Synthesis, Modification And Photocatalysis Of G-C₃N₄

Photocatalysis has become one of hotspots in scientific research due to the continued environmental deterioration and the urgent demand for renewable clean energy in the human world. As a kind of nonmetal semiconductor, graphitic carbon nitride?g-C₃N₄? with the analogue structure of graphite has great potential applications in the field of photocatalysis. But in practical applications, the photocatalytic activity of g-C₃N₄ still needs to be improved. This paper tried to synthesize g-C₃N₄ using the template method and carried out the modification on the chemical composition and microstructure of g-C₃N₄. Comparison was made before and after the modifications. At the same time, the effect of scavengers was also studied from the external aspects.Based on catalysis of inorganic salt, g-C₃N₄ with high crystallinty was successfully synthesized from dicyandiamide in a solid medium of sodium chloride. Sodium chloride accelerated polymerization of dicyandiamide and increased crystallinty of g-C₃N₄, but also brought some cyano groups into g-C₃N₄. The modified g-C₃N₄ showed lower band gap and weaker fluorescence. Catalysis of sodium chloride also precipitated some sodion into crystal lattice of g-C₃N₄. At these locations, electron-hole pairs rapidly recombined, which dramatically reduced photocatalytic activity of g-C₃N₄.Sufficiently utilizing catalytic pyrolysis of sodium chloride and space confinement of solid particles, we triumphantly got water-soluble nanodot and nanoribbon in the upper centrifuged dispersion liquid of g-C₃N₄. Mixing characteristic between dicyandiamide and sodium chloride affected the microstructure of g-C₃N₄. When dicyandiamide and sodium chloride were mixed by grinding and then directly calcined, g-C₃N₄ nanoribbon was got. Dicyandiamide and sodium chloride were mixed by freeze drying and calcined after being molded by compression, which produced g-C₃N₄ nanodot. Due to nanocrystallization, the band gap of nanodot and nanoribbon increased to more than 3.0e V, which decreased their responsibility to light. Different special assemblies of g-C₃N₄ nanoribbon, such as flower clusters, tubes and sticks, could be formed under the integrated influence of Van Der Waals' force, hydrogen bonding and steric hindrance of alcohols.In order to improve the separation of electron-hole pairs, a hybrid catalyst of g-C₃N₄/r GO was prepared by directly heating the mixture of melamine and graphene oxide in air. During process of heating, graphene oxide was reduced into r GO and melamine polymerized into g-C₃N₄. Meanwhile, the heterojunction between them was formed through ?-? interaction. r GO facilitated separation of electron-hole pairs, but also caused light-screen effect. Affected by the two factors, g-C₃N₄/r GO-800 showed the highest photocatalytic activity, as 2.6 times as pure g-C₃N₄.On account of variable contributions of active species to photocatalysis, the effect of scavengers was also studied. Hydrogen peroxide had an ability to accelerate photo-degradation of rhodamine B and triethanolamine drastically brought photocatalytic activity down. Due to the consumption of e- with the reaction of H+ and h+ with OH-, the photocatalytic activity was p H-sensitive. With decreasing of p H value, photocatalytic activity increased sharply. Nevertheless, alkaline environment invalidated photocatalst.