本文選題：多氯聯(lián)苯 + 蒙脫石　； 參考：《安徽師范大學(xué)》2015年碩士論文

【摘要】：多氯聯(lián)苯(PCBs)作為一類持久性有機(jī)污染物,能夠通過食物鏈富集作用危害人類的身體健康,土壤或沉積物是環(huán)境中PCBs主要的匯。蒙脫石黏土礦物是土壤的重要組成部分,在土壤或沉積物環(huán)境中分布廣泛且含量豐富,由于大比表面積、高陽離子交換量等結(jié)構(gòu)特征,能夠吸附多種類型的有機(jī)污染物,被廣泛的用作于環(huán)境污染的治理材料。在實(shí)際土壤中,黏土礦物多與土壤有機(jī)質(zhì)結(jié)合形成有機(jī)-無機(jī)復(fù)合體,二者很難單獨(dú)作用于有機(jī)污染物,包裹在黏土礦物外表的有機(jī)質(zhì)極大的影響了黏土的吸附特性,因其機(jī)理復(fù)雜,至今仍無法清楚解釋。本論文利用不同陽離子飽和具有特定層間距的蒙脫石礦物和腐殖質(zhì)-蒙脫石復(fù)合體,分別在有機(jī)溶劑助溶的混合體系內(nèi)進(jìn)行對(duì)一系列不同空間構(gòu)型的1~3氯取代PCBs的等溫吸附試驗(yàn),利用相關(guān)推導(dǎo)的宏觀熱力學(xué)參數(shù),結(jié)合分子動(dòng)力學(xué)模擬技術(shù),從層間陽離子類型、污染物分子的空間構(gòu)型和土壤有機(jī)質(zhì)角度解釋污染物與黏土礦物的相互作用機(jī)制。主要研究結(jié)果如下:1)吸附熱力學(xué)研究有機(jī)溶劑助溶-外推方法可以很好地解決低水溶解性有機(jī)污染物的定量吸附研究的困難。研究中所有吸附等溫線均可用線性模型進(jìn)行很好地?cái)M合,溶液PCBs濃度是影響吸附量的主要因素,且吸附過程為自發(fā)放熱的物理性吸附。蒙脫石層間域的疏水性硅氧烷表面是PCBs的主要吸附位點(diǎn)。K+、Cs+飽和蒙脫石(Mont)對(duì)2,4,4'-三氯聯(lián)苯(PCB28)的吸附能力強(qiáng)弱為:K+-MontCs+-Mont,與層間陽離子的水合半徑有關(guān)。盡管水合半徑較小的Cs+能夠提供更多層間疏水性的硅氧烷表面,但同時(shí)限制了黏土層間距的大小,無法提供足夠的垂直吸附空間供非共平面構(gòu)型PCB28插入;相反,水合半徑較大的K+可提供最優(yōu)的垂直間距和適當(dāng)?shù)酿ね翆颖砻嫖接?增強(qiáng)了PCB的吸附。腐殖質(zhì)-蒙脫石復(fù)合體(HA-Mont)和K+-Mont對(duì)PCB28的吸附能力表現(xiàn)為:HA-MontK-Mont,表明土壤有機(jī)質(zhì)能夠極大的促進(jìn)蒙脫石對(duì)PCBs的吸附。具體原因?yàn)閮煞矫?一,有機(jī)質(zhì)的分配作用;二,包裹在蒙脫石斷面位置的有機(jī)質(zhì)分子,通過限制了水分子的進(jìn)入增大黏土層間的疏水性,從而增大蒙脫石對(duì)PCB28的吸附。非共平面的2-氯聯(lián)苯(PCB1)和共平面的4-氯聯(lián)苯(PCB3)在K+-Mont的吸附能力為:PCB3PCB1,對(duì)于非共平面的2,2',6-三氯聯(lián)苯(PCB19)和共平面的3,3',5-三氯聯(lián)苯(PCB36),也存在著相同的規(guī)律,原因主要為PCB分子的空間位阻效應(yīng)。阻轉(zhuǎn)類非共平面的PCB的旋轉(zhuǎn)勢壘和二面角較大導(dǎo)致分子體積更大,進(jìn)入狹小的黏土疏水性層間需克服較大的勢壘;相反,共平面類PCB分子厚度很小,既能自由插入黏土層間也可與黏土層疏水表面產(chǎn)生較大的接觸面。PCB1、PCB3、PCB19和PCB36在HA-Mont上的吸附能力為:PCB36PCB19PCB3PCB1,表明除了疏水性的影響外,PCB分子構(gòu)型因素在HA-Mont上同樣是重要的影響因素。污染物分子構(gòu)型因素是影響有機(jī)污染物在實(shí)際土壤中遷移轉(zhuǎn)化的重要因素。2)分子動(dòng)力學(xué)模擬研究構(gòu)建不同含水量的SWy-2(蒙脫石)和PYRO(層間不帶電荷的蒙脫石)兩種水合黏土模型,通過對(duì)黏土水合系統(tǒng)中層間陽離子的運(yùn)動(dòng)軌跡的分析發(fā)現(xiàn),不同含水量的黏土水合系統(tǒng)中陽離子的移動(dòng)范圍存在顯著差異,黏土表面存在著相當(dāng)大的區(qū)域未被陽離子占據(jù),該區(qū)域大小相對(duì)恒定,對(duì)非極性有機(jī)污染物存在吸附親和力。分析層間水密度分布發(fā)現(xiàn),在SWy-2系統(tǒng)中,水分子與黏土表面存在H鍵作用,密度約為0.19?0.25個(gè)H鍵/黏土表面的氧原子。在PYRO系統(tǒng)中,層間水和表面氧的相互作用較弱,H鍵密度僅為0.06個(gè)H鍵/黏土表面的氧原子。PYRO層間表面較SWy-2表面的疏水性更強(qiáng)一些,可以作為后者層間陽離子未占據(jù)區(qū)域的理想特例;通過徑向分布函數(shù)分析發(fā)現(xiàn):所有水合SWy-2系統(tǒng)中,層間陽離子與層間水間的配合作用最強(qiáng),層間陽離子與PCBs分子之間沒有顯著作用;受到水與陽離子間強(qiáng)相互作用的排擠,PCB分子被驅(qū)離到相對(duì)疏水的硅氧烷表面區(qū)域。通過對(duì)不同構(gòu)型PCBs分子的芳環(huán)與層間二面角的分布分析發(fā)現(xiàn),共平面PCB分子的兩個(gè)芳環(huán)同時(shí)與黏土層表面直接接觸,而非平面PCB分子只能有一個(gè)芳環(huán)接觸黏土層表面,礙于空間位阻效應(yīng)非平面的PCB分子很難進(jìn)入層間,只可能吸附在黏土外表面。在黏土層間-微孔水兩相模型中,運(yùn)用加速分子動(dòng)力學(xué)自適應(yīng)偏置力方法(ABF)定量計(jì)算PCBs在黏土相和水相間的遷移自由能能,發(fā)現(xiàn)平面構(gòu)型的PCB36和PCB 3的吸附自由能均比對(duì)應(yīng)的非平面構(gòu)型的PCB 19、PCB 28和PCB 1的吸附自由能的絕對(duì)值大1?3kcal·mol-1,與吸附試驗(yàn)觀測到的趨勢相一致,進(jìn)一步證實(shí)了疏水作用和空間位阻效應(yīng)決定了不同結(jié)構(gòu)PCBs在黏土上的吸附。計(jì)算的到的吸附自由能ΔGABF平均比實(shí)驗(yàn)推導(dǎo)的吸附自由能ΔGw的絕對(duì)值大0.4kcal·mol-1,平均相對(duì)誤差為12.7%,與目前分子動(dòng)力學(xué)方法可以達(dá)到的精度相符。
[Abstract]:Polychlorinated biphenyls (PCBs), as a class of persistent organic pollutants, can harm human health through the enrichment of food chains. Soil or sediments are the main sinks of PCBs in the environment. Montmorillonite clay minerals are an important component of the soil, which are widely distributed in the soil or sediment environment, and are high in large specific surface area. The structure characteristics of cation exchange can be used to adsorb a variety of organic pollutants and are widely used as the treatment materials for environmental pollution. In the actual soil, clay minerals are combined with soil organic matter to form organic inorganic complexes. The two are difficult to act on organic pollutants alone and encapsulate the organic matter in the surface of clay minerals. The adsorption properties of clay are greatly influenced by the complex mechanism of the clay. The montmorillonite and humus montmorillonite complex with different cations are saturated with different cations, and a series of 1~3 chlorine substituted PCBs with different spatial configurations are carried out in the organic solvent assisted mixing system. The interaction mechanism of pollutants and clay minerals is explained from the interlayer cation type, the spatial configuration of contaminants molecules and the angle of soil organic matter. The main research results are as follows: 1) adsorption thermodynamics study on the solubilization and extrapolation of organic solvents The method can solve the difficulty of quantitative adsorption study of low water soluble organic pollutants. All adsorption isotherms in the study can be well fitted by linear model. The concentration of PCBs is the main factor affecting the adsorption amount, and the adsorption process is the physical adsorption of spontaneous exothermic. The hydrophobic siloxane in the interlayer of Montmorillonite. The surface is the main adsorption site.K+ of PCBs, and the adsorption capacity of Cs+ saturated montmorillonite (Mont) on 2,4,4'- three chlorobybenzene (PCB28) is: K+-MontCs+-Mont, which is related to the hydration radius of interlayer cations. Although Cs+ with smaller hydration radii can provide more interlayer hydrophobic siloxane surfaces, but at the same time limits the size of the clay layer spacing. Sufficient vertical adsorption space can not be provided for non common plane configuration PCB28 insertion; on the contrary, the K+ with the larger hydration radius provides the optimal vertical spacing and the appropriate surface adsorption domain of the clay layer, enhancing the adsorption of PCB. The adsorption capacity of the humus montmorillonite complex (HA-Mont) and K+-Mont to PCB28 is: HA-MontK-Mont, indicating the soil Organic matter can greatly promote the adsorption of montmorillonite to PCBs. The specific reasons are two aspects: first, the distribution of organic matter; two, the organic matter in the position of the montmorillonite section, by limiting the water molecules to increase the hydrophobicity between the clay layers, thus increasing the adsorption of the montmorillonite to the PCB28. The non coplanar 2- chlorinated biphenyl (PCB1) The adsorption capacity of the coplanar 4- chlorinated biphenyl (PCB3) at K+-Mont is PCB3PCB1. There is also the same rule for the non common plane 2,2', 6- three chlorinated biphenyl (PCB19) and the co plane 3,3', 5- three chlorinated biphenyl (PCB36), the main reason is the spatial steric effect of the PCB molecule. The rotating barrier and dihedral angle of the resistive non common plane PCB are caused by the larger dihedral angle. In addition, the thickness of the PCB molecules of the coplanar class is very small, which can either insert freely between the clay layer and produce a larger contact surface.PCB1 with the hydrophobic surface of the clay layer, and the adsorption capacity of PCB3, PCB19 and PCB36 on HA-Mont is PCB36PCB19PCB3PCB1, indicating that the hydrophobic surface is hydrophobic. The PCB molecular configuration factor is also an important factor on HA-Mont. The molecular configuration factor of the pollutants is an important factor affecting the migration and transformation of organic pollutants in the actual soil.2) molecular dynamics simulation study on the construction of two kinds of hydration of different water content SWy-2 (Meng Tuoshi) and PYRO (interlayer uncharged Meng Tuoshi). Clay model, through the analysis of the movement path of interlayer cations in the clay hydration system, it is found that there is a significant difference in the movement range of the cations in the clay hydration system with different water content, and there is a considerable area of the clay surface not occupied by the cation, the size of the region is relatively constant, and the adsorption of non polar organic pollutants exists. Affinity. The analysis of interlayer water density distribution shows that in the SWy-2 system, there is a H bond between the water molecules and the clay surface, and the density is about 0.19? 0.25 H bonds / clay surfaces. In the PYRO system, the interaction between the interlayer water and the surface oxygen is weak, and the H bond density is only 0.06 H bonds / the surface of the oxygen atom.PYRO on the clay surface than the SWy-2 table. The hydrophobicity of the surface is stronger, which can be used as an ideal case for the unoccupied region of the latter. Through the analysis of the radial distribution function, it is found that in all SWy-2 systems, the coordination of interlayer cations and interlayer water is the strongest, and there is no significant effect between the interlayer cations and the PCBs molecules; the strong interaction between water and cations is found. The PCB molecules were displaced to the surface of the relatively hydrophobic siloxane surface. Through the analysis of the distribution of the aromatic rings and interlayer dihedral angles of the different configuration PCBs molecules, it was found that the two aromatic rings of the co planar PCB molecules were directly exposed to the surface of the clay layer, while the non planar PCB molecules had only one aromatic ring to contact the surface of the clay layer, which was hindering space. The non planar PCB molecules are difficult to enter the interlayer and can only be adsorbed on the outer surface of the clay. In the interlayer microporous water two-phase model, the accelerated molecular dynamics adaptive bias method (ABF) is used to calculate the free energy of the migration of PCBs between the clay phase and the water phase, and the adsorption free energy of the PCB36 and PCB 3 of the plane configuration is found. The absolute values of the adsorption free energy of the PCB 19, PCB 28 and PCB 1 of the corresponding non planar configurations are 1? 3kcal. Mol-1, consistent with the trend observed by the adsorption test, and further confirm that the hydrophobic interaction and the spatial steric effect determine the adsorption of different structure PCBs on clay. The calculated adsorption free energy delta GABF average ratio is calculated. The absolute value of the adsorption free energy Gw is 0.4kcal. Mol-1, with an average relative error of 12.7%, which is consistent with the accuracy achieved by the present molecular dynamics method.

【學(xué)位授予單位】：安徽師范大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：X592

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相關(guān)博士學(xué)位論文 前1條

1 陳蕾;天然有機(jī)質(zhì)介導(dǎo)的多氯聯(lián)苯環(huán)境轉(zhuǎn)化與降解機(jī)制[D];浙江大學(xué);2012年

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本文編號(hào)：1880711