Preparation And Photocatalytic Performance Of Graphene Modified Carbon Nitride Composite Materials

g-C₃N₄ is a graphene-like polymer material,non-toxic,with chemical and thermal stability and suitable band gap,which can absorb visible light.However,single-component photocatalyst has low solar energy utilization,high electron-hole recombination rates,and low quantum efficiency,which limits their wide application.Therefore,broadening absorption range,inhibiting photocarrier recombination,and improving catalytic activity have become a research focus in materials,chemistry and environment field by modifying the photocatalyst.Layered structure materials such as graphene have excellent physical and chemical properties.Graphene and graphite-like carbon nitride are used as carrier materials to construct nano-composite photocatalytic materials,which not only retain their excellent properties,but also may produce synergistic effects to enhance photocatalytic activity.This paper focused on the morphology control,heterostructure construction,element doping and other methods to improve the photocatalytic degradation of the carbon nitride and graphene catalyst and mainly includes the following three parts:Urea,dicyandiamide and melamine as precursors are calcined at 550°C for 3 hours in a muffle furnace to prepare graphite phase carbon nitride.The characterization and analysis of the obtained product were performed by X-ray diffraction,scanning electron microscopy,ultraviolet-visible diffuse reflectance spectroscopy,and fluorescence emission spectroscopy and other instruments.The physical and chemical properties such as the morphology and properties of g-C₃N₄ prepared from different precursors were investigated.The photocatalytic degradation experiment was performed using Rhodamine B solution as simulated wastewater.The results show that the g-C₃N₄ obtained by calcining different precursors is different in physical chemistry such as morphology,energy band,carrier recombination rate,and specific surface area.Overall,the g-C₃N₄ obtained by calcining urea has better photocatalytic activity.Under visible light irradiation,the degradation rate can reach 95%in 2 h.A facile one-step calcination method for the preparation of g-C₃N₄/rGO photocatalysts using urea and GO is presented.The optimum conditions were determined by detecting catalyst amount.The experimental results show that the photocatalytic effect was the best when annealed at 550°C with 3 h and the composite ratio of graphene oxide and urea precursor is 0.004 wt‰.After 90 min,the degradation rate can reach more than 90%,which is1.4 times higher than that of the pristine g-C₃N₄.Compared with the sample without graphene of carbon nitride composite,recombination rate of photogenerated electron-hole was obviously suppressed and the transmission of photogenerated carriers was accelerated.Using urea as a reducing agent and nitrogen-doping agent,solvothermal method was used to reduce graphene oxide to a three-dimensional pore structure to prepare nitrogen-doped three-dimensional graphene.The melamine water bath was hydrothermally treated and evaporated to prepare a composite catalyst.The results show that the photodegradation rate of C₃N₄ after the composite nitrogen-doped three-dimensional graphene is 6.5 times than that of the C₃N₄ formed by direct calcination of melamine.The enhanced photocatalytic performance can be attributed to the greater specific surface area and the stronger carrier migration rate of the catalysts with a three-dimensional graphene skeleton.