and the most suitable catalytic catalyst was selected for F-Fe₃O₄-op-DES（In the synthesis fluorine was added in one step,op was oxidation precipitation,and DES was the reaction medium deep eutectic solvent）was used to investigate the effect of different reaction conditions on its catalytic degradation,under the conditions of 0.01 mM RhB,0.5 g/L of Fe₃O₄,40 mM of H₂O₂,and the degradation time 2 h at 25 ^oC and pH 6.5,the decolorization rate was 91.9%,reaction rate was 0.0198 min^-1,and salinity was 60.6%.Studies have shown that the degradation system contains very few F^-and Fe ions.The degradation of Rhodamine B is mainly attributed to the oxidation of F-Fe₃O₄-op-DES surface with H₂O₂,and the effect of eluted trace F^-（0.25 mg/L）and Fe ions（0.26mg/L）were negligible.Experiments with tert-butanol and p-benzoquinone by the addition of a free-radical trapping agent showed that hydroxyl radicals（·OH）was the active free radicals that play a leading role in the degradation process.Recycling experiments show that F-Fe₃O₄-op-DES has good reusability.