Study On Construction Of In-situ Photocatalytic Fenton System With Graphite Carbon Nitride-based Materials And Application On Pollutants Removal

As one of the most effective Advanced Oxidation Processes（AOPs）in the water purification field,Fenton oxidation technology can generate hydroxyl radicals with strong oxidizing,thereby effectively treating difficult-to-degrade and persistent organic pollutants.However,classical Fenton oxidation technology encounters problems,such as low utilization rate of hydrogen peroxide（H₂O₂）,difficult to handle for iron sludge and high comprehensive treatment costs.Novel Fenton oxidation technology needs to be developed.Graphitic carbon nitride（g-C₃N₄）-based materials are a kind of modified materials based on organic photocatalytic semiconductor g-C₃N₄.It can produce H₂O₂ in situ by using ambient oxygen under visible light irradiation.Iron can be introduced into the system for construction of an in-situ photocatalytic Fenton system to achieve high-efficiency removal of pollutants.Based on the available high-efficiency H₂O₂ production composite photocatalytic material g-C₃N₄/PDI constructed by the research group with g-C₃N₄ and pyromellitic diimide（PDI）,this study explored the construction of an in-situ photocatalytic Fenton system after the introduction of iron,and applied it to the degradation of organic pollutants.The related mechanism was also studied.At first,the g-C₃N₄/PDI/Fe（g CPF）photocatalytic system was constructed and the mechanism of the system was analyzed.X-ray photoelectron spectroscopy（XPS）results proved that iron was successfully loaded onto the material in the form of trivalent iron.The characterization results of ultraviolet-visible diffuse reflectance spectroscopy（UV-vis DRS）and photoluminescence spectroscopy（PL）proved that after loading iron,the ability of the material to absorb light was enhanced,and the recombination of photogenerated electrons and holes was slowed down.Electron paramagnetic resonance（EPR）results showed that after loading iron,an in-situ photocatalytic Fenton system was successfully constructed.The main reactive oxygen species in the system changed from superoxide radicals(O₂^·–)to hydroxyl radicals（·OH）and O₂^·–.However,since ferric iron competes with dissolved oxygen for conduction band electrons,the degradation of p-nitrophenol（PNP）by g CPF was inhibited.Nitrilotriacetic acid（NTA）was introduced into the system as a reducing agent for trivalent iron after which the degradation of PNP increased from33%to nearly 80%.In addition,the influence of p H,NTA dosage,concentration of dissolved oxygen in water,and the photocatalytic stability of materials were studied and discussed through experiments.Subsequently,the reduced g-C₃N₄/PDI/Fe（R-g CPF）photocatalytic system was constructed and the mechanism of the system was analyzed.Iron was loaded after the g-C₃N₄/PDI was reduced and the XPS characterization results proved that the iron element existed in the form of Fe₂O₃.Quenching experiments and EPR results proved that the in-situ photocatalytic Fenton system was successfully constructed and the water in the system could be directly oxidized to form·OH.The degradation of R-g CPF material for BA was significantly improved compared with iron-free materials（R-g CP）.Results of Mott-Schottky and UV-vis DRS confirmed the ability of the R-g CPF material to oxidize water in the valence band,the energy band structure of the material had been optimized after reduction treatment,and the oxidation capacity was significantly enhanced.PL results showed that loading iron was beneficial to promote the separation of photogenerated electrons and holes.The effects of p H,anions and cations,concentration of dissolved organic matter（DOM）on BA degradation and the stability of R-g CPF materials have been studied and analyzed through experiments.