Fabrication and visible light photocatalysis of rod-like graphitic carbon nitride

Due to the limited supply of fossile fuel and its harmful effects on environment, photocatalysis has become a promising method to solve the energy crisis and environmental problems. It is of great significance to develop the novel photocatalysts that can be used to degrade the organic pollutants and split the water to produce hydrogen under visible and UV light irradiation. Due to its excellent features (including unique semiconductor energy band of 2.7 eV, excellent chemical stability, easy preparation and non-toxic), graphite phase carbon nitride (g-C3N4) has received great research interests. It has been regarded as a new kind of visible light catalyst because it does not contain metal compound commonly used in solar photocatalysis area. In this article, rod-like g-C3N4 (RCN) was synthesized via a “top-down” hydrothermal method using blocky g-C3N4 as the precursor without using any other template and additive. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV/Vis diffuse reflectance spectra (DRS), Fourier-transform infrared spectroscopy (FTIR), photoluminescence spectroscopy (PL) and nitrogen adsorption-desorption (BET) analysis techniques were used to analyze the RCN. The results indicated that under the hydrothermal condition, the high temperature and high pressure provided by the solvent cracked the blocky g-C3N4 into tiny particles, and then, the tiny particles connected along with the rod axis direction; at 6 h, a rod-like structure with length of 2.4 μm and diameter of 45 nm was obtained. The RCN improved the BET of g-C3N4, accelerated the separation of photo-generated electron-hole pairs and affected the energy band structure. Because of these properties, the obtained RCN exhibited an enhanced visible light photocatalytic activity when compared with that of blocky g-C3N4 according to the results of visible-light photocatalytic degradation of methylene blue and H2 production from water splitting. Under the same conditions, the degradation rate of RCN on methylene blue was much higher than that of bulk g-C3N4 (58.15%), which reached 98.50%, and the RCN exhibited excellent cycle stability. The hydrogen production efficiency of RCN of 12.83 μmol/h was significantly increased when compared with that of blocky g-C3N4 (4.35 μmol/h), which was about three times of g-C3N4. The possibility of the improvement of visible light photocatalytic activity might be due to the synergistic effects that caused by the rod-like structure. On the one hand, the fluorescence emission peak position of the RCN had slightly blue shifted compared with the bulk g-C3N4, indicating the band gap width became larger. On the other hand, the larger specific surface area of RCN caused by its unique rod-shaped morphology could provide more active sites, which could adsorb more reactive molecules and promote the transfer of surface charge.