碳自掺杂g-C3N4光催化性能的原位光微量热-荧光光谱研究

通过在尿素前驱体中添加单宁酸, 原位缩聚形成碳自掺杂石墨相氮化碳(g-C₃N₄). 利用X射线光电子能谱(XPS)、 场发射扫描电子显微镜(FESEM)、 X射线衍射(XRD)仪和同步热分析(TG-DSC)等方法对碳自掺杂 g-C₃N₄的形貌、 物相结构和能带价态组分进行表征分析, 结合紫外-可见吸收光谱(UV-Vis)和原位光微量热-荧光光谱联用仪获得碳自掺杂g-C₃N₄降解罗丹明B的原位热/动力学信息和三维荧光光谱信息, 探讨了光催化降解罗丹明B的微观机制. 结果表明, 单宁酸浓度≤10 mg/mL时, 碳会取代七嗪单元结构的氮原子形成g-C₃N₄骨架碳自掺杂; 单宁酸浓度≥ 20 mg/mL时, 碳以无定形形式沉积负载在g-C₃N₄表面上形成无定形碳自掺杂. 骨架碳自掺杂g-C₃N₄形成的π电子有效缩短了禁带宽度, 减小了光生电子-空穴复合几率, 比无定形C掺杂g-C₃N₄显示出更优异的光催化性能, 催化主要活性物种为h⁺和·O{}_{\mathrm{2}}^{-}. 碳自掺杂g-C₃N₄光催化降解过程可分为光响应吸热、 降解污染物放热平衡过程和稳定放热3个过程. 其中骨架碳自掺杂g-C₃N₄(C/N摩尔比为0.844)在光照1000 s内, 三维荧光光谱检测的RhB降解率锐减, 光照1000 s后, 其RhB降解率为87.6%, 分别是原始g-C₃N₄和无定形碳自掺杂g-C₃N₄的3.13倍和1.95倍. 光照1000 s后, 光微量热计显示以矿化和降解非荧光发色中间产物为主, 并保持以热变速率为(0.9799±0.5356) μJ/s稳定放热, 为拟零级反应过程, 是光催化反应的决速步骤.

Study on the Photocatalytic Performance of Carbon Doped g-C3N4 Based on in situ Photomicrocalorimeter-fluorescence Spectrometry

Carbon-doped graphite nitride（g-C₃N₄） was synthesized by adding tannic acid to urea precursor. X-ray photoelectron spectroscopy（XPS）， field emission scanning electron microscopy（FESEM）， X-ray diffractometer（XRD）， synchronous thermal analysis（TG-DSC） and other methods were used to characterize the morphology phase and valence components of carbon doped g-C₃N_4. The photocatalytic degradation mechanism of Rhodamine B was investigated by using UV-Vis and in situ photomicrocalorimeter-fluorescence spectrometry to obtain in situ thermodynamics/kinetic information and 3D fluorescence spectral information of the degradation of Rhodamine B by carbon doped g-C₃N₄.The results showed that， when the tannic acid concentration was ≤10 mg/mL， the carbon would replace nitrogen atoms in the unit structure of heptazine to form g-C₃N₄ skeleton carbon doping. When the tannic acid concentration is ≥20 mg/mL， the carbon deposition load on the surface of g-C₃N₄ in amorphous form forms amorphous carbon doping . The skeleton carbon doped g-C₃N₄ to form π electrons effectively shorted the band gap width and reduced the photoelectron-hole recombination probability， showing excellent photocatalytic performance. The main active species of catalysis were h⁺ and ·O{}_{\mathrm{2}}^{-}. The photocatalytic degradation process of carbon doped g-C₃N₄ can be divided into three processes： endothermic of light responds， the balance process of endothermic of light responds and exothermic of pollutant degradation， and stable exothermic. The intensity of fluorescence emission peak of Rhodamine B over skeleton carbon doped g-C₃N₄（C/N=0.844） decreased sharply within the illumination of 1000 s， its degradation rate reached 87.6%，which was 3.13 times and 1.95 times over original g-C₃N₄ and amorphous carbon doped g-C₃N₄， respectively. After illumination of 1000 s， the photodegradation of the ring and intermediates without fluorescent chromophores were dominated， which maintained a stable exothermic rate of （0.9799±0.5356） μJ/s with a pseudo-zero order process. This process was the rate-determining step. Therefore， Rhodamine B photocatalysis was a pseudo-zero-order process rather than a first order process．