Preparation Of Fe₃O₄ Heterogeneous Fenton Catalysts And Their Treatment Of Refractory Organic Pollutants

Many organic pollutants,such as dyes and antibiotics,which are difficult to biodegrade,are produced by human beings in production and life.Due to their long retention time in the environment,complex composition,poor biodegradability,and easy accumulation and migration in water,they are difficult to be removed by conventional sewage and activated sludge treatment processes.Fenton reagent(Fe²⁺+H₂O₂)uses hydroxyl radical(·OH)to degrade organic pollutants that are difficult to biodegrade.However,Fenton method has some shortcomings such as narrow application range of p H,difficult regeneration of Fe(II),secondary pollution of iron sludge and low utilization rate of H₂O₂.Compared with homogeneous Fenton oxidation technology,heterogeneous Fenton technology has the advantages of wide application range and catalyst regeneration.Fe₃O₄is a common heterogeneous Fenton catalyst.Because of its superior physical and chemical properties,easy synthesis and functionalization,Fe₃O₄can be recovered and reused by magnetic separation,and can be used to activate H₂O₂to treat wastewater.However,Fe₃O₄has some problems such as low catalytic efficiency and easy deactivation.In order to solve these problems,the heterogeneous Fenton catalytic performance of commercial Fe₃O₄was investigated,the catalytic degradation effect of the system was promoted by adding polyphenols,and polyphenols Fe₃O₄composites were further prepared for heterogeneous Fenton system to degrade organic pollutants.At the same time,Fe₃O₄(CRC/Fe₃O₄)catalysts containing rich carboxylic acid carbon were prepared by sol-gel self-combustion method for the removal of organic pollutants.The main contents of this paper are as follows:(1)Using commercial Fe₃O₄as catalyst,a heterogeneous Fenton system was constructed to degrade Phenol.Catechol(CC)and Tea Polyphenols(TP)were added to promote Fe₃O₄heterogeneous Fenton system to degrade organic pollutants.In the process of oxidative degradation of polyphenols,there will be phenol-bin structure transformation,which can accelerate Fe³⁺to Fe²⁺cycle.In this chapter,we compared the degradation ability of Phenol before and after adding polyphenols,and analyzed the effects of Fe₃O₄dosage,initial p H,initial H₂O₂concentration and polyphenol dosage on the degradation rule of polyphenol-Fe₃O₄-H₂O₂system.The results show that the system has no degradation effect on Phenol by Fe₃O₄1.00 g L^-1,Phenol 1 m M,H₂O₂3 m M,initial p H 3,adding 0.05 mm CC and 0.05 mm TP,respectively.Phenol removal efficiency increased to 53%and 31%,respectively.Phenol can be degraded by Fe₃O₄heterogeneous Fenton system in the presence of CC and TP,and the Phenol can be degraded by high performance liquid chromatography(HPLC).Catechol,small molecular acid and other intermediate products are generated in the degradation process.(2)CC and TP can promote the degradation of organic matter by Fe₃O₄heterogeneous Fenton system.In this chapter,CC and TP modified Fe₃O₄magnetic nanocomposites(CC/Fe₃O₄and TP/Fe₃O₄)were prepared in situ by co-precipitation method,respectively.The catalytic performance of CC/Fe₃O₄and TP/Fe₃O₄was investigated.Phenol,benzoic acid(BA),tetracycline(TC),sulfadimidine(SMT)and methylene blue(MB)were selected as the target pollutants.The results showed that CC/Fe₃O₄and TP/Fe₃O₄could degrade Phenol by 99%and 95%respectively by Fe₃O₄1.00 g L^-1,Phenol 1 m M,H₂O₂3 m M,initial p H 3.After 10 cycles,the catalytic performance can be maintained at 80%and 70%.Both of the two catalysts have good catalytic performance and reusability.Simultaneously,Phenol,BA,SMT,TC and MB were degraded in the system CC/Fe₃O₄of 1.00 g L^-1,target pollutant of10 mg L^-1,H₂O₂of 40 m M and initial p H of 7.It was found that when the adsorption of tetracycline and methylene blue by CC/Fe₃O₄was higher(more than 40%),the removal rate of target pollutants was higher.When the adsorption of phenol,benzoic acid and sulfamethazine is low(less than 10%),the removal rate of target pollutants is low.The results show that the degradation of CC/Fe₃O₄and TP/Fe₃O₄under acidic conditions is mainly due to the homogenous reaction caused by the dissolution of promoting iron ions.The degradation of the target pollutants under neutral conditions is mainly due to the targeted absorption of organic matter,which enriches the pollutants on the surface of the material and is conducive to·OH attack.Adsorption promoted the degradation of heterogeneous Fenton.(3)Using FeCl₃·6H₂O as iron source and sodium gluconate as carboxylic acid functional group source and carbon source,Fe₃O₄containing carboxylic acid rich carbon(CRC/Fe₃O₄)was prepared by a simple sol-gel self-combustion method.The effects of preparation parameters on the formation of CRC/Fe₃O₄were investigated.The effects of initial p H,catalyst dosage,H₂O₂concentration and initial concentration of MB on the catalytic performance of the composite catalyst were studied.The results show that the catalyst CRC/Fe₃O₄can completely remove MB after 180min reaction at 1.00 g L^-1,10 mg L^-1,10 m M H₂O₂and initial p H 7,which indicates that the catalyst has a wide p H range.After five cycles,the catalytic activity remained high after five cycles through stability and repeated use experiments.At the same time,Phenol,BA,SMT,TC and MB were degraded in the system of CRC/Fe₃O₄1.00 g L^-1,target contaminant 10 mg L^-1,H₂O₂40 m M and initial p H 7.It was found that CRC/Fe₃O₄had high removal rate for pollutants with high adsorption,such as tetracycline and methylene blue,and low removal rate for phenol,benzoic acid and sulfamethazine.The experimental results show that the degradation of CRC/Fe₃O₄in neutral conditions is mainly due to the targeted absorption of organic matter,which enriches the pollutants on the surface of the material and is conducive to·OH attack.Adsorption promoted the degradation of heterogeneous Fenton.