Iron-doped Bismuth Tungstate For The Performance Of Pollutants Removal In Photocatalysis-fenton System

Fenton oxidation technology and semiconductor photocatalysis technology in advanced oxidation technology have been widely used in the field of environmental governance in recent years due to their advantages of high efficiency,environmentally friendly,and low energy consumption.However,Fenton oxidation technology and photocatalytic technology have disadvantages such as harsh p H conditions and low utilization of visible light,respectively,which are restricted by poor iron cycling and high carrier recombination rate,thus limiting the further applications.Based on the complementary relationship between Fenton technology and photocatalytic technology,photocatalysis-Fenton technology emerges as the times require.On the one hand,Fe³⁺promotes the separation of photogenerated carriers as a photogenerated electron acceptor;on the other hand,the rate-limiting step reaction of Fenton technology is accelerated via photogenerated electrons.Therefore,the photocatalysis-Fenton coupling technology exhibits a bright development prospect in dealing with environmental issues.As one of the Aurivillius oxide members,Bi₂WO₆ shows the characteristics of high oxidation ability,unique layer structure,and strong tunability.Given these,this study prepared bismuth tungstate（Fe-BWO）doped with different iron contents by a one-step solvothermal method based on Bi₂WO₆ semiconductor material,trying to make use of the interaction between photocatalysis and Fenton to make up for the deficiencies of Fenton oxidation technology,thereby improving the catalytic performance.And the possible mechanism of Photocatalytic-Fenton coupling in the removal of CIP and NO was explored.The specific contents are as follows:1.Iron-modified bismuth tungstate nanosheets were synthesized by adding Fe Cl₂into the precursor solution of bismuth tungstate.The prepared samples were characterized by XRD,TEM,HRTEM,and XPS to confirm that iron co-existing Fe²⁺and Fe³⁺and the former being the primarily valence state has been doped into the bismuth tungstate nanosheets.The results of the photoelectric performance test demonstrate that iron doping broadens the absorption of Bi₂WO₆ in the visible light region and promotes the separation efficiency of photogenerated carriers.Under the conditions of p H=3,H₂O₂concentration of 0.3 mmol/L,and 20 mg Fe-BWO catalyst,the degradation efficiency of50 m L of 50 ppm CIP can reach up to 83.7%in the photocatalysis-Fenton system,which is about 2.2 times that of the photocatalytic system.At the same time,Fe-BWO has a relatively stable degradation rate in the range of p H=3～11,and the removal efficiency of CIP is about 80%in the four cyclic degradation experiments.Through designed experiments,the mechanism of the effect of electrons among semiconductors,H₂O₂,and surface iron（≡Fe）in the Fe-BWO photocatalysis-Fenton system was investigated:H₂O₂was activated to·OH by≡Fe²⁺,and≡Fe²⁺were oxidized to≡Fe³⁺.At the same time,it caused the variation of the microenvironment near≡Fe³⁺with the experience of electron-rich Bi^（3-x）+region,which is more conducive to the adsorption and activation of O₂ to generate a large amount of·O₂^-.In addition,the Fe³⁺/Fe²⁺cycle was promoted by the reduction of≡Fe³⁺towards≡Fe²⁺induced by the generation of photogenerated-ecctrons with irradiation.2.Based on the Fe-BWO catalyst synthesized in Chapter 1,a micro-flow reactor for NO removal in photocatalysis-Fenton system with intermittent supplementation of H₂O₂was constructed.At room temperature,the 20 mg catalyst achieved a NO conversion rate of 75.8%and a NO_x removal rate of 56%with a single addition of 0.5 m L of 3 wt%H₂O₂and maintained a relatively stable NO removal capacity after 5 cycles.EPR and scavenger experiments demonstrated that the significant increase in reactive oxygen species·OH,·O₂^-and ¹O₂ within the photocatalysis-Fenton coupling system is one of the reasons for the improved NO removal activity.Among them,the greatest impact on NO removal efficiency caused by the quenching of e^-is attributed to the crucial role of e^-in promoting iron cycling and O₂ activation on the catalyst surface.Finally,the possible pathways for NO removal by the photocatalysis-Fenton system are proposed.