Design,Synthesis And Photocatalytic Properties Of Novel Two-dimensional Covalent Organic Polymers Based On Amide Bonds

With the development of modern industry,human has been paying grate attention to scientific and technological development,resulting in increasingly severe energy crisis and environmental pollution problems.Solar energy has become one of the most popular research area because of its inexhaustible,green,and pollution-free characteristics.In recent years,photocatalytic technology has been applied tophotocatalytic hydrogen generation and organic degradation.It is the key to design a catalyst with excellent performance to decompose water to produce hydrogen and catalyze the degradation of organic pollutants.Covalent organic polymer（COP）has excellent visible light absorption and structural designability,which has a great application prospect in the field of photocatalysis,but its application is limited by its fast photo-generated electron recombination efficiency and preparation process.In this paper,new covalent organic polymers（COP）based on the amide bond are designed and synthesized using different methods and reaction conditions,and then applied to the photocatalytic degradation of Rh B and photocatalytic hydrogen production.（1）A covalent organic polymer（MeTMC-COP）based on triazine ring structure was prepared by high-temperature solid state reaction method with melamine and trimethyl benzoyl chloride used as monomers.FT-IR,BET,SEM,XRD,UV-Vis DRS and M-S were used to characterize the structure,morphology and optical properties of the photocatalyst.Rhodamine B（Rh B）was used as the target pollutant to investigate the photocatalytic activity of the MeTMC-COP products.With the increase in reaction time,the crystallization performance of the catalyst is enhanced.When the duration time of solid-state reaction was assigned to 14 h,the bandgap of the MeTMC-COP catalyst was the smallest.The M-S curve calculation showed that the MeTMC-COP valence and conduction band were 1.615 and-0.625 e V,respectively.After visible light irradiation for 105 min,the degradation rate of Rh B solution reached 99%.（2）A fluorinated covalent organic polymer（6FAPTMC-COP）was synthesized from2,2-bis（3-amino-4-hydroxyphenyl）hexafluoropropane（6FAP）and trimethyl benzoyl chloride（TMC）by grinding and high-temperature solvothermal method.FT-IR,XRD,SEM,TEM,UV-Vis,DRS,EIS and M-S were used to characterize the structure,morphology and optical properties of the photocatalyst.Its photocatalytic performance under simulated visible light was studied,taking rhodamine B（Rh B）as the typical pollutant.The results showed that the sample prepared by the grinding method had a wide bandgap and poor photocatalytic performance.Compared with the grinding method,the photocatalytic degradation efficiency of Rh B by6FAPTMC-COP was the best when reacting with high-temperature solvothermal method for 18h.After 105 min of illumination,the degradation rate reached 98.6%,and the photocatalytic reaction rate constant was 2.43 times that of the grinding method.Covalent organic polymer（PBO-COP）containing benzoxazole structure was then prepared by high-temperature cyclization reaction with 6FAPTMC-COP as precursor.Compared with 6FAPTMC-COP,the benzoxazole structure in the PBO-COP reduced the bandgap of the catalyst and improved the photocatalytic degradation performance.The rate constant of photocatalytic hydrogen production from water is 11.3μmol?g^-1?h^-1.（3）g-C₃N₄ was prepared by high-temperature thermal polymerization with urea as raw material.MeTMC-COP supported g-C₃N₄ composite photocatalyst（g-C₃N₄/MeTMC-COP）was prepared by.SEM,BET,XRD,FT-IR,UV-Vis DRS,PL and EIS were used to characterize the morphology,structure,and optical properties of the composite photocatalyst.Rhodamine B（Rh B）was selected as the pollutant to study the photocatalytic degradation performance of different proportions of the composite photocatalyst and its photocatalytic hydrogen production rate.The results showed that when the mass ratio of g-C₃N₄ to MeTMC-COP was 3:1,the specific surface area of the g-C₃N₄/MeTMC-COP composite could reach 40.95 m~2g^-1,which was higher than that of g-C₃N₄(25.22 m~2g^-1).It can provide more active sites to participate in the photocatalytic pro cess,and its fluorescence peak is the weakest,and the recombination of photogenerated electrons and holes was inhibited.Compared with g-C₃N₄,after 75 min of visible light irradiation,the degradation rate of Rh B by 3:1 g-C₃N₄/MeTMC-COP is as high as100%.Its photocatalytic hydrogen production efficiency was 1.62 times higher than g-C₃N₄,and the rate constant was 11.8μmol·g^-1·h^-1.