典型持久性有机污染物在石英砂纳米孔中的分子行为模拟

发布时间：2019-03-04 18:14

【摘要】：经过长期的生产和使用,持久性有机污染物已经在各类环境介质中普遍存在,并通过食物链不断累积,对环境安全和人类健康构成了重大威胁。土壤和沉积物属于多孔介质且富含多种土壤有机质,由于持久性有机污染物具有较强的疏水性,土壤和沉积物成为其最主要的存储源和再释放源。本文利用分子模拟手段,选取两种典型的持久性有机污染物,16种多环芳烃和5种多溴联苯醚,建立4种孔径(2.0 nm、2.5 nm、3.0 nm、3.5 nm)的石英砂纳米孔模型,研究污染物在石英砂纳米孔中的分子行为,计算能量和均方位移等参数,并利用孔径变化模拟土壤的物理老化过程。在多环芳烃的吸附体系中,随着孔径的增大,体系能量升高,当孔径从2.0nm增大到3.5nm时,模拟系统的势能和非键能分别提高28.5%和25.4%。多环芳烃混合物在纳米孔中首先会紧贴着孔内壁吸附,当孔径从3.5nm缩小到2.0nm时,孔内自由体积分数由49%下降到4%。多环芳烃与石英砂纳米孔之间的吸附作用以范德华力为主,库伦静电力对总体吸附的贡献在30%以内。孔径的缩小严重束缚了多环芳烃的分子扩散性能,在2.0nm孔中多环芳烃的均方位移值最大不超过125?,而在2.5nm中均方位移的值可达到700?。多变量分析表明,多环芳烃在纳米孔中的吸附和扩散是诸多因素交互影响的结果。在多环芳烃的萃取体系中,通过正己烷和环糊精两种溶剂的萃取模拟可知,土壤的老化会增大萃取难度。在多溴联苯醚的吸附体系中,孔径的缩小也降低了体系的总势能和非键能,使其体系更加稳定;然而多溴联苯醚与石英砂之间的吸附能随孔径的缩小而增大,且该吸附能以范德华力为主,占体系吸附能的84.0%。土壤有机质LHA和SRFA的加入则导致体系的总势能和非键能,以及多溴联苯醚与石英砂之间的吸附能均降低。虽然与石英砂孔内表面的吸附能降低有利于多溴联苯醚分子的迁移,但由于土壤有机质与多溴联苯醚之间的吸附作用占主导,抑制了多溴联苯醚在纳米孔中的扩散,因此多溴联苯醚的均方位移值反而降低。在多溴联苯醚的分配体系中,3.5nm的大孔中分配能与分配系数可以拟合为线性关系。
[Abstract]:Through long-term production and use, persistent organic pollutants (pops) have been widespread in all kinds of environmental media and accumulated continuously through the food chain, which poses a major threat to environmental security and human health. Soil and sediment belong to porous medium and are rich in many kinds of soil organic matter. Because persistent organic pollutants have strong hydrophobicity, soil and sediment are the most important storage source and re-release source. Two typical persistent organic pollutants (pops), 16 polycyclic aromatic hydrocarbons (PAHs) and 5 PBDEs were selected by molecular simulation to establish four pore sizes (2.0 nm,2.5 nm,3.0 nm,). The molecular behavior of pollutants in quartz sand nanoporous pore was studied, the energy and mean square displacement parameters were calculated, and the physical aging process of soil was simulated by pore size change. 3. 5 nm) was used to study the molecular behavior of pollutants in quartz sand nanoporous pore and to calculate the energy and mean square displacement. In the adsorption system of polycyclic aromatic hydrocarbons, the energy of the system increases with the increase of pore size. When the pore size increases from 2.0nm to 3.5nm, the potential energy and non-bond energy of the simulated system are increased by 28.5% and 25.4%, respectively. When the pore size is reduced from 3.5nm to 2.0nm, the intrapore free volume fraction decreases from 49% to 4%. Van der Waals force is the main adsorption force between polycyclic aromatic hydrocarbons and quartz sand nano-pores, and the contribution of Coulomb electrostatic force to the overall adsorption is less than 30%. The molecular diffusion properties of polycyclic aromatic hydrocarbons (PAHs) are severely constrained by the reduction of pore size. The average azimuth shift of PAHs in 2.0nm pore is not more than 125 渭 m, while the average azimuth shift in 2.5nm is up to 700? Multivariate analysis shows that the adsorption and diffusion of PAHs in nano-pores are the result of interaction of many factors. Through the extraction simulation of n-hexane and cyclodextrin in the extraction system of polycyclic aromatic hydrocarbons (PAHs), it can be seen that the aging of soil will increase the difficulty of extraction. In the adsorption system of PBDEs, the reduction of pore size also reduced the total potential energy and non-bond energy of the system, which made the system more stable. However, the adsorption energy between PBDEs and quartz sand increases with the decrease of pore size, and the adsorption energy is dominated by van der Waals force, accounting for 84.0% of the adsorption energy of the system. The addition of LHA and SRFA in soil organic matter reduced the total potential energy and non-bond energy of the system and the adsorption energy between PBDEs and quartz sand. Although the adsorption of PBDEs on the inner surface of quartz sand is beneficial to the migration of PBDEs, the diffusion of PBDEs in nano-pores is inhibited due to the dominant adsorption between soil organic matter and PBDEs. As a result, the average azimuth shift of PBDEs is lower than that of PBDEs. In the distribution system of polybrominated diphenyl ether (PBDEs), the distribution energy and partition coefficient in macropores of 3.5nm can be fitted to a linear relationship.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X592;X131.3

【相似文献】