Online Detection of VOCs Based on LIBS and Raman Spectra
CHEN Geng-yin1, ZHANG Qi-hang1, LIU Yu-zhu1, 2*, ZHANGCHENG Yuan-zhe1, CHEN Yu1, CHEN Guo-qing1, HAN Bo-yuan1, ABULIMITI Bumaliya3*
1. Jiangsu Key Laboratory for Optoelectronic Detection of Atmosphere and Ocean, Nanjing University of Information Science & Technology, Nanjing 210044, China
2. Jiangsu Collaborative Innovation Center on Atmospheric Environment and Equipment Technology (CICAEET), Nanjing 210044, China
3. College of Physics and Electronic Engineering, Xinjiang Normal University, Urumqi 830054, China
Abstract：As the main substance of air pollution, volatile organic compounds (VOCs) have attracted wide attention because of their strong destructive and physiological toxicity to the atmospheric environment. On-line detection of volatile organic compounds in the atmosphere is a very challenging work. In this study, laser-induced breakdown spectroscopy (LIBS) was combined with Raman spectroscopy to analyze volatile organic compounds from the perspective of atomic emission spectroscopy and molecular structure information, respectively. The elements contained in the air, such as Br characteristic lines and N, O, H were observed in the LIBS spectra obtained by in-situ online detection. The experimental results reflect the detection effect of o-fluorobromobenzene in the air. For the detection of bromine in the atmosphere, LIBS reflects the presence of bromine in the atmosphere and provides a good reference for the study of its reaction mechanism. The mechanism of CN and C2 radical molecules produced by high energy laser was analyzed. The laser pulse can ionize and decompose nitrogen in the air and benzene of o-fluorobromobenzene. The carbon atom in o-fluorobromobenzene reacts with nitrogen in the air to form a high-temperature plasma. The carbon and nitrogen atoms in the plasma can be combined freely to form CN radical and spontaneous emission. The molecular spectrum of spontaneous emission of the free radical can be collected by the optical spectrometer. The o-fluorobromobenzene molecule of the sample to be tested contains a benzene ring, and there are many carbon atoms in the molecule. Under the action of the intense laser, o-fluorobromobenzene is photodissociated, which is easy to form C2 radical molecule, and the spectrum of C2 radical, as shown in the figure is produced by radiation. We can know that C2 radical comes from benzene ring group in o-fluorobromobenzene sample through experimental verification and data analysis. As a supplement to the molecular structure information of volatile organic compounds, the on-line detection of volatile organic compounds was improved by introducing Raman spectra. On the basis of the experimental results of the sample Raman spectrum, the vibration mode and distribution are calculated and fitted with density functional theory (DFT).The characteristic peaks generated by the vibration are calibrated, and the characteristic spectral fingerprints are obtained. The four peaks (310, 833, 1 036, 1 244 cm-1) with higher intensity showed C-Br bond and C-F bond vibration characterization, especially the former two (310, 833 cm-1) had bromine and fluorine atom shifts at the same time, which could be used as the characteristic spectral fingerprint to identify the molecule. The experimental results showed that the combination of LIBS and Raman spectrum was applied to the VOCs on-line detection, which has reference significance and value in its related detection work.
[1] Kapma M, Castanas E. Environmental Pollution, 2008, 151(2)：362.
[2] Volkamer R, Jimenez J L, Martini F S, et al. Geophysical Research Letters, 2006, 33(17)：L17811.
[3] Guo X Q, Zheng F, Li C L, et al. Optics and Lasers in Engineering, 2019, 15：243.
[4] Atkinson R. Atmospheric Environment, 2000, 34(12-14)：2063.
[5] Kroll J H, Seinfeld J H. Atmospheric Environment, 2008, 42(16)：3593.
[6] Guo H, Lee S C, Chan L Y, et al. Environmental Research, 2004, 94(1)：57.
[7] Molina M J, Rowland F S. Nature, 1974, 249：810.
[8] Li Y D, Yin S S, Yu S J, et al. Chemosphere, 2020, 250：126283.
[9] Baudelet M, Willis C C C, Shah L, et al. Optics Express, 2010, 18(8), 7905.
[10] Qu Y F, Zhang Q H, Yin W Y, et al. Optics Express, 2019, 27(12)：A790.
[11] Fortes F J, Moros J, Lucena P, et al. Analytical Chemistry, 2013, 85(2)：640.
[12] Ng Y W, Pang H F, Cheung S C. Chemical Physics Letters, 2011, 509(1): 16.
[13] Ram R S, Davis S P, Wallace L, et al. Journal of Molecular Spectroscopy, 2006, 237(2): 225.
[14] Wang L, Yang C L, Wang M S, et al. Computational & Theoretical Chemistry, 2011, 976(s1-3): 94.
[15] Mousavi S J, Farsani M H, Darbani S M R, et al. Appl. Phys. B, 2016, 122: 106.
[16] Frisch M J, Trucks G W, Schlegel H B, et al. Gaussian 09, Revision D. 01, Gaussian, Inc.: Wallingford, CT, 2009.
