Heterogeneous Fenton-like Degradation Of Sulfamethazine Catalyzed By Schwertmannite/few-layer Graphene Composite

In recent years,antibiotics were widely used especially in livestock and poultry farming,and the pollutation caused by antibiotics has received more attention.Antibiotics are toxic to organisms in environment,and result to the spread of antibiotic-resistant bacteria.The antibiotic resistance genes caused by the antibiotic pollution will persist and metastasize in environment,pose serious hazards and potential threats to the environment.At present,to remove the antibiotics contamination,there are mainly biological treatment methods,adsorption methods,membrane separation methods,and advanced oxidation methods.Among these treatment methods,the heterogeneous Fenton method which belongs to the advanced oxidation method has become the preferred method for removing antibiotic contamination with strong pollutant oxidation ability and good environmental adaptability.At present,the research on the improvement of the effect of heterogeneous Fenton oxidation technology is mainly focused on the catalyst’s performance.Among these researches,the supported catalysts are more mature and effective.Schwertmannite is an iron-containing mineral that can be used as a Fenton-like catalyst.It has good adaptability to the reaction pH.But its surface has a large amount of Fe(III)which limits the reaction rate of its catalysis.It can be loaded by the Few-layer graphene material with excellent electron conductivity to theoretically improve its catalytic ability.After loading Schwertmannite on Few-layer graphene,the degradation of sulfamethazine(SMT)is significantly improved.The best degradation effect is from the 1GPsch catalyst,the quality of Few-layer graphene in 1GP-sch is 13.26%.5 mg/L SMT can be completely degraded by the Fenton-like reaction in 90 min.The XRD pattern indicated that the crystal structure of Schwertmannite did not change significantly during the synthesis of the 1GP-sch;the TEM image indicated that the Schwertmannite was supported on the surface of the Few-layer graphene;It was inferred from XPS pattern analysis that in the 1GP-sch,the Schwertmannite is combined with the Few-layer graphene through the Fe-O-C bond,and the electrons can be transferred between the Schwertmannite and the Few-layer graphene through the Fe-O-C to improve the performance of the supported catalyst.The 1GP-sch has a certain adsorption property to sulfamethazine,and its equilibrium adsorption amount is 0.10 mg/g.The optimal reaction conditions of 1GP-sch catalyze the Fenton-like reaction to degradate 5 mg/L SMT are:1 g/L of 1 PG-sch catalyst,200 mg/L H2O2,initial reaction pH 3,reaction temperature 28℃.Under these conditions,the SMT in the system can be completely degradated within 90 min.The 1GP-sch catalyst can be adapted to the initial pH 3-9.The main oxidizing substance in the degradation system is hydroxyl radical and it is generated on the surface of the catalyst.A little concentration of iron ions eluted by the catalyst in the reaction,and the amount of iron leaching in 24 h is 2.8 mg/L,accounting for 0.28%of the total mass of the catalyst.99.82%of the iron ions were Fe(Ⅲ);XPS analysis showed that the surface Fe(Ⅲ)was reduced after the reaction;FTIR analysis showed that the surface of the catalyst was hydroxylated after the reaction;XRD analysis showed that the crystal structure of the catalyst did not change after the reaction.After 5 cycles of the catalystic reaction,the degradation rate can be maintained at 80%in 120 min,the iron dissolution is reduced to 0.34 mg/L.The catalyst has a good stability.During the degradation reaction,66.8%of TOC was mineralized within 24 h,and the utilization rate of H2O2 was 15.3%.The reaction intermediates were determined and the degradation pathway of SMT was inferred.The performence of the catalytic reaction is affected by the different water quality condition,like COD concentrations,it can reduce the degradation rate from 100%to 41.7%.NH4+,Cl-,SO42-,NO3-and H2PO4-concentrations in the reaction system.From results,COD has a great influence on the degradation effect by consuming OH in the system,and NH4+,Cl-,SO42-,NO3-have little effect on the degradation;The degradation rate can be reduced by 7.2%-18.6%.H2PO4-inhibits the catalytic generation of OH by forming a coordination compound with iron ions on the surface of the catalyst,which has a great influence on the degradation,and the degradation rate can be reduced by 81.2%.The research in this paper provides a theoretical reference for the application of Schwertmannite loaded by Few-layer graphene in Fenton-like oxidation technology and the mechanism for obtaining performance enhancement.