Effects Of Modification Of Carbon Quantum Dots And Construction Of Photocatalytic Self-fenton System On The Morphology And Photocatalytic Properties Of Carbon Nitride

As a new technology of environmental protection,semiconductor photocatalysis has great research value and social benefits in purifying air,producing hydrogen and oxygen,degrading pollutants and purifying water because of its effective use of solar energy.Among various photocatalysts,graphite carbon nitride（g-C₃N₄）,a non-metallic semiconductor photocatalyst,has been widely studied in the field of photocatalysis due to its advantages of green and simple synthesis,cheap raw materials,visible light response,appropriate band gap structure and stable physical and chemical properties.However,its inherent shortcomings still limit the practical application of g-C₃N₄.For example,the response range of visible light is narrow,the specific surface area is small,the migration efficiency and separation ability of photogenerated carriers are poor,and the hydroxyl radical（·OH）cannot be generated due to the limitation of band gap.In order to solve the above problems,g-C₃N₄ was modified by carbon quantum dots and a photocatalytic auto-fenton system was constructed in this study.On the one hand,the morphology of g-C₃N₄ synthesized by supramolecular self-assembly method was regulated and the photoelectrical properties were optimized by loading carbon quantum dots.On the other hand,the highly efficient photocatalytic autofenton system was constructed through the co-modification of Fe ions doping and carbon quantum dots loading.The Fenton reaction was introduced into the g-C₃N₄ system synthesized by supramolecular self-assembly method to realize the effective utilization of H₂O₂ and the generation of·OH with strong oxidation.The above two modification methods improved the degradation efficiency of g-C₃N₄ for organic pollutants in water environment,providing a new research idea for constructing efficient g-C₃N₄ photocatalytic system by optimizing supramolecular self-assembly method.The main contents and conclusions of this paper are as follows:（1）The morphology of supramolecular self-assembly g-C₃N₄（MCN）was regulated by adding an appropriate amount of carbon quantum dots（N-CQDs or CQDs）in the process of forming supramolecular self-assembly system with melamine and cyanuric acid.The morphology of MCN was regulated by the interaction force between MCN,which was influenced by the oxygen-containing groups on the surface of carbon quantum dots.The microstructure of the composite was characterized as a porous cone-shaped sphere,and the specific surface area was increased to 108.57 m²·g^-1,about 20 times that of g-C₃N₄(5.5m²·g^-1)prepared by direct thermal polymerization.（2）The degradation of tetracycline hydrochloride（TC-HCl）by carbon quantum dots modified supramolecular self-assembled carbon nitride photocatalysts（N-CQDs/MCNx）showed that N-CQDs/MCN1 had the best photocatalytic activity.The degradation rate of TC-HCl was 89%within 120 min.The enhanced photocatalytic activity of photocatalytic materials was due to the synergistic effect of the loose porous sphere structure and the improved photoelectric performance of N-CQDs.·OH,·O₂^-and h⁺are the main active substances in the photodegradation of TC-HCl due to the material’s energy band structure.Liquid chromatography-mass spectrometry（LC-MS）was used to identify the intermediates and speculate the possible degradation path.（3）A novel photofenton catalyst Fe/N-CQDs/MCN1 was synthesized by means of simple ultrasonic deposition and thermal polymerization.The photofenton system was constructed by doping appropriate Fe ions into N-CQDs/MCN1 photocatalyst.Taking organic pollutants（TC-HCl,ciprofloxacin and bisphenol A）in simulated wastewater as the target pollutants,Fe/N-CQDs/MCN1photofenton catalyst has a significant degradation effect on the target pollutants.The degradation rate of ciprofloxacin by 0.2Fe/N-CQDs/MCN1 was 76%within120 min.According to the results,the spontaneous and continuous photofenton reaction of Fe/N-CQDs/MCN1 and the modification of N-CQDs are the reasons for enhancing the catalytic activity of the materials,and·OH and·O₂^-are the main active substances for degrading pollutants.