Study On The Photocatalytic Degradation Of Cu-EDTA Complex By G-C₃N₄

Graphite phase carbon nitrogen（g-C₃N₄）is a new type of non-metallic semiconductor photo-catalyst,which has a brad application prospect in the field of environmental restoration.In this paper,four kinds of carbon nitrogen:g-C₃N₄-C、g-C₃N₄-D、g-C₃N₄-M和g-C₃N₄-U,were successfully prepared,and g-C₃N₄-O was prepared by oxygen doping.The micro-structure and properties of these five carbonated nitrogen were characterized by XRD,FTIR,EPR,BET,SEM,TEM,XPS and UV-vis DRS.The application of g-C₃N₄ in photo-catalytic degradation of Cu-EDTA was studied.The differences of photo-catalytic properties of g-C₃N₄ prepared by different precursors were compared,and the improvement of photo-catalytic ability of oxygen doping on nitrogen carbide was also verified.The relationship between g-C₃N₄ micro-structure and photo-catalytic ability was studied,and the mechanism of photo-degradation of Cu-EDTA by g-C₃N₄ was compared before and after adding oxygen.The results show that:（1）Among the carbonated nitrogen prepared by pyrolysisusing cyanamide,dicyandiamide,melamine and urea as precursors at various temperatures,the best photo-catalytic effect of each precursor isthermal polymerization of cyanamide at 550℃（g-C₃N₄-C）,dicyandiamide at 550℃（g-C₃N₄-D）,melamineat 450℃（g-C₃N₄-M）and urea550℃（g-C₃N₄-U）,which are four kinds of graphite phase carbonated nitrogen powders.These four materials all have obvious 3-striazine structure,but their micro-structures have obvious differences.（2）When the catalyst dosage was 0.2 g/L,pH=2 and the initial concentration of Cu-EDTA was 0.1 mmol/L,four kinds of graphite phase carbon nitrides removal rate from high to low ranking of Cu-EDTA,in which g-C₃N₄-U on the removal rate of Cu-EDTA is78%during 30 min.（3）The reason for the higher removal efficiency of g-C₃N₄-U is that the larger specific surface area and smaller size shorten the distance between the photo-excited electrons and holes transferred to the surface of g-C₃N₄,and improve the utilization efficiency of photo-generated electrons and holes.（4）g-C₃N₄-O doped with oxygen has better crystallinity,larger specific surface area and thinner lamellar structure compared with g-C₃N₄-U,and photo-catalytic performance is improved significantly.The removal rate of g-C₃N₄-O to Cu-EDTA is 98%,which is 20%higher than that of g-C₃N₄-U.（5）The experimental results of free radical quenching showed that the active factors of g-C₃N₄-U in photo-degradation of Cu-EDTA were O₂,hole and oh,all of which played an important role,while the active factors of g-C₃N₄-O were only holes and ohs,and holes played a major role in the degradation of Cu-EDTA.In this study,the influence of precursors on the micro-structure of g-C₃N₄ was further understood,and the enhancement of photo-oxidation ability of g-C₃N₄ by oxygen doping was also explored,which provided theoretical support for the application of g-C₃N₄photo-catalytic technology in waste-water treatment.