Study On The Preparation And Photocatalysis Of Graphitic Carbon Nitrides

The g-C3N4 photocatalyst has been synthesized by a facile chemical pyrolysis method, which is based on the self-condensation of cyanamide, dicyandiamide, and melamine to generate g-C3N4; and the M-g-C3N4 (M=Ag, Fe, Cu, Co, Ni) was synthesized by doped various transition metals; at the same time, we have synthesized the Ag-g-C3N4 by different methods. The samples were characterized by XRD, UV-vis spectroscopy, FT-IR spectroscopy, elemental analysis and TEM. Then, the methylene blue (MB) was selected as a photo-degrading goal to evaluate the photocatalytic activity of as-prepared samples. The aim is to investigate the effect of the precursors, calcination temperature, the doping metals on the structure and photocatalytic activities of the samples. The main research contents and results are as follows:(1) The bulk g-C3N4 power have been synthesized by directly heating the cyanamide, dicyandiamide, and melamine at different temperature, which is based on the self-condensation of the precursors. Photocatalytic activity of g-C3N4 was evaluated by the photodegradation of MB. The results indicate that the samples obtained from dicyandiamide at 520℃exhibite highest activity. The initial concentration of methylene blue is 50mg/L and the degradation rate could reach 66% after 5h visible-light irradiation;(2) The bulk g-C3N4 was modified by doping the metal Ag, Fe, Cu, Co, Ni and to prepare M-g-C3N4 (M=Ag, Fe, Cu, Co, Ni) heterojunctions. Photocatalytic activity of the obtained sample was evaluated by the photodegradation of MB. And the results show that the Ag-doped has the highest photocatalytic activity;(3) We compared the photocatalytic activities of the Ag-g-C3N4 samples which were prepared by photodeposition and impregnation and doping methods. The photocatalytic activity of Ag-g-C3N4 prepared by doping method is better than the other two methods, and the best doping content for Ag is 0.1wt.%. This is due to the appropriate amounts of Ag ions have been inserted into a g-C3N4 matrix and form new bonds. The metal components strongly modify the electronic properties of g-C3N4. Thus, the Ag may facilitate the electron transfer and improve chemical reactivity.