Studies On Preparation And Performance Of Iron/semiconductor Photo-fenton Catalysts

With the rapid development of society and economy,water pollution is becoming more and more serious.The development of advanced techniques for water treatment with low cost and high efficiency is crucial to improve the water environment and promote the sustainable development of our society and economy.The Fenton method has been widely used in the treatment of waste water because of its low cost,simple operation,mild reaction conditions and high degradation efficiency.However,the traditional homogeneous Fenton reaction has the problems of low H2O2 utilization efficiency,acidic operation condition,large amount of iron sludge after the reaction.The heterogeneous Fenton method solves some of the disadvantages of the homogeneous one,for example,it can be operated under neutral condition,and the catalyst can be recycled.However,the activity of the heterogeneous Fenton catalyst is much lower than the homogeneous Fenton reagent,and the active components are easily lost.Therefore,the development of heterogeneous Fenton catalysts with high activity and high stability has become of the key to realize the practical applications of heterogeneous Fenton technique.Iron/bismuth vanadate（Fe/BiVO₄）photo-Fenton catalysts with different iron contents were prepared by one-step hydrothermal method using bismuth nitrate,ammonium metavanadate and ferric nitrate as raw materials.The photo-Fenton reaction performance of the catalysts was evaluated using the degradation of methylene blue under visible light as a model reaction.The effects of different Fe contents and pH value of hydrothermal reaction on the exposed crystal plane and the morphology of the catalysts were investigated by X-ray diffraction（XRD）and scanning electron microscope（SEM）.When the molar ratio of Fe to Bi is 0.5%and the pH of the hydrothermal reaction is 7,the prepared Fe/BiVO₄-0.5-7 catalyst exhibits the highest removal efficiency for methylene blue under visible light.The removal efficiency is about 80%within 60 minutes,twice that of pure BiVO₄.In the Fenton reaction system assisted by the visible light,Fe³⁺in Fe/BiVO₄ accepts the photo-generated electrons from the semiconductor BiVO₄,which promotes the separation of photogenerated carriers.At the same time,itself is reduced to Fe²⁺,which accelerates the conversion of Fe³⁺to Fe²⁺.With strong oxidizing hydroxyl radicals·OH and superoxide radicals·O₂^-produced in the system,the organic pollutants can be degraded efficiently.A series of iron/graphitic carbon nitride（Fe/g-C3N4）photo-Fenton catalysts were prepared by one-step pyrolysis.The effects of different iron contents and different ammonium thiocyanate dosages on the morphology and the photo-Fenton reaction performance of the catalysts were studied.The results show that adding an appropriate amount of ammonium thiocyanate can lead to a fluffy and porous structure with large specific surface area,which can provide more active sites for the reaction.With moderate iron content,the iron species can be highly dispersed on the g-C3N4 support,and the catalyst has excellent photo-Fenton reaction activity and stability.When the dosages of Fe precursor ammonium thiocyanate was 0.4g and0.3g,respectively,the obtained catalyst could completely remove high concentration methylene blue（200mg/L）within 25 minutes and the Fe leaching was only 0.66 mg/L.The free radical quenching experiment proved that the both hydroxyl radical and superoxide radical play roles in the degradation of organic pollutants during the photo-Fenton system.