Design And Preparation Of Defect Engineered Graphitic Carbon Nitride Photocatalysts And Their Photocatalytic Performance

Photocatalysis,as a new,efficient and green technology,has a wide prospect in hydrogen energy preparation and environmental protection.Graphitic carbon nitride（g-C₃N₄）is widely used in photocatalysis owing to its suitable energy band structure,easy preparation method and good stability.However,g-C₃N₄ obtained by calcination of pure nitrogen-rich precursors still exhibits insufficient visible light absorption and severe photogenerated carriers combination.In this work,the author systematically researched the defect engineering to solve the bottlenecks of g-C₃N₄,which is significant to the improvement of visible light absorption and photogenerated carriers separation of g-C₃N₄,as follows:Firstly,the author synthesized ethyl-modified g-C₃N₄ by copolymerization of urea and ethyl-thiourea.XRD,FTIR,XPS and ¹³C NMR revealed that ethyl successfully attached to the nitrogen atom in the tri-s-triazine ring skeleton of g-C₃N₄.The concentration of ethyl defects in the g-C₃N₄ skeleton increased with the addition of ethyl-thiourea during the copolymerization process.When ethyl-thiourea was added about 75 mg,CN-E-75 exhibit a high photodegradation of tetracycline hydrochloride and photocatalytic water splitting into hydrogen rate,which are nearly 1.5 and 1.6 times higher than pristine g-C₃N₄（CN-E-0）,respectively.UV-vis DRS imply that the introduction of ethyl groups could reduce the band gap of g-C₃N₄ and enhance visible light harvesting.The PL,time-resolved PL spectra and photoelectrochemical measurements confirm that optimal ethyl defects can enhance the efficiency of photogenerated carriers separation,improving the utilization of photogenerated carriers and photocatalytic efficiency.Based on the above work,the author further synthesized defect-engineered g-C₃N₄photocatalysts by copolymerization of urea and o-sulfonylbenzimidate.FTIR,XPS,¹³C NMR,and EPR indicate the successful incorporation of methylene,benzene and oxygen atom into the tri-s-triazine ring skeleton of g-C₃N₄.The introduction of benzene defects can not only enhance the light absorption of g-C₃N₄,but also suppress the photo-generated electron-hole pairs combination.When o-sulfonylbenzimidate was added about 75 mg,the photocatalytic degradation of tetracycline and photocatalytic water splitting into hydrogen activity was the highest.However,the excess defect severely damaged the morphological structure and reduced redox ability of g-C₃N₄.In summary,the author tailor the defect concentration of the g-C₃N₄ to optimize the visible light absorption and photo-generated carriers separation,and thus improve the photocatalytic activity.The author anticipates this defect engineering strategy can provide a theoretical reference for designing other efficient photocatalysts.