Biomimetic Fabrication And Photocatalytic Performance Of G-C₃N₄-based Composite Photocatalytic Materials

In recent years,many efforts have been paid to developing high-performance visible-light photocatalysts for the potential applications in controlling environmental pollution and addressing energy shortage.Graphitic carbon nitride（g-C₃N₄）has become a typical photocatalyst and has been widely studied due to its visible light-driven band gap（2.7 e V）,high thermal stability and chemical stability,and easy preparation.In this paper,from the perspectives of sustainable chemistry and green chemistry,a platform strategy that takes advantages of the versatility of polydopamine（PDA）to biomimetically synthesize g-C₃N₄-based composite photocatalysts was designed.And then the platform strategy was verified via the synthesis of three kinds of g-C₃N₄-based composite photocatalysts.The fabrication of three composite photocatalysts promotes light absorption and separation rate of photo-generated electrons and holes,thus leading to efficient photocatalytic performance of g-C₃N₄.This platform approach will promote development of synthetic theory and technology of g-C₃N₄-based composite material and facilitate further development of high-efficiency and stable visible-light responsive photocatalysts.Firstly,g-C₃N₄ nanosheet/carbonized PDA（CNNS/CPDA）composite photocatalyst was prepared by the bioadhesion method.Compared with traditional synthetic processes,this strategy combines carbonization of PDA and exfoliation of bulk g-C₃N₄ simultaneously,simplifying the synthetic steps.CNNS/CPDA presents a continuous nanosheet structure with smooth surface.In contrast with g-C₃N₄,CNNS/CPDA composite photocatalyst exhibits higher photocatalytic activity for rhodamine B（Rh B）degradation,which can degrade 98%Rh B molecules under visible light irradiation within 60 min.The enhanced photocatalytic performance may be attributed to the enhanced light absorbtion and improved separation rate of photogenerated electrons and holes.Secondly,inspired by the bioadhesion and biomineralization mechanisms found in mussel and shellfish,the g-C₃N₄ nanosheet/Ti O₂（CNNS/Ti O₂）heterojunction was synthesized by using the PDA as both linker and inducer.In the as-prepared CNNS/Ti O₂ sample,Ti O₂ nanoparticles about 5 nm in size distribute uniformly on the CNNS surface and form the heterojunction structure with CNNS.Compared with pure Ti O₂ and CNNS,the CNNS/Ti O₂ heterojunction displays much higher photocatalytic performance for Rh B degradation,which can degrade nearly all Rh B molecules under visible light irradiation within 60 min and preserves excellent stability after four recycles.The enhanced photocatalytic activity can be attributed to the heterojunction structure formed between CNNS and Ti O₂,which can promote the separation of the photo-generated electrons and holes.Thirdly,CNNS/PDA/CdS composite photocatalyst was prepared by the biomimetic adhesion method.In the CNNS/PDA/CdS composite photocatalyst,CdS nanoparticles about 5-10 nm in size distribute uniformly on the CNNS surface.The CNNS/PDA/CdS composite photocatalyst possesses higher Rh B photocatalytic degradation performance than CdS and CNNS,which can degrade 97%Rh B molecules within 80 min under visible light irradiation.The enhanced photocatalytic performance may be attributed to the improved light absorbtion and separation rate of photogenerated electrons and holes.