Study On Pyrite?FeS₂? Heterogeneous Fenton For Catalytic Oxidation Of P-nitrophenol

With the development of industry,a large amount of organic wastewater is produced.If the untreated sewage was discharged directly,some environmental pollution problems would be caused.Most organic pollutants are harmful to human beings and other organisms,and they are difficult to be biodegraded in the natural environment and the treatment of organic wastewater has become a hot research topic.Fenton reaction,one of the advanced oxidation process that can rapidly and efficiently degrade these stubborn organic compounds,has also received extensive attention.By pyrite?FeS₂?as catalyst,p-nitrophenol?PNP?which widely exists in nature and has high toxicity as the goal pollutant,heterogeneous Pyrite Fenton reaction?Pyrite-F?and heterogeneous Pyrite Photo-Fenton reaction?Pyrite-PF?were studied for its ability of treating organic matter.The degradation reaction process,the stability of the catalyst,the effects of visible light on degradation,the degradation mechanism and PNP degradation path of the reaction are all studied here.The corresponding contents and conclusions are summarized as follows:?1?The solvothermally prepared catalyst was characterized by X-ray diffraction.The crystal structure of obtained black solid was consistent with that of pyrite crystal FeS₂?JCPDS 42-1340?.Scanning electron microscopy?SEM?with energy dispersive X-ray spectrometer?EDX?results showed that the FeS₂ black solid consisted of particles ranging from tens to hundreds nanometers,and atomic ratio of its elemental composition is Fe₂:S=1:2.The exposed crystal planes with lattice spacings of 0.313 nm and 0.221 nm corresponding to the crystal planes?111?and?211?were observed in high-resolution transmission electron microscopy?HRTEM?images.?2?FeS₂ could efficiently catalyze H₂O₂ to degrade PNP.The optimal reaction conditions in dark environment were optimized as:FeS₂ 0.5 g/L,H₂O₂ 5 mM,and the complete degradation of 50 mg/L PNP solution can be achieved within 10 min.FeS₂ could adjust the pH of PNP solution to be acidic.During the degradation reaction,H₂O₂ was uniformly consumed,and the concentration of Fe³⁺and SO₄^2-in the system increasesd.?3?When FeS₂ was used to degrade PNP for 3 continuous times(3^rd-FeS₂),the high degradation efficiency was kept well.The XRD,SEM,XPS characterization results showed that the physical and chemical properties of 3^rd-FeS₂ had no significant change,and a layer of oxide was formed on the surface consisted of Fe₂?SO₄?₃,FeSO₄,Fe₃O₄,Fe₂O₃ and so on.·OH and·O₂^-were generated in the degradation reaction,and the EPR results showed that the 3^rd-FeS₂ could generated·OH and·O₂^-more effectively.?4?Visible light could significantly promote the Fe²⁺/Fe³⁺cycle in the system and improve the efficiency of catalytic degradation.In the reaction process,the productions of·OH and·O₂^-increased significantly compared to the dark condition.h⁺was detected in both Pyrite-F and Pyrite-PF reactions,and·OH,·O₂^-and h⁺all played important roles in the degradation of PNP.?5?FeS₂?111?crystal surface has the smallest adsorption energy for H₂O₂ and it was most stable for adsorption of H₂O₂.In the process of FeS₂ catalyzing oxidation,an H₂O₂molecule was decomposed into a surface·OH and a free·OH to further degrade PNP.Degradation intermediates of PNP in Pyrite-F and Pyrite-PF reactions included4-nitrocatechol,4-nitropyrogallol,hydroquinone,hydroquinone,1,2,4-trihydroxybenzene and 2,4-dinitrophenol.The presence of 2,4-dinitrophenol also proved that h⁺can be produced in both Pyrite-F and Pyrite-PF reactions.In this article,FeS₂ catalyzing H₂O₂ for the degradation of PNP under dark and visible light irradiation was systematically studied,and its catalytic oxidation mechanism was further understood,which laid a certain foundation for the subsequent research.