简单分子在分子筛和碳纳米管上扩散的分子动力学模拟
发布时间：2018-10-31 19:26
【摘要】：本文运用分子动力学模拟的方法,对简单分子在分子筛和碳纳米管中的结构和扩散等动力学行为进行了研究。首先,基于过渡态理论模拟研究了甲烷和正丁烷的单组分以及不同比例的二元混合物在空腔结构分子筛ITQ-3中的扩散,分别计算了单组分分子在y、z方向孔道中的自扩散系数和二元混合分子在各比例下的扩散行为,并通过分子投影在ITQ-3分子筛中x-y和x-z平面上的频率等值线图对出现的现象进行了解释。研究发现,在ITQ-3分子筛中,单组分CH_4和C_4H_(10)随负载n的扩散表现出两种扩散模式:在z方向孔道中,当负载n增大时,自扩散系数也随着增大,当增大到一定数值时又开始减小;而在y方向孔道中,当负载n增大时,自扩散系数一直减小。而对CH_4和C_4H_(10)混合分子在ITQ-3分子筛中的扩散研究表明,混合分子中CH_4的扩散与原子总数相关:当负载n较小时,CH_4的扩散系数在z方向和y方向孔道中都表现为随原子总数的增多而增大;当负载n较大时,CH_4的扩散系数在z方向孔道中随原子总数的增多而减小,而在y方向孔道中,使z方向孔道发生堵塞效应而使CH_4的扩散系数减小的原子总数在y方向孔道中依然处于过渡状态。其次,采用分子动力学模拟的方法,研究了水在碳纳米管中的扩散行为,阐述了水在碳纳米管中扩散的传统计算的局限性并提出了水在碳纳米管中扩散的新的计算方法:根据碳纳米管中水以团簇作弹道运动的特点将其视为类布朗运动提出一种直接模拟计算纳米管中水的输运扩散系数的方法,这对理解限制在平滑孔道中的水之外的其他极性分子的扩散提供了一种新的视角。
[Abstract]:In this paper, the structure and diffusion behavior of simple molecules in molecular sieves and carbon nanotubes were studied by means of molecular dynamics simulation. First, based on the transition state theory, the diffusion of methane and n-butane and binary mixtures in ITQ-3 with different ratios were studied, and the single-component molecules were calculated in y. The self-diffusion coefficient in the Z channel and the diffusion behavior of binary mixed molecules in different proportions are explained. The phenomena are explained by the molecular projection on the x-y and x-z plane of ITQ-3 molecular sieve. It is found that in ITQ-3 molecular sieve, the diffusion modes of CH_4 and C4H10 show two diffusion modes with the diffusion of loading n: in the Z channel, the self-diffusion coefficient increases with the increase of loading n. When it increases to a certain value, it begins to decrease again. In the y-direction channel, the self-diffusion coefficient decreases when the load n increases. The diffusion of CH_4 and C _ 4H _ (10) in ITQ-3 molecular sieve shows that the diffusion of CH_4 in the mixed molecule is related to the total number of atoms: when the loading n is small, The diffusion coefficient of CH_4 increases with the increase of the total number of atoms in both z and y directions. When the load n is larger, the diffusion coefficient of CH_4 decreases with the increase of the total number of atoms in the Z direction, but in the y direction, the diffusion coefficient of the CH_4 decreases with the increase of the total number of atoms. The total number of atoms which make the diffusion coefficient of CH_4 decrease due to the blockage effect in the Z direction is still in the transition state in the y direction. Secondly, the diffusion behavior of water in carbon nanotubes was studied by molecular dynamics simulation. The limitation of traditional calculation of water diffusion in carbon nanotubes (CNTs) is expounded, and a new calculation method of water diffusion in CNTs is put forward: according to the characteristics of the ballistic motion of water clusters in CNTs, it is regarded as Brownian motion. A direct simulation method for calculating the transport and diffusion coefficients of water in nanotubes is presented. This provides a new perspective for understanding the diffusion of polar molecules other than water confined to smooth pores.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O552.2
本文编号：2303305
[Abstract]:In this paper, the structure and diffusion behavior of simple molecules in molecular sieves and carbon nanotubes were studied by means of molecular dynamics simulation. First, based on the transition state theory, the diffusion of methane and n-butane and binary mixtures in ITQ-3 with different ratios were studied, and the single-component molecules were calculated in y. The self-diffusion coefficient in the Z channel and the diffusion behavior of binary mixed molecules in different proportions are explained. The phenomena are explained by the molecular projection on the x-y and x-z plane of ITQ-3 molecular sieve. It is found that in ITQ-3 molecular sieve, the diffusion modes of CH_4 and C4H10 show two diffusion modes with the diffusion of loading n: in the Z channel, the self-diffusion coefficient increases with the increase of loading n. When it increases to a certain value, it begins to decrease again. In the y-direction channel, the self-diffusion coefficient decreases when the load n increases. The diffusion of CH_4 and C _ 4H _ (10) in ITQ-3 molecular sieve shows that the diffusion of CH_4 in the mixed molecule is related to the total number of atoms: when the loading n is small, The diffusion coefficient of CH_4 increases with the increase of the total number of atoms in both z and y directions. When the load n is larger, the diffusion coefficient of CH_4 decreases with the increase of the total number of atoms in the Z direction, but in the y direction, the diffusion coefficient of the CH_4 decreases with the increase of the total number of atoms. The total number of atoms which make the diffusion coefficient of CH_4 decrease due to the blockage effect in the Z direction is still in the transition state in the y direction. Secondly, the diffusion behavior of water in carbon nanotubes was studied by molecular dynamics simulation. The limitation of traditional calculation of water diffusion in carbon nanotubes (CNTs) is expounded, and a new calculation method of water diffusion in CNTs is put forward: according to the characteristics of the ballistic motion of water clusters in CNTs, it is regarded as Brownian motion. A direct simulation method for calculating the transport and diffusion coefficients of water in nanotubes is presented. This provides a new perspective for understanding the diffusion of polar molecules other than water confined to smooth pores.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O552.2
【参考文献】
相关期刊论文 前2条
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