Preparation Of Perylene Diimide Composite And Photocatalytic Degradation Of Phenolic Pollutants

Phenolic pollutants（phenol,bisphenol A,4-chlorophenol,etc.）are highly toxic pollutants that exist in raw water and industrial wastewater for a long time.Even at very low concentrations（about 10 ppm）,which will exhibit a great threat to the water environment and human health.Semiconductor-based photocatalytic technology is driven by solar energy,which can completely mineralize low-concentration organic pollutants and is one of the effective ways to remove phenolic pollutants.Compared with inorganic semiconductor materials,organic semiconductor materials have irreplaceable advantages of stronger structural adjustability,wider spectrum response range and wider raw material sources.Among organic semiconductors,perylene diimide（PDI）stands out for its excellent stability,high electron affinity and fast charge mobility.It is well known that commercial-grade PDI molecules have strong rigidity and not prone to self-assembly in conventional solvents.In addition,PDI usually has poor morphological characteristics due to its strong tendency to aggregate.Therefore,this paper first modified the molecular structure of commercial-grade PDI by introducing pentane substituents at its amide position.The treated PDI molecules exhibited spatial structure,which not only reduced the steric hindrance of PDI,effectively shortened the migration distance of photogenerated carriers,promoted theπ-πinteraction of PDI,but also changed the morphology of PDI supramolecular photocatalyst,affecting the speed and degree of photocatalytic reaction.Further based on the modified PDI,the photocatalyst was modified by introducing cocatalyst and semiconductor coupling strategy to enhance the carrier separation efficiency,to achieve deep mineralization of bisphenol A（BPA）.The main research results of this paper are as follows:（1）A series of all-organic composite perylene diimide/mesoporous graphite carbon nitride（PDI/mpg-C₃N₄）with spatial three-dimensional structure was prepared successfully by in-situ electrostatic adsorption.The structure of the material was characterized by various methods,and it was proved that PDI and mpg-C₃N₄ were successfully combined to form a heterojunction withπ-πinteraction.The performance of the catalyst in photocatalytic degradation of BPA under visible light was evaluated,and the degradation rate of BPA by the composite reached 90.03%within 2 h.In addition,free radical capture experiments and electron spin resonance spectroscopy were used to study the active species generated by PDI/mpg-C₃N₄ heterojunction under visible irradiation.The intermediate and final products in the photocatalytic process were analyzed by liquid chromatography-mass spectrometry（LC-MS）,and the photocatalytic mechanism of the experimental system was clarified by combining the light absorption characteristics of the material,the migration and transformation behavior of photogenerated carriers,and the free radical capture experiment.（2）Co-NG/PDI composites were constructed using nitrogen-doped graphene doped with Co single atom as the substrate for the self-assembly process of PDI.Co-NG as the co-catalyst of PDI can effectively improve the photocatalytic degradation of BPA by PDI.After proportional control,the optimal load of Co-NG is 7%.Under the same experimental conditions,the degradation rate of BPA by 7%Co-NG/PDI composites was 6.6 times and 7.2 times that of PDI monomer and Co-NG,respectively.The prepared materials were characterized by X-ray photoelectron spectroscopy（XPS）,X-ray diffraction（XRD）,Raman spectroscopy（Raman）,electron transmission microscope（TEM）,scanning electron microscope（SEM）,high-angle annular dark-field scanning transmission electron microscopy（HAADF-STEM）,Brunauer-Emmett Teller（BET）.The results show that the N-Co coordination can improve the catalytic performance of Co-NG,and the nitrogen-doped graphene can act as a charge transfer bridge,promoting the transfer of charge from PDI to the Co monatomic catalytic center.（3）In order to prepare more economical and efficient visible light photocatalyst,Co-W₁₈O₄₉/PDI heterojunction photocatalyst was prepared by one-step method.The crystal phase and chemical composition of the Co-W₁₈O₄₉/PDI heterojunction were studied by phase test,which proved the successful synthesis of the material.The large contact area between Co-W₁₈O₄₉and PDI was observed by TEM,which was beneficial to shorten the migration distance of photogenerated carrier and improve the photocatalytic activity of the material.Co-W₁₈O₄₉/PDI composites showed excellent photocatalytic activity for BPA degradation,and the degradation rate of BPA reached 91.2%within 150 min.The photoelectric test shows that Co-W₁₈O₄₉/PDI has excellent photogenic charge transfer ability.The optical test and the energy band relationship conclude that Co-W₁₈O₄₉/PDI forms a Z-scheme interface charge transfer path.The plasmon resonance effect of W₁₈O₄₉ semiconductor and heterojunction cooperate to promote electron hole separation and transfer of photocatalyst.