Preparation Of Nano-Fe₃O₄-Supported Biochar And Its Application As Heterogeneous Fenton Catalyst

Magnetite(Fe3O4)exists widely in nature,and the Fe2+/Fe3+ redox reaction can be continuously cycled on its surface,so Fe3O4 is a kind of excellent heterogeneous Fenton catalyst.However,Fe3O4 is easy to agglomerate because of its magnetism.Therefore,this paper selects biochar(BC)as carrier to disperse Fe3O4 uniformly for its wide source,low cost and easy preparation to promote the contact of Fe3O4 with pollutants and improve the utilization of Fe3O4.In this paper,we synthetise Fe3O4/BC heterogeneous Fenton catalyst by co-precipitation method,using a variety of characterization means to characterize the sample,and the reaction process of removing nitrobenzene(NB)by Fe3O4/BC adsorption and heterogeneous Fenton was investigated in depth.We get the following conclusions:(1)The synthesized Fe3O4/BC catalyst has a porous structure.The Fe3O4 particles are dispersed uniformly on the surface of the biochar,and the surface of the material has abundant functional groups.The material has certain magnetic properties.The saturation magnetization of Fe3O4/BC with a loading of 28 wt%was 22.6 emu/g and the specific surface area was 301.7 m2/g.(2)The effects of preparation conditions on the properties of Fe3O4/BC catalysts were studied.The results show that the increase of pyrolysis temperature and pyrolysis time is conducive to the improvement of material properties within a certain range.The optimum preparation conditions of Fe3O4/BC were:pyrolysis temperature at 600?,pyrolysis time was 60 min and heating rate was 10?/min.The prepared BC was washed with acid,alkali and ethanol.The NaOH solution was precipitant in the co-precipitation process.Fe2+ and Fe3+molar ratio of iron salt solution was 1:2 and the loading was 28 wt%.(3)The influencing factors of removing nitrobenzene by heterogeneous Fenton of Fe3O4/BC and the stability of the catalyst were studied.The results showed that the addition of catalyst,H2O2 concentration,dissolved oxygen concentration and reaction temperature all significantly promoted the removal of nitrobenzene,but the removal rate of nitrobenzene decreased with the increase of reaction pH and initial concentration of NB.After 240 min of reaction,the nitrobenzene removal rate of the best material was about 95%.The catalyst has a strong stability which Fe3O4 and BC combined firmly,and after ten rounds of cycle experiments,nitrobenzene removal effect decreased slightly,but the removal rate is still as high as 84%.(4)The mechanism of nitrobenzene removal by heterogeneous Fenton of Fe3O4/BC was investigated.The results show that the degradation of NB by FC3O4/BC conforms to the first-order kinetic equation.The adsorption of NB on Fe3O4/BC conforms to the Freundich isothermal adsorption model,indicating that the adsorption behavior of NB on Fe3O4/BC belongs to the chemisorption.The initial TOC concentration of 100 mg/L NB solution was 43 mg/L.After 240 min of degradation reaction,the removal rates of NB and TOC reached 84%and 75%,respectively,indicating that the Fe3O4/BC can almost remove NB and degradation products in water simultaneously.Only a small amount of the intermediate remained in solution.