Study on the Effect of Temperature on Deep Eutectic Solvent by Two-Dimensional Raman Spectroscopy
WU Xiao-jing1, LI Zi-xuan1, ZHANG Yan-dong1, CHENG Long-jiu2
1. School of Chemistry and Chemical Engineering, Hefei University of Technology, Hefei 230009, China
2. College of Chemistry & Chemical Engineering, Anhui University, Hefei 230601, China
Abstract：A new green solvent, deep eutectic solvent (DES) performs well in many chemical processes. It should have broad application prospects in popular fields. The spectral analysis of DES is usually based on one-dimensional spectroscopy. However, the spectral data are inaccurate due to low resolution and overlapping peaks. Two-dimensional Raman spectroscopy (2D Raman) can significantly improve spectral resolution and find overlapping peaks. In addition, important conclusions such as the changing order of different spectral peaks and their interaction under external disturbance could be obtained to realize the accurate analysis of complex systems. In this article, DES has been synthesized from choline chloride (ChCl) and ZnCl2. Raman experiments of ChCl and DES have been carried out by micro confocal laser Raman spectrometer. It has been found that the overall intensity of each peak in DES is significantly decreased compared with that of ChCl, and the original spectral peaks remain, indicating that Zn2+ dose not damage the skeleton structure of ChCl. A new characteristic peak appears at 287 cm-1, which is speculated to be the stretching vibration of the Zn—Cl coordination bond, and the Raman experiment of DES is conducted with the temperature rising. The results have shown that, with the increase of temperature, the intensity of asymmetric stretching vibration peak of NC4 decreases, the peak width increases and the peak shape slows down. Furthermore, the intensity of stretching vibration peak of Zn—Cl decreases gradually, the position of the peak remains unchanged, and the peak shape overlaps obviously. 2D Raman studies the characteristic peaks of NC4 and Zn—Cl. The results reveal that the dissociation process of ChCl to Ch+ occurs in the solution, and Zn2+ forms various complexes with Cl-. There is a mutual transformation between ZnCl-3, Zn2Cl-5 and Zn3Cl-7. The peaks at different positions have different orders of temperature change. The characteristic peaks and clusters are assigned, and the sensitivity of each cluster to temperature is obtained. The structure optimization and parameter calculation of the speculated material structure are carried out, which confirm the possibility of its existence. Meanwhile, the feasibility of 2D Raman analysis results is also verified. These results will provide theoretical reference for the research of DES and further expand the application scope of two-dimensional spectroscopy.
Key words：Deep eutectic solvent; Two-dimensional Raman spectroscopy; Density functional theory
吴晓静，李子轩，张雁东，程龙玖. 温度对低共熔溶剂影响的二维拉曼光谱研究[J]. 光谱学与光谱分析, 2022, 42(01): 99-103.
WU Xiao-jing, LI Zi-xuan, ZHANG Yan-dong, CHENG Long-jiu. Study on the Effect of Temperature on Deep Eutectic Solvent by Two-Dimensional Raman Spectroscopy. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2022, 42(01): 99-103.
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