基于理论化学计算研究探针物质在紫外/氯体系中的反应机理
Quantum chemical study on reaction mechanism of reactive radical mediated probe compounds degradation in the UV/chlorine process
彭涛 1杨滨 2徐超 2应光国2
作者信息
- 1. 中国科学院广州地球化学研究所,有机地球化学国家重点实验室,广州,510640;中国科学院大学,北京,100049
- 2. 华南师范大学环境学院,广东省化学品污染与环境安全重点实验室,广州,510006;华南师范大学环境学院,环境理论化学教育部重点实验室,广州,510006
- 折叠
摘要
紫外/氯体系是将氯化消毒与紫外线辐射相结合的一种水处理高级氧化技术.硝基苯、苯甲酸和对氯苯甲酸常被作为探针化合物,广泛用于研究紫外/氯体系中生成的羟基自由基(OH)和活性氯自由基(·ClO和·Cl等).采用理论化学计算的方法研究了硝基苯、苯甲酸和对氯苯甲酸与紫外/氯体系中生成的3种主要自由基·OH、·ClO和·Cl的反应机理.在酸性条件下(pH＜4.0),硝基苯、苯甲酸和对氯苯甲酸与·OH、·ClO和·Cl的反应包括抽氢反应、加成反应和单电子转移反应.OH与3种探针化合物反应的 ΔG0,≠分别为 7.7-20.1 kcal·mol-1、5.6-10.1 kcal·mol-1 和 5.2-12.4 kcal·mol-1.·ClO 与 3 种化合物的ΔG0,≠则相对较高为11.8-25.1 kcal·mol-1.·Cl引发的反应中,与硝基苯(10.3-14.1 kcal·mol-1)和对氯苯甲酸反应能垒较高(10.2-12.4 kcal·mol-1),与苯甲酸则反应能垒较低(5.4-11.9 kcal·mol-1),其中单电子转移反应起重要作用.因此在紫外/氯体系中,起主要反应的是·OH,·ClO作用较小,·Cl的贡献则主要体现在抽氢反应和单电子转移反应中,这与在中性条件下的反应机理相吻合.总体而言,对于探针化合物的不同形态,其反应速率的顺序为负离子态＞分子态＞正离子态.本文的研究结果为探究紫外/氯体系当中各种自由基的反应机理提供了数据支撑.
Abstract
The UV/chlorine process,by combining chlorination with UV irradiation,has been recently considered as a highly efficient advanced oxidation process in water treatment.Nitrobenzene(NB),benzoic acid(BA)and p-chlorobenzoic acid(pCBA)are widely used as model probe compounds in UV/chlorine system to investigate the second-order rate constants of specific radical-reaction with target contaminants by a competitive kinetics method.Here we evaluated the radical mediated reaction kinetics and mechanisms of NB,BA and pCBA in UV/chlorine process at pH＜4.0 by theoretical calculations.The main reactive radicals·OH,·ClO and·Cl in UV/chlorine process for the reaction with NB,BA and pCBA can be explained by H-abstraction,addition pathways and electron transfer reaction.The ΔG0,≠ values for OH reaction with NB,BA and pCBA were in the range of 7.7-20.1 kcal·mol-1,5.6-10.1 kcal·mol-1 and 5.2-12.4 kcal·mol-1,respectively.TheΔG0,≠ values for·ClO reactions with these three probe compounds were in the range of 11.8-25.1 kcal·mol-1,which were higher than those of·OH.The ΔG0,≠ values for·Cl reactions with NB and pCBA were in the range of 10.3-14.1 kcal·mol-1 and 10.2-12.4 kcal·mol-1.As for BA,theΔG0,≠ values were in the range of 5.4-15.7 kcal·mol-1 due to the dominant role of the electron transfer reaction.This is consistent with the results under neutral conditions.For the different forms of probe compounds,the order of reaction rates is as follows:anionic form＞molecular form＞cationic form.The results of this study provided some basic data for investigations into the reaction kinetics and mechanisms of reactive radicals in UV/chlorine process.
关键词
紫外/氯体系/探针化合物/量子化学Key words
UV/Chlorine/probe compounds/quantum chemistry引用本文复制引用
出版年
2024
NETL
NSTL
万方数据