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题名: 全氟辛烷磺酸在土壤矿物上的吸附机理研究
作者: 张锐明
学位类别: 博士
答辩日期: 2014-11
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 景传勇
关键词: 全氟辛烷磺酸(PFOS) ; 吸附 ; 光谱技术 ; 吸附构型 ; DFT,Perfluorooctane sulfonate (PFOS) ; adsorption ; spectroscopic technology ; complex configuration ; DFT
其他题名: Adsorption Mechanisms of Perfluorooctane Sulfonate on Soil Minerals
学位专业: 环境科学
中文摘要:        全氟辛烷磺酸(PFOS)是一种在全球范围内广泛分布的持久性有机污染物(POPs)。PFOS在环境介质界面上的固液分配决定它在环境中的迁移和归趋。 本文分别研究了PFOS在土壤沉积物、粘土矿物、针铁矿等多种环境介质上吸附行为,结合同步辐射、原位红外、X射线光谱等表征技术手段和密度泛函 (DFT)及分子动力学(MD)等理论计算化学方法,探讨PFOS在环境介质界面上的微观吸附机理,对明确PFOS在环境中的界面作用过程具有重要意义。
      1) 考察了有机质和无机矿物对PFOS在土壤和沉积物上吸附的影响及作用机理。研究发现PFOS在土壤和沉积物上吸附符合拟二级动力学模型。吸附等温线符合 Langmuir吸附模型。腐殖酸(HA)/富里酸(FA)对PFOS的吸附量贡献为6.2-16.4%,胡敏质的贡献为29.9-55.1%,无机矿物 为35.1-53.6%。分子动力学模拟结果显示不同组分对PFOS吸附的大小顺序是:胡敏质 ≥ 无机矿物 > HA/FA,与实验结果相一致。胡敏质具有大量脂肪族、芳香烃等疏水性基质,可以与PFOS形成强疏水作用和促进相吸收过程,增加PFOS吸附。而HA /FA由于具有较胡敏质强的亲水性和极性,明显增加了对PFOS的静电斥力,并减弱了疏水作用,从而减弱了对PFOS的吸附。无机矿物可以通过疏水作用和 形成内层复合物的形式吸附PFOS。
      2) 研究了PFOS在粘土矿物上吸附的作用机理及腐殖酸的影响。Zeta电位数据显示高岭土和蒙脱土表面均呈现负电荷,与溶液中PFOS阴离子存在较强的静电 排斥作用。但吸附实验结果显示PFOS在高岭土和蒙脱土上的吸附量分别达到77.6 μg/g和54.5 μg/g,说明PFOS在粘土矿物上存在除静电力以外的其它吸附力。ATR-FTIR结果显示PFOS特征峰在吸附前后基本不变,说明存在外层吸附。在吸 附过程中,800-1150 cm-1波数范围内出现明显倒峰及峰位置变化,说明PFOS与高岭土和蒙脱土发生界面作用,推测是配体交换和软硬酸碱反应的结果。此外,PFOS在负载了 HA的高岭土和蒙脱土上的吸附量分别下降了19.8%和25.3%,C-F键红外吸收峰强度也分别了4.8%和68.0%。S的近边X射线吸收精细结构 (NEXAFS)光谱显示,PFOS在高岭土和蒙脱土上吸附后均出现三个边前峰,说明PFOS中磺酸基团与粘土矿物中铁、锰等过渡金属形成化学键,存在化 学吸附。X射线衍射(XRD)结果表明PFOS在蒙脱土表面还存在层间吸附,而在高岭土上没有层间吸附。
      3) 研究了PFOS在针铁矿上的微观吸附机理,考察了pH、离子强度以及腐殖酸对PFOS吸附的影响。动力学实验结果表明,PFOS能够在针铁矿上的吸附符合 拟二级动力学模型。当pH < 零电点(PZC = 8.9)时,针铁矿对PFOS的吸附随着pH值的升高而减弱,随着离子强度的增加而降低;当pH > PZC时,PFOS的吸附量随着pH值的升高而有所增强,随着离子强度的增加而上升,说明存在其他吸附作用。NEXAFS结果显示PFOS吸附后出现边前 峰,表明PFOS在针铁矿上形成Fe-O-S化学键。ATR-FTIR分析发现,吸附后在877 cm-1处出现新峰,进一步确证了Fe-O-S键的形成。XPS分析表明在吸附过程中氟原子上电子向碳链和磺酸基团转移。同时,电化学阻抗谱(EIS)表 明PFOS分子上电子有向针铁矿传递的趋势。密度泛函理论(DFT)计算的表面吸附能结果表明PFOS在针铁矿表面化学吸附是可以自发进行的,形成单齿单 核的稳定吸附构型(-29.0 kJ/mol)。态密度分布结果表明,Fe 3d, O 2p 和S 3p轨道发生重叠,证明铁和硫原子轨道发生了杂化。
英文摘要:       Perfluorooctane sulfonate (C8F17SO3-, PFOS) has been classified as one of persistent organic pollutant (POPs), which has been detected worldwide. Its transport and fate in the environment largely depended on the partitioning between solid-aqueous environmental phases. The objective of this work is to investigate the molecular-scale mechanisms of PFOS adsorption on environmental micro-interfaces, such as soil/sediment, clay minerals, and goethite. For this purpose, multiple complimentary advanced spectroscopic techniques including synchrotron radiation, infrared spectroscopy, X-ray spectrometry, and theoretical calculation, such as molecular dynamic (MD) and density functional theory (DFT) were employed:
      1) The impact of organic substance and inorganic minerals to PFOS adsorption on soil/sediment were investigated. The kinetics adsorption of PFOS on soil/sediment could be well simulated using the pseudo-second-order model, and the adsorption isotherms of PFOS conformed to Langmuir model. It was found that HA/FA component contributed about 6.2-16.4% to the PFOS adsorption, humin contributed up to 29.9-55.1%, and inorganic component accounted for about 35.1-53.6%. The results were consist with the results of molecular dynamic (MD) simulation that the order of the PFOS affinity on different component surfaces followed humin ≥ inorganic minerals > HA/FA. These results suggested that organic substances dominated the PFOS adsorption, and inorganic minerals also play an important role. Due to its aliphatic and nonpolar parts, humin dominated PFOS adsorption by phase transfer and hydrophobic effect. Compared with humin, HA/FA were more hydrophilic and polar, which increased the electrostatic repulsion and weaken the hydrophobic effect, resulting in weaker PFOS adsorption. The inorganic minerals also played an important role in the PFOS adsorption by both the hydrophobic effect and the formation of chemical bond on the surface.
      2) Adsorption of PFOS on kaolinite/montmorillonite and the influence of HA coating were studied. The results of zeta potentials suggested that both kaolinite and montmorillonite were negatively charged, resulting in strong electrostatic repulsion. However, our batch experiment displayed that the adsorption capacities of PFOS on kaolinite and montmorillonite were 77.6 and 54.5 μg g-1, respectively, indicating the existence of other adsorption forces. The ATR-FTIR spectroscopies showed the spectra of adsorbed PFOS on the two clay minerals were similar to that of the aqueous PFOS, indicating PFOS adsorbed on clays mainly as an outer-sphere complex by hydrophobic interaction. Notably, the negative peaks and shifts at 800-1150 cm-1 occurred during PFOS adsorption and desorption process. The changes demonstrated that the surfaces of clay minerals reacted with PFOS by ligand exchange and hard-soft acid-base reaction. We also investigated the influence of HA coating. The results showed that the PFOS adsorption reduced by 19.8% on kaolinite and by 25.3% on montmorillonite after HA coated, and the intensity of C-F bond (or PFOS adsorption) in ATR-FTIR also decreased by 4.8% and 68.0%, respectively. Besides, three pre-edge peaks in the S K-edge near-edge X-ray absorption fine structure (NEXAFS) spectroscopy appeared after PFOS adsorbed on both clay minerals, suggesting that the sulfonate group chemically bonded with Fe/Mn transition metals in clay minerals. X-Ray Diffraction (XRD) results indicated that interlayer adsorption existed on montmorillonite rather than on kaolinite.
      3) The molecular-scale mechanism of PFOS adsorption on goethite and the influences of pH, ionic strength and HA in solution were investigated. Kinetics results suggested that PFOS adsorption on goethite followed pseudo-second-order kinetics when pH was less than PZC (8.9), the adsorption of PFOS decreased with pH and ion strength increasing, but slightly raised at pH above PZC, suggesting other adsorption mechanisms occurred. The   S  K-edge   NEXAFS spectroscopy illustrated that  the pre-edge peaks  also appeared after PFOS  adsorbed on goethite, suggesting  that the  sulfonate  group in  PFOS specifically  adsorbed  on goethite  with  a Fe-O-S bond. ATR-FTIR results exhibited that  a new peak centered at 877 cm-1 was detected  upon PFOS adsorption,  confirming the  formation  of  Fe-O-S bond.  The  X-ray  photoelectron spectroscopy (XPS) suggested that  electron transformation from fluorine  atoms to carbon chain  and sulfonate group occurred  when PFOS adsorption.  The results of  electrochemical impedance spectroscopy (EIS) proved that the electrons on PFOS inclined to transfer to goethite surface.
      The density function theory (DFT) simulation pointed out that PFOS chemical adsorption on goethite could be  spontaneous, and monodentate mononuclear configuration was  the most stable inner-sphere complex (-29.0 kJ/mol). The  partial density of states (PDOS) illustrated the orbitals of Fe 3d, O 2p and S 3p were overlapped, confirming the occurrence of the orbitals  hybridization of Fe and S atoms.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/34540
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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Recommended Citation:
张锐明. 全氟辛烷磺酸在土壤矿物上的吸附机理研究[D]. 北京. 中国科学院研究生院. 2014.
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