Study On Synthesis And Visible-Light-Induced Photodegradation Properties Of G-C₃N₄-Based Catalysts

Photocatalytic oxidation has emerged as useful method for mineralizing organic compounds in aqueous media. Graphitic carbon nitride（g-C₃N₄） is known as a kind of advanced non-mental visible-light semiconductor photocatalyst, exhibiting superior photodegradation ability towards organic pollutants. p H values of the system play an important role in the degradation process. In the present work, the influences of p H values on the photodegradable rate of Rh B for g-C₃N₄ system are studied extensively. In addition, the photocatalytic efficiencies of g-C₃N₄/Bi OI composites are also investigated. The photocatalytic mechanisms for pure g-C₃N₄ and g-C₃N₄/Bi OI composites are deduced reasonably and further confirmed experimentally.1. g-C₃N₄ was prepared by calcining urea. The obtained products were characterized using X-ray powder diffraction（XRD）, UV-Vis diffuse reflectance spectroscopy（DRS）, Fourier transform infrared（IR） and X-ray photoelectron spectroscopy（XPS）. The photodegradation performance of the samples was evaluated by degradation of Rh B, a kind of pollutant model. The effect of p H value of solution on degradation efficiency was investigated systematically. The types and relative amount of the intermediate products were determined by high performance liquid chromatography（HPLC） and high performance liquid chromatography-mass spectrometry（HPLC-MS）. The results show that the photocatalyst exhibits excellent degradation activity at a lower p H value. A large number of protons presented on the surface of g-C₃N₄ are considered to be conducive to the generation of hydroxyl radical, and thus accelerating the destruction of anthracene ring in Rh B. In contrast, Rh B was proved to be degraded through the removal of deethethyl in neutral condition.2. g-C₃N₄/Bi OI heterostructures were prepared by modulating the hydrolysis of Bi（NO3）3 in the presence of KI at room temperature with the g-C₃N₄ as a template. The as-prepared catalyst was characterized and analysized by XRD, DRS, XPS and HRTEM. The photocatalytic activities of the composites with different content of g-C₃N₄ were investigated by measuring the degradation efficiency of Rh B and MO under visible light irradiation. The degradation pathway of MO was also explored. Results show that in the the g-C₃N₄/Bi OI heterostructures, the three-dimensional globular flower like Bi OI was attached on the surface of g-C₃N₄ sheets. The degradation efficiency of MO is changed with the content of g-C₃N₄ and the optimal photocatalyst is 20.7wt% g-C₃N₄/Bi OI. The study on the mechanism indicats that in weak-acidic catalyst system the structure of MO changed from azo structure to quinoid structure, which is prone to be oxidized and mineralized finally by reactive radicals.