Construction and Catalytic Mechanism of Photocatalytic and Heterogeneous Fenton System Based on γ-FeOOH Coupled Semiconductor with Visible Light Activity

Author:He Dong Lin

Supervisor:huang hong zhong li


Degree Year:2019





The environmental problems in modern society are becoming more and more serious.The treatment of waste and wastewater brings great challenges to environmental protection.The organic pollutants containing azo bonds(N=N)in printing and dyeing wastewater are not only toxic,but also difficult to decompose in the natural environment.Photocatalytic reactions and Fenton are both hot topics in the degradation of organic pollutants today.The photocatalytic reaction utilizes the photocatalyst to generate an active group for degrading organic pollutants under simulated sunlight,while in the Fenton reaction,hydrogen peroxide react with iron to form hydroxyl radical,which can react with organic pollutants.However,the Fenton reaction has the following disadvantages:(1)The pH of the reaction is generally 2-3,and special conditions are required before and after the reaction;(2)iron exists in the form of ions,which is easily lost with the solution;(3)it can be concluded that the rate of conversion of Fe3+to Fe2+is extremely low,so the reaction needs the addition of a large amount of Fe2+.Therefore,in order to overcome the shortcomings of the Fenton reaction,modern research uses solid iron oxide instead of iron ions to carry out the reaction,which is a Fenton-like reaction,which solves the loss of iron ions and the limitation of pH in the system.For the conversion between ferric iron and divalent iron,in view of the fact that electrons can be generated in the photocatalytic reaction and need to be separated from the holes,the photocatalytic reaction and the Fenton-like reaction are combined into the same system.The electrons in the photocatalysis are transferred to the Fenton-like reaction,so that the electrons can reduce the ferric iron to divalent iron,thereby circulating the Fenton-like reaction.In this paper,iron oxyhydroxide(γ-FeOOH)is used as a catalyst for the Fenton-like reaction.In the experiment,iron oxyhydroxide is first prepared,and then iron oxyhydroxide is combined with other visible light-active semiconductors to obtain a novel catalyst.Various characterization and photocatalytic activity detection were carried out,and finally the mechanism of photocatalysis and Fenton reaction synergistically degrading organic matter was analyzed.The main research contents are as follows:(1)g-C3N4/Ag/γ-FeOOH photocatalyst was prepared and the synergy of photocatalysis with heterogeneous fenton-like process was measured by degrading methyl Orange(MO).g-C3N4 can apply electron forγ-FeOOH to change Fe3+to Fe2+,andγ-FeOOH can help g-C3N4 to enhance the absorption of visible light.The Ag nanoparticles were photo deposited on the layer ofγ-FeOOH and g-C3N4 for the separation of electron-holes.g-C3N4(5%)/Ag/γ-FeOOH showed the great ability to degrade MO that 10 mg/L methyl orange can be completely degraded in 60 minutes.And the optimal concentration of H2O2,the effect of pH and the stability of the photocatalyst and synergistic mechanism of photocatalysity with heterogeneous fenton-like process were also discussed in this study.Finally,we also studied the mineralization process in which methyl orange was degraded into carbon dioxide and water.(2)In order to improve the catalytic efficiency of the photocatalytic coupled heterogeneous Fenton system,γ-FeOOH was grown in situ on the surface of rod Bi2O3 to construct a perfect cycle coupling photocatalysis and heterogeneous Fenton-like process.The degradation efficiency of this system was detected under visible light.γ-FeOOH/Bi2O3showed great better degradation efficiency than pure Bi2O3 andγ-FeOOH that it can degrade20 mg/L methyl orange solution in 80 minutes.And the amount of TOC was decreased to 4.3,suggests the system with great ability of oxidation that MO could be degraded to CO2 and H2O totally.PL spectra,trapping experiments and ESR test were also carried out to confirm the mechanism of photocatalysis with heterogeneous Fenton-like process,and the suitable conduction band(CB)of Bi2O3 matches the electric potential of iron ions was proved to be the key to keep the perfect cycle.Then optimal concentration of H2O2,the effect of pH and the stability of the photocatalyst were also detected.(3)In order to improve the stability of silver oxide with strong oxidizing ability and further improve the catalytic activity of the system,hydrothermal preparation of Ag in situ supported Ag3PO4 was coated withγ-FeOOH that the novel catalyst with high stability and high catalytic activity formed by electron transferation and coating structure.The silver element is grown in situ by hydrothermal method and supported on the surface of Ag3PO4,and then combined with Ag/Ag3PO4 withγ-FeOOH.The SEM and TEM images clearly show that the Ag/Ag3PO4 is encapsulated byγ-FeOOH,and Ag is between theγ-FeOOH and the Ag3PO4.Degradation experiments show that 15%γ-FeOOH/Ag/Ag3PO4 exhibits higher catalytic activity than Ag3PO4,γ-FeOOH,10%γ-FeOOH/Ag/Ag3PO4 and20%γ-FeOOH/Ag/Ag3PO4,in which it can degrade 30 mg/L methyl orange solution in 25minutes.And the cycle experiment proves that 15%γ-FeOOH/Ag/Ag3PO4 high stability.The high catalytic activity comes from the stability of Ag3PO4 and the photocatalysis and Fenton-like reaction synergistically degrade methyl orange.The high stability of Ag3PO4 is derived from the fact that encapsulated byγ-FeOOH and the electrons are transferred from Ag to γ-FeOOH.(4)In order to reduce the loss of hydrogen peroxide in the system,a carbonitride/iron oxyhydroxide system is constructed to produce hydrogen peroxide,and the two-electron reaction is driven by the Fenton-like reaction..In the experiment carbon nitride was combined with iron oxyhydroxide,and the SEM image shows that the iron oxyhydroxide is supported on the surface of carbon nitride sheet.By comparing the presence or absence of the addition of hydrogen peroxide in the reaction,it was found that under the condition of adding hydrogen peroxide,the g-C3N4/γ-FeOOH exhibited stronger catalytic activity and its hydrogen peroxide production was increased by more than 10 times.30%g-C3N4/γ-FeOOH exhibits the strongest catalytic activity and the strongest ability to generate hydrogen peroxide,and its excellent performance comes from the structure of 30%g-C3N4/γ-FeOOH and the appropriate mass ratio of g-C3N4 andγ-FeOOH.