喹啉水溶液真空紫外降解过程中的吸收光谱分析

Absorption Spectra Analysis in the Degradation Process of Quinoline in Aqueous Solution by VUV Lights

在以低压石英汞灯为真空紫外光源降解喹啉水溶液的过程中，通过监测体系吸收光谱的变化，绘制不同时刻吸收光谱图，探讨了用紫外-可见吸收光谱作为在线检测反应进程的可行性。结合体系中底物浓度、COD、TOC和pH的变化，分析了各吸收光谱的变化特征和机制。研究表明，受吡啶环上N原子的影响，喹啉在不同pH环境下以不同的形式存在，吸收光谱也有较大的差异。在降解的过程中，体系的吸收光谱受到底物降解、中间产物生成和体系pH的共同影响。由于中间产物质子酸的生成，使喹啉以质子化的形式存在，当质子化产生的吸收增加与降解导致的吸收减少相等时，特征吸收峰313 nm处的吸收在1～3 min会出现平台，然后持续衰减。254 nm处的吸收先在5 min时增加到一个极大值，然后持续衰减，至30 min时衰减至0，而且此时溶液的吸收仅在220 nm以下区域，说明底物已降低得比较彻底。文章的研究结果表明，可以用吸收光谱来在线监测喹啉真空紫外降解的进程。

The feasibility of monitoring the degradation progress on line by UV-Vis absorption spectra in the degradation process of quinoline in aqueous solution using the low-pressure quartz mercury lamp as vacuum ultraviolet source was evaluated by the monitoring and protracting of the UV-Vis absorption spectra at different time. The characteristic and mechanism of the change in the UV absorption spectra were analyzed by monitoring the concentration of the substrate, COD （chemical oxygen demand）, TOC （total organic carbon） and pH value of the solution. It was showed that quinoline occurs in different forms under different pH conditions and consequently causes different UV-Vis absorption spectra due to the N atom in the pyridine ring. In the degradation progress, the UV-Vis absorption spectra were impacted by the degradation rate of the substrates, the production rate of the intermediates and the pH value of the solution. Proton acids were produced as intermediates and make quinoline occur in the form of its conjugated acid. When the increase in the absorption produced by the protonation was equal to the decrease induced by the degradation, the curve of the absorption at 313 nm, the characteristic absorption peak of quinoline, showed a flat in the duration of 1-3 min and then decayed continuously. In addition, the absorption at 254 nm reached a maximum at 5 min and then decayed continuously to nearly 0 at 30 min, when the absorption of the system only occurred in the region of wavelength shorter than 220 nm, indicating that the substrate was degraded completely. The research revealed that UV absorption spectra could be used to monitor the degradation process of quinoline in aqueous solution by VUV lights.