Preparation Of Iron-based Graphite Phase Carbon Nitride Photocatalyst And Its Catalytic Performance

As a new kind of nonmetallic and visible light catalytic material,g-C₃N₄ has the advantages of visible light catalytic activity,high chemical/thermal stability,nontoxic and easy preparation.In this paper,a series of Fe₃O₄/g-C₃N₄ and BiFeO₃/g-C₃N₄composites with different contents of Fe₃O₄ and BiFeO₃ were prepared and controlled.XRD,SEM,TEM,UV-vis DRS and XPS methods were used to analyze the crystal structure,morphology,chemical composition and valence structure of the compounds.The synthesized composites photocatalytic degradation of simulated organic pollutants?Rh B and tetracycline?to determine the optimal reaction conditions.The possible reaction mechanism was proposed by the radical quenching experiment and the band structure of the prepared composite catalyst.1.Preparation and Characterization of Fe₃O₄/g-C₃N₄Using melamine as a precursor,g-C₃N₄ was prepared by thermal polycondensation.On this basis,Fe₃O₄/g-C₃N₄ with different content of Fe₃O₄ was synthesized by coprecipitation method using ferric chloride and ferrous chloride as iron sources.The experiment used different characterization methods to analyze the prepared samples.The results show that the Fe₃O₄ nanoparticles successfully deposited on the surface of g-C3N4 and dispersed evenly,the combination of the two reduces the bandgap of g-C3N4 from 2.86e V to 2.11e V,showing good absorption of visible light.2.Study on the Photocatalytic Activity and Photocatalytic Mechanism of Fe₃O₄/g-C₃N₄ CompositesUsing Rh B as a simulated pollutant,photocatalytic degradation experiments were carried out under simulated sunlight.The results show that the photocatalytic activity of Fe₃O₄/g-C₃N₄ is obviously stronger than that of pure g-C₃N₄ at a certain Fe₃O₄content,of which the photocatalytic activity of FOCN-10 is the best,and the degradation process of Rh B accords with the first-order kinetic model.Under the conditions of p H=3⁵ and catalyst dosage is 0.5g L^-1,the Rh B removal efficiency was better.From the TOC removal rate of Rh B solution,The Rh B molecule can be finally degraded into CO₂ and H₂O.In addition,the prepared Fe₃O₄/g-C₃N₄ composite photocatalyst shows good stability and is easy to be magnetically recovered.The good photocatalytic activity of FOCN-10 is mainly due to the uniform dispersion of Fe₃O₄ nanoparticles with small particle size and good conductivity on the surface of g-C₃N₄,reducing the forbidden band width,expanding the visible light absorption range,and improving the visible light absorption ability.In addition,heterostructures were formed between Fe₃O₄ and g-C₃N₄,and Fe₃O₄ nanoparticles were used as the electron storage body to inhibit the recombination of photogenerated carriers.Through the free radical quenching experiments we know that h⁺,·O₂^-and·OH are involved in the degradation process of Rh B,the order of influence is h⁺>·O₂^->·OH.3.Preparation and characterization of BiFeO₃/g-C₃N₄ compositesBiFeO₃ was prepared by sol-gel method using ferric nitrate and bismuth nitrate as iron source and bismuth source respectively.BiFeO3/g-C3N4 with different BiFeO3content was synthesized and controlled by a simple mechanical grinding-calcination method.The prepared samples were characterized by different techniques and the results showed that BiFeO₃ particles of about 0.2um⁰.6um were successfully composited with layered g-C₃N₄.The morphologies and crystal forms of the two composites did not change obviously after the composite.The combination of g-C3N4and BiFeO₃ effectively expanded the g-C₃N₄ visible light response range,there by increasing the absorption of visible light.4.Study on the Photocatalytic Activity and Photocatalytic Mechanism of BiFeO₃/g-C₃N₄ CompositesThe prepared catalyst was combined with persulfate to form a visible light Fenton-like reaction system under the simulated sunlight,and the tetracycline degradation experiment was carried out.The results show that BiFeO₃/g-C₃N₄composite photocatalyst can activate persulphate under visible light better than g-C3N4and BiFeO₃,and exhibit good degradation effect on tetracycline.Among them,the BFO/CN-10 had the best Fenton-like photocatalytic activity and the degradation of tetracycline was in accordance with the second-order kinetic model.The photocatalytic activity of tetracycline was better under the conditions of p H=3⁶,catalyst dosage is1.5g L^-1 and PS concentration is 2mmol L^-1.As can be seen from the TOC removal rate of tetracycline solution,the composite catalyst can eventually degrade tetracycline to harmless H2O and CO2.From the cycling runs experiments we can see that the prepared BiFeO₃/g-C₃N₄ composite photocatalyst showed good stability.Compared with single-component photocatalysts,such as g-C₃N₄ and BiFeO₃,BiFeO₃/g-C₃N₄ composites have a wider visible-light response range and lower photogenerated electron-hole recombination rate due to the suitable valence band structure and Schottky junction between the two composite components.In addition,Fe³⁺in the material can effectively activate PS in the system after combining with photoelectrons.Therefore,the composite exhibits good Fenton-like photocatalytic performance and is capable of photocatalytically degrading tetracycline in combination with PS.Through the free radical quenching experiment and ESR test,we know that h⁺,·O₂^-and·OH and·SO₄^-are involved in the degradation process of tetracycline in the visible light Fenton-like reaction system.