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题名: 全氟磺酸化合物环境界面行为的理论研究
作者: 冯鸿儒1
学位类别: 博士
答辩日期: 2017-05
授予单位: 中国科学院大学
授予地点: 北京
导师: 张爱茜
关键词: 全氟磺酸化合物,界面行为,量化计算,分子动力学,耗散粒子动力 学 ; perfluorinated sulfonic acids, interfacial behavior, quantum chemical calculation, molecular dynamics, dissipative particle dynamics
其他题名: Theoretical Study on Interfacial Behavior of Perfluorinated Sulfonic Acids in Environment
学位专业: 有机化学
中文摘要: 有机污染物的环境界面过程一直是环境有机化学研究的核心与热点。计算 模拟因可获得实验手段受限于方法灵敏度所难获得的原子水平信息,而受到广 泛关注。遗憾的是,常用计算方法虽各有所长亦各有局限,如量子力学虽擅长 分析涉及化学键生成和断裂的有机污染物界面作用,但只能处理包含有限原子 的体系;全原子分子动力学虽可获得有机污染物在有水等存在的情况下环境体 系模型中的界面行为,但是在计算复杂体系时效率偏低;而粗粒化模型则更擅 长处理介观尺度的问题,适合解决真实环境界面体系组成复杂且计算需求量过 高这一难题。针对这一环境界面行为计算评价方法瓶颈,本研究提出基于量子 力学计算、分子动力学模拟、粗粒化模型以及耗散粒子动力学等不同手段有机 集成的新型计算方法,实现不依赖于实验数据的有机污染物环境界面行为及其 化学机制的解析和预测。论文以典型的离子型有机污染物全氟磺酸化合物为研 究对象,采用赤铁矿和腐殖酸分别作为环境固相的代表性无机和有机成分,系 统开展了全氟磺酸化合物环境界面行为的理论研究,主要开展了以下三个方面 的工作: 1.全氟磺酸化合物在水中形成胶束的理论研究 短链全氟磺酸化合物作为全氟辛基磺酸的替代产品,其毒性研究虽已引起 重视,但其环境界面行为的研究却少有报道。为开展全氟磺酸化合物环境界面 行为的理论研究,本研究采用全原子分子动力学和基于粗粒化模型的耗散粒子 动力学两种计算模拟手段研究了水中全氟磺酸化合物的行为,以期为后续的界 面作用计算奠定基础。计算结果研究表明,当模型中包含不止一个全氟磺酸化 合物时,其会在动力学模拟过程中逐渐形成团簇乃至胶束。考虑到实际水环境 中全氟磺酸化合物的浓度较低,不足以达到形成临界胶束的水平。考虑实际计 算能力和应用需求,后期搭建的模型均只包含一个全氟磺酸化合物。 2.全氟磺酸化合物在水-赤铁矿体系界面吸附构型与化学机制的理论研究 水-金属氧化物界面是对有机污染物环境吸附和迁移有重要影响的典型环 境界面。本研究采用分子动力学模拟与量化计算相耦合的方法研究全氟磺酸化 合物在水-赤铁矿(α-Fe2O3)界面的吸附行为。在自然环境浓度下全氟磺酸化合物 以长轴平行于表面的单分子层吸附方式吸附在赤铁矿 (0001)表面,而非以碳链 垂直于表面的方式吸附。不同于已报道的全氟辛基磺酸以垂直吸附构型作用于 二氧化钛表面,全氟磺酸化合物的这种表面平行吸附构型从未被报道过。全氟 磺酸化合物的氟原子与赤铁矿表面羟基氢原子间形成的氢键为这一独特构型提 供了稳定作用。因此,吸附作用随着碳链增长而增强。基于第一性原理的密度 泛函理论进一步计算获得的吸附能和偏态密度分析证实这一构型由静电相互作 用以及全氟磺酸化合物中氟原子 2p轨道和赤铁矿羟基化表面氢原子 1s轨道相 互重叠构成的 F•••H氢键所稳定。全氟磺酸化合物层平均厚度约 0.5nm,表面形 貌很难为原子力显微镜所观察,而本研究所采用的 QM和 MD耦合计算新策略 有助于阐明有机污染物环境界面行为机制,为准确评估有机污染物的环境影响 提供了可能性。 3.基于粗粒化模型的全氟磺酸化合物在水 -腐殖酸体系界面行为的耗散粒子动 力学研究 腐殖酸在各种环境固相中广泛存在,且对环境有机化学品的迁移、转化和 生物有效性具有重要的影响。目前有大量的环境有机化学研究集中于诠释污染 物与腐殖酸的相互作用。本研究以粗粒化方法搭建水-腐殖酸体系模型,采用耗 散粒子动力学计算评估水-腐殖酸体系中全氟磺酸化合物的界面行为。计算结果 表明全氟磺酸化合物有吸附到腐殖酸层的倾向且其在该体系的移动性虽碳链长 度增加而降低。在所建立的水-腐殖酸体系模型中,全氟磺酸化合物的极性端倾 向于保持在水相中而其疏水尾部则埋于腐殖酸层中。计算所得的全氟丁基磺酸 的扩散系数(2.27×10-7 cm2/s)是全氟辛基磺酸扩散系数(7.43×10-8 cm2/s)的 三倍多,这一结果恰好解释了之前报道的随着沉积物泥芯样本深度的增加,检 测到的短链全氟丁基磺酸所占的比例逐渐增加的现象。研究表明粗粒化模型与 耗散粒子动力学分析相结合为有机化学品环境行为的研究和管理提供了一个高 效的评价新方法。进一步将该方法运用于六氯苯和六氯丁二烯在水-腐殖酸体系 界面行为的研究中,证实该方法有较好的适用性。
英文摘要: Interfacial process of organic pollutants always stands in the main stream of environmental organic chemistry. Computational simulation methods have been widely applied in revealing the interaction mechanism of the environmental interfaces with various pollutants, which is hard to obtain from the experimental research. However, each computational method has its own limitation except for its own strengths. For example, quantum chemical calculations are confined to small system with limited atoms, while all-atom molecular dynamics simulations may not suitable for analyzing mesoscopic issues presenting features of soft matter, which can be easily solved by coarse-grained models. In order to breaking such bottleneck for methodology, novel computational methods based on effective integration of different caculation tools have been proposed to realize the experiment-independent mechanism analysis and behavior prediction for environmental migration and transformation of pollutants. In the present study, systematic study was carried out to gain an insight into the possible mechanisms and behavior characteristics for perfluorinated sulfonic acids (PFSAs) with selected environmental interfaces, including hydrated hematite surface and water-humic acid interface, respectively representing the typical water-oxide interface and water-environmental organic phase. The work mainly consists of three parts: 1. Theoretical study on the behavior of perfluorinated sulfonic acids in water Short chain perfluorinated sulfonic acids that were introduced as alternatives for perfluorooctane sulfonic acid have been widely produced and used. However, few studies have investigated the environmental process of short chain PFSAs, and the related interfacial behavior and its mechanisms still need to be uncovered. Both all-atom molecular dynamics and coarse-grained model-based dissipative particle dynamics were adopted to study the behavior of perfluorinated sulfonic acids in water to get essential parameters for the subsequent calculations for interfacial interaction. The results showed that perfluorinated sulfonic acids would form molecular cluster or even micelle in the dynamic process when the simulation system contains more than one organic molecule. Considering that the real concentration of the compounds in environment is lower than their cprresponding critical micelle concentrations, the established model system only contain one perfluorinated sulfonic acid molecule. 2. Theoretical study on the adsorption configuration and mechanism for the perfluorinated sulfonic acids on hydrated hematite surface The water-oxide interface is one of the major environmental interfaces that plays an important role in affecting the adsorption behaviour and transport potential of the environmental pollutant. In this study, we established a new computational method coupling molecular dynamics simulations with quantum chemistry calculations to investigate the adsorption mechanisms of five perfluorinated sulfonic acids on hydrated hematite surface. Different to the vertical configuration reported for PFOS on titanium oxide, all PFSAs share the same adsorption configuration as the long carbon chains parallel to the surface. The formation of hydrogen bonds between F and inter-surface H helps to stabilize the unique configuration. As a result, the sorption capacity increases with increasing C-F chain length. Moreover, both calculated adsorption energy and partial density of states analysis demonstrate a PFSAs adsorption mechanism in between physical and chemical adsorption because the hydrogen bonds formed by the overlap of F (p) orbital and H (s) orbital are weak intermolecular interactions while the physical adsorption are mainly ascribed to the electrostatic interactions. In addition, the presence of a film of PFSAs on the iron oxide is only of 0.5 nm mean height, and such surface morphology is difficult to be observed by normal AFM. Instead, the proposed new computational method provides a new insight into the pollutant interfacial behaviour, and in particular, may help to evaluate the environmental influence of pollutants. 3. Theoretical study on the interfacial behavior and mobility of perfluorinated sulfonic acids in water/humic acid system via an integrated method coupling the coarse-grained model with dissipative particle dynamics simulation Humic acid is ubiquitous in environment. Intensive efforts have been made to find the effective ways to assess the HA interaction with contaminants since it is one of the important criterions to evaluate the migration, persistency and bioavailability of chemcials in the environment. This study is an effort aiming to extend the application of coarse-grained method to modeling water/humic acid system and predicting the contaminant mobility in the system. A series of dissipative particle dynamics were applied to investigate the interfacial behavior and mobility of perfluorinated sulfonic acids in the system. The polar head of perfluorinated sulfonic acids preferred to stay on the water/humic acid interface while their hydrophobic tails tended to be buried in the humic acid layer. The simulation results indicated that PFSAs showed a significant adsorption potential on HA and thus the mobility of PFSAs in the modeled system decrease with the increasing length of carbon chain. The finding is in accordance with the previously reported experimental data. Especially,the simulated diffusion coefficient of perfluorobutane sulfonic acid (2.27 ×10-7 cm2/s), a short chain alternative for perfluorooctane sulfonic acid, was more than thrice that of perfluorooctane sulfonic acid (7.43×10-8 cm2/s), which helps to explain the phenomena that compared to perfluorooctane sulfonic acid, the proportion of perfluorobutane sulfonic acid gradually increased with the increasing sediment core depth. Thus, an integrated method coupling the coarse-grained model with dissipative particle dynamics simulation provides a new tool of high efficiency for assessment of the mobility and interfacial behavior of organic chemicals in environment.The successful application of the method to comparison analysis of the diffusion behavior of hexachlorobenzene and hexacholorobutadiene in water-humic acid sytem verified its wide applicability.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/38617
Appears in Collections:环境化学与生态毒理学国家重点实验室_学位论文

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作者单位: 1.中国科学院生态环境研究中心
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