基于超高分辨质谱的溶解性有机质分子转化机理分析

doi:10.6023/A22010044

摘要/Abstract

本研究对比分析了不同处理工艺对制药废水中溶解性有机质(DOM)的降解, 通过三维荧光图谱(EEM)、总有机碳(TOC)、zeta电位以及动态光散射技术进行表征分析, 并利用超高分辨质谱进一步探究了过硫酸钾(PS), 碳纳米管(CNTs), CNTs/PS工艺诱导的DOM分子转化机制. 结果表明, PS通过静电聚合作用和氧化作用对DOM中的缩合芳香类化合物(76%)和蛋白质/多肽类(65%)去除较大, CNTs通过吸附作用对不饱和水平较低的含氧化合物(木质素类、蛋白质/多肽类和氨基糖类(90%))的去除最为显著, 而CNTs/PS则是通过吸附作用、电子转移以及单线态氧(¹O₂)的生成以实现不同组分的DOM的高效去除. 化学参数定量分布以及线性拟合分析表明, PS和CNTs/PS体系对于DOM分子的化学参数分布影响较小, 而CNTs的吸附作用会导致残留分子的平均氧碳比(O/C)、芳香指数(AI_mod)、等价双键(DBE)和碳的名义氧化态(NOSC)数值增加, 且氧原子对DBE的贡献作用增大. 本研究结果为进一步理解DOM在水环境中的去除和分子转化提供了理论依据.

关键词: 溶解性有机质, 过硫酸钾, 碳纳米管, 高分辨质谱, 分子转化

In this study, the removal of dissolved organic matter (DOM) in pharmaceutical wastewater effluent by five treatment processes [including ultraviolet (UV), UV/H₂O₂, potassium persulfate (PS), carbon nano tubes (CNTs) and CNTs/PS] was investigated, which was characterized by excitation-emission matrix spectra spectroscopy (EEM), total dissolved carbon (TOC), zeta potential and dynamic light scattering analysis, while the transformation mechanism of DOM fractionations induced by PS, CNTs and CNTs/PS processes was further explored by ultra-high-resolution mass spectrometry (UPLC-Q-TOF-MS). The results suggested that the PS, CNTs and CNTs/PS processes proved to have the best treatment effect for the removal of DOM via EEM analysis, with TOC removal of 128, 204 and 243 mg/L, respectively. Zeta potential and dynamic light scattering analysis indicated that DOM molecules were removed by PS process through electrostatic polymerization and oxidation, and by CNTs process via adsorption, while CNTs/PS process degraded DOM by combining adsorption, electron transfer and the generation of strongly oxidizing singlet oxygen (¹O₂). Molecular characterization analysis demonstrated that the condensed aromatic compounds (76%) and proteins/lipids (65%) in DOM were the most vulnerable to PS attack, and the adsorption of CNTs was more effective for oxygenated compounds with lower levels of unsaturation (such as lignin, protein polypeptides and amino sugars (90%)), while the CNTs/PS process achieved indiscriminate degradation of various DOM molecules, which was a complement and enhancement to the separate CNT and PS treatment processes. In terms of different elemental compositions, the PS process had little effect on the elemental composition of the residual DOM molecules, while the CNTs and CNTs/PS processes showed a more obvious effect on the removal of CHON and CHONS molecules. Furthermore, by combining the quantitative distribution of chemical parameters of DOM molecules and linear fitting analysis, PS and CNTs/PS system had little effect on the distribution of chemical parameters of residual DOM molecules, while the adsorption of CNTs would lead to an increase in the average O/C, aromaticity index (AI_mod), double bond equivalence (DBE) and nominal oxidation state of carbon (NOSC) value of residual molecules, and the contribution of oxygen atoms to DBE. The results of this study provide important information for further understanding the behavior of DOM in the aquatic environment during various processes.

Key words: dissolved organic matter, potassium persulfate, carbon nanotubes, high resolution mass spectrum, molecular transformation

引用此文

成受明, 周波. 基于超高分辨质谱的溶解性有机质分子转化机理分析[J]. 化学学报, 2022, 80(8): 1106-1114.

Shouming Cheng, Bo Zhou. Molecular Insights into the Transformation Mechanisms of Dissolved Organic Matter Based on Ultrahigh Resolution Mass Spectrometry[J]. Acta Chimica Sinica, 2022, 80(8): 1106-1114.

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图/表 10

图1. 原水样(a)以及经过(b) UV、(c) UV/H2O2、(d) PS、(e) CNTs和(f) CNTs/PS体系处理后水样的EEM图

Figure 1. EEM spectra of (a) pristine samples, and the samples reaction after (b) UV, (c) UV/H2O2, (d) PS, (e) CNTs and (f) CNTs/PS processes [H2O2]=100 mmol/L, [PS]=100 mmol/L, [CNTs]=1 g/L, pH 8.5, [DOC]0=1258 mg/L, processing time t=60 min

Region	Typical substance class	Excitation wavelength/nm	Emission wavelength/nm
I	Aromatic protein I	200~250	280~330
II	Aromatic protein II	200~250	330~380
III	Fulvic acid-like	200~250	380~550
IV	Soluble microbial byproduct-like	250~400	280~380
V	Humic acid-like	250~400	380~550

表1. EEM光谱五个区域的激发和发射波长边界

Table 1. Excitation and emission wavelength boundaries of the five regions of the EEM spectrum

图2. (a) 处理前后水样的Zeta电位和平均分子尺寸对比; (b)处理前后水样的分子尺寸分布和累积分布百分比

Figure 2. (a) Zeta potential and average molecular size analysis of water samples before and after treatment; (b) molecular size distribution and cumulative distribution percentage of water samples before and after treatment [PS]=100 mmol/L, [CNTs]=1 g/L, pH 8.5, [DOC]0=1258 mg/L

图3. (a) PS、(b) CNTs和 (c) CNTs/PS体系处理后水样的质谱图; (d) DOM分子量分布对比

Figure 3. Mass spectrum of pristine samples and after reaction in (a) PS process, (b) CNTs process and (c) CNTs/PS process; (d) distribution comparation of DOM molecules weight [PS]=100 mmol/L, [CNTs]=1 g/L, pH 8.5, [DOC]0=1258 mg/L, processing time t=60 min

图4. (a) PS、(b) CNTs、(c) CNTs/PS体系处理后水样中DOM分子的Van Krevelen图; (d)去除、残留和生成分子的数量统计分析. 绿色的点表示反应后消失的峰(去除), 粉色的点表示反应后不变的峰(残留), 蓝色的点表示反应后出现的新峰(生成)

Figure 4. Van Krevelen diagrams of DOM in pharmaceutical wastewater effluent after reaction in (a) PS process, (b) CNTs process and (c) CNTs/PS process; (d) statistics on the number of removed, residual and product molecules. Points in green represent peaks that disappeared after reaction (removed), points in pink represent peaks that were unchanged (resistant), and points in blue denote new peaks that appeared after reaction (produced)

Region	Compound class	H/C	O/C
I	Lipids	1.5~2.0	0~0.3
II	Proteins	1.5~2.2	0.3~0.52
III	Aminosugars	1.5~2.2	0.67~1.2
IV	Lignins	0.7~1.5	0.1~0.67
V	Carbohydrates	1.5~2.4	0.67~1.2
VI	Unsaturated hydrocarbons	0.7~1.5	0~0.1
VII	Condensed aromatic structures	0.2~0.7	0~0.67
VIII	Tannins	0.5~1.5	0.67~1.2

表2. 基于van Krevelen图的不同生化组分的划分边界

Table 2. Demarcation boundary of different biochemical components based on van Krevelen diagram

图5. (a)基于van Krevelen图所识别的不同生化组分的雷达图; (b)不同分子结构组分的雷达图

Figure 5. (a) Radar charts of different biochemical classifications recognized in the Van Krevelen diagrams; (b) Radar charts of different molecular formula classifications

图6. (a)四种主要元素组成的分子(CHO、CHON、CHOS、CHONS)反应前后的数量变化; (b)四种主要元素组成的分子(CHO、CHON、CHOS、CHONS)的相对百分比变化

Figure 6. (a) Changes of molecule number of the four major subcategories (CHO, CHON, CHOS, CHONS) before and after reaction; (b) changes of relative percentage contribution of the four major subcategories

图7. PS、CNTs和CNTs/PS体系处理前后DOM分子O/C (a)、H/C (b)、AImod (c)、DBE (d)和NOSC (e)的定量分布

Figure 7. Quantitative distributions of O/C (a), H/C (b), AImod (c), DBE (d) and NOSC (e) of molecules before and after reaction in PS, CNTs and CNTs/PS processes

图8. 原水样(a)以及经过(b) PS、(c) CNTs和(d) CNTs/PS体系处理后分子中O原子数与DBEaverage的函数拟合原水样(a)以及经过(b) PS、(c) CNTs和(d) CNTs/PS体系处理后分子中O原子数与DBEaverage的函数拟合

Figure 8. DBEaverage as a function of the number of O atoms in molecular formulas before (a) and after reaction in (b) PS, (c) CNTs and (d) CNTs/PS processes DBEaverage as a function of the number of O atoms in molecular formulas before (a) and after reaction in (b) PS, (c) CNTs and (d) CNTs/PS processes

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