过硫酸盐氧化降解2,4-二硝基甲苯的光谱特征变化解析

doi:10.3964/j.issn.1000-0593(2020)03-0849-06

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Abstract With the intensification of human activities, refractory organic compounds have become one of the groundwater pollutants. groundwater is a nutrient-poor and anaerobic environment, which will aggravate the long-term risk of refractory organic matter. Therefore, the remediation of groundwater contaminated by 2,4-dinitrotoluene has been a difficult and hot issue in the field of environment. Currently, Fe0 activated persulfate technology is widely used to repair 2,4-DNT in groundwater. In order to identify the degradation process, mass spectrometry is generally used to identify the intermediate products and degradation products of oxidative degradation and the order of formation. However, it is unable to effectively identify the change order of organic functional groups in the process of oxidative degradation. Therefore, three-dimensional excitation emission matrix fluorescence spectroscopy (3D-EEM), Fourier transform infrared spectroscopy (FTIR), and two-dimensional correlation analysis were applied to investigate the composition of products and the variation of functional groups over time in the persulfate oxidation system. The results showed that 2,4-dinitrotoluene showed no fluorescence peak, but its products with fluorescence groups were generated. As the benzene ring broken down in the reaction, the unsaturated fatty acids might generated. With the increase of reaction time, the products with the structure of fulvic acid degraded continuously, while the products with the structure of humic-like degraded gradually in the later stage. The proportion of zone II and IV increased, which was mainly due to the increasing content of 2,4-diaminotoluene in the products. Infrared absorption peaks were mainly 3 334, 2 844, 2 954, 2 357, 2 126, 1 643, 1 410, 1 110 and 700 cm^-1. The functional groups of the products were mainly amino, methylene, carboxyl, phenol hydroxyl and olefin methyl. But the difference of infrared absorption peak was not significantly with time. Two-dimensional correlation analysis was performed on FTIR during the time change process. Four auto-peaks were observed at the λ₁/λ₂ wavelength pairs of 3 334/3 334, 1 643/1 643, 1 015/1 015 and 700/700 in the synchronous map, and there were six positively correlated cross peaks at 1 643/3 334，1 015/3 334，700/3 334，1 015/1 634，700/1 634 and 700/1 015, all of which were positive, and the change direction of spectral band strength was consistent. The above four functional groups generated over time in the system, and the transformation/degradation was synchronous. Only cross-peaks were detected in the asynchronous maps. The asynchronous spectrum had 5 negative correlation cross peaks and 1 positive correlation peak at the same position in the synchronous spectrum. The spectral features could lead to an interpretation of the changes in the following sequence: 3 334＞1 634＞1 015＞700. Therefore, with the increase of time, the order of groups in the 2,4-DNT degradation systemwas amino>carboxyl>olefin>phenolic hydroxyl. The above indicated that in the degradation process, the nitro group on the benzene ring was firstly converted to —NH₂, and then the methyl group on the benzene ring was oxidized to —COOH. The phenolic hydroxyl group and olefin should be the carbon chain transformation after the destruction of the benzene ring structure. The results were important to understand persulfate oxidized organic matter.

Key words：Persulfate; 2,4-dinitrotoluene; Therefore three-dimensional excitation emission matrix; Fourier transform infrared spectroscopy; Two-dimensional correlation analysis; Spectral signature

Received: 2019-02-14 Accepted: 2019-05-19

ZTFLH:

O656.4

Corresponding Authors: WU Dai-she E-mail: dswu@ ncu.edu.cn

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https://www.gpxygpfx.com/EN/10.3964/j.issn.1000-0593(2020)03-0849-06 OR https://www.gpxygpfx.com/EN/Y2020/V40/I03/849