Synthesis And Characterization Of C₃N₄-base Composite Photocatalysts

Graphitic carbon nitride (g-C3N4) as a new novel metal-free polymeric photocatalysthas attracted much attention in the field of photocatalysis because it is inexpensive,non-toxic and easy to prepare. However, as a photocatalyst, there still exists some problemsin g-C3N4, such as the high recombination rate of photogenerated electron-hole pairs, therelatively low quantum efficiency, and only can absorb blue light, whose wavelength lessthan460nm, leading to the low sunlight utilization efficiency. Coupling g-C3N4with othersemiconductors is a common and effective technique for g-C3N4to enhance the lightabsorption, charge separation and the photocatalytic activity under the visible light.Therefore, in this work, the core-shell structure ZnO@mpg-C3N4photocatalyst wassynthesized by a ultrasonic dispersion method, the ZnO/mpg-C3N4was by a solvothermalmethod, and the CuTCPP/g-C3N4was by a ethanol stirring-dispersion method, makingcharge separation more efficient and reducing the probability of recombination, and thenenhancing photocatalytic activity significantly.The mpg-C3N4was preparated with the hard template method and then theZnO@mpg-C3N4photocatalysts with core-shell structure were synthesized via a facileultrasonic dispersion method. The results showed that the thickness of the shell can beadjusted by tuning the amount of mpg-C3N4. The photocatalytic properties of the core-shellstructure photocatalyst were much better than that of single C3N4or ZnO. TheZnO@mpg-C3N4sample at a weight ration of4%(mpg-C3N4/ZnO) has the highest UVlight photocatalytic activity which is almost2.0times as high as that of pure ZnO. TheZnO@mpg-C3N4-20%has the highest visible light photocatalytic activity which is almost5.0times as high as that of pure mpg-C3N4. The enhanced UV photocatalytic activity of theZnO@mpg-C3N4photocatalysts could be attributed to the hybridized effect between ZnOand mpg-C3N4, and the enhancement under the visible light irradiation is ascribed to thehigh separation and easy transfer of photogenerated electron-hole pairs at the heterojunctioninterfaces derived from the match of lattice and energy level between the mpg-C3N4shelland ZnO core.The ZnO/mpg-C3N4composite photocatalyst was successfully synthesized by a facilesolvothermal method. The characterization results indicated that ZnO particles dispersed uniformly on the mpg-C3N4sheet. The photocatalytic activity of ZnO/mpg-C3N4forphotodegradation of MB was much higher than that of pure mpg-C3N4both under thevisible light and simulated solar irradiation. The optimal mpg-C3N4content for thephotocatalytic activity of the ZnO/mpg-C3N4composites is75.1%, which is almost2.3times as high as that of pure mpg-C3N4under the visible light, and1.9times under thesimulated solar irradiation. This enhancement has been demonstrated to be due to the highseparation and easy transfer of photogenerated electron-hole pairs at the heterojunctioninterfaces derived from the match energy level between the ZnO and mpg-C3N4.The CuTCPP/g-C3N4photocatalysts were synthesized via the ethanolstirring-dispersion method. The results indicated that the photocatalytic activity wassignificantly enhanced by adding a small amount of CuTCPP. the optimum CuTCPPcontent for the photocatalytic activity of the CuTCPP/C3N4composites is0.75%, which isalmost2.2times as high as that of pure mpg-C3N4under the visible light. And the resultalso showed that CuTCPP can expand long wavelength light absorption of g-C3N4todegradate organics. The high separation and easy transfer of photogenerated electron-holepairs and then the enhanced visible photocatalytic activity of the CuTCPP/C3N4photocatalysts could be attributed to the hybridized effect between CuTCPP and g-C3N4.