Preparation Of Graphite Phase Carbon Nitride/Bipyridine Ru(?)Complex Z-Scheme Catalyst And Its Photocatalytic Reduction Of CO₂

The large-scale use of fossil fuels has gradually increased the concentration of carbon dioxide in the air,which is the main cause of the greenhouse effect.The photocatalytic conversion of carbon dioxide to small organic molecules is significantly important to solve both energy crisis and environmental problems.Reducing carbon dioxide using traditional chemical methods requires simultaneous supply of hydrogen and higher energy.photocatalytic reduction of CO₂ can convert solar energy into chemical energy under mild reaction conditions.The photocatalyst for photocatalytic reduction of CO₂ mainly include semiconductor materials such as TiO₂ and C₃N₄,metal complexes and molecular sieves.At present,the Z-scheme composite photocatalytic system composed of semiconductor/metal complexes has become a research hotspot in the field of photocatalysis because of its high activity and selectivity.Semiconductor materials are used as photosensitive centers and metal complexes as catalytic centers.photosensitive centers generate electrons and holes under visible light irradiation.The photogenerated holes are consumed by the electron donor,and the electrons are transferred to the catalytic center to finally catalyze the reduction of CO₂.First,graphite-phase carbon nitride semiconductor materials(bulk-g-C₃N₄)were prepared by calcination with different precursors such as urea.The morphology,structure and chemical elements of carbon nitride were characterized by SEM,BET,XRD,XPS and FT-IR.Bipyridine Ru(?)metal complexes containing different anchoring groups,such as phosphoric acid,methyl group,carboxyl group and methyl ethyl ester group,were successfully synthesized.The intermediates and products were characterized by FT-IR and¹H-NMR.Semiconductor/metal complex Z-type photocatalyst was successfully prepared by loading bipyridine Ru(?)complex with carbon nitride semiconductor materials via?-?stacking.The composite catalyst was characterized by Uv-vis-DRS and PL.Graphite-phase carbon nitride/bipyridine Ru(?)complexes were used in visible-light photocatalytic reduction of CO₂.The results showed that bulk-g-C₃N₄/Ru CP had better catalytic performance and selectivity when carbon nitride was prepared with urea as precursor and loaded bipyridine Ru(?)complex containing phosphoric acid group.Then,in order to further improve the catalytic reduction performance of photocatalysts,g-C₃N₄-nanosheets were successfully prepared by ultrasonic stripping of bulk-g-C₃N₄.The morphology of g-C₃N₄-nanosheets was characterized by SEM,TEM and AFM.The crystal structure and chemical state were characterized by XRD,FT-IR and XPS.The optical properties were determined by PL and UV-vis-DRS.The prepared g-C₃N₄-nanosheets material is loaded with nano Ag particles by photocatalytic reduction method.The g-C₃N₄-nanosheets/Ag/Ru composite catalyst was prepared by combine g-C₃N₄-nanosheets/Ag and Ru complex through?-?stacking,and characterized by FT-IR,UV-vis-DRS and PL.The g-C₃N₄-nanosheets/Ag/Ru composite catalyst was used for visible-light photocatalytic reduction of CO₂ to formic acid.The results show that g-C₃N₄-nanosheets/Ag/Ru has excellent catalytic performance.In photocatalytic reduction of CO₂,TON is 290 at 5 h and selectivity to formic acid is 78.3%.