棒状石墨相氮化碳的制备及可见光催化性能

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

利用太阳能光解水制氢和降解有机污染物对解决能源和环境问题具有重要意义.本文通过"由上到下"水热法处理块状石墨相氮化碳(g-C_3N_4),得到棒状g-C_3N_4.采用X射线衍射分析(XRD)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、紫外-可见漫反射光谱(DRS)、傅里叶变换红外光谱(FTIR)、荧光光谱(PL)和比表面积测试(BET)等分析手段对棒状g-C_3N_4进行了表征.结果表明,棒状g-C_3N_4为长约2.4μm,宽约45 nm的棒状结构,该结构能增大g-C_3N_4的比表面积;同时观察到光生电子-空穴对的复合几率降低,并且由于缩聚程度的不同可能会影响能带结构.以可见光光催化降解亚甲蓝水溶液和光解水制氢的实验结果为依据评价了棒状g-C_3N_4的可见光催化活性,棒状g-C_3N_4的活性远优于块状g-C_3N_4.

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 ~tm 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 ~tmol/h was significantly increased when compared with that of blocky g-C3N4 （4.35 ~tmol/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.