Preparation And Photocatalytic Performance Of Graphitic Carbon Nitride And Three Dimension Graphene-based Photocatalysts

Photocatalytic degradation of organic pollutant with inexhaustible solar energy has already been widely researched for solving the growing pollution issues.Developing an active and stable visible-light responsive photocatalyst is crucial for practical applications of photocatalysis technology.As a metal-free polymeric semi-conducting material,graphitic carbon nitride?g-C₃N₄?has become a very hot research topic since the pioneering work in 2009 for visible-light photocatalytic water splitting.And g-C₃N₄ has been recognized as a novel photocatalyst in multifaceted applications due to its appropriate band structures,excellent chemical and thermal stability,low-cost and environmentally friendly features.However,the photocatalytic performance of bulk g-C₃N₄ was severely restricted by its low specific surface area,insufficient solar-light absorption,and fast recombination of photo-generated electrons and holes caused by?–?conjugated electronic system.In this study,we modify g-C₃N₄ in different ways to improve its photocatalytic activity and stability.The details are as follows:?1?Graphitic carbon nitride?g-C₃N₄?was prepared by different precursors under the same conditions.After a series of comparative experiments and various characterization,it was concluded that dicyanamide could be used as the best precursor for the preparation of g-C₃N₄.Considering that the g-C₃N₄ nanosheets?CNN?exhibited enhanced activity and were easier to form a three-dimensional porous aerogel with graphene sheet compared with the bulky phase,H₂SO₄ was regarded as exfoliation reagent to obtain high stability CNN by combining ultrasonic treatment.It was found that acid and ultrasonic treatment had great influence on the structure and properties of carbon nitride,which not only reduced the size of the particles significantly,but also improved the photocatalytic performance.And it was helpful for the preparation of the subsequent g-C₃N₄-based composites.?2?A new type of three-dimensional?3D?ternary graphene-carbon quantum dots/g-C₃N₄nanosheet aerogel?GA-CQDs/CNN?visible-light-driven photocatalyst was synthesized via a two-step hydrothermal method.In this unique ternary photocatalyst,both carbon quantum dots?CQDs?and reduced graphene oxide?rGO?could improve the visible light absorption and promote the charge separation.Furthermore,reduced graphene oxide?rGO?could act as a supportor for the 3D framework.Such a ternary system overcame the drawbacks of bulk g-C₃N₄and achieved the enhanced photocatalytic activity and long-term stability.A series of GA-CQDs/CNN photocatalysts were prepared by changing the mass ratio of GO to CNN.As a result,the methyl orange?MO?removal ratio of GA-CQDs/CNN-24%was up to 91.1%,which was much higher than that of CNN under the identical conditions.Moreover that GA-CQDs/CNN-24%exhibited inappreciable loss of photocatalytic activity after four-cycle degradation processes.It is believed that such a well-designed approach may pave the way for preparing other 3D ternary photocatalysts with high photocatalytic activity and further utilizations in the field of environment.?3?Another new type of three-dimensional?3D?ternary graphene-g-C₃N₄ nanosheet-AgBr?GA-CNN-AgBr?photocatalyst was synthesized by introducing AgBr nanoparticles into GA-CN aerogel via hydrothermal method for the first time.This kind of distinctive GA-CNN-AgBr superhybrid photocatalytic system has greatly overcomed the drawbacks of the single component and realized high charge separation efficiency,strong photocatalytic activity and long-term stability.Furthermore,due to its macroscopic block appearance,GA-CNN-AgBr were easy to recover and recycle,and therefore showed a good prospects in the practical application of pollutant degradation.