Investigations On The Mechanism About Efficient Degradation Of Organic Pollutants By Perylene Dimide Under Visible Light

Photocatalytic oxidation technology utilizes semiconductors to apply solar energy to purify water,which has received extensive research.Perylene dimide（PDI）with high optical and thermal stability,suitable energy band structure（Eg=1.78 e V）and excellent visible light absorption range（PDI can absorb light<700 nm）,is a photocatalytic material with practical application prospects.However,the photogenerated charge recombination of the intrinsic PDI photocatalytic material is severe,which makes the photocatalytic activity of the PDI photocatalytic material low.At present,researchers have proposed a variety of methods and strategies to improve the photocatalytic performance of PDI materials,but most of them focus on combining PDI materials with other photocatalytic materials to suppress the recombination of photogenerated charges.There are few studies on the photogenerated carrier separation efficiency of the PDI material itself.Based on the above background,this thesis takes PDI as the research object,systematically studies to improve the photocatalytic degradation performance of PDI materials by constructing an internal electric field and accelerating the interfacial charge transfer,and expounds the mechanism of improving the photocatalytic degradation activity of PDI materials in detail.The main research contents and conclusions are as follows:Through molecular structure control,PDI-CH₃（0.0034 D）,PDI-NH₂(1.1715 D and PDI-COOH（2.3257 D）photocatalytic materials with different molecular dipole strengths were synthesized.Visible light photocatalytic degradation of organic pollutants and H₂O₂preparation experiments found that the PDI-COOH photocatalytic material with the robust molecular dipole strength showed the highest photocatalytic activity,while the PDI material with the smaller molecular dipole strength showed the smaller photocatalytic activity.Relevant tests showed that the presence of molecular dipoles induces a larger internal electric field,and the internal electric field can effectively promote the photogenerated electrons and holes separation,so that the photocatalytic oxidation performance and reduction performance can be significantly improved.The above findings provide a basis for enhancing the internal electric field by means of molecular structure modulation and ultimately significantly improving the photocatalytic performance.Since theπ-electron delocalized channel in PDI photocatalytic materials is beneficial to electron transport and migration,the electron acceptor Fe³⁺was added to the PDI photocatalytic system to enhance the interfacial charge transfer and improve the visible light photocatalytic degradation of organic pollutants in water.Photocatalytic degradation experiments found that the addition of electron acceptor Fe³⁺can greatly improve the degradation rate of PDI photocatalytic system.At the same time,the structure of the PDI material can be more stabilized.Mechanistic study suggested that Fe³⁺plays the role of electron acceptor in PDI/Fe³⁺system.When the PDI photocatalyst is excited by light to generate photogenerated electron-hole pairs,Fe³⁺will undergo a reduction reaction with its photogenerated electrons at a faster speed to generate Fe²⁺.At this time,the effective separation of photogenerated charges is achieved to a certain extent.The photogenerated holes are also rapidly released for oxidation reaction with the organic pollutants adsorbed on the surface of the PDI material.Based on the above research findings,an effective method is provided for improving the photocatalytic activity of PDI materials for further practical applications.In this paper,the research findings not only provide experimental and method references for the development of highly active PDI materials but also explore an effective method for constructing an efficient photocatalytic degradation system.