表面分形和生物炭对纳米颗粒与污染物在石英砂中协同运移的影响机制

发布时间：2018-07-10 10:00

本文选题：表面元积分法 + 扩展DLVO理论　；参考：《中国农业大学》2017年博士论文

【摘要】：充分了解纳米颗粒在不同物理和化学条件下与多孔介质之间的相互作用,对预测其在自然环境和工程环境中的应用、对水土环境中污染物运移的影响以及对动植物健康的危害具有极其重要的意义。很多研究人员发现胶体在多孔介质当中的运移,特别是在不利条件下,受到表面粗糙度的影响较大。目前描述表面粗糙度大多是采用规则的几何形状进行模拟,不能准确地表征收集器表面形貌。生物炭对污染物吸附去除方面大多集中于采用批量平衡吸附方法进行机理研究,缺乏对污染物在生物炭修复土壤中迁移的研究。因此,本文一方面采用分形几何的方法模拟石英砂粗糙表面,研究乳胶纳米颗粒与分形粗糙表面之间的相互作用势能;另一方面通过土柱实验研究二氧化硅纳米颗粒和啶虫脒在生物炭改性石英砂多孔介质中的协同运移。具体的研究结果如下:第一,采用表面元积分和扩展DLVO理论结合的方法进行了不同粒径的乳胶纳米颗粒与分形表面之间相互作用势能的计算。通过运用Weierstrass-Mandelbrot函数并设置不同的分形维数D和分形粗糙参数G形成了表面粗糙度不同的分形表面。通过分析在不同分离距离条件下乳胶纳米颗粒与两个代表性的分形表面之间的横向相互作用势能图发现,相互作用势能的大小变化与分形粗糙参数G成正相关关系,而且总体上呈现吸附-排斥-吸附的趋势。30 nm乳胶颗粒相比于10 nm乳胶颗粒而言,与分形表面之间的相互作用面积较大,从而得到的相互作用势能也较大,而且分布比较均匀。乳胶纳米颗粒与分形表面之间排斥势能占优分布的分离距离会随着离子强度和粒径的不同而发生变化。当分离距离为0.1 nm的时候,存在依赖于离子强度和粒径的"临界表面粗糙度"影响乳胶纳米颗粒与分形表面之间吸附势能占优的分布。从乳胶纳米颗粒与分形表面之间的纵向相互作用势能图发现,不管是高于零平面还是低于零平面的凸起部位都会降低初级势阱和排斥势垒,而凹陷部位会增强次级势阱和排斥势垒。第二,通过研究乳胶纳米颗粒与分形表面之间的排斥势垒、平均粘附效率以及典型部位的相互作用势能来分析乳胶纳米颗粒的吸附和解吸情况。乳胶纳米颗粒与分形表面之间的排斥势垒会随着分形维数D的减小或者分形粗糙参数G的增大而减小。乳胶纳米颗粒与分形表面之间相互作用排斥势垒图中的"白斑"区域分布于分形表面最低点附近。"白斑"区域的分布受离子强度、分形维数D和分形粗糙参数G的影响。在低离子强度条件下,"白斑"区域容易发生30 nm乳胶颗粒的解吸,而在高离子强度条件下有利于30 nm乳胶颗粒的吸附。平均粘附效率随着分形维数D的减小或者分形粗糙参数G的增大而减小。不同的离散尺度对30nm乳胶颗粒的平均粘附效率几乎没有影响。在离子强度为10 mM时存在"临界粒径"影响乳胶纳米颗粒平均粘附效率的变化,而其它离子强度条件下平均粘附效率随着乳胶颗粒粒径的增大而减小。在低离子强度下低于零平面的粗糙表面的凸起部位有利于乳胶纳米颗粒的解吸;在高离子强度条件下,光滑表面的凸起部位有利于乳胶纳米颗粒的吸附。低于零平面的粗糙表面的凹陷部位乳胶纳米颗粒的吸附和解吸现象受乳胶粒径和离子强度的影响比较复杂。第三,开展了农药啶虫脒和二氧化硅纳米颗粒在石英砂和生物炭改性多孔介质中的协同运移研究。农药啶虫脒在石英砂多孔介质中几乎没有滞留,而在生物炭改性多孔介质当中的滞留很多且与pH有显著的相关关系。在离子强度为10 mM NaCl和pH6.4的条件下,农药啶虫脒在生物炭改性多孔介质中的吸附和微生物降解是最多的。生物炭吸附啶虫脒的机制包括π-πEDA和孔隙吸附。运用包含一阶吸附常数、一阶解吸常数和降解常数的对流-弥散方程能够准确地描述啶虫脒在多孔介质当中的穿透曲线。采用对流-弥散方程拟合得到的参数可知,啶虫脒的吸附速率不会受到pH的影响,原因是啶虫脒是非离子型化合物不会通过质子化或者是去质子化方式与生物炭结合。啶虫脒的解吸速率不会受到溶液化学条件的影响,从而证明啶虫脒的解吸是一个物理过程(孔隙扩散)。背景溶液为NaCl时,二氧化硅纳米颗粒在石英砂和生物炭改性多孔介质中的运移几乎没有影响;而当背景溶液为CaCl2时,二氧化硅纳米颗粒在生物炭改性多孔介质中的吸附增多,特别是在离子强度为10 mM的时候,前三个孔隙体积几乎没有二氧化硅纳米颗粒流出。通过SEM-EDX分析,发现二氧化硅纳米颗粒与生物炭表面某些官能团通过Ca2+的桥连作用而结合到一起。啶虫脒和二氧化硅纳米颗粒协同运移通过占据吸附位点从而起到相互促进的作用。本研究表明:采用分形几何能够更加准确地描述表面形貌,能够准确预测纳米颗粒与收集器表面之间的相互作用;采用生物炭修复土壤的过程必须要考虑污染物与纳米颗粒在不同化学条件下的协同作用,才能够达到更好的修复效果。
[Abstract]:It is very important to predict the interaction between nanoparticles and porous media under different physical and chemical conditions, to predict its application in natural environment and engineering environment, to influence the transport of pollutants in soil and water environment and to the health of animals and plants. Many researchers have found that colloids are in porous media. The migration, especially in the adverse conditions, is greatly influenced by the surface roughness. At present, the surface roughness is mostly simulated by the rule geometry, and the surface morphology of the collector can not be collected accurately. In the study, there is a lack of research on the migration of pollutants in the remediation of soil by biological carbon. Therefore, on the one hand, the fractal geometry method is used to simulate the rough surface of quartz sand and study the potential energy of the interaction between the latex nanoparticles and the fractal rough surface. On the other hand, the silica nanoparticles and Acetamiprid in the biological carbon are studied by the soil column experiment. The research results are as follows: first, the interaction potential energy between the latex nanoparticles and the fractal surface of different particle sizes is calculated by combining the surface integral and the extended DLVO theory. The Weierstrass-Mandelbrot function and the different fractal dimension D are used. The fractal roughness parameter G forms a fractal surface with different surface roughness. By analyzing the potential energy map of the transverse interaction between the latex nanoparticles and the two representative fractal surfaces, it is found that the change of the potential energy of the interaction is positively related to the fractal rough parameter G, and it is presented as a whole. The adsorption - rejection - adsorption trend of.30 nm latex particles, compared with 10 nm latex particles, has a larger interaction area between the fractal surface and the fractal surface. Thus the potential energy of the interaction is larger and the distribution is more uniform. The separation distance between the latex nanoparticles and the fractal surface is superior to the ionic strength and the ionic strength. When the separation distance is different, when the separation distance is 0.1 nm, the "critical surface roughness" dependent on the ionic strength and particle size affects the dominant distribution of the adsorption potential between the latex nanoparticles and the fractal surface. The potential energy diagram of the longitudinal interaction between the latex nanoparticles and the fractal surface is found to be higher than zero. The initial potential well and the repulsive barrier will be reduced by the plane or the convex part below the zero plane, and the secondary potential well and the exclusion barrier will be enhanced in the depression. Second, the absorption of the latex nanoparticles and the fractal surface, the average adhesion efficiency and the interaction potential energy of the typical parts are studied to analyze the absorption of the latex nanoparticles. The exclusion barrier between the latex nanoparticles and the fractal surface decreases with the decrease of the fractal dimension D or the increase of the fractal roughness parameter G. The "leukoplakia" region in the exclusion barrier map between the latex nanoparticles and the fractal surface is distributed near the lowest point of the fractal surface. The distribution of the "white spot" area is affected by the distribution of the "white spot" area. The influence of ionic strength, fractal dimension D and fractal roughness parameter G. Under low ionic strength, 30 nm latex particles are easily desorbed in the "white spot" region, while the adsorption of 30 nm latex particles is favorable under high ionic strength. The average adhesion efficiency decreases with the decrease of the fractal dimension D or the increase of the fractal roughness parameter G. The same discrete scale has little effect on the average adhesion efficiency of 30nm latex particles. When the ionic strength is 10 mM, the "critical particle size" affects the change of the average adhesion efficiency of latex nanoparticles, while the average adhesion efficiency decreases with the increase of the size of the latex particles under the other ionic strength conditions. Under low ionic strength, the average adhesion is lower than the zero level. The convex parts of the surface of the surface are beneficial to the desorption of latex nanoparticles. Under high ionic strength, the protruding parts of the smooth surface are beneficial to the adsorption of latex nanoparticles. The adsorption and desorption of latex nanoparticles under the rough surface below the zero plane are compared with the effects of latex particle size and ionic strength. Third, the synergistic transport of acetamiprid and silica nanoparticles in quartz sand and Biocharcoal modified porous media was carried out. The pesticide acetamiprid had almost no retention in the porous medium of quartz sand, but there was a lot of retention in the porous medium of biological carbon, and there was a significant correlation with pH. The ionic strength was 10 m. Under the conditions of M NaCl and pH6.4, the adsorption and microbial degradation of Acetamiprid in biological carbon modified porous media is the most. The mechanism of acetamiprid by Biocharcoal includes Pi Pi EDA and pore adsorption. The convection diffusion equation containing first order adsorption constant, first order desorption constant and degradation constant can accurately describe Acetamiprid in the form of acetamiprid The penetration curves in porous media. Using the parameters obtained by convection diffusion equation, the adsorption rate of acetamiprid is not affected by the pH, because the acetamidine is nonionic and does not combine with the protonations or deprotonations. The desorption rate of acetamiprid is not subject to the chemical conditions of the solution. It is proved that the desorption of acetamiprid is a physical process (pore diffusion). When the background solution is NaCl, the migration of silica nanoparticles in quartz sand and Biocharcoal modified porous media is almost not affected. When the background solution is CaCl2, the adsorption of silica nanometers in the porous medium of biological carbon is increased. Especially when the ionic strength is 10 mM, the first three pore volume is almost without silica nanoparticles. Through SEM-EDX analysis, it is found that the silica nanoparticles are combined with some functional groups on the surface of biological carbon through the bridging action of Ca2+. Acetamiprid and two oxygen silicon nanoparticles are transported together by occupying adsorption. This study shows that the fractal geometry can describe the surface morphology more accurately, and can accurately predict the interaction between the nanoparticles and the collector surface. The synergistic effect of pollutants and nanoparticles under different chemical conditions must be considered by using biological carbon to repair the soil. A better repair effect can be achieved.
【学位授予单位】：中国农业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：X53

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