Study On The Preparation Of Iron-based Oxide Heterogenerous Fenton-like Catalysts And The Degradation Of Tetracycline

Tetracycline(TC)is the second largest class of antibiotic drugs in production and usage in the world,which is frequently detected in the water environment and the main source of antibiotic pollution.Such antibiotics have strong antibacterial properties and chemical stability,and are difficult to decompose naturally.Traditional treatment technologies cannot completely degrade them.Fenton technology is one of the most popular advanced oxidation processes,which can effectively degrade various organic substances.Fenton technology has the advantages of high performance,simple operation and environmentally friendly reagents.However,the practical application of the traditional Fenton reaction is still limited by its narrow working pH range(2.5-4),large demand for hydrogen peroxide,and large amounts of iron precipitation.Based on this,the purpose of this paper is to explore efficient heterogeneous Fenton-like systems,which can be applied to the removal of TC in wastewater.Iron-based oxide materials have good catalytic performance and stability,showing excellent application prospects in the removal of organic pollutants.We design and prepare iron-based oxide materials,which form heterogeneous Fenton systems with hydrogen peroxide for the removal of TC.And the degradation performance of these heterogeneous Fenton-like systems on TC is investigated.In addition,the possible catalytic mechanism and degradation pathways of tetracycline are further explored.The main research contents are as follows:(1)Fe3O4 nanospheres(Fe3O4-S)synthesized via a facile one-pot solvothermal method were used for the H2O2 activation and TC elimination from aqueous solutions.Besides,batch experiments were conducted to optimize several key influencing factors such as catalyst dosage,H2O2 concentration,pH value and temperature,and these experimental results were also described by the pseudo-first-order model.It can be found that more than 80%of TC was degraded in the Fe3O4-S/H2O2 system.The catalytic mechanism of Fe3O4-S/H2O2 system was discussed in detail through free radical quenching experiments,electron paramagnetic resonance(EPR)and X-ray photoelectron spectroscopy(XPS)techniques.The results showed that ·OH and ·O2-/·HO2 participated in the heterogeneous Fenton-like reaction,the·OH on the surface of Fe3O4-S played a major role in the degradation of TC,and the surface FeⅡparticipated in the activation of H2O2 through the redox reactions.Moreover,thirteen intermediate products were monitored by the LC-MS and possible degradation pathways of TC were accordingly proposed.The surface morphology of the used Fe3O4-S was almost the same as that of the fresh one,and the structure was not destroyed;the catalytic performance of Fe3O4-S didn’t not show any significant decrease even after five trials.It was worth noting that the optimal pH for TC degradation was expanded to neutral pH conditions by using the Fe3O4-S/H2O2 system.Additionally,Fe3O4-S possessed a large saturation magnetization(66.8 emu/g),which was beneficial to the recycling of the catalyst.(2)Ultrathin iron-cobalt oxide nanosheets(CoFe-ONSs)synthesized via a facile one-step routine by using NaBH4 as the reductant were used as heterogeneous Fenton-like catalysts to remove TC in water.The CoFe-ONSs exhibited superior catalytic performance for TC degradation:83.5%removal of TC was realized without the assistance of external energy after 50 min with 0.3 g/L catalyst,20 mM H2O2 and 50 mg/L TC at T=25℃.The effects of catalyst dosage,H2O2 concentration,initial pH,temperature,initial TC concentration,anions and water sources on TC degradation were studied.Hydroxyl(·OH)radicals were the main active species in the entire reaction,which was demonstrated by quenching experiments,fluorescence detection and the electron paramagnetic resonance(EPR)technology.Additionally,X-ray photoelectron spectroscopy(XPS)analysis further proved that the redox cycles of FeⅡ/FeⅢ and CoⅡ/CoⅢ were participated in OH generation.What’s more,the plausible degradation pathways were put forward followed with detected intermediates.The CoFe-ONSs displayed negligible metal ions leaching and held high TC elimination performance even after five trials.What merits a special note was that the optimal pH for TC degradation was extended to neutral conditions by CoFe-ONSs/H2O2 system.Therefore,the CoFe-ONSs may expand the heterogeneous Fenton-like catalysts family and display great potential in eliminating antibiotic contaminants from wastewater.