The Design And Catalytic Performance Of Modified Carbon Nitride-based Catalysts

Graphite carbon nitride（g-C₃N₄）is widely used in the field of catalysis because of its abundant basic sites and a suitable visible light-driven band gap（2.7 e V）.Moreover,the layered structure often facilitates mass transfer during reaction,which makes g-C₃N₄ an idea supporter in heterogeneous catalysis.Based on the unique properties of graphite-phase carbon nitride,a series of modified carbon nitride-based catalysts have been designed and prepared in this work.We found that the obtained catalysts were highly efficient in Knoevenagel condensation,sulfa-Michael addition or visible light-mediated aerobic oxidation of olefins.Based on the abundant basic sites on g-C₃N₄,the two-dimensional（2D）layered g-C₃N₄ nanosheets（PCNS）was prepared by the exfoliation of bulk g-C₃N₄via ultrasound treatment.Characterization results showed that the obtained PCNS exposed more alkaline sites and has better dispersibility in water than bulk g-C₃N₄.As a result,it was highly efficient and universal in Knoevenagel condensation of aromatic aldehydes and active methylene compounds in water.In addition,the PCNS could be recovered by centrifugation and reused without significant reduction in catalytic activity.Based on the rich basic sites of graphite phase carbon nitride and the electron-deficient nature of boron atoms,we doped the boron（B）atoms in the tri-s-triazine ring of g-C₃N₄ framework,to develop the acid-base cooperative catalyst for nucleophilic addition.Characterization results demonstrated a foam-like hierarchical porous structure,as well as the coexistence of Lewis acid and base sites in the as-synthesized samples.As a result,the B-doped g-C₃N₄ acted as the efficient acid-base cooperative catalysts,significantly promoting the Knoevenagel condensation whose key step involves in nucleophilic addition.In addition,the bifunctional catalysts exhibited excellent reusability with simple treatment.Based on the suitable visible light-driven bandgap（2.7 e V）of g-C₃N₄nanosheets,we supported gold nanoparticles on the g-C₃N₄ nanosheets through liquid phase reducing method,to develop the photocatalysts of Au-_X/PCNS.Characterization results demonstrated that gold nanoparticles with the size of 1-4 nm were uniformly dispersed on the surface of g-C₃N₄nanosheets.The catalyst was highly efficient and reusable in visible light-driven oxidation of olefins with oxygen.