Abstract:

g-C₃N₄, a semiconductor photocatalyst, was successfully prepared from NH₄SCN by thermal polymerization and was modified by secondary isothermal condensation. The phase structure and surface morphology of the product sample were characterized by XRD and SEM/TEM, and the photocatalyst activity was evaluated by degradation of the organic dye RhB. The results showed that the polymerization degree of the catalyst was increased and the layer spacing was shortened by secondary isothermal condensation modification. With the adjustment of isothermal condensation treatment time, the specific surface area and pore volume increased by 2.3 times and 4.7 times, respectively. In addition, a large number of amino groups, such as —NH—and —NH₂, resulted in a higher adsorption capacity of oxygen. The band gap width of the catalyst samples was widened from 2.77eV to 2.81eV after secondary isothermal condensation modification, the position of the valence band also increased to +1.625eV, and the photo-cavitation oxidation degradation ability was enhanced. There were N defects in the C—N\stackrel{\text{????}}{?}C position of the edge triazine rings, which significantly reduced the consumption of the photogenerated charges. At the same time, the intensity of the emission peak of the fluorescence spectrum decreased significantly, indicating that the photoelectron-hole binding rate decreased, and the effective utilization of the carrier significantly increased the catalytic reaction rate. After the irradiation under 420nm visible light for 90 min, the photocatalytic reaction rate constant increased from 0.006 to 0.031, the reaction rate increased by 5.2 times, and the degradation rate increased from 42% to 98%.

Key words: photochemical, catalytic, degradation, graphitic carbon nitride (g-C₃N₄), secondary isothermal condensation, nitrogen space, honeycomb orifice laminate

摘要：

采用二次等温热缩聚方式对通过NH₄SCN制得的g-C₃N₄进行处理，通过XRD和SEM/TEM等手段对所制备样品的物相结构、表面形貌等结构特性及有机染料RhB的降解效果进行了研究。结果表明，二次等温热缩聚改性使催化剂聚合度增加，层间距缩短，通过调节等温热缩聚处理时间构建了蜂窝孔洞薄片层表面结构，比表面积和孔容积分别增加了2.3倍和4.7倍；大量—NH—、—NH₂等氨基基团的产生，带来了更高的吸附氧含量；带隙宽度由2.77eV拓宽至2.81eV，且价带位置增至+1.625eV，使光生空穴拥有更强的氧化降解能力；边缘三嗪环结构单元中C—N\stackrel{\text{????}}{?}C位置上N元素缺失，减少了大量光生电荷的复合消耗，PL荧光光谱显示了明显降低的光生电子-空穴复合率，对载流子的充分利用使催化速率明显提高。有机污染物RhB催化降解效果显著，光催化反应速率常数由0.006提高到0.031，反应速率提高了5.2倍，在420nm可见光下照射90min，降解率由42%提高至98%。

关键词: 光化学, 催化, 降解, 石墨相氮化碳, 二次等温热缩聚, 氮空位, 蜂窝孔洞薄片层