Studies On Doped Carbon Nitride Photocatalysts With Organic Molecules Containing The M-Amino Group

Semiconductor photocatalytic technology has great applicate prospect in degrading environmental pollutants, generating H2 from water, capturing CO2 and synthesizing organic chemicals. The key of semiconductor photocatalytic technology is developing photocatalysts which are high efficient, environmentally friendly, stable and resonponding to visible light irradiation. Graphitic carbon nitride is an organic polymeric semiconductor with a band gap of 2.7 e V and an appropriate band structure for H2 and O2 evolution from water, as well as great chemical stability and good bio-compatibility, which make it a hot pot in photocatalytic technology field. However, the photocatalytic efficiency of carbon nitride is not satisfying because its narrow responding wavelenth range in visible light, and heavy photogenerated electron-hole pairs recombination. In this paper, molecule doping is used to modify carbon nitride for better photocatalytic performance.As the intermidiate of synthesizing graphitic carbon nitride from dicyandiamide has the characteristic structure of m-amino group(Figure 1-9), it’s rational to presume the molecules containing m-amino group could be used to dope carbon nitirde. So we choose three molecules, 2,6-diaminopyridine(DPY), 2,6-diaminopurine(DPU) and 2,4-diaminoquiazuoline(DQU) as the molecule examples containing m-amino group. The rationality and feasibility of m-amino group is verified and evaluated in theoretical calculations and actual test in detail.The electronegativity calculations and DFT calculations demostrate that doping carbon nitride with the three molecules could narrow its band gap. Moreover, the electronegativity and band struchture of doped carbon nitride are different because of the different group in the three molecules.Molecule doping carbon nitride in this research is synthesized through thermal polymerization with dicyandiamide as precursor, and copolymerized with different amount of the three moleules.The structural, optical, photoelectric and photocatalytic properties of the as-prepared samples were evaluated in detail. The results show that molecule doping samples have better visible light absorption and more narrow band gap, which is agreed to DFT calculations. Besides, the three molecules can also decrease the recombination of photogenerated electron-hole pairs, leading to better photocatalytic activity. The sample doped with 0.07 g DPY shows the best performance of double MO degradation rate comparing to pure carbon nitirde.In a word, molecules with m-amino group could achieve successful doping of carbon nitride, and its band structure can be controlled by the different group of molecules containing m-amino group. It’s an effective way for doping carbon nitride with organic molecules.